[oweals/busybox.git] / shell / hush.c

/* vi: set sw=4 ts=4: */
/*
 * A prototype Bourne shell grammar parser.
 * Intended to follow the original Thompson and Ritchie
 * "small and simple is beautiful" philosophy, which
 * incidentally is a good match to today's BusyBox.
 *
 * Copyright (C) 2000,2001  Larry Doolittle <larry@doolittle.boa.org>
 * Copyright (C) 2008,2009  Denys Vlasenko <vda.linux@googlemail.com>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 *
 * Credits:
 *      The parser routines proper are all original material, first
 *      written Dec 2000 and Jan 2001 by Larry Doolittle.  The
 *      execution engine, the builtins, and much of the underlying
 *      support has been adapted from busybox-0.49pre's lash, which is
 *      Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
 *      written by Erik Andersen <andersen@codepoet.org>.  That, in turn,
 *      is based in part on ladsh.c, by Michael K. Johnson and Erik W.
 *      Troan, which they placed in the public domain.  I don't know
 *      how much of the Johnson/Troan code has survived the repeated
 *      rewrites.
 *
 * Other credits:
 *      o_addchr derived from similar w_addchar function in glibc-2.2.
 *      parse_redirect, redirect_opt_num, and big chunks of main
 *      and many builtins derived from contributions by Erik Andersen.
 *      Miscellaneous bugfixes from Matt Kraai.
 *
 * There are two big (and related) architecture differences between
 * this parser and the lash parser.  One is that this version is
 * actually designed from the ground up to understand nearly all
 * of the Bourne grammar.  The second, consequential change is that
 * the parser and input reader have been turned inside out.  Now,
 * the parser is in control, and asks for input as needed.  The old
 * way had the input reader in control, and it asked for parsing to
 * take place as needed.  The new way makes it much easier to properly
 * handle the recursion implicit in the various substitutions, especially
 * across continuation lines.
 *
 * TODOs:
 *      grep for "TODO" and fix (some of them are easy)
 *      special variables (done: PWD, PPID, RANDOM)
 *      tilde expansion
 *      aliases
 *      follow IFS rules more precisely, including update semantics
 *      builtins mandated by standards we don't support:
 *          [un]alias, command, fc, getopts, newgrp, readonly, times
 *      make complex ${var%...} constructs support optional
 *      make here documents optional
 *
 * Bash compat TODO:
 *      redirection of stdout+stderr: &> and >&
 *      reserved words: function select
 *      advanced test: [[ ]]
 *      process substitution: <(list) and >(list)
 *      =~: regex operator
 *      let EXPR [EXPR...]
 *          Each EXPR is an arithmetic expression (ARITHMETIC EVALUATION)
 *          If the last arg evaluates to 0, let returns 1; 0 otherwise.
 *          NB: let `echo 'a=a + 1'` - error (IOW: multi-word expansion is used)
 *      ((EXPR))
 *          The EXPR is evaluated according to ARITHMETIC EVALUATION.
 *          This is exactly equivalent to let "EXPR".
 *      $[EXPR]: synonym for $((EXPR))
 *
 * Won't do:
 *      In bash, export builtin is special, its arguments are assignments
 *          and therefore expansion of them should be "one-word" expansion:
 *              $ export i=`echo 'a  b'` # export has one arg: "i=a  b"
 *          compare with:
 *              $ ls i=`echo 'a  b'`     # ls has two args: "i=a" and "b"
 *              ls: cannot access i=a: No such file or directory
 *              ls: cannot access b: No such file or directory
 *          Note1: same applies to local builtin.
 *          Note2: bash 3.2.33(1) does this only if export word itself
 *          is not quoted:
 *              $ export i=`echo 'aaa  bbb'`; echo "$i"
 *              aaa  bbb
 *              $ "export" i=`echo 'aaa  bbb'`; echo "$i"
 *              aaa
 */
#include "busybox.h"  /* for APPLET_IS_NOFORK/NOEXEC */
#if !(defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__NetBSD__) \
        || defined(__APPLE__) \
    )
# include <malloc.h>   /* for malloc_trim */
#endif
#include <glob.h>
/* #include <dmalloc.h> */
#if ENABLE_HUSH_CASE
# include <fnmatch.h>
#endif

#include "shell_common.h"
#include "math.h"
#include "match.h"
#if ENABLE_HUSH_RANDOM_SUPPORT
# include "random.h"
#else
# define CLEAR_RANDOM_T(rnd) ((void)0)
#endif
#ifndef PIPE_BUF
# define PIPE_BUF 4096  /* amount of buffering in a pipe */
#endif

//applet:IF_HUSH(APPLET(hush, _BB_DIR_BIN, _BB_SUID_DROP))
//applet:IF_MSH(APPLET(msh, _BB_DIR_BIN, _BB_SUID_DROP))
//applet:IF_FEATURE_SH_IS_HUSH(APPLET_ODDNAME(sh, hush, _BB_DIR_BIN, _BB_SUID_DROP, sh))
//applet:IF_FEATURE_BASH_IS_HUSH(APPLET_ODDNAME(bash, hush, _BB_DIR_BIN, _BB_SUID_DROP, bash))

//kbuild:lib-$(CONFIG_HUSH) += hush.o match.o shell_common.o
//kbuild:lib-$(CONFIG_HUSH_RANDOM_SUPPORT) += random.o

//config:config HUSH
//config:       bool "hush"
//config:       default y
//config:       help
//config:         hush is a small shell (25k). It handles the normal flow control
//config:         constructs such as if/then/elif/else/fi, for/in/do/done, while loops,
//config:         case/esac. Redirections, here documents, $((arithmetic))
//config:         and functions are supported.
//config:
//config:         It will compile and work on no-mmu systems.
//config:
//config:         It does not handle select, aliases, tilde expansion,
//config:         &>file and >&file redirection of stdout+stderr.
//config:
//config:config HUSH_BASH_COMPAT
//config:       bool "bash-compatible extensions"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable bash-compatible extensions.
//config:
//config:config HUSH_BRACE_EXPANSION
//config:       bool "Brace expansion"
//config:       default y
//config:       depends on HUSH_BASH_COMPAT
//config:       help
//config:         Enable {abc,def} extension.
//config:
//config:config HUSH_HELP
//config:       bool "help builtin"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable help builtin in hush. Code size + ~1 kbyte.
//config:
//config:config HUSH_INTERACTIVE
//config:       bool "Interactive mode"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable interactive mode (prompt and command editing).
//config:         Without this, hush simply reads and executes commands
//config:         from stdin just like a shell script from a file.
//config:         No prompt, no PS1/PS2 magic shell variables.
//config:
//config:config HUSH_SAVEHISTORY
//config:       bool "Save command history to .hush_history"
//config:       default y
//config:       depends on HUSH_INTERACTIVE && FEATURE_EDITING_SAVEHISTORY
//config:       help
//config:         Enable history saving in hush.
//config:
//config:config HUSH_JOB
//config:       bool "Job control"
//config:       default y
//config:       depends on HUSH_INTERACTIVE
//config:       help
//config:         Enable job control: Ctrl-Z backgrounds, Ctrl-C interrupts current
//config:         command (not entire shell), fg/bg builtins work. Without this option,
//config:         "cmd &" still works by simply spawning a process and immediately
//config:         prompting for next command (or executing next command in a script),
//config:         but no separate process group is formed.
//config:
//config:config HUSH_TICK
//config:       bool "Process substitution"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable process substitution `command` and $(command) in hush.
//config:
//config:config HUSH_IF
//config:       bool "Support if/then/elif/else/fi"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable if/then/elif/else/fi in hush.
//config:
//config:config HUSH_LOOPS
//config:       bool "Support for, while and until loops"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable for, while and until loops in hush.
//config:
//config:config HUSH_CASE
//config:       bool "Support case ... esac statement"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable case ... esac statement in hush. +400 bytes.
//config:
//config:config HUSH_FUNCTIONS
//config:       bool "Support funcname() { commands; } syntax"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable support for shell functions in hush. +800 bytes.
//config:
//config:config HUSH_LOCAL
//config:       bool "Support local builtin"
//config:       default y
//config:       depends on HUSH_FUNCTIONS
//config:       help
//config:         Enable support for local variables in functions.
//config:
//config:config HUSH_RANDOM_SUPPORT
//config:       bool "Pseudorandom generator and $RANDOM variable"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         Enable pseudorandom generator and dynamic variable "$RANDOM".
//config:         Each read of "$RANDOM" will generate a new pseudorandom value.
//config:
//config:config HUSH_EXPORT_N
//config:       bool "Support 'export -n' option"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         export -n unexports variables. It is a bash extension.
//config:
//config:config HUSH_MODE_X
//config:       bool "Support 'hush -x' option and 'set -x' command"
//config:       default y
//config:       depends on HUSH
//config:       help
//config:         This instructs hush to print commands before execution.
//config:         Adds ~300 bytes.
//config:
//config:config MSH
//config:       bool "msh (deprecated: aliased to hush)"
//config:       default n
//config:       select HUSH
//config:       help
//config:         msh is deprecated and will be removed, please migrate to hush.
//config:

/* -i (interactive) and -s (read stdin) are also accepted,
 * but currently do nothing, therefore aren't shown in help.
 * NOMMU-specific options are not meant to be used by users,
 * therefore we don't show them either.
 */
//usage:#define hush_trivial_usage
//usage:       "[-nx] [-c SCRIPT]"
//usage:#define hush_full_usage ""
//usage:#define msh_trivial_usage hush_trivial_usage
//usage:#define msh_full_usage ""
//usage:#define sh_trivial_usage NOUSAGE_STR
//usage:#define sh_full_usage ""
//usage:#define bash_trivial_usage NOUSAGE_STR
//usage:#define bash_full_usage ""


/* Build knobs */
#define LEAK_HUNTING 0
#define BUILD_AS_NOMMU 0
/* Enable/disable sanity checks. Ok to enable in production,
 * only adds a bit of bloat. Set to >1 to get non-production level verbosity.
 * Keeping 1 for now even in released versions.
 */
#define HUSH_DEBUG 1
/* Slightly bigger (+200 bytes), but faster hush.
 * So far it only enables a trick with counting SIGCHLDs and forks,
 * which allows us to do fewer waitpid's.
 * (we can detect a case where neither forks were done nor SIGCHLDs happened
 * and therefore waitpid will return the same result as last time)
 */
#define ENABLE_HUSH_FAST 0
/* TODO: implement simplified code for users which do not need ${var%...} ops
 * So far ${var%...} ops are always enabled:
 */
#define ENABLE_HUSH_DOLLAR_OPS 1


#if BUILD_AS_NOMMU
# undef BB_MMU
# undef USE_FOR_NOMMU
# undef USE_FOR_MMU
# define BB_MMU 0
# define USE_FOR_NOMMU(...) __VA_ARGS__
# define USE_FOR_MMU(...)
#endif

#include "NUM_APPLETS.h"
#if NUM_APPLETS == 1
/* STANDALONE does not make sense, and won't compile */
# undef CONFIG_FEATURE_SH_STANDALONE
# undef ENABLE_FEATURE_SH_STANDALONE
# undef IF_FEATURE_SH_STANDALONE
# undef IF_NOT_FEATURE_SH_STANDALONE
# define ENABLE_FEATURE_SH_STANDALONE 0
# define IF_FEATURE_SH_STANDALONE(...)
# define IF_NOT_FEATURE_SH_STANDALONE(...) __VA_ARGS__
#endif

#if !ENABLE_HUSH_INTERACTIVE
# undef ENABLE_FEATURE_EDITING
# define ENABLE_FEATURE_EDITING 0
# undef ENABLE_FEATURE_EDITING_FANCY_PROMPT
# define ENABLE_FEATURE_EDITING_FANCY_PROMPT 0
#endif

/* Do we support ANY keywords? */
#if ENABLE_HUSH_IF || ENABLE_HUSH_LOOPS || ENABLE_HUSH_CASE
# define HAS_KEYWORDS 1
# define IF_HAS_KEYWORDS(...) __VA_ARGS__
# define IF_HAS_NO_KEYWORDS(...)
#else
# define HAS_KEYWORDS 0
# define IF_HAS_KEYWORDS(...)
# define IF_HAS_NO_KEYWORDS(...) __VA_ARGS__
#endif

/* If you comment out one of these below, it will be #defined later
 * to perform debug printfs to stderr: */
#define debug_printf(...)        do {} while (0)
/* Finer-grained debug switches */
#define debug_printf_parse(...)  do {} while (0)
#define debug_print_tree(a, b)   do {} while (0)
#define debug_printf_exec(...)   do {} while (0)
#define debug_printf_env(...)    do {} while (0)
#define debug_printf_jobs(...)   do {} while (0)
#define debug_printf_expand(...) do {} while (0)
#define debug_printf_varexp(...) do {} while (0)
#define debug_printf_glob(...)   do {} while (0)
#define debug_printf_list(...)   do {} while (0)
#define debug_printf_subst(...)  do {} while (0)
#define debug_printf_clean(...)  do {} while (0)

#define ERR_PTR ((void*)(long)1)

#define JOB_STATUS_FORMAT    "[%d] %-22s %.40s\n"

#define _SPECIAL_VARS_STR     "_*@$!?#"
#define SPECIAL_VARS_STR     ("_*@$!?#" + 1)
#define NUMERIC_SPECVARS_STR ("_*@$!?#" + 3)
#if ENABLE_HUSH_BASH_COMPAT
/* Support / and // replace ops */
/* Note that // is stored as \ in "encoded" string representation */
# define VAR_ENCODED_SUBST_OPS      "\\/%#:-=+?"
# define VAR_SUBST_OPS             ("\\/%#:-=+?" + 1)
# define MINUS_PLUS_EQUAL_QUESTION ("\\/%#:-=+?" + 5)
#else
# define VAR_ENCODED_SUBST_OPS      "%#:-=+?"
# define VAR_SUBST_OPS              "%#:-=+?"
# define MINUS_PLUS_EQUAL_QUESTION ("%#:-=+?" + 3)
#endif

#define SPECIAL_VAR_SYMBOL   3

struct variable;

static const char hush_version_str[] ALIGN1 = "HUSH_VERSION="BB_VER;

/* This supports saving pointers malloced in vfork child,
 * to be freed in the parent.
 */
#if !BB_MMU
typedef struct nommu_save_t {
        char **new_env;
        struct variable *old_vars;
        char **argv;
        char **argv_from_re_execing;
} nommu_save_t;
#endif

enum {
        RES_NONE  = 0,
#if ENABLE_HUSH_IF
        RES_IF    ,
        RES_THEN  ,
        RES_ELIF  ,
        RES_ELSE  ,
        RES_FI    ,
#endif
#if ENABLE_HUSH_LOOPS
        RES_FOR   ,
        RES_WHILE ,
        RES_UNTIL ,
        RES_DO    ,
        RES_DONE  ,
#endif
#if ENABLE_HUSH_LOOPS || ENABLE_HUSH_CASE
        RES_IN    ,
#endif
#if ENABLE_HUSH_CASE
        RES_CASE  ,
        /* three pseudo-keywords support contrived "case" syntax: */
        RES_CASE_IN,   /* "case ... IN", turns into RES_MATCH when IN is observed */
        RES_MATCH ,    /* "word)" */
        RES_CASE_BODY, /* "this command is inside CASE" */
        RES_ESAC  ,
#endif
        RES_XXXX  ,
        RES_SNTX
};

typedef struct o_string {
        char *data;
        int length; /* position where data is appended */
        int maxlen;
        int o_expflags;
        /* At least some part of the string was inside '' or "",
         * possibly empty one: word"", wo''rd etc. */
        smallint has_quoted_part;
        smallint has_empty_slot;
        smallint o_assignment; /* 0:maybe, 1:yes, 2:no */
} o_string;
enum {
        EXP_FLAG_SINGLEWORD     = 0x80, /* must be 0x80 */
        EXP_FLAG_GLOB           = 0x2,
        /* Protect newly added chars against globbing
         * by prepending \ to *, ?, [, \ */
        EXP_FLAG_ESC_GLOB_CHARS = 0x1,
};
enum {
        MAYBE_ASSIGNMENT      = 0,
        DEFINITELY_ASSIGNMENT = 1,
        NOT_ASSIGNMENT        = 2,
        /* Not an assigment, but next word may be: "if v=xyz cmd;" */
        WORD_IS_KEYWORD       = 3,
};
/* Used for initialization: o_string foo = NULL_O_STRING; */
#define NULL_O_STRING { NULL }

/* I can almost use ordinary FILE*.  Is open_memstream() universally
 * available?  Where is it documented? */
typedef struct in_str {
        const char *p;
        /* eof_flag=1: last char in ->p is really an EOF */
        char eof_flag; /* meaningless if ->p == NULL */
        char peek_buf[2];
#if ENABLE_HUSH_INTERACTIVE
        smallint promptme;
        smallint promptmode; /* 0: PS1, 1: PS2 */
#endif
        FILE *file;
        int (*get) (struct in_str *) FAST_FUNC;
        int (*peek) (struct in_str *) FAST_FUNC;
} in_str;
#define i_getch(input) ((input)->get(input))
#define i_peek(input) ((input)->peek(input))

/* The descrip member of this structure is only used to make
 * debugging output pretty */
static const struct {
        int mode;
        signed char default_fd;
        char descrip[3];
} redir_table[] = {
        { O_RDONLY,                  0, "<"  },
        { O_CREAT|O_TRUNC|O_WRONLY,  1, ">"  },
        { O_CREAT|O_APPEND|O_WRONLY, 1, ">>" },
        { O_CREAT|O_RDWR,            1, "<>" },
        { O_RDONLY,                  0, "<<" },
/* Should not be needed. Bogus default_fd helps in debugging */
/*      { O_RDONLY,                 77, "<<" }, */
};

struct redir_struct {
        struct redir_struct *next;
        char *rd_filename;          /* filename */
        int rd_fd;                  /* fd to redirect */
        /* fd to redirect to, or -3 if rd_fd is to be closed (n>&-) */
        int rd_dup;
        smallint rd_type;           /* (enum redir_type) */
        /* note: for heredocs, rd_filename contains heredoc delimiter,
         * and subsequently heredoc itself; and rd_dup is a bitmask:
         * bit 0: do we need to trim leading tabs?
         * bit 1: is heredoc quoted (<<'delim' syntax) ?
         */
};
typedef enum redir_type {
        REDIRECT_INPUT     = 0,
        REDIRECT_OVERWRITE = 1,
        REDIRECT_APPEND    = 2,
        REDIRECT_IO        = 3,
        REDIRECT_HEREDOC   = 4,
        REDIRECT_HEREDOC2  = 5, /* REDIRECT_HEREDOC after heredoc is loaded */

        REDIRFD_CLOSE      = -3,
        REDIRFD_SYNTAX_ERR = -2,
        REDIRFD_TO_FILE    = -1,
        /* otherwise, rd_fd is redirected to rd_dup */

        HEREDOC_SKIPTABS = 1,
        HEREDOC_QUOTED   = 2,
} redir_type;


struct command {
        pid_t pid;                  /* 0 if exited */
        int assignment_cnt;         /* how many argv[i] are assignments? */
        smallint is_stopped;        /* is the command currently running? */
        smallint cmd_type;          /* CMD_xxx */
#define CMD_NORMAL   0
#define CMD_SUBSHELL 1
#if ENABLE_HUSH_BASH_COMPAT
/* used for "[[ EXPR ]]" */
# define CMD_SINGLEWORD_NOGLOB 2
#endif
#if ENABLE_HUSH_FUNCTIONS
# define CMD_FUNCDEF 3
#endif

        smalluint cmd_exitcode;
        /* if non-NULL, this "command" is { list }, ( list ), or a compound statement */
        struct pipe *group;
#if !BB_MMU
        char *group_as_string;
#endif
#if ENABLE_HUSH_FUNCTIONS
        struct function *child_func;
/* This field is used to prevent a bug here:
 * while...do f1() {a;}; f1; f1() {b;}; f1; done
 * When we execute "f1() {a;}" cmd, we create new function and clear
 * cmd->group, cmd->group_as_string, cmd->argv[0].
 * When we execute "f1() {b;}", we notice that f1 exists,
 * and that its "parent cmd" struct is still "alive",
 * we put those fields back into cmd->xxx
 * (struct function has ->parent_cmd ptr to facilitate that).
 * When we loop back, we can execute "f1() {a;}" again and set f1 correctly.
 * Without this trick, loop would execute a;b;b;b;...
 * instead of correct sequence a;b;a;b;...
 * When command is freed, it severs the link
 * (sets ->child_func->parent_cmd to NULL).
 */
#endif
        char **argv;                /* command name and arguments */
/* argv vector may contain variable references (^Cvar^C, ^C0^C etc)
 * and on execution these are substituted with their values.
 * Substitution can make _several_ words out of one argv[n]!
 * Example: argv[0]=='.^C*^C.' here: echo .$*.
 * References of the form ^C`cmd arg^C are `cmd arg` substitutions.
 */
        struct redir_struct *redirects; /* I/O redirections */
};
/* Is there anything in this command at all? */
#define IS_NULL_CMD(cmd) \
        (!(cmd)->group && !(cmd)->argv && !(cmd)->redirects)

struct pipe {
        struct pipe *next;
        int num_cmds;               /* total number of commands in pipe */
        int alive_cmds;             /* number of commands running (not exited) */
        int stopped_cmds;           /* number of commands alive, but stopped */
#if ENABLE_HUSH_JOB
        int jobid;                  /* job number */
        pid_t pgrp;                 /* process group ID for the job */
        char *cmdtext;              /* name of job */
#endif
        struct command *cmds;       /* array of commands in pipe */
        smallint followup;          /* PIPE_BG, PIPE_SEQ, PIPE_OR, PIPE_AND */
        IF_HAS_KEYWORDS(smallint pi_inverted;) /* "! cmd | cmd" */
        IF_HAS_KEYWORDS(smallint res_word;) /* needed for if, for, while, until... */
};
typedef enum pipe_style {
        PIPE_SEQ = 1,
        PIPE_AND = 2,
        PIPE_OR  = 3,
        PIPE_BG  = 4,
} pipe_style;
/* Is there anything in this pipe at all? */
#define IS_NULL_PIPE(pi) \
        ((pi)->num_cmds == 0 IF_HAS_KEYWORDS( && (pi)->res_word == RES_NONE))

/* This holds pointers to the various results of parsing */
struct parse_context {
        /* linked list of pipes */
        struct pipe *list_head;
        /* last pipe (being constructed right now) */
        struct pipe *pipe;
        /* last command in pipe (being constructed right now) */
        struct command *command;
        /* last redirect in command->redirects list */
        struct redir_struct *pending_redirect;
#if !BB_MMU
        o_string as_string;
#endif
#if HAS_KEYWORDS
        smallint ctx_res_w;
        smallint ctx_inverted; /* "! cmd | cmd" */
#if ENABLE_HUSH_CASE
        smallint ctx_dsemicolon; /* ";;" seen */
#endif
        /* bitmask of FLAG_xxx, for figuring out valid reserved words */
        int old_flag;
        /* group we are enclosed in:
         * example: "if pipe1; pipe2; then pipe3; fi"
         * when we see "if" or "then", we malloc and copy current context,
         * and make ->stack point to it. then we parse pipeN.
         * when closing "then" / fi" / whatever is found,
         * we move list_head into ->stack->command->group,
         * copy ->stack into current context, and delete ->stack.
         * (parsing of { list } and ( list ) doesn't use this method)
         */
        struct parse_context *stack;
#endif
};

/* On program start, environ points to initial environment.
 * putenv adds new pointers into it, unsetenv removes them.
 * Neither of these (de)allocates the strings.
 * setenv allocates new strings in malloc space and does putenv,
 * and thus setenv is unusable (leaky) for shell's purposes */
#define setenv(...) setenv_is_leaky_dont_use()
struct variable {
        struct variable *next;
        char *varstr;        /* points to "name=" portion */
#if ENABLE_HUSH_LOCAL
        unsigned func_nest_level;
#endif
        int max_len;         /* if > 0, name is part of initial env; else name is malloced */
        smallint flg_export; /* putenv should be done on this var */
        smallint flg_read_only;
};

enum {
        BC_BREAK = 1,
        BC_CONTINUE = 2,
};

#if ENABLE_HUSH_FUNCTIONS
struct function {
        struct function *next;
        char *name;
        struct command *parent_cmd;
        struct pipe *body;
# if !BB_MMU
        char *body_as_string;
# endif
};
#endif


/* set -/+o OPT support. (TODO: make it optional)
 * bash supports the following opts:
 * allexport       off
 * braceexpand     on
 * emacs           on
 * errexit         off
 * errtrace        off
 * functrace       off
 * hashall         on
 * histexpand      off
 * history         on
 * ignoreeof       off
 * interactive-comments    on
 * keyword         off
 * monitor         on
 * noclobber       off
 * noexec          off
 * noglob          off
 * nolog           off
 * notify          off
 * nounset         off
 * onecmd          off
 * physical        off
 * pipefail        off
 * posix           off
 * privileged      off
 * verbose         off
 * vi              off
 * xtrace          off
 */
static const char o_opt_strings[] ALIGN1 =
        "pipefail\0"
        "noexec\0"
#if ENABLE_HUSH_MODE_X
        "xtrace\0"
#endif
        ;
enum {
        OPT_O_PIPEFAIL,
        OPT_O_NOEXEC,
#if ENABLE_HUSH_MODE_X
        OPT_O_XTRACE,
#endif
        NUM_OPT_O
};


/* "Globals" within this file */
/* Sorted roughly by size (smaller offsets == smaller code) */
struct globals {
        /* interactive_fd != 0 means we are an interactive shell.
         * If we are, then saved_tty_pgrp can also be != 0, meaning
         * that controlling tty is available. With saved_tty_pgrp == 0,
         * job control still works, but terminal signals
         * (^C, ^Z, ^Y, ^\) won't work at all, and background
         * process groups can only be created with "cmd &".
         * With saved_tty_pgrp != 0, hush will use tcsetpgrp()
         * to give tty to the foreground process group,
         * and will take it back when the group is stopped (^Z)
         * or killed (^C).
         */
#if ENABLE_HUSH_INTERACTIVE
        /* 'interactive_fd' is a fd# open to ctty, if we have one
         * _AND_ if we decided to act interactively */
        int interactive_fd;
        const char *PS1;
        const char *PS2;
# define G_interactive_fd (G.interactive_fd)
#else
# define G_interactive_fd 0
#endif
#if ENABLE_FEATURE_EDITING
        line_input_t *line_input_state;
#endif
        pid_t root_pid;
        pid_t root_ppid;
        pid_t last_bg_pid;
#if ENABLE_HUSH_RANDOM_SUPPORT
        random_t random_gen;
#endif
#if ENABLE_HUSH_JOB
        int run_list_level;
        int last_jobid;
        pid_t saved_tty_pgrp;
        struct pipe *job_list;
# define G_saved_tty_pgrp (G.saved_tty_pgrp)
#else
# define G_saved_tty_pgrp 0
#endif
        char o_opt[NUM_OPT_O];
#if ENABLE_HUSH_MODE_X
# define G_x_mode (G.o_opt[OPT_O_XTRACE])
#else
# define G_x_mode 0
#endif
        smallint flag_SIGINT;
#if ENABLE_HUSH_LOOPS
        smallint flag_break_continue;
#endif
#if ENABLE_HUSH_FUNCTIONS
        /* 0: outside of a function (or sourced file)
         * -1: inside of a function, ok to use return builtin
         * 1: return is invoked, skip all till end of func
         */
        smallint flag_return_in_progress;
#endif
        smallint exiting; /* used to prevent EXIT trap recursion */
        /* These four support $?, $#, and $1 */
        smalluint last_exitcode;
        /* are global_argv and global_argv[1..n] malloced? (note: not [0]) */
        smalluint global_args_malloced;
        smalluint inherited_set_is_saved;
        /* how many non-NULL argv's we have. NB: $# + 1 */
        int global_argc;
        char **global_argv;
#if !BB_MMU
        char *argv0_for_re_execing;
#endif
#if ENABLE_HUSH_LOOPS
        unsigned depth_break_continue;
        unsigned depth_of_loop;
#endif
        const char *ifs;
        const char *cwd;
        struct variable *top_var;
        char **expanded_assignments;
#if ENABLE_HUSH_FUNCTIONS
        struct function *top_func;
# if ENABLE_HUSH_LOCAL
        struct variable **shadowed_vars_pp;
        unsigned func_nest_level;
# endif
#endif
        /* Signal and trap handling */
#if ENABLE_HUSH_FAST
        unsigned count_SIGCHLD;
        unsigned handled_SIGCHLD;
        smallint we_have_children;
#endif
        /* which signals have non-DFL handler (even with no traps set)? */
        unsigned non_DFL_mask;
        char **traps; /* char *traps[NSIG] */
        sigset_t blocked_set;
        sigset_t inherited_set;
#if HUSH_DEBUG
        unsigned long memleak_value;
        int debug_indent;
#endif
        char user_input_buf[ENABLE_FEATURE_EDITING ? CONFIG_FEATURE_EDITING_MAX_LEN : 2];
};
#define G (*ptr_to_globals)
/* Not #defining name to G.name - this quickly gets unwieldy
 * (too many defines). Also, I actually prefer to see when a variable
 * is global, thus "G." prefix is a useful hint */
#define INIT_G() do { \
        SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
} while (0)


/* Function prototypes for builtins */
static int builtin_cd(char **argv) FAST_FUNC;
static int builtin_echo(char **argv) FAST_FUNC;
static int builtin_eval(char **argv) FAST_FUNC;
static int builtin_exec(char **argv) FAST_FUNC;
static int builtin_exit(char **argv) FAST_FUNC;
static int builtin_export(char **argv) FAST_FUNC;
#if ENABLE_HUSH_JOB
static int builtin_fg_bg(char **argv) FAST_FUNC;
static int builtin_jobs(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_HELP
static int builtin_help(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_LOCAL
static int builtin_local(char **argv) FAST_FUNC;
#endif
#if HUSH_DEBUG
static int builtin_memleak(char **argv) FAST_FUNC;
#endif
#if ENABLE_PRINTF
static int builtin_printf(char **argv) FAST_FUNC;
#endif
static int builtin_pwd(char **argv) FAST_FUNC;
static int builtin_read(char **argv) FAST_FUNC;
static int builtin_set(char **argv) FAST_FUNC;
static int builtin_shift(char **argv) FAST_FUNC;
static int builtin_source(char **argv) FAST_FUNC;
static int builtin_test(char **argv) FAST_FUNC;
static int builtin_trap(char **argv) FAST_FUNC;
static int builtin_type(char **argv) FAST_FUNC;
static int builtin_true(char **argv) FAST_FUNC;
static int builtin_umask(char **argv) FAST_FUNC;
static int builtin_unset(char **argv) FAST_FUNC;
static int builtin_wait(char **argv) FAST_FUNC;
#if ENABLE_HUSH_LOOPS
static int builtin_break(char **argv) FAST_FUNC;
static int builtin_continue(char **argv) FAST_FUNC;
#endif
#if ENABLE_HUSH_FUNCTIONS
static int builtin_return(char **argv) FAST_FUNC;
#endif

/* Table of built-in functions.  They can be forked or not, depending on
 * context: within pipes, they fork.  As simple commands, they do not.
 * When used in non-forking context, they can change global variables
 * in the parent shell process.  If forked, of course they cannot.
 * For example, 'unset foo | whatever' will parse and run, but foo will
 * still be set at the end. */
struct built_in_command {
        const char *b_cmd;
        int (*b_function)(char **argv) FAST_FUNC;
#if ENABLE_HUSH_HELP
        const char *b_descr;
# define BLTIN(cmd, func, help) { cmd, func, help }
#else
# define BLTIN(cmd, func, help) { cmd, func }
#endif
};

static const struct built_in_command bltins1[] = {
        BLTIN("."        , builtin_source  , "Run commands in a file"),
        BLTIN(":"        , builtin_true    , NULL),
#if ENABLE_HUSH_JOB
        BLTIN("bg"       , builtin_fg_bg   , "Resume a job in the background"),
#endif
#if ENABLE_HUSH_LOOPS
        BLTIN("break"    , builtin_break   , "Exit from a loop"),
#endif
        BLTIN("cd"       , builtin_cd      , "Change directory"),
#if ENABLE_HUSH_LOOPS
        BLTIN("continue" , builtin_continue, "Start new loop iteration"),
#endif
        BLTIN("eval"     , builtin_eval    , "Construct and run shell command"),
        BLTIN("exec"     , builtin_exec    , "Execute command, don't return to shell"),
        BLTIN("exit"     , builtin_exit    , "Exit"),
        BLTIN("export"   , builtin_export  , "Set environment variables"),
#if ENABLE_HUSH_JOB
        BLTIN("fg"       , builtin_fg_bg   , "Bring job into the foreground"),
#endif
#if ENABLE_HUSH_HELP
        BLTIN("help"     , builtin_help    , NULL),
#endif
#if ENABLE_HUSH_JOB
        BLTIN("jobs"     , builtin_jobs    , "List jobs"),
#endif
#if ENABLE_HUSH_LOCAL
        BLTIN("local"    , builtin_local   , "Set local variables"),
#endif
#if HUSH_DEBUG
        BLTIN("memleak"  , builtin_memleak , NULL),
#endif
        BLTIN("read"     , builtin_read    , "Input into variable"),
#if ENABLE_HUSH_FUNCTIONS
        BLTIN("return"   , builtin_return  , "Return from a function"),
#endif
        BLTIN("set"      , builtin_set     , "Set/unset positional parameters"),
        BLTIN("shift"    , builtin_shift   , "Shift positional parameters"),
#if ENABLE_HUSH_BASH_COMPAT
        BLTIN("source"   , builtin_source  , "Run commands in a file"),
#endif
        BLTIN("trap"     , builtin_trap    , "Trap signals"),
        BLTIN("type"     , builtin_type    , "Show command type"),
        BLTIN("ulimit"   , shell_builtin_ulimit  , "Control resource limits"),
        BLTIN("umask"    , builtin_umask   , "Set file creation mask"),
        BLTIN("unset"    , builtin_unset   , "Unset variables"),
        BLTIN("wait"     , builtin_wait    , "Wait for process"),
};
/* For now, echo and test are unconditionally enabled.
 * Maybe make it configurable? */
static const struct built_in_command bltins2[] = {
        BLTIN("["        , builtin_test    , NULL),
        BLTIN("echo"     , builtin_echo    , NULL),
#if ENABLE_PRINTF
        BLTIN("printf"   , builtin_printf  , NULL),
#endif
        BLTIN("pwd"      , builtin_pwd     , NULL),
        BLTIN("test"     , builtin_test    , NULL),
};


/* Debug printouts.
 */
#if HUSH_DEBUG
/* prevent disasters with G.debug_indent < 0 */
# define indent() fdprintf(2, "%*s", (G.debug_indent * 2) & 0xff, "")
# define debug_enter() (G.debug_indent++)
# define debug_leave() (G.debug_indent--)
#else
# define indent()      ((void)0)
# define debug_enter() ((void)0)
# define debug_leave() ((void)0)
#endif

#ifndef debug_printf
# define debug_printf(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_parse
# define debug_printf_parse(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_exec
#define debug_printf_exec(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_env
# define debug_printf_env(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_jobs
# define debug_printf_jobs(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_JOBS 1
#else
# define DEBUG_JOBS 0
#endif

#ifndef debug_printf_expand
# define debug_printf_expand(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_EXPAND 1
#else
# define DEBUG_EXPAND 0
#endif

#ifndef debug_printf_varexp
# define debug_printf_varexp(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_glob
# define debug_printf_glob(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_GLOB 1
#else
# define DEBUG_GLOB 0
#endif

#ifndef debug_printf_list
# define debug_printf_list(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_subst
# define debug_printf_subst(...) (indent(), fdprintf(2, __VA_ARGS__))
#endif

#ifndef debug_printf_clean
# define debug_printf_clean(...) (indent(), fdprintf(2, __VA_ARGS__))
# define DEBUG_CLEAN 1
#else
# define DEBUG_CLEAN 0
#endif

#if DEBUG_EXPAND
static void debug_print_strings(const char *prefix, char **vv)
{
        indent();
        fdprintf(2, "%s:\n", prefix);
        while (*vv)
                fdprintf(2, " '%s'\n", *vv++);
}
#else
# define debug_print_strings(prefix, vv) ((void)0)
#endif


/* Leak hunting. Use hush_leaktool.sh for post-processing.
 */
#if LEAK_HUNTING
static void *xxmalloc(int lineno, size_t size)
{
        void *ptr = xmalloc((size + 0xff) & ~0xff);
        fdprintf(2, "line %d: malloc %p\n", lineno, ptr);
        return ptr;
}
static void *xxrealloc(int lineno, void *ptr, size_t size)
{
        ptr = xrealloc(ptr, (size + 0xff) & ~0xff);
        fdprintf(2, "line %d: realloc %p\n", lineno, ptr);
        return ptr;
}
static char *xxstrdup(int lineno, const char *str)
{
        char *ptr = xstrdup(str);
        fdprintf(2, "line %d: strdup %p\n", lineno, ptr);
        return ptr;
}
static void xxfree(void *ptr)
{
        fdprintf(2, "free %p\n", ptr);
        free(ptr);
}
# define xmalloc(s)     xxmalloc(__LINE__, s)
# define xrealloc(p, s) xxrealloc(__LINE__, p, s)
# define xstrdup(s)     xxstrdup(__LINE__, s)
# define free(p)        xxfree(p)
#endif


/* Syntax and runtime errors. They always abort scripts.
 * In interactive use they usually discard unparsed and/or unexecuted commands
 * and return to the prompt.
 * HUSH_DEBUG >= 2 prints line number in this file where it was detected.
 */
#if HUSH_DEBUG < 2
# define die_if_script(lineno, ...)             die_if_script(__VA_ARGS__)
# define syntax_error(lineno, msg)              syntax_error(msg)
# define syntax_error_at(lineno, msg)           syntax_error_at(msg)
# define syntax_error_unterm_ch(lineno, ch)     syntax_error_unterm_ch(ch)
# define syntax_error_unterm_str(lineno, s)     syntax_error_unterm_str(s)
# define syntax_error_unexpected_ch(lineno, ch) syntax_error_unexpected_ch(ch)
#endif

static void die_if_script(unsigned lineno, const char *fmt, ...)
{
        va_list p;

#if HUSH_DEBUG >= 2
        bb_error_msg("hush.c:%u", lineno);
#endif
        va_start(p, fmt);
        bb_verror_msg(fmt, p, NULL);
        va_end(p);
        if (!G_interactive_fd)
                xfunc_die();
}

static void syntax_error(unsigned lineno, const char *msg)
{
        if (msg)
                die_if_script(lineno, "syntax error: %s", msg);
        else
                die_if_script(lineno, "syntax error", NULL);
}

static void syntax_error_at(unsigned lineno, const char *msg)
{
        die_if_script(lineno, "syntax error at '%s'", msg);
}

static void syntax_error_unterm_str(unsigned lineno, const char *s)
{
        die_if_script(lineno, "syntax error: unterminated %s", s);
}

/* It so happens that all such cases are totally fatal
 * even if shell is interactive: EOF while looking for closing
 * delimiter. There is nowhere to read stuff from after that,
 * it's EOF! The only choice is to terminate.
 */
static void syntax_error_unterm_ch(unsigned lineno, char ch) NORETURN;
static void syntax_error_unterm_ch(unsigned lineno, char ch)
{
        char msg[2] = { ch, '\0' };
        syntax_error_unterm_str(lineno, msg);
        xfunc_die();
}

static void syntax_error_unexpected_ch(unsigned lineno, int ch)
{
        char msg[2];
        msg[0] = ch;
        msg[1] = '\0';
        die_if_script(lineno, "syntax error: unexpected %s", ch == EOF ? "EOF" : msg);
}

#if HUSH_DEBUG < 2
# undef die_if_script
# undef syntax_error
# undef syntax_error_at
# undef syntax_error_unterm_ch
# undef syntax_error_unterm_str
# undef syntax_error_unexpected_ch
#else
# define die_if_script(...)             die_if_script(__LINE__, __VA_ARGS__)
# define syntax_error(msg)              syntax_error(__LINE__, msg)
# define syntax_error_at(msg)           syntax_error_at(__LINE__, msg)
# define syntax_error_unterm_ch(ch)     syntax_error_unterm_ch(__LINE__, ch)
# define syntax_error_unterm_str(s)     syntax_error_unterm_str(__LINE__, s)
# define syntax_error_unexpected_ch(ch) syntax_error_unexpected_ch(__LINE__, ch)
#endif


#if ENABLE_HUSH_INTERACTIVE
static void cmdedit_update_prompt(void);
#else
# define cmdedit_update_prompt() ((void)0)
#endif


/* Utility functions
 */
/* Replace each \x with x in place, return ptr past NUL. */
static char *unbackslash(char *src)
{
        char *dst = src = strchrnul(src, '\\');
        while (1) {
                if (*src == '\\')
                        src++;
                if ((*dst++ = *src++) == '\0')
                        break;
        }
        return dst;
}

static char **add_strings_to_strings(char **strings, char **add, int need_to_dup)
{
        int i;
        unsigned count1;
        unsigned count2;
        char **v;

        v = strings;
        count1 = 0;
        if (v) {
                while (*v) {
                        count1++;
                        v++;
                }
        }
        count2 = 0;
        v = add;
        while (*v) {
                count2++;
                v++;
        }
        v = xrealloc(strings, (count1 + count2 + 1) * sizeof(char*));
        v[count1 + count2] = NULL;
        i = count2;
        while (--i >= 0)
                v[count1 + i] = (need_to_dup ? xstrdup(add[i]) : add[i]);
        return v;
}
#if LEAK_HUNTING
static char **xx_add_strings_to_strings(int lineno, char **strings, char **add, int need_to_dup)
{
        char **ptr = add_strings_to_strings(strings, add, need_to_dup);
        fdprintf(2, "line %d: add_strings_to_strings %p\n", lineno, ptr);
        return ptr;
}
#define add_strings_to_strings(strings, add, need_to_dup) \
        xx_add_strings_to_strings(__LINE__, strings, add, need_to_dup)
#endif

/* Note: takes ownership of "add" ptr (it is not strdup'ed) */
static char **add_string_to_strings(char **strings, char *add)
{
        char *v[2];
        v[0] = add;
        v[1] = NULL;
        return add_strings_to_strings(strings, v, /*dup:*/ 0);
}
#if LEAK_HUNTING
static char **xx_add_string_to_strings(int lineno, char **strings, char *add)
{
        char **ptr = add_string_to_strings(strings, add);
        fdprintf(2, "line %d: add_string_to_strings %p\n", lineno, ptr);
        return ptr;
}
#define add_string_to_strings(strings, add) \
        xx_add_string_to_strings(__LINE__, strings, add)
#endif

static void free_strings(char **strings)
{
        char **v;

        if (!strings)
                return;
        v = strings;
        while (*v) {
                free(*v);
                v++;
        }
        free(strings);
}


/* Helpers for setting new $n and restoring them back
 */
typedef struct save_arg_t {
        char *sv_argv0;
        char **sv_g_argv;
        int sv_g_argc;
        smallint sv_g_malloced;
} save_arg_t;

static void save_and_replace_G_args(save_arg_t *sv, char **argv)
{
        int n;

        sv->sv_argv0 = argv[0];
        sv->sv_g_argv = G.global_argv;
        sv->sv_g_argc = G.global_argc;
        sv->sv_g_malloced = G.global_args_malloced;

        argv[0] = G.global_argv[0]; /* retain $0 */
        G.global_argv = argv;
        G.global_args_malloced = 0;

        n = 1;
        while (*++argv)
                n++;
        G.global_argc = n;
}

static void restore_G_args(save_arg_t *sv, char **argv)
{
        char **pp;

        if (G.global_args_malloced) {
                /* someone ran "set -- arg1 arg2 ...", undo */
                pp = G.global_argv;
                while (*++pp) /* note: does not free $0 */
                        free(*pp);
                free(G.global_argv);
        }
        argv[0] = sv->sv_argv0;
        G.global_argv = sv->sv_g_argv;
        G.global_argc = sv->sv_g_argc;
        G.global_args_malloced = sv->sv_g_malloced;
}


/* Basic theory of signal handling in shell
 * ========================================
 * This does not describe what hush does, rather, it is current understanding
 * what it _should_ do. If it doesn't, it's a bug.
 * http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#trap
 *
 * Signals are handled only after each pipe ("cmd | cmd | cmd" thing)
 * is finished or backgrounded. It is the same in interactive and
 * non-interactive shells, and is the same regardless of whether
 * a user trap handler is installed or a shell special one is in effect.
 * ^C or ^Z from keyboard seems to execute "at once" because it usually
 * backgrounds (i.e. stops) or kills all members of currently running
 * pipe.
 *
 * Wait builtin in interruptible by signals for which user trap is set
 * or by SIGINT in interactive shell.
 *
 * Trap handlers will execute even within trap handlers. (right?)
 *
 * User trap handlers are forgotten when subshell ("(cmd)") is entered,
 * except for handlers set to '' (empty string).
 *
 * If job control is off, backgrounded commands ("cmd &")
 * have SIGINT, SIGQUIT set to SIG_IGN.
 *
 * Commands which are run in command substitution ("`cmd`")
 * have SIGTTIN, SIGTTOU, SIGTSTP set to SIG_IGN.
 *
 * Ordinary commands have signals set to SIG_IGN/DFL as inherited
 * by the shell from its parent.
 *
 * Signals which differ from SIG_DFL action
 * (note: child (i.e., [v]forked) shell is not an interactive shell):
 *
 * SIGQUIT: ignore
 * SIGTERM (interactive): ignore
 * SIGHUP (interactive):
 *    send SIGCONT to stopped jobs, send SIGHUP to all jobs and exit
 * SIGTTIN, SIGTTOU, SIGTSTP (if job control is on): ignore
 *    Note that ^Z is handled not by trapping SIGTSTP, but by seeing
 *    that all pipe members are stopped. Try this in bash:
 *    while :; do :; done - ^Z does not background it
 *    (while :; do :; done) - ^Z backgrounds it
 * SIGINT (interactive): wait for last pipe, ignore the rest
 *    of the command line, show prompt. NB: ^C does not send SIGINT
 *    to interactive shell while shell is waiting for a pipe,
 *    since shell is bg'ed (is not in foreground process group).
 *    Example 1: this waits 5 sec, but does not execute ls:
 *    "echo $$; sleep 5; ls -l" + "kill -INT <pid>"
 *    Example 2: this does not wait and does not execute ls:
 *    "echo $$; sleep 5 & wait; ls -l" + "kill -INT <pid>"
 *    Example 3: this does not wait 5 sec, but executes ls:
 *    "sleep 5; ls -l" + press ^C
 *
 * (What happens to signals which are IGN on shell start?)
 * (What happens with signal mask on shell start?)
 *
 * Implementation in hush
 * ======================
 * We use in-kernel pending signal mask to determine which signals were sent.
 * We block all signals which we don't want to take action immediately,
 * i.e. we block all signals which need to have special handling as described
 * above, and all signals which have traps set.
 * After each pipe execution, we extract any pending signals via sigtimedwait()
 * and act on them.
 *
 * unsigned non_DFL_mask: a mask of such "special" signals
 * sigset_t blocked_set:  current blocked signal set
 *
 * "trap - SIGxxx":
 *    clear bit in blocked_set unless it is also in non_DFL_mask
 * "trap 'cmd' SIGxxx":
 *    set bit in blocked_set (even if 'cmd' is '')
 * after [v]fork, if we plan to be a shell:
 *    unblock signals with special interactive handling
 *    (child shell is not interactive),
 *    unset all traps except '' (note: regardless of child shell's type - {}, (), etc)
 * after [v]fork, if we plan to exec:
 *    POSIX says fork clears pending signal mask in child - no need to clear it.
 *    Restore blocked signal set to one inherited by shell just prior to exec.
 *
 * Note: as a result, we do not use signal handlers much. The only uses
 * are to count SIGCHLDs
 * and to restore tty pgrp on signal-induced exit.
 *
 * Note 2 (compat):
 * Standard says "When a subshell is entered, traps that are not being ignored
 * are set to the default actions". bash interprets it so that traps which
 * are set to '' (ignore) are NOT reset to defaults. We do the same.
 */
enum {
        SPECIAL_INTERACTIVE_SIGS = 0
                | (1 << SIGTERM)
                | (1 << SIGINT)
                | (1 << SIGHUP)
                ,
        SPECIAL_JOB_SIGS = 0
#if ENABLE_HUSH_JOB
                | (1 << SIGTTIN)
                | (1 << SIGTTOU)
                | (1 << SIGTSTP)
#endif
};

#if ENABLE_HUSH_FAST
static void SIGCHLD_handler(int sig UNUSED_PARAM)
{
        G.count_SIGCHLD++;
//bb_error_msg("[%d] SIGCHLD_handler: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
}
#endif

#if ENABLE_HUSH_JOB

/* After [v]fork, in child: do not restore tty pgrp on xfunc death */
# define disable_restore_tty_pgrp_on_exit() (die_sleep = 0)
/* After [v]fork, in parent: restore tty pgrp on xfunc death */
# define enable_restore_tty_pgrp_on_exit()  (die_sleep = -1)

/* Restores tty foreground process group, and exits.
 * May be called as signal handler for fatal signal
 * (will resend signal to itself, producing correct exit state)
 * or called directly with -EXITCODE.
 * We also call it if xfunc is exiting. */
static void sigexit(int sig) NORETURN;
static void sigexit(int sig)
{
        /* Disable all signals: job control, SIGPIPE, etc. */
        sigprocmask_allsigs(SIG_BLOCK);

        /* Careful: we can end up here after [v]fork. Do not restore
         * tty pgrp then, only top-level shell process does that */
        if (G_saved_tty_pgrp && getpid() == G.root_pid)
                tcsetpgrp(G_interactive_fd, G_saved_tty_pgrp);

        /* Not a signal, just exit */
        if (sig <= 0)
                _exit(- sig);

        kill_myself_with_sig(sig); /* does not return */
}
#else

# define disable_restore_tty_pgrp_on_exit() ((void)0)
# define enable_restore_tty_pgrp_on_exit()  ((void)0)

#endif

/* Restores tty foreground process group, and exits. */
static void hush_exit(int exitcode) NORETURN;
static void hush_exit(int exitcode)
{
        if (G.exiting <= 0 && G.traps && G.traps[0] && G.traps[0][0]) {
                /* Prevent recursion:
                 * trap "echo Hi; exit" EXIT; exit
                 */
                char *argv[3];
                /* argv[0] is unused */
                argv[1] = G.traps[0];
                argv[2] = NULL;
                G.exiting = 1; /* prevent EXIT trap recursion */
                /* Note: G.traps[0] is not cleared!
                 * "trap" will still show it, if executed
                 * in the handler */
                builtin_eval(argv);
        }

#if ENABLE_FEATURE_CLEAN_UP
        {
                struct variable *cur_var;
                if (G.cwd != bb_msg_unknown)
                        free((char*)G.cwd);
                cur_var = G.top_var;
                while (cur_var) {
                        struct variable *tmp = cur_var;
                        if (!cur_var->max_len)
                                free(cur_var->varstr);
                        cur_var = cur_var->next;
                        free(tmp);
                }
        }
#endif

#if ENABLE_HUSH_JOB
        fflush_all();
        sigexit(- (exitcode & 0xff));
#else
        exit(exitcode);
#endif
}


static int check_and_run_traps(int sig)
{
        /* I want it in rodata, not in bss.
         * gcc 4.2.1 puts it in rodata only if it has { 0, 0 }
         * initializer. But other compilers may still use bss.
         * TODO: find more portable solution.
         */
        static const struct timespec zero_timespec = { 0, 0 };
        smalluint save_rcode;
        int last_sig = 0;

        if (sig)
                goto jump_in;
        while (1) {
                sig = sigtimedwait(&G.blocked_set, NULL, &zero_timespec);
                if (sig <= 0)
                        break;
 jump_in:
                last_sig = sig;
                if (G.traps && G.traps[sig]) {
                        if (G.traps[sig][0]) {
                                /* We have user-defined handler */
                                char *argv[3];
                                /* argv[0] is unused */
                                argv[1] = G.traps[sig];
                                argv[2] = NULL;
                                save_rcode = G.last_exitcode;
                                builtin_eval(argv);
                                G.last_exitcode = save_rcode;
                        } /* else: "" trap, ignoring signal */
                        continue;
                }
                /* not a trap: special action */
                switch (sig) {
#if ENABLE_HUSH_FAST
                case SIGCHLD:
                        G.count_SIGCHLD++;
//bb_error_msg("[%d] check_and_run_traps: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
                        break;
#endif
                case SIGINT:
                        /* Builtin was ^C'ed, make it look prettier: */
                        bb_putchar('\n');
                        G.flag_SIGINT = 1;
                        break;
#if ENABLE_HUSH_JOB
                case SIGHUP: {
                        struct pipe *job;
                        /* bash is observed to signal whole process groups,
                         * not individual processes */
                        for (job = G.job_list; job; job = job->next) {
                                if (job->pgrp <= 0)
                                        continue;
                                debug_printf_exec("HUPing pgrp %d\n", job->pgrp);
                                if (kill(- job->pgrp, SIGHUP) == 0)
                                        kill(- job->pgrp, SIGCONT);
                        }
                        sigexit(SIGHUP);
                }
#endif
                default: /* ignored: */
                        /* SIGTERM, SIGQUIT, SIGTTIN, SIGTTOU, SIGTSTP */
                        break;
                }
        }
        return last_sig;
}


static const char *get_cwd(int force)
{
        if (force || G.cwd == NULL) {
                /* xrealloc_getcwd_or_warn(arg) calls free(arg),
                 * we must not try to free(bb_msg_unknown) */
                if (G.cwd == bb_msg_unknown)
                        G.cwd = NULL;
                G.cwd = xrealloc_getcwd_or_warn((char *)G.cwd);
                if (!G.cwd)
                        G.cwd = bb_msg_unknown;
        }
        return G.cwd;
}


/*
 * Shell and environment variable support
 */
static struct variable **get_ptr_to_local_var(const char *name, unsigned len)
{
        struct variable **pp;
        struct variable *cur;

        pp = &G.top_var;
        while ((cur = *pp) != NULL) {
                if (strncmp(cur->varstr, name, len) == 0 && cur->varstr[len] == '=')
                        return pp;
                pp = &cur->next;
        }
        return NULL;
}

static const char* FAST_FUNC get_local_var_value(const char *name)
{
        struct variable **vpp;
        unsigned len = strlen(name);

        if (G.expanded_assignments) {
                char **cpp = G.expanded_assignments;
                while (*cpp) {
                        char *cp = *cpp;
                        if (strncmp(cp, name, len) == 0 && cp[len] == '=')
                                return cp + len + 1;
                        cpp++;
                }
        }

        vpp = get_ptr_to_local_var(name, len);
        if (vpp)
                return (*vpp)->varstr + len + 1;

        if (strcmp(name, "PPID") == 0)
                return utoa(G.root_ppid);
        // bash compat: UID? EUID?
#if ENABLE_HUSH_RANDOM_SUPPORT
        if (strcmp(name, "RANDOM") == 0)
                return utoa(next_random(&G.random_gen));
#endif
        return NULL;
}

/* str holds "NAME=VAL" and is expected to be malloced.
 * We take ownership of it.
 * flg_export:
 *  0: do not change export flag
 *     (if creating new variable, flag will be 0)
 *  1: set export flag and putenv the variable
 * -1: clear export flag and unsetenv the variable
 * flg_read_only is set only when we handle -R var=val
 */
#if !BB_MMU && ENABLE_HUSH_LOCAL
/* all params are used */
#elif BB_MMU && ENABLE_HUSH_LOCAL
#define set_local_var(str, flg_export, local_lvl, flg_read_only) \
        set_local_var(str, flg_export, local_lvl)
#elif BB_MMU && !ENABLE_HUSH_LOCAL
#define set_local_var(str, flg_export, local_lvl, flg_read_only) \
        set_local_var(str, flg_export)
#elif !BB_MMU && !ENABLE_HUSH_LOCAL
#define set_local_var(str, flg_export, local_lvl, flg_read_only) \
        set_local_var(str, flg_export, flg_read_only)
#endif
static int set_local_var(char *str, int flg_export, int local_lvl, int flg_read_only)
{
        struct variable **var_pp;
        struct variable *cur;
        char *eq_sign;
        int name_len;

        eq_sign = strchr(str, '=');
        if (!eq_sign) { /* not expected to ever happen? */
                free(str);
                return -1;
        }

        name_len = eq_sign - str + 1; /* including '=' */
        var_pp = &G.top_var;
        while ((cur = *var_pp) != NULL) {
                if (strncmp(cur->varstr, str, name_len) != 0) {
                        var_pp = &cur->next;
                        continue;
                }
                /* We found an existing var with this name */
                if (cur->flg_read_only) {
#if !BB_MMU
                        if (!flg_read_only)
#endif
                                bb_error_msg("%s: readonly variable", str);
                        free(str);
                        return -1;
                }
                if (flg_export == -1) { // "&& cur->flg_export" ?
                        debug_printf_env("%s: unsetenv '%s'\n", __func__, str);
                        *eq_sign = '\0';
                        unsetenv(str);
                        *eq_sign = '=';
                }
#if ENABLE_HUSH_LOCAL
                if (cur->func_nest_level < local_lvl) {
                        /* New variable is declared as local,
                         * and existing one is global, or local
                         * from enclosing function.
                         * Remove and save old one: */
                        *var_pp = cur->next;
                        cur->next = *G.shadowed_vars_pp;
                        *G.shadowed_vars_pp = cur;
                        /* bash 3.2.33(1) and exported vars:
                         * # export z=z
                         * # f() { local z=a; env | grep ^z; }
                         * # f
                         * z=a
                         * # env | grep ^z
                         * z=z
                         */
                        if (cur->flg_export)
                                flg_export = 1;
                        break;
                }
#endif
                if (strcmp(cur->varstr + name_len, eq_sign + 1) == 0) {
 free_and_exp:
                        free(str);
                        goto exp;
                }
                if (cur->max_len != 0) {
                        if (cur->max_len >= strlen(str)) {
                                /* This one is from startup env, reuse space */
                                strcpy(cur->varstr, str);
                                goto free_and_exp;
                        }
                } else {
                        /* max_len == 0 signifies "malloced" var, which we can
                         * (and has to) free */
                        free(cur->varstr);
                }
                cur->max_len = 0;
                goto set_str_and_exp;
        }

        /* Not found - create new variable struct */
        cur = xzalloc(sizeof(*cur));
#if ENABLE_HUSH_LOCAL
        cur->func_nest_level = local_lvl;
#endif
        cur->next = *var_pp;
        *var_pp = cur;

 set_str_and_exp:
        cur->varstr = str;
#if !BB_MMU
        cur->flg_read_only = flg_read_only;
#endif
 exp:
        if (flg_export == 1)
                cur->flg_export = 1;
        if (name_len == 4 && cur->varstr[0] == 'P' && cur->varstr[1] == 'S')
                cmdedit_update_prompt();
        if (cur->flg_export) {
                if (flg_export == -1) {
                        cur->flg_export = 0;
                        /* unsetenv was already done */
                } else {
                        debug_printf_env("%s: putenv '%s'\n", __func__, cur->varstr);
                        return putenv(cur->varstr);
                }
        }
        return 0;
}

/* Used at startup and after each cd */
static void set_pwd_var(int exp)
{
        set_local_var(xasprintf("PWD=%s", get_cwd(/*force:*/ 1)),
                /*exp:*/ exp, /*lvl:*/ 0, /*ro:*/ 0);
}

static int unset_local_var_len(const char *name, int name_len)
{
        struct variable *cur;
        struct variable **var_pp;

        if (!name)
                return EXIT_SUCCESS;
        var_pp = &G.top_var;
        while ((cur = *var_pp) != NULL) {
                if (strncmp(cur->varstr, name, name_len) == 0 && cur->varstr[name_len] == '=') {
                        if (cur->flg_read_only) {
                                bb_error_msg("%s: readonly variable", name);
                                return EXIT_FAILURE;
                        }
                        *var_pp = cur->next;
                        debug_printf_env("%s: unsetenv '%s'\n", __func__, cur->varstr);
                        bb_unsetenv(cur->varstr);
                        if (name_len == 3 && cur->varstr[0] == 'P' && cur->varstr[1] == 'S')
                                cmdedit_update_prompt();
                        if (!cur->max_len)
                                free(cur->varstr);
                        free(cur);
                        return EXIT_SUCCESS;
                }
                var_pp = &cur->next;
        }
        return EXIT_SUCCESS;
}

static int unset_local_var(const char *name)
{
        return unset_local_var_len(name, strlen(name));
}

static void unset_vars(char **strings)
{
        char **v;

        if (!strings)
                return;
        v = strings;
        while (*v) {
                const char *eq = strchrnul(*v, '=');
                unset_local_var_len(*v, (int)(eq - *v));
                v++;
        }
        free(strings);
}

static void FAST_FUNC set_local_var_from_halves(const char *name, const char *val)
{
        char *var = xasprintf("%s=%s", name, val);
        set_local_var(var, /*flags:*/ 0, /*lvl:*/ 0, /*ro:*/ 0);
}


/*
 * Helpers for "var1=val1 var2=val2 cmd" feature
 */
static void add_vars(struct variable *var)
{
        struct variable *next;

        while (var) {
                next = var->next;
                var->next = G.top_var;
                G.top_var = var;
                if (var->flg_export) {
                        debug_printf_env("%s: restoring exported '%s'\n", __func__, var->varstr);
                        putenv(var->varstr);
                } else {
                        debug_printf_env("%s: restoring variable '%s'\n", __func__, var->varstr);
                }
                var = next;
        }
}

static struct variable *set_vars_and_save_old(char **strings)
{
        char **s;
        struct variable *old = NULL;

        if (!strings)
                return old;
        s = strings;
        while (*s) {
                struct variable *var_p;
                struct variable **var_pp;
                char *eq;

                eq = strchr(*s, '=');
                if (eq) {
                        var_pp = get_ptr_to_local_var(*s, eq - *s);
                        if (var_pp) {
                                /* Remove variable from global linked list */
                                var_p = *var_pp;
                                debug_printf_env("%s: removing '%s'\n", __func__, var_p->varstr);
                                *var_pp = var_p->next;
                                /* Add it to returned list */
                                var_p->next = old;
                                old = var_p;
                        }
                        set_local_var(*s, /*exp:*/ 1, /*lvl:*/ 0, /*ro:*/ 0);
                }
                s++;
        }
        return old;
}


/*
 * in_str support
 */
static int FAST_FUNC static_get(struct in_str *i)
{
        int ch = *i->p;
        if (ch != '\0') {
                i->p++;
                return ch;
        }
        return EOF;
}

static int FAST_FUNC static_peek(struct in_str *i)
{
        return *i->p;
}

#if ENABLE_HUSH_INTERACTIVE

static void cmdedit_update_prompt(void)
{
        if (ENABLE_FEATURE_EDITING_FANCY_PROMPT) {
                G.PS1 = get_local_var_value("PS1");
                if (G.PS1 == NULL)
                        G.PS1 = "\\w \\$ ";
                G.PS2 = get_local_var_value("PS2");
        } else {
                G.PS1 = NULL;
        }
        if (G.PS2 == NULL)
                G.PS2 = "> ";
}

static const char *setup_prompt_string(int promptmode)
{
        const char *prompt_str;
        debug_printf("setup_prompt_string %d ", promptmode);
        if (!ENABLE_FEATURE_EDITING_FANCY_PROMPT) {
                /* Set up the prompt */
                if (promptmode == 0) { /* PS1 */
                        free((char*)G.PS1);
                        /* bash uses $PWD value, even if it is set by user.
                         * It uses current dir only if PWD is unset.
                         * We always use current dir. */
                        G.PS1 = xasprintf("%s %c ", get_cwd(0), (geteuid() != 0) ? '$' : '#');
                        prompt_str = G.PS1;
                } else
                        prompt_str = G.PS2;
        } else
                prompt_str = (promptmode == 0) ? G.PS1 : G.PS2;
        debug_printf("result '%s'\n", prompt_str);
        return prompt_str;
}

static void get_user_input(struct in_str *i)
{
        int r;
        const char *prompt_str;

        prompt_str = setup_prompt_string(i->promptmode);
# if ENABLE_FEATURE_EDITING
        /* Enable command line editing only while a command line
         * is actually being read */
        do {
                G.flag_SIGINT = 0;
                /* buglet: SIGINT will not make new prompt to appear _at once_,
                 * only after <Enter>. (^C will work) */
                r = read_line_input(prompt_str, G.user_input_buf, CONFIG_FEATURE_EDITING_MAX_LEN-1, G.line_input_state);
                /* catch *SIGINT* etc (^C is handled by read_line_input) */
                check_and_run_traps(0);
        } while (r == 0 || G.flag_SIGINT); /* repeat if ^C or SIGINT */
        i->eof_flag = (r < 0);
        if (i->eof_flag) { /* EOF/error detected */
                G.user_input_buf[0] = EOF; /* yes, it will be truncated, it's ok */
                G.user_input_buf[1] = '\0';
        }
# else
        do {
                G.flag_SIGINT = 0;
                fputs(prompt_str, stdout);
                fflush_all();
                G.user_input_buf[0] = r = fgetc(i->file);
                /*G.user_input_buf[1] = '\0'; - already is and never changed */
//do we need check_and_run_traps(0)? (maybe only if stdin)
        } while (G.flag_SIGINT);
        i->eof_flag = (r == EOF);
# endif
        i->p = G.user_input_buf;
}

#endif  /* INTERACTIVE */

/* This is the magic location that prints prompts
 * and gets data back from the user */
static int FAST_FUNC file_get(struct in_str *i)
{
        int ch;

        /* If there is data waiting, eat it up */
        if (i->p && *i->p) {
#if ENABLE_HUSH_INTERACTIVE
 take_cached:
#endif
                ch = *i->p++;
                if (i->eof_flag && !*i->p)
                        ch = EOF;
                /* note: ch is never NUL */
        } else {
                /* need to double check i->file because we might be doing something
                 * more complicated by now, like sourcing or substituting. */
#if ENABLE_HUSH_INTERACTIVE
                if (G_interactive_fd && i->promptme && i->file == stdin) {
                        do {
                                get_user_input(i);
                        } while (!*i->p); /* need non-empty line */
                        i->promptmode = 1; /* PS2 */
                        i->promptme = 0;
                        goto take_cached;
                }
#endif
                do ch = fgetc(i->file); while (ch == '\0');
        }
        debug_printf("file_get: got '%c' %d\n", ch, ch);
#if ENABLE_HUSH_INTERACTIVE
        if (ch == '\n')
                i->promptme = 1;
#endif
        return ch;
}

/* All callers guarantee this routine will never
 * be used right after a newline, so prompting is not needed.
 */
static int FAST_FUNC file_peek(struct in_str *i)
{
        int ch;
        if (i->p && *i->p) {
                if (i->eof_flag && !i->p[1])
                        return EOF;
                return *i->p;
                /* note: ch is never NUL */
        }
        do ch = fgetc(i->file); while (ch == '\0');
        i->eof_flag = (ch == EOF);
        i->peek_buf[0] = ch;
        i->peek_buf[1] = '\0';
        i->p = i->peek_buf;
        debug_printf("file_peek: got '%c' %d\n", ch, ch);
        return ch;
}

static void setup_file_in_str(struct in_str *i, FILE *f)
{
        i->peek = file_peek;
        i->get = file_get;
#if ENABLE_HUSH_INTERACTIVE
        i->promptme = 1;
        i->promptmode = 0; /* PS1 */
#endif
        i->file = f;
        i->p = NULL;
}

static void setup_string_in_str(struct in_str *i, const char *s)
{
        i->peek = static_peek;
        i->get = static_get;
#if ENABLE_HUSH_INTERACTIVE
        i->promptme = 1;
        i->promptmode = 0; /* PS1 */
#endif
        i->p = s;
        i->eof_flag = 0;
}


/*
 * o_string support
 */
#define B_CHUNK  (32 * sizeof(char*))

static void o_reset_to_empty_unquoted(o_string *o)
{
        o->length = 0;
        o->has_quoted_part = 0;
        if (o->data)
                o->data[0] = '\0';
}

static void o_free(o_string *o)
{
        free(o->data);
        memset(o, 0, sizeof(*o));
}

static ALWAYS_INLINE void o_free_unsafe(o_string *o)
{
        free(o->data);
}

static void o_grow_by(o_string *o, int len)
{
        if (o->length + len > o->maxlen) {
                o->maxlen += (2*len > B_CHUNK ? 2*len : B_CHUNK);
                o->data = xrealloc(o->data, 1 + o->maxlen);
        }
}

static void o_addchr(o_string *o, int ch)
{
        debug_printf("o_addchr: '%c' o->length=%d o=%p\n", ch, o->length, o);
        o_grow_by(o, 1);
        o->data[o->length] = ch;
        o->length++;
        o->data[o->length] = '\0';
}

static void o_addblock(o_string *o, const char *str, int len)
{
        o_grow_by(o, len);
        memcpy(&o->data[o->length], str, len);
        o->length += len;
        o->data[o->length] = '\0';
}

static void o_addstr(o_string *o, const char *str)
{
        o_addblock(o, str, strlen(str));
}

#if !BB_MMU
static void nommu_addchr(o_string *o, int ch)
{
        if (o)
                o_addchr(o, ch);
}
#else
# define nommu_addchr(o, str) ((void)0)
#endif

static void o_addstr_with_NUL(o_string *o, const char *str)
{
        o_addblock(o, str, strlen(str) + 1);
}

/*
 * HUSH_BRACE_EXPANSION code needs corresponding quoting on variable expansion side.
 * Currently, "v='{q,w}'; echo $v" erroneously expands braces in $v.
 * Apparently, on unquoted $v bash still does globbing
 * ("v='*.txt'; echo $v" prints all .txt files),
 * but NOT brace expansion! Thus, there should be TWO independent
 * quoting mechanisms on $v expansion side: one protects
 * $v from brace expansion, and other additionally protects "$v" against globbing.
 * We have only second one.
 */

#if ENABLE_HUSH_BRACE_EXPANSION
# define MAYBE_BRACES "{}"
#else
# define MAYBE_BRACES ""
#endif

/* My analysis of quoting semantics tells me that state information
 * is associated with a destination, not a source.
 */
static void o_addqchr(o_string *o, int ch)
{
        int sz = 1;
        char *found = strchr("*?[\\" MAYBE_BRACES, ch);
        if (found)
                sz++;
        o_grow_by(o, sz);
        if (found) {
                o->data[o->length] = '\\';
                o->length++;
        }
        o->data[o->length] = ch;
        o->length++;
        o->data[o->length] = '\0';
}

static void o_addQchr(o_string *o, int ch)
{
        int sz = 1;
        if ((o->o_expflags & EXP_FLAG_ESC_GLOB_CHARS)
         && strchr("*?[\\" MAYBE_BRACES, ch)
        ) {
                sz++;
                o->data[o->length] = '\\';
                o->length++;
        }
        o_grow_by(o, sz);
        o->data[o->length] = ch;
        o->length++;
        o->data[o->length] = '\0';
}

static void o_addqblock(o_string *o, const char *str, int len)
{
        while (len) {
                char ch;
                int sz;
                int ordinary_cnt = strcspn(str, "*?[\\" MAYBE_BRACES);
                if (ordinary_cnt > len) /* paranoia */
                        ordinary_cnt = len;
                o_addblock(o, str, ordinary_cnt);
                if (ordinary_cnt == len)
                        return;
                str += ordinary_cnt;
                len -= ordinary_cnt + 1; /* we are processing + 1 char below */

                ch = *str++;
                sz = 1;
                if (ch) { /* it is necessarily one of "*?[\\" MAYBE_BRACES */
                        sz++;
                        o->data[o->length] = '\\';
                        o->length++;
                }
                o_grow_by(o, sz);
                o->data[o->length] = ch;
                o->length++;
                o->data[o->length] = '\0';
        }
}

static void o_addQblock(o_string *o, const char *str, int len)
{
        if (!(o->o_expflags & EXP_FLAG_ESC_GLOB_CHARS)) {
                o_addblock(o, str, len);
                return;
        }
        o_addqblock(o, str, len);
}

static void o_addQstr(o_string *o, const char *str)
{
        o_addQblock(o, str, strlen(str));
}

/* A special kind of o_string for $VAR and `cmd` expansion.
 * It contains char* list[] at the beginning, which is grown in 16 element
 * increments. Actual string data starts at the next multiple of 16 * (char*).
 * list[i] contains an INDEX (int!) into this string data.
 * It means that if list[] needs to grow, data needs to be moved higher up
 * but list[i]'s need not be modified.
 * NB: remembering how many list[i]'s you have there is crucial.
 * o_finalize_list() operation post-processes this structure - calculates
 * and stores actual char* ptrs in list[]. Oh, it NULL terminates it as well.
 */
#if DEBUG_EXPAND || DEBUG_GLOB
static void debug_print_list(const char *prefix, o_string *o, int n)
{
        char **list = (char**)o->data;
        int string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);
        int i = 0;

        indent();
        fdprintf(2, "%s: list:%p n:%d string_start:%d length:%d maxlen:%d glob:%d quoted:%d escape:%d\n",
                        prefix, list, n, string_start, o->length, o->maxlen,
                        !!(o->o_expflags & EXP_FLAG_GLOB),
                        o->has_quoted_part,
                        !!(o->o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
        while (i < n) {
                indent();
                fdprintf(2, " list[%d]=%d '%s' %p\n", i, (int)(uintptr_t)list[i],
                                o->data + (int)(uintptr_t)list[i] + string_start,
                                o->data + (int)(uintptr_t)list[i] + string_start);
                i++;
        }
        if (n) {
                const char *p = o->data + (int)(uintptr_t)list[n - 1] + string_start;
                indent();
                fdprintf(2, " total_sz:%ld\n", (long)((p + strlen(p) + 1) - o->data));
        }
}
#else
# define debug_print_list(prefix, o, n) ((void)0)
#endif

/* n = o_save_ptr_helper(str, n) "starts new string" by storing an index value
 * in list[n] so that it points past last stored byte so far.
 * It returns n+1. */
static int o_save_ptr_helper(o_string *o, int n)
{
        char **list = (char**)o->data;
        int string_start;
        int string_len;

        if (!o->has_empty_slot) {
                string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);
                string_len = o->length - string_start;
                if (!(n & 0xf)) { /* 0, 0x10, 0x20...? */
                        debug_printf_list("list[%d]=%d string_start=%d (growing)\n", n, string_len, string_start);
                        /* list[n] points to string_start, make space for 16 more pointers */
                        o->maxlen += 0x10 * sizeof(list[0]);
                        o->data = xrealloc(o->data, o->maxlen + 1);
                        list = (char**)o->data;
                        memmove(list + n + 0x10, list + n, string_len);
                        o->length += 0x10 * sizeof(list[0]);
                } else {
                        debug_printf_list("list[%d]=%d string_start=%d\n",
                                        n, string_len, string_start);
                }
        } else {
                /* We have empty slot at list[n], reuse without growth */
                string_start = ((n+1 + 0xf) & ~0xf) * sizeof(list[0]); /* NB: n+1! */
                string_len = o->length - string_start;
                debug_printf_list("list[%d]=%d string_start=%d (empty slot)\n",
                                n, string_len, string_start);
                o->has_empty_slot = 0;
        }
        list[n] = (char*)(uintptr_t)string_len;
        return n + 1;
}

/* "What was our last o_save_ptr'ed position (byte offset relative o->data)?" */
static int o_get_last_ptr(o_string *o, int n)
{
        char **list = (char**)o->data;
        int string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);

        return ((int)(uintptr_t)list[n-1]) + string_start;
}

#if ENABLE_HUSH_BRACE_EXPANSION
/* There in a GNU extension, GLOB_BRACE, but it is not usable:
 * first, it processes even {a} (no commas), second,
 * I didn't manage to make it return strings when they don't match
 * existing files. Need to re-implement it.
 */

/* Helper */
static int glob_needed(const char *s)
{
        while (*s) {
                if (*s == '\\') {
                        if (!s[1])
                                return 0;
                        s += 2;
                        continue;
                }
                if (*s == '*' || *s == '[' || *s == '?' || *s == '{')
                        return 1;
                s++;
        }
        return 0;
}
/* Return pointer to next closing brace or to comma */
static const char *next_brace_sub(const char *cp)
{
        unsigned depth = 0;
        cp++;
        while (*cp != '\0') {
                if (*cp == '\\') {
                        if (*++cp == '\0')
                                break;
                        cp++;
                        continue;
                }
                if ((*cp == '}' && depth-- == 0) || (*cp == ',' && depth == 0))
                        break;
                if (*cp++ == '{')
                        depth++;
        }

        return *cp != '\0' ? cp : NULL;
}
/* Recursive brace globber. Note: may garble pattern[]. */
static int glob_brace(char *pattern, o_string *o, int n)
{
        char *new_pattern_buf;
        const char *begin;
        const char *next;
        const char *rest;
        const char *p;
        size_t rest_len;

        debug_printf_glob("glob_brace('%s')\n", pattern);

        begin = pattern;
        while (1) {
                if (*begin == '\0')
                        goto simple_glob;
                if (*begin == '{') {
                        /* Find the first sub-pattern and at the same time
                         * find the rest after the closing brace */
                        next = next_brace_sub(begin);
                        if (next == NULL) {
                                /* An illegal expression */
                                goto simple_glob;
                        }
                        if (*next == '}') {
                                /* "{abc}" with no commas - illegal
                                 * brace expr, disregard and skip it */
                                begin = next + 1;
                                continue;
                        }
                        break;
                }
                if (*begin == '\\' && begin[1] != '\0')
                        begin++;
                begin++;
        }
        debug_printf_glob("begin:%s\n", begin);
        debug_printf_glob("next:%s\n", next);

        /* Now find the end of the whole brace expression */
        rest = next;
        while (*rest != '}') {
                rest = next_brace_sub(rest);
                if (rest == NULL) {
                        /* An illegal expression */
                        goto simple_glob;
                }
                debug_printf_glob("rest:%s\n", rest);
        }
        rest_len = strlen(++rest) + 1;

        /* We are sure the brace expression is well-formed */

        /* Allocate working buffer large enough for our work */
        new_pattern_buf = xmalloc(strlen(pattern));

        /* We have a brace expression.  BEGIN points to the opening {,
         * NEXT points past the terminator of the first element, and REST
         * points past the final }.  We will accumulate result names from
         * recursive runs for each brace alternative in the buffer using
         * GLOB_APPEND.  */

        p = begin + 1;
        while (1) {
                /* Construct the new glob expression */
                memcpy(
                        mempcpy(
                                mempcpy(new_pattern_buf,
                                        /* We know the prefix for all sub-patterns */
                                        pattern, begin - pattern),
                                p, next - p),
                        rest, rest_len);

                /* Note: glob_brace() may garble new_pattern_buf[].
                 * That's why we re-copy prefix every time (1st memcpy above).
                 */
                n = glob_brace(new_pattern_buf, o, n);
                if (*next == '}') {
                        /* We saw the last entry */
                        break;
                }
                p = next + 1;
                next = next_brace_sub(next);
        }
        free(new_pattern_buf);
        return n;

 simple_glob:
        {
                int gr;
                glob_t globdata;

                memset(&globdata, 0, sizeof(globdata));
                gr = glob(pattern, 0, NULL, &globdata);
                debug_printf_glob("glob('%s'):%d\n", pattern, gr);
                if (gr != 0) {
                        if (gr == GLOB_NOMATCH) {
                                globfree(&globdata);
                                /* NB: garbles parameter */
                                unbackslash(pattern);
                                o_addstr_with_NUL(o, pattern);
                                debug_printf_glob("glob pattern '%s' is literal\n", pattern);
                                return o_save_ptr_helper(o, n);
                        }
                        if (gr == GLOB_NOSPACE)
                                bb_error_msg_and_die(bb_msg_memory_exhausted);
                        /* GLOB_ABORTED? Only happens with GLOB_ERR flag,
                         * but we didn't specify it. Paranoia again. */
                        bb_error_msg_and_die("glob error %d on '%s'", gr, pattern);
                }
                if (globdata.gl_pathv && globdata.gl_pathv[0]) {
                        char **argv = globdata.gl_pathv;
                        while (1) {
                                o_addstr_with_NUL(o, *argv);
                                n = o_save_ptr_helper(o, n);
                                argv++;
                                if (!*argv)
                                        break;
                        }
                }
                globfree(&globdata);
        }
        return n;
}
/* Performs globbing on last list[],
 * saving each result as a new list[].
 */
static int perform_glob(o_string *o, int n)
{
        char *pattern, *copy;

        debug_printf_glob("start perform_glob: n:%d o->data:%p\n", n, o->data);
        if (!o->data)
                return o_save_ptr_helper(o, n);
        pattern = o->data + o_get_last_ptr(o, n);
        debug_printf_glob("glob pattern '%s'\n", pattern);
        if (!glob_needed(pattern)) {
                /* unbackslash last string in o in place, fix length */
                o->length = unbackslash(pattern) - o->data;
                debug_printf_glob("glob pattern '%s' is literal\n", pattern);
                return o_save_ptr_helper(o, n);
        }

        copy = xstrdup(pattern);
        /* "forget" pattern in o */
        o->length = pattern - o->data;
        n = glob_brace(copy, o, n);
        free(copy);
        if (DEBUG_GLOB)
                debug_print_list("perform_glob returning", o, n);
        return n;
}

#else /* !HUSH_BRACE_EXPANSION */

/* Helper */
static int glob_needed(const char *s)
{
        while (*s) {
                if (*s == '\\') {
                        if (!s[1])
                                return 0;
                        s += 2;
                        continue;
                }
                if (*s == '*' || *s == '[' || *s == '?')
                        return 1;
                s++;
        }
        return 0;
}
/* Performs globbing on last list[],
 * saving each result as a new list[].
 */
static int perform_glob(o_string *o, int n)
{
        glob_t globdata;
        int gr;
        char *pattern;

        debug_printf_glob("start perform_glob: n:%d o->data:%p\n", n, o->data);
        if (!o->data)
                return o_save_ptr_helper(o, n);
        pattern = o->data + o_get_last_ptr(o, n);
        debug_printf_glob("glob pattern '%s'\n", pattern);
        if (!glob_needed(pattern)) {
 literal:
                /* unbackslash last string in o in place, fix length */
                o->length = unbackslash(pattern) - o->data;
                debug_printf_glob("glob pattern '%s' is literal\n", pattern);
                return o_save_ptr_helper(o, n);
        }

        memset(&globdata, 0, sizeof(globdata));
        /* Can't use GLOB_NOCHECK: it does not unescape the string.
         * If we glob "*.\*" and don't find anything, we need
         * to fall back to using literal "*.*", but GLOB_NOCHECK
         * will return "*.\*"!
         */
        gr = glob(pattern, 0, NULL, &globdata);
        debug_printf_glob("glob('%s'):%d\n", pattern, gr);
        if (gr != 0) {
                if (gr == GLOB_NOMATCH) {
                        globfree(&globdata);
                        goto literal;
                }
                if (gr == GLOB_NOSPACE)
                        bb_error_msg_and_die(bb_msg_memory_exhausted);
                /* GLOB_ABORTED? Only happens with GLOB_ERR flag,
                 * but we didn't specify it. Paranoia again. */
                bb_error_msg_and_die("glob error %d on '%s'", gr, pattern);
        }
        if (globdata.gl_pathv && globdata.gl_pathv[0]) {
                char **argv = globdata.gl_pathv;
                /* "forget" pattern in o */
                o->length = pattern - o->data;
                while (1) {
                        o_addstr_with_NUL(o, *argv);
                        n = o_save_ptr_helper(o, n);
                        argv++;
                        if (!*argv)
                                break;
                }
        }
        globfree(&globdata);
        if (DEBUG_GLOB)
                debug_print_list("perform_glob returning", o, n);
        return n;
}

#endif /* !HUSH_BRACE_EXPANSION */

/* If o->o_expflags & EXP_FLAG_GLOB, glob the string so far remembered.
 * Otherwise, just finish current list[] and start new */
static int o_save_ptr(o_string *o, int n)
{
        if (o->o_expflags & EXP_FLAG_GLOB) {
                /* If o->has_empty_slot, list[n] was already globbed
                 * (if it was requested back then when it was filled)
                 * so don't do that again! */
                if (!o->has_empty_slot)
                        return perform_glob(o, n); /* o_save_ptr_helper is inside */
        }
        return o_save_ptr_helper(o, n);
}

/* "Please convert list[n] to real char* ptrs, and NULL terminate it." */
static char **o_finalize_list(o_string *o, int n)
{
        char **list;
        int string_start;

        n = o_save_ptr(o, n); /* force growth for list[n] if necessary */
        if (DEBUG_EXPAND)
                debug_print_list("finalized", o, n);
        debug_printf_expand("finalized n:%d\n", n);
        list = (char**)o->data;
        string_start = ((n + 0xf) & ~0xf) * sizeof(list[0]);
        list[--n] = NULL;
        while (n) {
                n--;
                list[n] = o->data + (int)(uintptr_t)list[n] + string_start;
        }
        return list;
}

static void free_pipe_list(struct pipe *pi);

/* Returns pi->next - next pipe in the list */
static struct pipe *free_pipe(struct pipe *pi)
{
        struct pipe *next;
        int i;

        debug_printf_clean("free_pipe (pid %d)\n", getpid());
        for (i = 0; i < pi->num_cmds; i++) {
                struct command *command;
                struct redir_struct *r, *rnext;

                command = &pi->cmds[i];
                debug_printf_clean("  command %d:\n", i);
                if (command->argv) {
                        if (DEBUG_CLEAN) {
                                int a;
                                char **p;
                                for (a = 0, p = command->argv; *p; a++, p++) {
                                        debug_printf_clean("   argv[%d] = %s\n", a, *p);
                                }
                        }
                        free_strings(command->argv);
                        //command->argv = NULL;
                }
                /* not "else if": on syntax error, we may have both! */
                if (command->group) {
                        debug_printf_clean("   begin group (cmd_type:%d)\n",
                                        command->cmd_type);
                        free_pipe_list(command->group);
                        debug_printf_clean("   end group\n");
                        //command->group = NULL;
                }
                /* else is crucial here.
                 * If group != NULL, child_func is meaningless */
#if ENABLE_HUSH_FUNCTIONS
                else if (command->child_func) {
                        debug_printf_exec("cmd %p releases child func at %p\n", command, command->child_func);
                        command->child_func->parent_cmd = NULL;
                }
#endif
#if !BB_MMU
                free(command->group_as_string);
                //command->group_as_string = NULL;
#endif
                for (r = command->redirects; r; r = rnext) {
                        debug_printf_clean("   redirect %d%s",
                                        r->rd_fd, redir_table[r->rd_type].descrip);
                        /* guard against the case >$FOO, where foo is unset or blank */
                        if (r->rd_filename) {
                                debug_printf_clean(" fname:'%s'\n", r->rd_filename);
                                free(r->rd_filename);
                                //r->rd_filename = NULL;
                        }
                        debug_printf_clean(" rd_dup:%d\n", r->rd_dup);
                        rnext = r->next;
                        free(r);
                }
                //command->redirects = NULL;
        }
        free(pi->cmds);   /* children are an array, they get freed all at once */
        //pi->cmds = NULL;
#if ENABLE_HUSH_JOB
        free(pi->cmdtext);
        //pi->cmdtext = NULL;
#endif

        next = pi->next;
        free(pi);
        return next;
}

static void free_pipe_list(struct pipe *pi)
{
        while (pi) {
#if HAS_KEYWORDS
                debug_printf_clean("pipe reserved word %d\n", pi->res_word);
#endif
                debug_printf_clean("pipe followup code %d\n", pi->followup);
                pi = free_pipe(pi);
        }
}


/*** Parsing routines ***/

#ifndef debug_print_tree
static void debug_print_tree(struct pipe *pi, int lvl)
{
        static const char *const PIPE[] = {
                [PIPE_SEQ] = "SEQ",
                [PIPE_AND] = "AND",
                [PIPE_OR ] = "OR" ,
                [PIPE_BG ] = "BG" ,
        };
        static const char *RES[] = {
                [RES_NONE ] = "NONE" ,
# if ENABLE_HUSH_IF
                [RES_IF   ] = "IF"   ,
                [RES_THEN ] = "THEN" ,
                [RES_ELIF ] = "ELIF" ,
                [RES_ELSE ] = "ELSE" ,
                [RES_FI   ] = "FI"   ,
# endif
# if ENABLE_HUSH_LOOPS
                [RES_FOR  ] = "FOR"  ,
                [RES_WHILE] = "WHILE",
                [RES_UNTIL] = "UNTIL",
                [RES_DO   ] = "DO"   ,
                [RES_DONE ] = "DONE" ,
# endif
# if ENABLE_HUSH_LOOPS || ENABLE_HUSH_CASE
                [RES_IN   ] = "IN"   ,
# endif
# if ENABLE_HUSH_CASE
                [RES_CASE ] = "CASE" ,
                [RES_CASE_IN ] = "CASE_IN" ,
                [RES_MATCH] = "MATCH",
                [RES_CASE_BODY] = "CASE_BODY",
                [RES_ESAC ] = "ESAC" ,
# endif
                [RES_XXXX ] = "XXXX" ,
                [RES_SNTX ] = "SNTX" ,
        };
        static const char *const CMDTYPE[] = {
                "{}",
                "()",
                "[noglob]",
# if ENABLE_HUSH_FUNCTIONS
                "func()",
# endif
        };

        int pin, prn;

        pin = 0;
        while (pi) {
                fdprintf(2, "%*spipe %d res_word=%s followup=%d %s\n", lvl*2, "",
                                pin, RES[pi->res_word], pi->followup, PIPE[pi->followup]);
                prn = 0;
                while (prn < pi->num_cmds) {
                        struct command *command = &pi->cmds[prn];
                        char **argv = command->argv;

                        fdprintf(2, "%*s cmd %d assignment_cnt:%d",
                                        lvl*2, "", prn,
                                        command->assignment_cnt);
                        if (command->group) {
                                fdprintf(2, " group %s: (argv=%p)%s%s\n",
                                                CMDTYPE[command->cmd_type],
                                                argv
# if !BB_MMU
                                                , " group_as_string:", command->group_as_string
# else
                                                , "", ""
# endif
                                );
                                debug_print_tree(command->group, lvl+1);
                                prn++;
                                continue;
                        }
                        if (argv) while (*argv) {
                                fdprintf(2, " '%s'", *argv);
                                argv++;
                        }
                        fdprintf(2, "\n");
                        prn++;
                }
                pi = pi->next;
                pin++;
        }
}
#endif /* debug_print_tree */

static struct pipe *new_pipe(void)
{
        struct pipe *pi;
        pi = xzalloc(sizeof(struct pipe));
        /*pi->followup = 0; - deliberately invalid value */
        /*pi->res_word = RES_NONE; - RES_NONE is 0 anyway */
        return pi;
}

/* Command (member of a pipe) is complete, or we start a new pipe
 * if ctx->command is NULL.
 * No errors possible here.
 */
static int done_command(struct parse_context *ctx)
{
        /* The command is really already in the pipe structure, so
         * advance the pipe counter and make a new, null command. */
        struct pipe *pi = ctx->pipe;
        struct command *command = ctx->command;

        if (command) {
                if (IS_NULL_CMD(command)) {
                        debug_printf_parse("done_command: skipping null cmd, num_cmds=%d\n", pi->num_cmds);
                        goto clear_and_ret;
                }
                pi->num_cmds++;
                debug_printf_parse("done_command: ++num_cmds=%d\n", pi->num_cmds);
                //debug_print_tree(ctx->list_head, 20);
        } else {
                debug_printf_parse("done_command: initializing, num_cmds=%d\n", pi->num_cmds);
        }

        /* Only real trickiness here is that the uncommitted
         * command structure is not counted in pi->num_cmds. */
        pi->cmds = xrealloc(pi->cmds, sizeof(*pi->cmds) * (pi->num_cmds+1));
        ctx->command = command = &pi->cmds[pi->num_cmds];
 clear_and_ret:
        memset(command, 0, sizeof(*command));
        return pi->num_cmds; /* used only for 0/nonzero check */
}

static void done_pipe(struct parse_context *ctx, pipe_style type)
{
        int not_null;

        debug_printf_parse("done_pipe entered, followup %d\n", type);
        /* Close previous command */
        not_null = done_command(ctx);
        ctx->pipe->followup = type;
#if HAS_KEYWORDS
        ctx->pipe->pi_inverted = ctx->ctx_inverted;
        ctx->ctx_inverted = 0;
        ctx->pipe->res_word = ctx->ctx_res_w;
#endif

        /* Without this check, even just <enter> on command line generates
         * tree of three NOPs (!). Which is harmless but annoying.
         * IOW: it is safe to do it unconditionally. */
        if (not_null
#if ENABLE_HUSH_IF
         || ctx->ctx_res_w == RES_FI
#endif
#if ENABLE_HUSH_LOOPS
         || ctx->ctx_res_w == RES_DONE
         || ctx->ctx_res_w == RES_FOR
         || ctx->ctx_res_w == RES_IN
#endif
#if ENABLE_HUSH_CASE
         || ctx->ctx_res_w == RES_ESAC
#endif
        ) {
                struct pipe *new_p;
                debug_printf_parse("done_pipe: adding new pipe: "
                                "not_null:%d ctx->ctx_res_w:%d\n",
                                not_null, ctx->ctx_res_w);
                new_p = new_pipe();
                ctx->pipe->next = new_p;
                ctx->pipe = new_p;
                /* RES_THEN, RES_DO etc are "sticky" -
                 * they remain set for pipes inside if/while.
                 * This is used to control execution.
                 * RES_FOR and RES_IN are NOT sticky (needed to support
                 * cases where variable or value happens to match a keyword):
                 */
#if ENABLE_HUSH_LOOPS
                if (ctx->ctx_res_w == RES_FOR
                 || ctx->ctx_res_w == RES_IN)
                        ctx->ctx_res_w = RES_NONE;
#endif
#if ENABLE_HUSH_CASE
                if (ctx->ctx_res_w == RES_MATCH)
                        ctx->ctx_res_w = RES_CASE_BODY;
                if (ctx->ctx_res_w == RES_CASE)
                        ctx->ctx_res_w = RES_CASE_IN;
#endif
                ctx->command = NULL; /* trick done_command below */
                /* Create the memory for command, roughly:
                 * ctx->pipe->cmds = new struct command;
                 * ctx->command = &ctx->pipe->cmds[0];
                 */
                done_command(ctx);
                //debug_print_tree(ctx->list_head, 10);
        }
        debug_printf_parse("done_pipe return\n");
}

static void initialize_context(struct parse_context *ctx)
{
        memset(ctx, 0, sizeof(*ctx));
        ctx->pipe = ctx->list_head = new_pipe();
        /* Create the memory for command, roughly:
         * ctx->pipe->cmds = new struct command;
         * ctx->command = &ctx->pipe->cmds[0];
         */
        done_command(ctx);
}

/* If a reserved word is found and processed, parse context is modified
 * and 1 is returned.
 */
#if HAS_KEYWORDS
struct reserved_combo {
        char literal[6];
        unsigned char res;
        unsigned char assignment_flag;
        int flag;
};
enum {
        FLAG_END   = (1 << RES_NONE ),
# if ENABLE_HUSH_IF
        FLAG_IF    = (1 << RES_IF   ),
        FLAG_THEN  = (1 << RES_THEN ),
        FLAG_ELIF  = (1 << RES_ELIF ),
        FLAG_ELSE  = (1 << RES_ELSE ),
        FLAG_FI    = (1 << RES_FI   ),
# endif
# if ENABLE_HUSH_LOOPS
        FLAG_FOR   = (1 << RES_FOR  ),
        FLAG_WHILE = (1 << RES_WHILE),
        FLAG_UNTIL = (1 << RES_UNTIL),
        FLAG_DO    = (1 << RES_DO   ),
        FLAG_DONE  = (1 << RES_DONE ),
        FLAG_IN    = (1 << RES_IN   ),
# endif
# if ENABLE_HUSH_CASE
        FLAG_MATCH = (1 << RES_MATCH),
        FLAG_ESAC  = (1 << RES_ESAC ),
# endif
        FLAG_START = (1 << RES_XXXX ),
};

static const struct reserved_combo* match_reserved_word(o_string *word)
{
        /* Mostly a list of accepted follow-up reserved words.
         * FLAG_END means we are done with the sequence, and are ready
         * to turn the compound list into a command.
         * FLAG_START means the word must start a new compound list.
         */
        static const struct reserved_combo reserved_list[] = {
# if ENABLE_HUSH_IF
                { "!",     RES_NONE,  NOT_ASSIGNMENT , 0 },
                { "if",    RES_IF,    WORD_IS_KEYWORD, FLAG_THEN | FLAG_START },
                { "then",  RES_THEN,  WORD_IS_KEYWORD, FLAG_ELIF | FLAG_ELSE | FLAG_FI },
                { "elif",  RES_ELIF,  WORD_IS_KEYWORD, FLAG_THEN },
                { "else",  RES_ELSE,  WORD_IS_KEYWORD, FLAG_FI   },
                { "fi",    RES_FI,    NOT_ASSIGNMENT , FLAG_END  },
# endif
# if ENABLE_HUSH_LOOPS
                { "for",   RES_FOR,   NOT_ASSIGNMENT , FLAG_IN | FLAG_DO | FLAG_START },
                { "while", RES_WHILE, WORD_IS_KEYWORD, FLAG_DO | FLAG_START },
                { "until", RES_UNTIL, WORD_IS_KEYWORD, FLAG_DO | FLAG_START },
                { "in",    RES_IN,    NOT_ASSIGNMENT , FLAG_DO   },
                { "do",    RES_DO,    WORD_IS_KEYWORD, FLAG_DONE },
                { "done",  RES_DONE,  NOT_ASSIGNMENT , FLAG_END  },
# endif
# if ENABLE_HUSH_CASE
                { "case",  RES_CASE,  NOT_ASSIGNMENT , FLAG_MATCH | FLAG_START },
                { "esac",  RES_ESAC,  NOT_ASSIGNMENT , FLAG_END  },
# endif
        };
        const struct reserved_combo *r;

        for (r = reserved_list; r < reserved_list + ARRAY_SIZE(reserved_list); r++) {
                if (strcmp(word->data, r->literal) == 0)
                        return r;
        }
        return NULL;
}
/* Return 0: not a keyword, 1: keyword
 */
static int reserved_word(o_string *word, struct parse_context *ctx)
{
# if ENABLE_HUSH_CASE
        static const struct reserved_combo reserved_match = {
                "",        RES_MATCH, NOT_ASSIGNMENT , FLAG_MATCH | FLAG_ESAC
        };
# endif
        const struct reserved_combo *r;

        if (word->has_quoted_part)
                return 0;
        r = match_reserved_word(word);
        if (!r)
                return 0;

        debug_printf("found reserved word %s, res %d\n", r->literal, r->res);
# if ENABLE_HUSH_CASE
        if (r->res == RES_IN && ctx->ctx_res_w == RES_CASE_IN) {
                /* "case word IN ..." - IN part starts first MATCH part */
                r = &reserved_match;
        } else
# endif
        if (r->flag == 0) { /* '!' */
                if (ctx->ctx_inverted) { /* bash doesn't accept '! ! true' */
                        syntax_error("! ! command");
                        ctx->ctx_res_w = RES_SNTX;
                }
                ctx->ctx_inverted = 1;
                return 1;
        }
        if (r->flag & FLAG_START) {
                struct parse_context *old;

                old = xmalloc(sizeof(*old));
                debug_printf_parse("push stack %p\n", old);
                *old = *ctx;   /* physical copy */
                initialize_context(ctx);
                ctx->stack = old;
        } else if (/*ctx->ctx_res_w == RES_NONE ||*/ !(ctx->old_flag & (1 << r->res))) {
                syntax_error_at(word->data);
                ctx->ctx_res_w = RES_SNTX;
                return 1;
        } else {
                /* "{...} fi" is ok. "{...} if" is not
                 * Example:
                 * if { echo foo; } then { echo bar; } fi */
                if (ctx->command->group)
                        done_pipe(ctx, PIPE_SEQ);
        }

        ctx->ctx_res_w = r->res;
        ctx->old_flag = r->flag;
        word->o_assignment = r->assignment_flag;

        if (ctx->old_flag & FLAG_END) {
                struct parse_context *old;

                done_pipe(ctx, PIPE_SEQ);
                debug_printf_parse("pop stack %p\n", ctx->stack);
                old = ctx->stack;
                old->command->group = ctx->list_head;
                old->command->cmd_type = CMD_NORMAL;
# if !BB_MMU
                o_addstr(&old->as_string, ctx->as_string.data);
                o_free_unsafe(&ctx->as_string);
                old->command->group_as_string = xstrdup(old->as_string.data);
                debug_printf_parse("pop, remembering as:'%s'\n",
                                old->command->group_as_string);
# endif
                *ctx = *old;   /* physical copy */
                free(old);
        }
        return 1;
}
#endif /* HAS_KEYWORDS */

/* Word is complete, look at it and update parsing context.
 * Normal return is 0. Syntax errors return 1.
 * Note: on return, word is reset, but not o_free'd!
 */
static int done_word(o_string *word, struct parse_context *ctx)
{
        struct command *command = ctx->command;

        debug_printf_parse("done_word entered: '%s' %p\n", word->data, command);
        if (word->length == 0 && !word->has_quoted_part) {
                debug_printf_parse("done_word return 0: true null, ignored\n");
                return 0;
        }

        if (ctx->pending_redirect) {
                /* We do not glob in e.g. >*.tmp case. bash seems to glob here
                 * only if run as "bash", not "sh" */
                /* http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html
                 * "2.7 Redirection
                 * ...the word that follows the redirection operator
                 * shall be subjected to tilde expansion, parameter expansion,
                 * command substitution, arithmetic expansion, and quote
                 * removal. Pathname expansion shall not be performed
                 * on the word by a non-interactive shell; an interactive
                 * shell may perform it, but shall do so only when
                 * the expansion would result in one word."
                 */
                ctx->pending_redirect->rd_filename = xstrdup(word->data);
                /* Cater for >\file case:
                 * >\a creates file a; >\\a, >"\a", >"\\a" create file \a
                 * Same with heredocs:
                 * for <<\H delim is H; <<\\H, <<"\H", <<"\\H" - \H
                 */
                if (ctx->pending_redirect->rd_type == REDIRECT_HEREDOC) {
                        unbackslash(ctx->pending_redirect->rd_filename);
                        /* Is it <<"HEREDOC"? */
                        if (word->has_quoted_part) {
                                ctx->pending_redirect->rd_dup |= HEREDOC_QUOTED;
                        }
                }
                debug_printf_parse("word stored in rd_filename: '%s'\n", word->data);
                ctx->pending_redirect = NULL;
        } else {
                /* If this word wasn't an assignment, next ones definitely
                 * can't be assignments. Even if they look like ones. */
                if (word->o_assignment != DEFINITELY_ASSIGNMENT
                 && word->o_assignment != WORD_IS_KEYWORD
                ) {
                        word->o_assignment = NOT_ASSIGNMENT;
                } else {
                        if (word->o_assignment == DEFINITELY_ASSIGNMENT)
                                command->assignment_cnt++;
                        word->o_assignment = MAYBE_ASSIGNMENT;
                }

#if HAS_KEYWORDS
# if ENABLE_HUSH_CASE
                if (ctx->ctx_dsemicolon
                 && strcmp(word->data, "esac") != 0 /* not "... pattern) cmd;; esac" */
                ) {
                        /* already done when ctx_dsemicolon was set to 1: */
                        /* ctx->ctx_res_w = RES_MATCH; */
                        ctx->ctx_dsemicolon = 0;
                } else
# endif
                if (!command->argv /* if it's the first word... */
# if ENABLE_HUSH_LOOPS
                 && ctx->ctx_res_w != RES_FOR /* ...not after FOR or IN */
                 && ctx->ctx_res_w != RES_IN
# endif
# if ENABLE_HUSH_CASE
                 && ctx->ctx_res_w != RES_CASE
# endif
                ) {
                        debug_printf_parse("checking '%s' for reserved-ness\n", word->data);
                        if (reserved_word(word, ctx)) {
                                o_reset_to_empty_unquoted(word);
                                debug_printf_parse("done_word return %d\n",
                                                (ctx->ctx_res_w == RES_SNTX));
                                return (ctx->ctx_res_w == RES_SNTX);
                        }
# if ENABLE_HUSH_BASH_COMPAT
                        if (strcmp(word->data, "[[") == 0) {
                                command->cmd_type = CMD_SINGLEWORD_NOGLOB;
                        }
                        /* fall through */
# endif
                }
#endif
                if (command->group) {
                        /* "{ echo foo; } echo bar" - bad */
                        syntax_error_at(word->data);
                        debug_printf_parse("done_word return 1: syntax error, "
                                        "groups and arglists don't mix\n");
                        return 1;
                }
                if (word->has_quoted_part
                 /* optimization: and if it's ("" or '') or ($v... or `cmd`...): */
                 && (word->data[0] == '\0' || word->data[0] == SPECIAL_VAR_SYMBOL)
                 /* (otherwise it's known to be not empty and is already safe) */
                ) {
                        /* exclude "$@" - it can expand to no word despite "" */
                        char *p = word->data;
                        while (p[0] == SPECIAL_VAR_SYMBOL
                            && (p[1] & 0x7f) == '@'
                            && p[2] == SPECIAL_VAR_SYMBOL
                        ) {
                                p += 3;
                        }
                        if (p == word->data || p[0] != '\0') {
                                /* saw no "$@", or not only "$@" but some
                                 * real text is there too */
                                /* insert "empty variable" reference, this makes
                                 * e.g. "", $empty"" etc to not disappear */
                                o_addchr(word, SPECIAL_VAR_SYMBOL);
                                o_addchr(word, SPECIAL_VAR_SYMBOL);
                        }
                }
                command->argv = add_string_to_strings(command->argv, xstrdup(word->data));
                debug_print_strings("word appended to argv", command->argv);
        }

#if ENABLE_HUSH_LOOPS
        if (ctx->ctx_res_w == RES_FOR) {
                if (word->has_quoted_part
                 || !is_well_formed_var_name(command->argv[0], '\0')
                ) {
                        /* bash says just "not a valid identifier" */
                        syntax_error("not a valid identifier in for");
                        return 1;
                }
                /* Force FOR to have just one word (variable name) */
                /* NB: basically, this makes hush see "for v in ..."
                 * syntax as if it is "for v; in ...". FOR and IN become
                 * two pipe structs in parse tree. */
                done_pipe(ctx, PIPE_SEQ);
        }
#endif
#if ENABLE_HUSH_CASE
        /* Force CASE to have just one word */
        if (ctx->ctx_res_w == RES_CASE) {
                done_pipe(ctx, PIPE_SEQ);
        }
#endif

        o_reset_to_empty_unquoted(word);

        debug_printf_parse("done_word return 0\n");
        return 0;
}


/* Peek ahead in the input to find out if we have a "&n" construct,
 * as in "2>&1", that represents duplicating a file descriptor.
 * Return:
 * REDIRFD_CLOSE if >&- "close fd" construct is seen,
 * REDIRFD_SYNTAX_ERR if syntax error,
 * REDIRFD_TO_FILE if no & was seen,
 * or the number found.
 */
#if BB_MMU
#define parse_redir_right_fd(as_string, input) \
        parse_redir_right_fd(input)
#endif
static int parse_redir_right_fd(o_string *as_string, struct in_str *input)
{
        int ch, d, ok;

        ch = i_peek(input);
        if (ch != '&')
                return REDIRFD_TO_FILE;

        ch = i_getch(input);  /* get the & */
        nommu_addchr(as_string, ch);
        ch = i_peek(input);
        if (ch == '-') {
                ch = i_getch(input);
                nommu_addchr(as_string, ch);
                return REDIRFD_CLOSE;
        }
        d = 0;
        ok = 0;
        while (ch != EOF && isdigit(ch)) {
                d = d*10 + (ch-'0');
                ok = 1;
                ch = i_getch(input);
                nommu_addchr(as_string, ch);
                ch = i_peek(input);
        }
        if (ok) return d;

//TODO: this is the place to catch ">&file" bashism (redirect both fd 1 and 2)

        bb_error_msg("ambiguous redirect");
        return REDIRFD_SYNTAX_ERR;
}

/* Return code is 0 normal, 1 if a syntax error is detected
 */
static int parse_redirect(struct parse_context *ctx,
                int fd,
                redir_type style,
                struct in_str *input)
{
        struct command *command = ctx->command;
        struct redir_struct *redir;
        struct redir_struct **redirp;
        int dup_num;

        dup_num = REDIRFD_TO_FILE;
        if (style != REDIRECT_HEREDOC) {
                /* Check for a '>&1' type redirect */
                dup_num = parse_redir_right_fd(&ctx->as_string, input);
                if (dup_num == REDIRFD_SYNTAX_ERR)
                        return 1;
        } else {
                int ch = i_peek(input);
                dup_num = (ch == '-'); /* HEREDOC_SKIPTABS bit is 1 */
                if (dup_num) { /* <<-... */
                        ch = i_getch(input);
                        nommu_addchr(&ctx->as_string, ch);
                        ch = i_peek(input);
                }
        }

        if (style == REDIRECT_OVERWRITE && dup_num == REDIRFD_TO_FILE) {
                int ch = i_peek(input);
                if (ch == '|') {
                        /* >|FILE redirect ("clobbering" >).
                         * Since we do not support "set -o noclobber" yet,
                         * >| and > are the same for now. Just eat |.
                         */
                        ch = i_getch(input);
                        nommu_addchr(&ctx->as_string, ch);
                }
        }

        /* Create a new redir_struct and append it to the linked list */
        redirp = &command->redirects;
        while ((redir = *redirp) != NULL) {
                redirp = &(redir->next);
        }
        *redirp = redir = xzalloc(sizeof(*redir));
        /* redir->next = NULL; */
        /* redir->rd_filename = NULL; */
        redir->rd_type = style;
        redir->rd_fd = (fd == -1) ? redir_table[style].default_fd : fd;

        debug_printf_parse("redirect type %d %s\n", redir->rd_fd,
                                redir_table[style].descrip);

        redir->rd_dup = dup_num;
        if (style != REDIRECT_HEREDOC && dup_num != REDIRFD_TO_FILE) {
                /* Erik had a check here that the file descriptor in question
                 * is legit; I postpone that to "run time"
                 * A "-" representation of "close me" shows up as a -3 here */
                debug_printf_parse("duplicating redirect '%d>&%d'\n",
                                redir->rd_fd, redir->rd_dup);
        } else {
                /* Set ctx->pending_redirect, so we know what to do at the
                 * end of the next parsed word. */
                ctx->pending_redirect = redir;
        }
        return 0;
}

/* If a redirect is immediately preceded by a number, that number is
 * supposed to tell which file descriptor to redirect.  This routine
 * looks for such preceding numbers.  In an ideal world this routine
 * needs to handle all the following classes of redirects...
 *     echo 2>foo     # redirects fd  2 to file "foo", nothing passed to echo
 *     echo 49>foo    # redirects fd 49 to file "foo", nothing passed to echo
 *     echo -2>foo    # redirects fd  1 to file "foo",    "-2" passed to echo
 *     echo 49x>foo   # redirects fd  1 to file "foo",   "49x" passed to echo
 *
 * http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html
 * "2.7 Redirection
 * ... If n is quoted, the number shall not be recognized as part of
 * the redirection expression. For example:
 * echo \2>a
 * writes the character 2 into file a"
 * We are getting it right by setting ->has_quoted_part on any \<char>
 *
 * A -1 return means no valid number was found,
 * the caller should use the appropriate default for this redirection.
 */
static int redirect_opt_num(o_string *o)
{
        int num;

        if (o->data == NULL)
                return -1;
        num = bb_strtou(o->data, NULL, 10);
        if (errno || num < 0)
                return -1;
        o_reset_to_empty_unquoted(o);
        return num;
}

#if BB_MMU
#define fetch_till_str(as_string, input, word, skip_tabs) \
        fetch_till_str(input, word, skip_tabs)
#endif
static char *fetch_till_str(o_string *as_string,
                struct in_str *input,
                const char *word,
                int heredoc_flags)
{
        o_string heredoc = NULL_O_STRING;
        unsigned past_EOL;
        int prev = 0; /* not \ */
        int ch;

        goto jump_in;
        while (1) {
                ch = i_getch(input);
                if (ch != EOF)
                        nommu_addchr(as_string, ch);
                if ((ch == '\n' || ch == EOF)
                 && ((heredoc_flags & HEREDOC_QUOTED) || prev != '\\')
                ) {
                        if (strcmp(heredoc.data + past_EOL, word) == 0) {
                                heredoc.data[past_EOL] = '\0';
                                debug_printf_parse("parsed heredoc '%s'\n", heredoc.data);
                                return heredoc.data;
                        }
                        while (ch == '\n') {
                                o_addchr(&heredoc, ch);
                                prev = ch;
 jump_in:
                                past_EOL = heredoc.length;
                                do {
                                        ch = i_getch(input);
                                        if (ch != EOF)
                                                nommu_addchr(as_string, ch);
                                } while ((heredoc_flags & HEREDOC_SKIPTABS) && ch == '\t');
                        }
                }
                if (ch == EOF) {
                        o_free_unsafe(&heredoc);
                        return NULL;
                }
                o_addchr(&heredoc, ch);
                nommu_addchr(as_string, ch);
                if (prev == '\\' && ch == '\\')
                        /* Correctly handle foo\\<eol> (not a line cont.) */
                        prev = 0; /* not \ */
                else
                        prev = ch;
        }
}

/* Look at entire parse tree for not-yet-loaded REDIRECT_HEREDOCs
 * and load them all. There should be exactly heredoc_cnt of them.
 */
static int fetch_heredocs(int heredoc_cnt, struct parse_context *ctx, struct in_str *input)
{
        struct pipe *pi = ctx->list_head;

        while (pi && heredoc_cnt) {
                int i;
                struct command *cmd = pi->cmds;

                debug_printf_parse("fetch_heredocs: num_cmds:%d cmd argv0:'%s'\n",
                                pi->num_cmds,
                                cmd->argv ? cmd->argv[0] : "NONE");
                for (i = 0; i < pi->num_cmds; i++) {
                        struct redir_struct *redir = cmd->redirects;

                        debug_printf_parse("fetch_heredocs: %d cmd argv0:'%s'\n",
                                        i, cmd->argv ? cmd->argv[0] : "NONE");
                        while (redir) {
                                if (redir->rd_type == REDIRECT_HEREDOC) {
                                        char *p;

                                        redir->rd_type = REDIRECT_HEREDOC2;
                                        /* redir->rd_dup is (ab)used to indicate <<- */
                                        p = fetch_till_str(&ctx->as_string, input,
                                                        redir->rd_filename, redir->rd_dup);
                                        if (!p) {
                                                syntax_error("unexpected EOF in here document");
                                                return 1;
                                        }
                                        free(redir->rd_filename);
                                        redir->rd_filename = p;
                                        heredoc_cnt--;
                                }
                                redir = redir->next;
                        }
                        cmd++;
                }
                pi = pi->next;
        }
#if 0
        /* Should be 0. If it isn't, it's a parse error */
        if (heredoc_cnt)
                bb_error_msg_and_die("heredoc BUG 2");
#endif
        return 0;
}


static int run_list(struct pipe *pi);
#if BB_MMU
#define parse_stream(pstring, input, end_trigger) \
        parse_stream(input, end_trigger)
#endif
static struct pipe *parse_stream(char **pstring,
                struct in_str *input,
                int end_trigger);


#if !ENABLE_HUSH_FUNCTIONS
#define parse_group(dest, ctx, input, ch) \
        parse_group(ctx, input, ch)
#endif
static int parse_group(o_string *dest, struct parse_context *ctx,
        struct in_str *input, int ch)
{
        /* dest contains characters seen prior to ( or {.
         * Typically it's empty, but for function defs,
         * it contains function name (without '()'). */
        struct pipe *pipe_list;
        int endch;
        struct command *command = ctx->command;

        debug_printf_parse("parse_group entered\n");
#if ENABLE_HUSH_FUNCTIONS
        if (ch == '(' && !dest->has_quoted_part) {
                if (dest->length)
                        if (done_word(dest, ctx))
                                return 1;
                if (!command->argv)
                        goto skip; /* (... */
                if (command->argv[1]) { /* word word ... (... */
                        syntax_error_unexpected_ch('(');
                        return 1;
                }
                /* it is "word(..." or "word (..." */
                do
                        ch = i_getch(input);
                while (ch == ' ' || ch == '\t');
                if (ch != ')') {
                        syntax_error_unexpected_ch(ch);
                        return 1;
                }
                nommu_addchr(&ctx->as_string, ch);
                do
                        ch = i_getch(input);
                while (ch == ' ' || ch == '\t' || ch == '\n');
                if (ch != '{') {
                        syntax_error_unexpected_ch(ch);
                        return 1;
                }
                nommu_addchr(&ctx->as_string, ch);
                command->cmd_type = CMD_FUNCDEF;
                goto skip;
        }
#endif

#if 0 /* Prevented by caller */
        if (command->argv /* word [word]{... */
         || dest->length /* word{... */
         || dest->has_quoted_part /* ""{... */
        ) {
                syntax_error(NULL);
                debug_printf_parse("parse_group return 1: "
                        "syntax error, groups and arglists don't mix\n");
                return 1;
        }
#endif

#if ENABLE_HUSH_FUNCTIONS
 skip:
#endif
        endch = '}';
        if (ch == '(') {
                endch = ')';
                command->cmd_type = CMD_SUBSHELL;
        } else {
                /* bash does not allow "{echo...", requires whitespace */
                ch = i_getch(input);
                if (ch != ' ' && ch != '\t' && ch != '\n') {
                        syntax_error_unexpected_ch(ch);
                        return 1;
                }
                nommu_addchr(&ctx->as_string, ch);
        }

        {
#if BB_MMU
# define as_string NULL
#else
                char *as_string = NULL;
#endif
                pipe_list = parse_stream(&as_string, input, endch);
#if !BB_MMU
                if (as_string)
                        o_addstr(&ctx->as_string, as_string);
#endif
                /* empty ()/{} or parse error? */
                if (!pipe_list || pipe_list == ERR_PTR) {
                        /* parse_stream already emitted error msg */
                        if (!BB_MMU)
                                free(as_string);
                        debug_printf_parse("parse_group return 1: "
                                "parse_stream returned %p\n", pipe_list);
                        return 1;
                }
                command->group = pipe_list;
#if !BB_MMU
                as_string[strlen(as_string) - 1] = '\0'; /* plink ')' or '}' */
                command->group_as_string = as_string;
                debug_printf_parse("end of group, remembering as:'%s'\n",
                                command->group_as_string);
#endif
#undef as_string
        }
        debug_printf_parse("parse_group return 0\n");
        return 0;
        /* command remains "open", available for possible redirects */
}

#if ENABLE_HUSH_TICK || ENABLE_SH_MATH_SUPPORT || ENABLE_HUSH_DOLLAR_OPS
/* Subroutines for copying $(...) and `...` things */
static void add_till_backquote(o_string *dest, struct in_str *input, int in_dquote);
/* '...' */
static void add_till_single_quote(o_string *dest, struct in_str *input)
{
        while (1) {
                int ch = i_getch(input);
                if (ch == EOF) {
                        syntax_error_unterm_ch('\'');
                        /*xfunc_die(); - redundant */
                }
                if (ch == '\'')
                        return;
                o_addchr(dest, ch);
        }
}
/* "...\"...`..`...." - do we need to handle "...$(..)..." too? */
static void add_till_double_quote(o_string *dest, struct in_str *input)
{
        while (1) {
                int ch = i_getch(input);
                if (ch == EOF) {
                        syntax_error_unterm_ch('"');
                        /*xfunc_die(); - redundant */
                }
                if (ch == '"')
                        return;
                if (ch == '\\') {  /* \x. Copy both chars. */
                        o_addchr(dest, ch);
                        ch = i_getch(input);
                }
                o_addchr(dest, ch);
                if (ch == '`') {
                        add_till_backquote(dest, input, /*in_dquote:*/ 1);
                        o_addchr(dest, ch);
                        continue;
                }
                //if (ch == '$') ...
        }
}
/* Process `cmd` - copy contents until "`" is seen. Complicated by
 * \` quoting.
 * "Within the backquoted style of command substitution, backslash
 * shall retain its literal meaning, except when followed by: '$', '`', or '\'.
 * The search for the matching backquote shall be satisfied by the first
 * backquote found without a preceding backslash; during this search,
 * if a non-escaped backquote is encountered within a shell comment,
 * a here-document, an embedded command substitution of the $(command)
 * form, or a quoted string, undefined results occur. A single-quoted
 * or double-quoted string that begins, but does not end, within the
 * "`...`" sequence produces undefined results."
 * Example                               Output
 * echo `echo '\'TEST\`echo ZZ\`BEST`    \TESTZZBEST
 */
static void add_till_backquote(o_string *dest, struct in_str *input, int in_dquote)
{
        while (1) {
                int ch = i_getch(input);
                if (ch == '`')
                        return;
                if (ch == '\\') {
                        /* \x. Copy both unless it is \`, \$, \\ and maybe \" */
                        ch = i_getch(input);
                        if (ch != '`'
                         && ch != '$'
                         && ch != '\\'
                         && (!in_dquote || ch != '"')
                        ) {
                                o_addchr(dest, '\\');
                        }
                }
                if (ch == EOF) {
                        syntax_error_unterm_ch('`');
                        /*xfunc_die(); - redundant */
                }
                o_addchr(dest, ch);
        }
}
/* Process $(cmd) - copy contents until ")" is seen. Complicated by
 * quoting and nested ()s.
 * "With the $(command) style of command substitution, all characters
 * following the open parenthesis to the matching closing parenthesis
 * constitute the command. Any valid shell script can be used for command,
 * except a script consisting solely of redirections which produces
 * unspecified results."
 * Example                              Output
 * echo $(echo '(TEST)' BEST)           (TEST) BEST
 * echo $(echo 'TEST)' BEST)            TEST) BEST
 * echo $(echo \(\(TEST\) BEST)         ((TEST) BEST
 *
 * Also adapted to eat ${var%...} and $((...)) constructs, since ... part
 * can contain arbitrary constructs, just like $(cmd).
 * In bash compat mode, it needs to also be able to stop on ':' or '/'
 * for ${var:N[:M]} and ${var/P[/R]} parsing.
 */
#define DOUBLE_CLOSE_CHAR_FLAG 0x80
static int add_till_closing_bracket(o_string *dest, struct in_str *input, unsigned end_ch)
{
        int ch;
        char dbl = end_ch & DOUBLE_CLOSE_CHAR_FLAG;
# if ENABLE_HUSH_BASH_COMPAT
        char end_char2 = end_ch >> 8;
# endif
        end_ch &= (DOUBLE_CLOSE_CHAR_FLAG - 1);

        while (1) {
                ch = i_getch(input);
                if (ch == EOF) {
                        syntax_error_unterm_ch(end_ch);
                        /*xfunc_die(); - redundant */
                }
                if (ch == end_ch  IF_HUSH_BASH_COMPAT( || ch == end_char2)) {
                        if (!dbl)
                                break;
                        /* we look for closing )) of $((EXPR)) */
                        if (i_peek(input) == end_ch) {
                                i_getch(input); /* eat second ')' */
                                break;
                        }
                }
                o_addchr(dest, ch);
                if (ch == '(' || ch == '{') {
                        ch = (ch == '(' ? ')' : '}');
                        add_till_closing_bracket(dest, input, ch);
                        o_addchr(dest, ch);
                        continue;
                }
                if (ch == '\'') {
                        add_till_single_quote(dest, input);
                        o_addchr(dest, ch);
                        continue;
                }
                if (ch == '"') {
                        add_till_double_quote(dest, input);
                        o_addchr(dest, ch);
                        continue;
                }
                if (ch == '`') {
                        add_till_backquote(dest, input, /*in_dquote:*/ 0);
                        o_addchr(dest, ch);
                        continue;
                }
                if (ch == '\\') {
                        /* \x. Copy verbatim. Important for  \(, \) */
                        ch = i_getch(input);
                        if (ch == EOF) {
                                syntax_error_unterm_ch(')');
                                /*xfunc_die(); - redundant */
                        }
                        o_addchr(dest, ch);
                        continue;
                }
        }
        return ch;
}
#endif /* ENABLE_HUSH_TICK || ENABLE_SH_MATH_SUPPORT || ENABLE_HUSH_DOLLAR_OPS */

/* Return code: 0 for OK, 1 for syntax error */
#if BB_MMU
#define parse_dollar(as_string, dest, input, quote_mask) \
        parse_dollar(dest, input, quote_mask)
#define as_string NULL
#endif
static int parse_dollar(o_string *as_string,
                o_string *dest,
                struct in_str *input, unsigned char quote_mask)
{
        int ch = i_peek(input);  /* first character after the $ */

        debug_printf_parse("parse_dollar entered: ch='%c'\n", ch);
        if (isalpha(ch)) {
                ch = i_getch(input);
                nommu_addchr(as_string, ch);
 make_var:
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
                while (1) {
                        debug_printf_parse(": '%c'\n", ch);
                        o_addchr(dest, ch | quote_mask);
                        quote_mask = 0;
                        ch = i_peek(input);
                        if (!isalnum(ch) && ch != '_')
                                break;
                        ch = i_getch(input);
                        nommu_addchr(as_string, ch);
                }
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
        } else if (isdigit(ch)) {
 make_one_char_var:
                ch = i_getch(input);
                nommu_addchr(as_string, ch);
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
                debug_printf_parse(": '%c'\n", ch);
                o_addchr(dest, ch | quote_mask);
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
        } else switch (ch) {
        case '$': /* pid */
        case '!': /* last bg pid */
        case '?': /* last exit code */
        case '#': /* number of args */
        case '*': /* args */
        case '@': /* args */
                goto make_one_char_var;
        case '{': {
                o_addchr(dest, SPECIAL_VAR_SYMBOL);

                ch = i_getch(input); /* eat '{' */
                nommu_addchr(as_string, ch);

                ch = i_getch(input); /* first char after '{' */
                /* It should be ${?}, or ${#var},
                 * or even ${?+subst} - operator acting on a special variable,
                 * or the beginning of variable name.
                 */
                if (ch == EOF
                 || (!strchr(_SPECIAL_VARS_STR, ch) && !isalnum(ch)) /* not one of those */
                ) {
 bad_dollar_syntax:
                        syntax_error_unterm_str("${name}");
                        debug_printf_parse("parse_dollar return 1: unterminated ${name}\n");
                        return 1;
                }
                nommu_addchr(as_string, ch);
                ch |= quote_mask;

                /* It's possible to just call add_till_closing_bracket() at this point.
                 * However, this regresses some of our testsuite cases
                 * which check invalid constructs like ${%}.
                 * Oh well... let's check that the var name part is fine... */

                while (1) {
                        unsigned pos;

                        o_addchr(dest, ch);
                        debug_printf_parse(": '%c'\n", ch);

                        ch = i_getch(input);
                        nommu_addchr(as_string, ch);
                        if (ch == '}')
                                break;

                        if (!isalnum(ch) && ch != '_') {
                                unsigned end_ch;
                                unsigned char last_ch;
                                /* handle parameter expansions
                                 * http://www.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02
                                 */
                                if (!strchr(VAR_SUBST_OPS, ch)) /* ${var<bad_char>... */
                                        goto bad_dollar_syntax;

                                /* Eat everything until closing '}' (or ':') */
                                end_ch = '}';
                                if (ENABLE_HUSH_BASH_COMPAT
                                 && ch == ':'
                                 && !strchr(MINUS_PLUS_EQUAL_QUESTION, i_peek(input))
                                ) {
                                        /* It's ${var:N[:M]} thing */
                                        end_ch = '}' * 0x100 + ':';
                                }
                                if (ENABLE_HUSH_BASH_COMPAT
                                 && ch == '/'
                                ) {
                                        /* It's ${var/[/]pattern[/repl]} thing */
                                        if (i_peek(input) == '/') { /* ${var//pattern[/repl]}? */
                                                i_getch(input);
                                                nommu_addchr(as_string, '/');
                                                ch = '\\';
                                        }
                                        end_ch = '}' * 0x100 + '/';
                                }
                                o_addchr(dest, ch);
 again:
                                if (!BB_MMU)
                                        pos = dest->length;
#if ENABLE_HUSH_DOLLAR_OPS
                                last_ch = add_till_closing_bracket(dest, input, end_ch);
#else
#error Simple code to only allow ${var} is not implemented
#endif
                                if (as_string) {
                                        o_addstr(as_string, dest->data + pos);
                                        o_addchr(as_string, last_ch);
                                }

                                if (ENABLE_HUSH_BASH_COMPAT && (end_ch & 0xff00)) {
                                        /* close the first block: */
                                        o_addchr(dest, SPECIAL_VAR_SYMBOL);
                                        /* while parsing N from ${var:N[:M]}
                                         * or pattern from ${var/[/]pattern[/repl]} */
                                        if ((end_ch & 0xff) == last_ch) {
                                                /* got ':' or '/'- parse the rest */
                                                end_ch = '}';
                                                goto again;
                                        }
                                        /* got '}' */
                                        if (end_ch == '}' * 0x100 + ':') {
                                                /* it's ${var:N} - emulate :999999999 */
                                                o_addstr(dest, "999999999");
                                        } /* else: it's ${var/[/]pattern} */
                                }
                                break;
                        }
                }
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
                break;
        }
#if ENABLE_SH_MATH_SUPPORT || ENABLE_HUSH_TICK
        case '(': {
                unsigned pos;

                ch = i_getch(input);
                nommu_addchr(as_string, ch);
# if ENABLE_SH_MATH_SUPPORT
                if (i_peek(input) == '(') {
                        ch = i_getch(input);
                        nommu_addchr(as_string, ch);
                        o_addchr(dest, SPECIAL_VAR_SYMBOL);
                        o_addchr(dest, /*quote_mask |*/ '+');
                        if (!BB_MMU)
                                pos = dest->length;
                        add_till_closing_bracket(dest, input, ')' | DOUBLE_CLOSE_CHAR_FLAG);
                        if (as_string) {
                                o_addstr(as_string, dest->data + pos);
                                o_addchr(as_string, ')');
                                o_addchr(as_string, ')');
                        }
                        o_addchr(dest, SPECIAL_VAR_SYMBOL);
                        break;
                }
# endif
# if ENABLE_HUSH_TICK
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
                o_addchr(dest, quote_mask | '`');
                if (!BB_MMU)
                        pos = dest->length;
                add_till_closing_bracket(dest, input, ')');
                if (as_string) {
                        o_addstr(as_string, dest->data + pos);
                        o_addchr(as_string, ')');
                }
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
# endif
                break;
        }
#endif
        case '_':
                ch = i_getch(input);
                nommu_addchr(as_string, ch);
                ch = i_peek(input);
                if (isalnum(ch)) { /* it's $_name or $_123 */
                        ch = '_';
                        goto make_var;
                }
                /* else: it's $_ */
        /* TODO: $_ and $-: */
        /* $_ Shell or shell script name; or last argument of last command
         * (if last command wasn't a pipe; if it was, bash sets $_ to "");
         * but in command's env, set to full pathname used to invoke it */
        /* $- Option flags set by set builtin or shell options (-i etc) */
        default:
                o_addQchr(dest, '$');
        }
        debug_printf_parse("parse_dollar return 0\n");
        return 0;
#undef as_string
}

#if BB_MMU
# if ENABLE_HUSH_BASH_COMPAT
#define encode_string(as_string, dest, input, dquote_end, process_bkslash) \
        encode_string(dest, input, dquote_end, process_bkslash)
# else
/* only ${var/pattern/repl} (its pattern part) needs additional mode */
#define encode_string(as_string, dest, input, dquote_end, process_bkslash) \
        encode_string(dest, input, dquote_end)
# endif
#define as_string NULL

#else /* !MMU */

# if ENABLE_HUSH_BASH_COMPAT
/* all parameters are needed, no macro tricks */
# else
#define encode_string(as_string, dest, input, dquote_end, process_bkslash) \
        encode_string(as_string, dest, input, dquote_end)
# endif
#endif
static int encode_string(o_string *as_string,
                o_string *dest,
                struct in_str *input,
                int dquote_end,
                int process_bkslash)
{
#if !ENABLE_HUSH_BASH_COMPAT
        const int process_bkslash = 1;
#endif
        int ch;
        int next;

 again:
        ch = i_getch(input);
        if (ch != EOF)
                nommu_addchr(as_string, ch);
        if (ch == dquote_end) { /* may be only '"' or EOF */
                debug_printf_parse("encode_string return 0\n");
                return 0;
        }
        /* note: can't move it above ch == dquote_end check! */
        if (ch == EOF) {
                syntax_error_unterm_ch('"');
                /*xfunc_die(); - redundant */
        }
        next = '\0';
        if (ch != '\n') {
                next = i_peek(input);
        }
        debug_printf_parse("\" ch=%c (%d) escape=%d\n",
                        ch, ch, !!(dest->o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
        if (process_bkslash && ch == '\\') {
                if (next == EOF) {
                        syntax_error("\\<eof>");
                        xfunc_die();
                }
                /* bash:
                 * "The backslash retains its special meaning [in "..."]
                 * only when followed by one of the following characters:
                 * $, `, ", \, or <newline>.  A double quote may be quoted
                 * within double quotes by preceding it with a backslash."
                 * NB: in (unquoted) heredoc, above does not apply to ",
                 * therefore we check for it by "next == dquote_end" cond.
                 */
                if (next == dquote_end || strchr("$`\\\n", next)) {
                        ch = i_getch(input); /* eat next */
                        if (ch == '\n')
                                goto again; /* skip \<newline> */
                } /* else: ch remains == '\\', and we double it below: */
                o_addqchr(dest, ch); /* \c if c is a glob char, else just c */
                nommu_addchr(as_string, ch);
                goto again;
        }
        if (ch == '$') {
                if (parse_dollar(as_string, dest, input, /*quote_mask:*/ 0x80) != 0) {
                        debug_printf_parse("encode_string return 1: "
                                        "parse_dollar returned non-0\n");
                        return 1;
                }
                goto again;
        }
#if ENABLE_HUSH_TICK
        if (ch == '`') {
                //unsigned pos = dest->length;
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
                o_addchr(dest, 0x80 | '`');
                add_till_backquote(dest, input, /*in_dquote:*/ dquote_end == '"');
                o_addchr(dest, SPECIAL_VAR_SYMBOL);
                //debug_printf_subst("SUBST RES3 '%s'\n", dest->data + pos);
                goto again;
        }
#endif
        o_addQchr(dest, ch);
        goto again;
#undef as_string
}

/*
 * Scan input until EOF or end_trigger char.
 * Return a list of pipes to execute, or NULL on EOF
 * or if end_trigger character is met.
 * On syntax error, exit is shell is not interactive,
 * reset parsing machinery and start parsing anew,
 * or return ERR_PTR.
 */
static struct pipe *parse_stream(char **pstring,
                struct in_str *input,
                int end_trigger)
{
        struct parse_context ctx;
        o_string dest = NULL_O_STRING;
        int heredoc_cnt;

        /* Single-quote triggers a bypass of the main loop until its mate is
         * found.  When recursing, quote state is passed in via dest->o_expflags.
         */
        debug_printf_parse("parse_stream entered, end_trigger='%c'\n",
                        end_trigger ? end_trigger : 'X');
        debug_enter();

        /* If very first arg is "" or '', dest.data may end up NULL.
         * Preventing this: */
        o_addchr(&dest, '\0');
        dest.length = 0;

        /* We used to separate words on $IFS here. This was wrong.
         * $IFS is used only for word splitting when $var is expanded,
         * here we should use blank chars as separators, not $IFS
         */

 reset: /* we come back here only on syntax errors in interactive shell */

#if ENABLE_HUSH_INTERACTIVE
        input->promptmode = 0; /* PS1 */
#endif
        if (MAYBE_ASSIGNMENT != 0)
                dest.o_assignment = MAYBE_ASSIGNMENT;
        initialize_context(&ctx);
        heredoc_cnt = 0;
        while (1) {
                const char *is_blank;
                const char *is_special;
                int ch;
                int next;
                int redir_fd;
                redir_type redir_style;

                ch = i_getch(input);
                debug_printf_parse(": ch=%c (%d) escape=%d\n",
                                ch, ch, !!(dest.o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
                if (ch == EOF) {
                        struct pipe *pi;

                        if (heredoc_cnt) {
                                syntax_error_unterm_str("here document");
                                goto parse_error;
                        }
                        /* end_trigger == '}' case errors out earlier,
                         * checking only ')' */
                        if (end_trigger == ')') {
                                syntax_error_unterm_ch('('); /* exits */
                                /* goto parse_error; */
                        }

                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        o_free(&dest);
                        done_pipe(&ctx, PIPE_SEQ);
                        pi = ctx.list_head;
                        /* If we got nothing... */
                        /* (this makes bare "&" cmd a no-op.
                         * bash says: "syntax error near unexpected token '&'") */
                        if (pi->num_cmds == 0
                            IF_HAS_KEYWORDS( && pi->res_word == RES_NONE)
                        ) {
                                free_pipe_list(pi);
                                pi = NULL;
                        }
#if !BB_MMU
                        debug_printf_parse("as_string '%s'\n", ctx.as_string.data);
                        if (pstring)
                                *pstring = ctx.as_string.data;
                        else
                                o_free_unsafe(&ctx.as_string);
#endif
                        debug_leave();
                        debug_printf_parse("parse_stream return %p\n", pi);
                        return pi;
                }
                nommu_addchr(&ctx.as_string, ch);

                next = '\0';
                if (ch != '\n')
                        next = i_peek(input);

                is_special = "{}<>;&|()#'" /* special outside of "str" */
                                "\\$\"" IF_HUSH_TICK("`"); /* always special */
                /* Are { and } special here? */
                if (ctx.command->argv /* word [word]{... - non-special */
                 || dest.length       /* word{... - non-special */
                 || dest.has_quoted_part     /* ""{... - non-special */
                 || (next != ';'             /* }; - special */
                    && next != ')'           /* }) - special */
                    && next != '&'           /* }& and }&& ... - special */
                    && next != '|'           /* }|| ... - special */
                    && !strchr(defifs, next) /* {word - non-special */
                    )
                ) {
                        /* They are not special, skip "{}" */
                        is_special += 2;
                }
                is_special = strchr(is_special, ch);
                is_blank = strchr(defifs, ch);

                if (!is_special && !is_blank) { /* ordinary char */
 ordinary_char:
                        o_addQchr(&dest, ch);
                        if ((dest.o_assignment == MAYBE_ASSIGNMENT
                            || dest.o_assignment == WORD_IS_KEYWORD)
                         && ch == '='
                         && is_well_formed_var_name(dest.data, '=')
                        ) {
                                dest.o_assignment = DEFINITELY_ASSIGNMENT;
                        }
                        continue;
                }

                if (is_blank) {
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        if (ch == '\n') {
                                /* Is this a case when newline is simply ignored?
                                 * Some examples:
                                 * "cmd | <newline> cmd ..."
                                 * "case ... in <newline> word) ..."
                                 */
                                if (IS_NULL_CMD(ctx.command)
                                 && dest.length == 0 && !dest.has_quoted_part
                                ) {
                                        /* This newline can be ignored. But...
                                         * without the below check, interactive shell
                                         * will ignore even lines with bare <newline>,
                                         * and show the continuation prompt:
                                         * ps1_prompt$ <enter>
                                         * ps2> _   <=== wrong prompt, should be ps1
                                         */
                                        struct pipe *pi = ctx.list_head;
                                        if (pi->num_cmds != 0)
                                                continue;
                                }
                                /* Treat newline as a command separator. */
                                done_pipe(&ctx, PIPE_SEQ);
                                debug_printf_parse("heredoc_cnt:%d\n", heredoc_cnt);
                                if (heredoc_cnt) {
                                        if (fetch_heredocs(heredoc_cnt, &ctx, input)) {
                                                goto parse_error;
                                        }
                                        heredoc_cnt = 0;
                                }
                                dest.o_assignment = MAYBE_ASSIGNMENT;
                                ch = ';';
                                /* note: if (is_blank) continue;
                                 * will still trigger for us */
                        }
                }

                /* "cmd}" or "cmd }..." without semicolon or &:
                 * } is an ordinary char in this case, even inside { cmd; }
                 * Pathological example: { ""}; } should exec "}" cmd
                 */
                if (ch == '}') {
                        if (!IS_NULL_CMD(ctx.command) /* cmd } */
                         || dest.length != 0 /* word} */
                         || dest.has_quoted_part    /* ""} */
                        ) {
                                goto ordinary_char;
                        }
                        if (!IS_NULL_PIPE(ctx.pipe)) /* cmd | } */
                                goto skip_end_trigger;
                        /* else: } does terminate a group */
                }

                if (end_trigger && end_trigger == ch
                 && (ch != ';' || heredoc_cnt == 0)
#if ENABLE_HUSH_CASE
                 && (ch != ')'
                    || ctx.ctx_res_w != RES_MATCH
                    || (!dest.has_quoted_part && strcmp(dest.data, "esac") == 0)
                    )
#endif
                ) {
                        if (heredoc_cnt) {
                                /* This is technically valid:
                                 * { cat <<HERE; }; echo Ok
                                 * heredoc
                                 * heredoc
                                 * HERE
                                 * but we don't support this.
                                 * We require heredoc to be in enclosing {}/(),
                                 * if any.
                                 */
                                syntax_error_unterm_str("here document");
                                goto parse_error;
                        }
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        done_pipe(&ctx, PIPE_SEQ);
                        dest.o_assignment = MAYBE_ASSIGNMENT;
                        /* Do we sit outside of any if's, loops or case's? */
                        if (!HAS_KEYWORDS
                         IF_HAS_KEYWORDS(|| (ctx.ctx_res_w == RES_NONE && ctx.old_flag == 0))
                        ) {
                                o_free(&dest);
#if !BB_MMU
                                debug_printf_parse("as_string '%s'\n", ctx.as_string.data);
                                if (pstring)
                                        *pstring = ctx.as_string.data;
                                else
                                        o_free_unsafe(&ctx.as_string);
#endif
                                debug_leave();
                                debug_printf_parse("parse_stream return %p: "
                                                "end_trigger char found\n",
                                                ctx.list_head);
                                return ctx.list_head;
                        }
                }
 skip_end_trigger:
                if (is_blank)
                        continue;

                /* Catch <, > before deciding whether this word is
                 * an assignment. a=1 2>z b=2: b=2 is still assignment */
                switch (ch) {
                case '>':
                        redir_fd = redirect_opt_num(&dest);
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        redir_style = REDIRECT_OVERWRITE;
                        if (next == '>') {
                                redir_style = REDIRECT_APPEND;
                                ch = i_getch(input);
                                nommu_addchr(&ctx.as_string, ch);
                        }
#if 0
                        else if (next == '(') {
                                syntax_error(">(process) not supported");
                                goto parse_error;
                        }
#endif
                        if (parse_redirect(&ctx, redir_fd, redir_style, input))
                                goto parse_error;
                        continue; /* back to top of while (1) */
                case '<':
                        redir_fd = redirect_opt_num(&dest);
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        redir_style = REDIRECT_INPUT;
                        if (next == '<') {
                                redir_style = REDIRECT_HEREDOC;
                                heredoc_cnt++;
                                debug_printf_parse("++heredoc_cnt=%d\n", heredoc_cnt);
                                ch = i_getch(input);
                                nommu_addchr(&ctx.as_string, ch);
                        } else if (next == '>') {
                                redir_style = REDIRECT_IO;
                                ch = i_getch(input);
                                nommu_addchr(&ctx.as_string, ch);
                        }
#if 0
                        else if (next == '(') {
                                syntax_error("<(process) not supported");
                                goto parse_error;
                        }
#endif
                        if (parse_redirect(&ctx, redir_fd, redir_style, input))
                                goto parse_error;
                        continue; /* back to top of while (1) */
                case '#':
                        if (dest.length == 0 && !dest.has_quoted_part) {
                                /* skip "#comment" */
                                while (1) {
                                        ch = i_peek(input);
                                        if (ch == EOF || ch == '\n')
                                                break;
                                        i_getch(input);
                                        /* note: we do not add it to &ctx.as_string */
                                }
                                nommu_addchr(&ctx.as_string, '\n');
                                continue; /* back to top of while (1) */
                        }
                        break;
                case '\\':
                        if (next == '\n') {
                                /* It's "\<newline>" */
#if !BB_MMU
                                /* Remove trailing '\' from ctx.as_string */
                                ctx.as_string.data[--ctx.as_string.length] = '\0';
#endif
                                ch = i_getch(input); /* eat it */
                                continue; /* back to top of while (1) */
                        }
                        break;
                }

                if (dest.o_assignment == MAYBE_ASSIGNMENT
                 /* check that we are not in word in "a=1 2>word b=1": */
                 && !ctx.pending_redirect
                ) {
                        /* ch is a special char and thus this word
                         * cannot be an assignment */
                        dest.o_assignment = NOT_ASSIGNMENT;
                }

                /* Note: nommu_addchr(&ctx.as_string, ch) is already done */

                switch (ch) {
                case '#': /* non-comment #: "echo a#b" etc */
                        o_addQchr(&dest, ch);
                        break;
                case '\\':
                        if (next == EOF) {
                                syntax_error("\\<eof>");
                                xfunc_die();
                        }
                        ch = i_getch(input);
                        /* note: ch != '\n' (that case does not reach this place) */
                        o_addchr(&dest, '\\');
                        /*nommu_addchr(&ctx.as_string, '\\'); - already done */
                        o_addchr(&dest, ch);
                        nommu_addchr(&ctx.as_string, ch);
                        /* Example: echo Hello \2>file
                         * we need to know that word 2 is quoted */
                        dest.has_quoted_part = 1;
                        break;
                case '$':
                        if (parse_dollar(&ctx.as_string, &dest, input, /*quote_mask:*/ 0) != 0) {
                                debug_printf_parse("parse_stream parse error: "
                                        "parse_dollar returned non-0\n");
                                goto parse_error;
                        }
                        break;
                case '\'':
                        dest.has_quoted_part = 1;
                        while (1) {
                                ch = i_getch(input);
                                if (ch == EOF) {
                                        syntax_error_unterm_ch('\'');
                                        /*xfunc_die(); - redundant */
                                }
                                nommu_addchr(&ctx.as_string, ch);
                                if (ch == '\'')
                                        break;
                                o_addqchr(&dest, ch);
                        }
                        break;
                case '"':
                        dest.has_quoted_part = 1;
                        if (dest.o_assignment == NOT_ASSIGNMENT)
                                dest.o_expflags |= EXP_FLAG_ESC_GLOB_CHARS;
                        if (encode_string(&ctx.as_string, &dest, input, '"', /*process_bkslash:*/ 1))
                                goto parse_error;
                        dest.o_expflags &= ~EXP_FLAG_ESC_GLOB_CHARS;
                        break;
#if ENABLE_HUSH_TICK
                case '`': {
                        unsigned pos;

                        o_addchr(&dest, SPECIAL_VAR_SYMBOL);
                        o_addchr(&dest, '`');
                        pos = dest.length;
                        add_till_backquote(&dest, input, /*in_dquote:*/ 0);
# if !BB_MMU
                        o_addstr(&ctx.as_string, dest.data + pos);
                        o_addchr(&ctx.as_string, '`');
# endif
                        o_addchr(&dest, SPECIAL_VAR_SYMBOL);
                        //debug_printf_subst("SUBST RES3 '%s'\n", dest.data + pos);
                        break;
                }
#endif
                case ';':
#if ENABLE_HUSH_CASE
 case_semi:
#endif
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        done_pipe(&ctx, PIPE_SEQ);
#if ENABLE_HUSH_CASE
                        /* Eat multiple semicolons, detect
                         * whether it means something special */
                        while (1) {
                                ch = i_peek(input);
                                if (ch != ';')
                                        break;
                                ch = i_getch(input);
                                nommu_addchr(&ctx.as_string, ch);
                                if (ctx.ctx_res_w == RES_CASE_BODY) {
                                        ctx.ctx_dsemicolon = 1;
                                        ctx.ctx_res_w = RES_MATCH;
                                        break;
                                }
                        }
#endif
 new_cmd:
                        /* We just finished a cmd. New one may start
                         * with an assignment */
                        dest.o_assignment = MAYBE_ASSIGNMENT;
                        break;
                case '&':
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
                        if (next == '&') {
                                ch = i_getch(input);
                                nommu_addchr(&ctx.as_string, ch);
                                done_pipe(&ctx, PIPE_AND);
                        } else {
                                done_pipe(&ctx, PIPE_BG);
                        }
                        goto new_cmd;
                case '|':
                        if (done_word(&dest, &ctx)) {
                                goto parse_error;
                        }
#if ENABLE_HUSH_CASE
                        if (ctx.ctx_res_w == RES_MATCH)
                                break; /* we are in case's "word | word)" */
#endif
                        if (next == '|') { /* || */
                                ch = i_getch(input);
                                nommu_addchr(&ctx.as_string, ch);
                                done_pipe(&ctx, PIPE_OR);
                        } else {
                                /* we could pick up a file descriptor choice here
                                 * with redirect_opt_num(), but bash doesn't do it.
                                 * "echo foo 2| cat" yields "foo 2". */
                                done_command(&ctx);
#if !BB_MMU
                                o_reset_to_empty_unquoted(&ctx.as_string);
#endif
                        }
                        goto new_cmd;
                case '(':
#if ENABLE_HUSH_CASE
                        /* "case... in [(]word)..." - skip '(' */
                        if (ctx.ctx_res_w == RES_MATCH
                         && ctx.command->argv == NULL /* not (word|(... */
                         && dest.length == 0 /* not word(... */
                         && dest.has_quoted_part == 0 /* not ""(... */
                        ) {
                                continue;
                        }
#endif
                case '{':
                        if (parse_group(&dest, &ctx, input, ch) != 0) {
                                goto parse_error;
                        }
                        goto new_cmd;
                case ')':
#if ENABLE_HUSH_CASE
                        if (ctx.ctx_res_w == RES_MATCH)
                                goto case_semi;
#endif
                case '}':
                        /* proper use of this character is caught by end_trigger:
                         * if we see {, we call parse_group(..., end_trigger='}')
                         * and it will match } earlier (not here). */
                        syntax_error_unexpected_ch(ch);
                        goto parse_error;
                default:
                        if (HUSH_DEBUG)
                                bb_error_msg_and_die("BUG: unexpected %c\n", ch);
                }
        } /* while (1) */

 parse_error:
        {
                struct parse_context *pctx;
                IF_HAS_KEYWORDS(struct parse_context *p2;)

                /* Clean up allocated tree.
                 * Sample for finding leaks on syntax error recovery path.
                 * Run it from interactive shell, watch pmap `pidof hush`.
                 * while if false; then false; fi; do break; fi
                 * Samples to catch leaks at execution:
                 * while if (true | {true;}); then echo ok; fi; do break; done
                 * while if (true | {true;}); then echo ok; fi; do (if echo ok; break; then :; fi) | cat; break; done
                 */
                pctx = &ctx;
                do {
                        /* Update pipe/command counts,
                         * otherwise freeing may miss some */
                        done_pipe(pctx, PIPE_SEQ);
                        debug_printf_clean("freeing list %p from ctx %p\n",
                                        pctx->list_head, pctx);
                        debug_print_tree(pctx->list_head, 0);
                        free_pipe_list(pctx->list_head);
                        debug_printf_clean("freed list %p\n", pctx->list_head);
#if !BB_MMU
                        o_free_unsafe(&pctx->as_string);
#endif
                        IF_HAS_KEYWORDS(p2 = pctx->stack;)
                        if (pctx != &ctx) {
                                free(pctx);
                        }
                        IF_HAS_KEYWORDS(pctx = p2;)
                } while (HAS_KEYWORDS && pctx);
                /* Free text, clear all dest fields */
                o_free(&dest);
                /* If we are not in top-level parse, we return,
                 * our caller will propagate error.
                 */
                if (end_trigger != ';') {
#if !BB_MMU
                        if (pstring)
                                *pstring = NULL;
#endif
                        debug_leave();
                        return ERR_PTR;
                }
                /* Discard cached input, force prompt */
                input->p = NULL;
                IF_HUSH_INTERACTIVE(input->promptme = 1;)
                goto reset;
        }
}


/*** Execution routines ***/

/* Expansion can recurse, need forward decls: */
#if !ENABLE_HUSH_BASH_COMPAT
/* only ${var/pattern/repl} (its pattern part) needs additional mode */
#define expand_string_to_string(str, do_unbackslash) \
        expand_string_to_string(str)
#endif
static char *expand_string_to_string(const char *str, int do_unbackslash);
#if ENABLE_HUSH_TICK
static int process_command_subs(o_string *dest, const char *s);
#endif

/* expand_strvec_to_strvec() takes a list of strings, expands
 * all variable references within and returns a pointer to
 * a list of expanded strings, possibly with larger number
 * of strings. (Think VAR="a b"; echo $VAR).
 * This new list is allocated as a single malloc block.
 * NULL-terminated list of char* pointers is at the beginning of it,
 * followed by strings themselves.
 * Caller can deallocate entire list by single free(list). */

/* A horde of its helpers come first: */

static void o_addblock_duplicate_backslash(o_string *o, const char *str, int len)
{
        while (--len >= 0) {
                char c = *str++;

#if ENABLE_HUSH_BRACE_EXPANSION
                if (c == '{' || c == '}') {
                        /* { -> \{, } -> \} */
                        o_addchr(o, '\\');
                        /* And now we want to add { or } and continue:
                         *  o_addchr(o, c);
                         *  continue;
                         * luckily, just falling throught achieves this.
                         */
                }
#endif
                o_addchr(o, c);
                if (c == '\\') {
                        /* \z -> \\\z; \<eol> -> \\<eol> */
                        o_addchr(o, '\\');
                        if (len) {
                                len--;
                                o_addchr(o, '\\');
                                o_addchr(o, *str++);
                        }
                }
        }
}

/* Store given string, finalizing the word and starting new one whenever
 * we encounter IFS char(s). This is used for expanding variable values.
 * End-of-string does NOT finalize word: think about 'echo -$VAR-' */
static int expand_on_ifs(o_string *output, int n, const char *str)
{
        while (1) {
                int word_len = strcspn(str, G.ifs);
                if (word_len) {
                        if (!(output->o_expflags & EXP_FLAG_GLOB)) {
                                o_addblock(output, str, word_len);
                        } else {
                                /* Protect backslashes against globbing up :)
                                 * Example: "v='\*'; echo b$v" prints "b\*"
                                 * (and does not try to glob on "*")
                                 */
                                o_addblock_duplicate_backslash(output, str, word_len);
                                /*/ Why can't we do it easier? */
                                /*o_addblock(output, str, word_len); - WRONG: "v='\*'; echo Z$v" prints "Z*" instead of "Z\*" */
                                /*o_addqblock(output, str, word_len); - WRONG: "v='*'; echo Z$v" prints "Z*" instead of Z* files */
                        }
                        str += word_len;
                }
                if (!*str)  /* EOL - do not finalize word */
                        break;
                o_addchr(output, '\0');
                debug_print_list("expand_on_ifs", output, n);
                n = o_save_ptr(output, n);
                str += strspn(str, G.ifs); /* skip ifs chars */
        }
        debug_print_list("expand_on_ifs[1]", output, n);
        return n;
}

/* Helper to expand $((...)) and heredoc body. These act as if
 * they are in double quotes, with the exception that they are not :).
 * Just the rules are similar: "expand only $var and `cmd`"
 *
 * Returns malloced string.
 * As an optimization, we return NULL if expansion is not needed.
 */
#if !ENABLE_HUSH_BASH_COMPAT
/* only ${var/pattern/repl} (its pattern part) needs additional mode */
#define encode_then_expand_string(str, process_bkslash, do_unbackslash) \
        encode_then_expand_string(str)
#endif
static char *encode_then_expand_string(const char *str, int process_bkslash, int do_unbackslash)
{
        char *exp_str;
        struct in_str input;
        o_string dest = NULL_O_STRING;

        if (!strchr(str, '$')
         && !strchr(str, '\\')
#if ENABLE_HUSH_TICK
         && !strchr(str, '`')
#endif
        ) {
                return NULL;
        }

        /* We need to expand. Example:
         * echo $(($a + `echo 1`)) $((1 + $((2)) ))
         */
        setup_string_in_str(&input, str);
        encode_string(NULL, &dest, &input, EOF, process_bkslash);
        //bb_error_msg("'%s' -> '%s'", str, dest.data);
        exp_str = expand_string_to_string(dest.data, /*unbackslash:*/ do_unbackslash);
        //bb_error_msg("'%s' -> '%s'", dest.data, exp_str);
        o_free_unsafe(&dest);
        return exp_str;
}

#if ENABLE_SH_MATH_SUPPORT
static arith_t expand_and_evaluate_arith(const char *arg, const char **errmsg_p)
{
        arith_state_t math_state;
        arith_t res;
        char *exp_str;

        math_state.lookupvar = get_local_var_value;
        math_state.setvar = set_local_var_from_halves;
        //math_state.endofname = endofname;
        exp_str = encode_then_expand_string(arg, /*process_bkslash:*/ 1, /*unbackslash:*/ 1);
        res = arith(&math_state, exp_str ? exp_str : arg);
        free(exp_str);
        if (errmsg_p)
                *errmsg_p = math_state.errmsg;
        if (math_state.errmsg)
                die_if_script(math_state.errmsg);
        return res;
}
#endif

#if ENABLE_HUSH_BASH_COMPAT
/* ${var/[/]pattern[/repl]} helpers */
static char *strstr_pattern(char *val, const char *pattern, int *size)
{
        while (1) {
                char *end = scan_and_match(val, pattern, SCAN_MOVE_FROM_RIGHT + SCAN_MATCH_LEFT_HALF);
                debug_printf_varexp("val:'%s' pattern:'%s' end:'%s'\n", val, pattern, end);
                if (end) {
                        *size = end - val;
                        return val;
                }
                if (*val == '\0')
                        return NULL;
                /* Optimization: if "*pat" did not match the start of "string",
                 * we know that "tring", "ring" etc will not match too:
                 */
                if (pattern[0] == '*')
                        return NULL;
                val++;
        }
}
static char *replace_pattern(char *val, const char *pattern, const char *repl, char exp_op)
{
        char *result = NULL;
        unsigned res_len = 0;
        unsigned repl_len = strlen(repl);

        while (1) {
                int size;
                char *s = strstr_pattern(val, pattern, &size);
                if (!s)
                        break;

                result = xrealloc(result, res_len + (s - val) + repl_len + 1);
                memcpy(result + res_len, val, s - val);
                res_len += s - val;
                strcpy(result + res_len, repl);
                res_len += repl_len;
                debug_printf_varexp("val:'%s' s:'%s' result:'%s'\n", val, s, result);

                val = s + size;
                if (exp_op == '/')
                        break;
        }
        if (val[0] && result) {
                result = xrealloc(result, res_len + strlen(val) + 1);
                strcpy(result + res_len, val);
                debug_printf_varexp("val:'%s' result:'%s'\n", val, result);
        }
        debug_printf_varexp("result:'%s'\n", result);
        return result;
}
#endif

/* Helper:
 * Handles <SPECIAL_VAR_SYMBOL>varname...<SPECIAL_VAR_SYMBOL> construct.
 */
static NOINLINE const char *expand_one_var(char **to_be_freed_pp, char *arg, char **pp)
{
        const char *val = NULL;
        char *to_be_freed = NULL;
        char *p = *pp;
        char *var;
        char first_char;
        char exp_op;
        char exp_save = exp_save; /* for compiler */
        char *exp_saveptr; /* points to expansion operator */
        char *exp_word = exp_word; /* for compiler */
        char arg0;

        *p = '\0'; /* replace trailing SPECIAL_VAR_SYMBOL */
        var = arg;
        exp_saveptr = arg[1] ? strchr(VAR_ENCODED_SUBST_OPS, arg[1]) : NULL;
        arg0 = arg[0];
        first_char = arg[0] = arg0 & 0x7f;
        exp_op = 0;

        if (first_char == '#'      /* ${#... */
         && arg[1] && !exp_saveptr /* not ${#} and not ${#<op_char>...} */
        ) {
                /* It must be length operator: ${#var} */
                var++;
                exp_op = 'L';
        } else {
                /* Maybe handle parameter expansion */
                if (exp_saveptr /* if 2nd char is one of expansion operators */
                 && strchr(NUMERIC_SPECVARS_STR, first_char) /* 1st char is special variable */
                ) {
                        /* ${?:0}, ${#[:]%0} etc */
                        exp_saveptr = var + 1;
                } else {
                        /* ${?}, ${var}, ${var:0}, ${var[:]%0} etc */
                        exp_saveptr = var+1 + strcspn(var+1, VAR_ENCODED_SUBST_OPS);
                }
                exp_op = exp_save = *exp_saveptr;
                if (exp_op) {
                        exp_word = exp_saveptr + 1;
                        if (exp_op == ':') {
                                exp_op = *exp_word++;
//TODO: try ${var:} and ${var:bogus} in non-bash config
                                if (ENABLE_HUSH_BASH_COMPAT
                                 && (!exp_op || !strchr(MINUS_PLUS_EQUAL_QUESTION, exp_op))
                                ) {
                                        /* oops... it's ${var:N[:M]}, not ${var:?xxx} or some such */
                                        exp_op = ':';
                                        exp_word--;
                                }
                        }
                        *exp_saveptr = '\0';
                } /* else: it's not an expansion op, but bare ${var} */
        }

        /* Look up the variable in question */
        if (isdigit(var[0])) {
                /* parse_dollar should have vetted var for us */
                int n = xatoi_positive(var);
                if (n < G.global_argc)
                        val = G.global_argv[n];
                /* else val remains NULL: $N with too big N */
        } else {
                switch (var[0]) {
                case '$': /* pid */
                        val = utoa(G.root_pid);
                        break;
                case '!': /* bg pid */
                        val = G.last_bg_pid ? utoa(G.last_bg_pid) : "";
                        break;
                case '?': /* exitcode */
                        val = utoa(G.last_exitcode);
                        break;
                case '#': /* argc */
                        val = utoa(G.global_argc ? G.global_argc-1 : 0);
                        break;
                default:
                        val = get_local_var_value(var);
                }
        }

        /* Handle any expansions */
        if (exp_op == 'L') {
                debug_printf_expand("expand: length(%s)=", val);
                val = utoa(val ? strlen(val) : 0);
                debug_printf_expand("%s\n", val);
        } else if (exp_op) {
                if (exp_op == '%' || exp_op == '#') {
                        /* Standard-mandated substring removal ops:
                         * ${parameter%word} - remove smallest suffix pattern
                         * ${parameter%%word} - remove largest suffix pattern
                         * ${parameter#word} - remove smallest prefix pattern
                         * ${parameter##word} - remove largest prefix pattern
                         *
                         * Word is expanded to produce a glob pattern.
                         * Then var's value is matched to it and matching part removed.
                         */
                        if (val && val[0]) {
                                char *t;
                                char *exp_exp_word;
                                char *loc;
                                unsigned scan_flags = pick_scan(exp_op, *exp_word);
                                if (exp_op == *exp_word)  /* ## or %% */
                                        exp_word++;
                                exp_exp_word = encode_then_expand_string(exp_word, /*process_bkslash:*/ 1, /*unbackslash:*/ 1);
                                if (exp_exp_word)
                                        exp_word = exp_exp_word;
                                /* HACK ALERT. We depend here on the fact that
                                 * G.global_argv and results of utoa and get_local_var_value
                                 * are actually in writable memory:
                                 * scan_and_match momentarily stores NULs there. */
                                t = (char*)val;
                                loc = scan_and_match(t, exp_word, scan_flags);
                                //bb_error_msg("op:%c str:'%s' pat:'%s' res:'%s'",
                                //              exp_op, t, exp_word, loc);
                                free(exp_exp_word);
                                if (loc) { /* match was found */
                                        if (scan_flags & SCAN_MATCH_LEFT_HALF) /* #[#] */
                                                val = loc; /* take right part */
                                        else /* %[%] */
                                                val = to_be_freed = xstrndup(val, loc - val); /* left */
                                }
                        }
                }
#if ENABLE_HUSH_BASH_COMPAT
                else if (exp_op == '/' || exp_op == '\\') {
                        /* It's ${var/[/]pattern[/repl]} thing.
                         * Note that in encoded form it has TWO parts:
                         * var/pattern<SPECIAL_VAR_SYMBOL>repl<SPECIAL_VAR_SYMBOL>
                         * and if // is used, it is encoded as \:
                         * var\pattern<SPECIAL_VAR_SYMBOL>repl<SPECIAL_VAR_SYMBOL>
                         */
                        /* Empty variable always gives nothing: */
                        // "v=''; echo ${v/*/w}" prints "", not "w"
                        if (val && val[0]) {
                                /* pattern uses non-standard expansion.
                                 * repl should be unbackslashed and globbed
                                 * by the usual expansion rules:
                                 * >az; >bz;
                                 * v='a bz'; echo "${v/a*z/a*z}" prints "a*z"
                                 * v='a bz'; echo "${v/a*z/\z}"  prints "\z"
                                 * v='a bz'; echo ${v/a*z/a*z}   prints "az"
                                 * v='a bz'; echo ${v/a*z/\z}    prints "z"
                                 * (note that a*z _pattern_ is never globbed!)
                                 */
                                char *pattern, *repl, *t;
                                pattern = encode_then_expand_string(exp_word, /*process_bkslash:*/ 0, /*unbackslash:*/ 0);
                                if (!pattern)
                                        pattern = xstrdup(exp_word);
                                debug_printf_varexp("pattern:'%s'->'%s'\n", exp_word, pattern);
                                *p++ = SPECIAL_VAR_SYMBOL;
                                exp_word = p;
                                p = strchr(p, SPECIAL_VAR_SYMBOL);
                                *p = '\0';
                                repl = encode_then_expand_string(exp_word, /*process_bkslash:*/ arg0 & 0x80, /*unbackslash:*/ 1);
                                debug_printf_varexp("repl:'%s'->'%s'\n", exp_word, repl);
                                /* HACK ALERT. We depend here on the fact that
                                 * G.global_argv and results of utoa and get_local_var_value
                                 * are actually in writable memory:
                                 * replace_pattern momentarily stores NULs there. */
                                t = (char*)val;
                                to_be_freed = replace_pattern(t,
                                                pattern,
                                                (repl ? repl : exp_word),
                                                exp_op);
                                if (to_be_freed) /* at least one replace happened */
                                        val = to_be_freed;
                                free(pattern);
                                free(repl);
                        }
                }
#endif
                else if (exp_op == ':') {
#if ENABLE_HUSH_BASH_COMPAT && ENABLE_SH_MATH_SUPPORT
                        /* It's ${var:N[:M]} bashism.
                         * Note that in encoded form it has TWO parts:
                         * var:N<SPECIAL_VAR_SYMBOL>M<SPECIAL_VAR_SYMBOL>
                         */
                        arith_t beg, len;
                        const char *errmsg;

                        beg = expand_and_evaluate_arith(exp_word, &errmsg);
                        if (errmsg)
                                goto arith_err;
                        debug_printf_varexp("beg:'%s'=%lld\n", exp_word, (long long)beg);
                        *p++ = SPECIAL_VAR_SYMBOL;
                        exp_word = p;
                        p = strchr(p, SPECIAL_VAR_SYMBOL);
                        *p = '\0';
                        len = expand_and_evaluate_arith(exp_word, &errmsg);
                        if (errmsg)
                                goto arith_err;
                        debug_printf_varexp("len:'%s'=%lld\n", exp_word, (long long)len);
                        if (len >= 0) { /* bash compat: len < 0 is illegal */
                                if (beg < 0) /* bash compat */
                                        beg = 0;
                                debug_printf_varexp("from val:'%s'\n", val);
                                if (len == 0 || !val || beg >= strlen(val)) {
 arith_err:
                                        val = NULL;
                                } else {
                                        /* Paranoia. What if user entered 9999999999999
                                         * which fits in arith_t but not int? */
                                        if (len >= INT_MAX)
                                                len = INT_MAX;
                                        val = to_be_freed = xstrndup(val + beg, len);
                                }
                                debug_printf_varexp("val:'%s'\n", val);
                        } else
#endif
                        {
                                die_if_script("malformed ${%s:...}", var);
                                val = NULL;
                        }
                } else { /* one of "-=+?" */
                        /* Standard-mandated substitution ops:
                         * ${var?word} - indicate error if unset
                         *      If var is unset, word (or a message indicating it is unset
                         *      if word is null) is written to standard error
                         *      and the shell exits with a non-zero exit status.
                         *      Otherwise, the value of var is substituted.
                         * ${var-word} - use default value
                         *      If var is unset, word is substituted.
                         * ${var=word} - assign and use default value
                         *      If var is unset, word is assigned to var.
                         *      In all cases, final value of var is substituted.
                         * ${var+word} - use alternative value
                         *      If var is unset, null is substituted.
                         *      Otherwise, word is substituted.
                         *
                         * Word is subjected to tilde expansion, parameter expansion,
                         * command substitution, and arithmetic expansion.
                         * If word is not needed, it is not expanded.
                         *
                         * Colon forms (${var:-word}, ${var:=word} etc) do the same,
                         * but also treat null var as if it is unset.
                         */
                        int use_word = (!val || ((exp_save == ':') && !val[0]));
                        if (exp_op == '+')
                                use_word = !use_word;
                        debug_printf_expand("expand: op:%c (null:%s) test:%i\n", exp_op,
                                        (exp_save == ':') ? "true" : "false", use_word);
                        if (use_word) {
                                to_be_freed = encode_then_expand_string(exp_word, /*process_bkslash:*/ 1, /*unbackslash:*/ 1);
                                if (to_be_freed)
                                        exp_word = to_be_freed;
                                if (exp_op == '?') {
                                        /* mimic bash message */
                                        die_if_script("%s: %s",
                                                var,
                                                exp_word[0] ? exp_word : "parameter null or not set"
                                        );
//TODO: how interactive bash aborts expansion mid-command?
                                } else {
                                        val = exp_word;
                                }

                                if (exp_op == '=') {
                                        /* ${var=[word]} or ${var:=[word]} */
                                        if (isdigit(var[0]) || var[0] == '#') {
                                                /* mimic bash message */
                                                die_if_script("$%s: cannot assign in this way", var);
                                                val = NULL;
                                        } else {
                                                char *new_var = xasprintf("%s=%s", var, val);
                                                set_local_var(new_var, /*exp:*/ 0, /*lvl:*/ 0, /*ro:*/ 0);
                                        }
                                }
                        }
                } /* one of "-=+?" */

                *exp_saveptr = exp_save;
        } /* if (exp_op) */

        arg[0] = arg0;

        *pp = p;
        *to_be_freed_pp = to_be_freed;
        return val;
}

/* Expand all variable references in given string, adding words to list[]
 * at n, n+1,... positions. Return updated n (so that list[n] is next one
 * to be filled). This routine is extremely tricky: has to deal with
 * variables/parameters with whitespace, $* and $@, and constructs like
 * 'echo -$*-'. If you play here, you must run testsuite afterwards! */
static NOINLINE int expand_vars_to_list(o_string *output, int n, char *arg)
{
        /* output->o_expflags & EXP_FLAG_SINGLEWORD (0x80) if we are in
         * expansion of right-hand side of assignment == 1-element expand.
         */
        char cant_be_null = 0; /* only bit 0x80 matters */
        char *p;

        debug_printf_expand("expand_vars_to_list: arg:'%s' singleword:%x\n", arg,
                        !!(output->o_expflags & EXP_FLAG_SINGLEWORD));
        debug_print_list("expand_vars_to_list", output, n);
        n = o_save_ptr(output, n);
        debug_print_list("expand_vars_to_list[0]", output, n);

        while ((p = strchr(arg, SPECIAL_VAR_SYMBOL)) != NULL) {
                char first_ch;
                char *to_be_freed = NULL;
                const char *val = NULL;
#if ENABLE_HUSH_TICK
                o_string subst_result = NULL_O_STRING;
#endif
#if ENABLE_SH_MATH_SUPPORT
                char arith_buf[sizeof(arith_t)*3 + 2];
#endif
                o_addblock(output, arg, p - arg);
                debug_print_list("expand_vars_to_list[1]", output, n);
                arg = ++p;
                p = strchr(p, SPECIAL_VAR_SYMBOL);

                /* Fetch special var name (if it is indeed one of them)
                 * and quote bit, force the bit on if singleword expansion -
                 * important for not getting v=$@ expand to many words. */
                first_ch = arg[0] | (output->o_expflags & EXP_FLAG_SINGLEWORD);

                /* Is this variable quoted and thus expansion can't be null?
                 * "$@" is special. Even if quoted, it can still
                 * expand to nothing (not even an empty string),
                 * thus it is excluded. */
                if ((first_ch & 0x7f) != '@')
                        cant_be_null |= first_ch;

                switch (first_ch & 0x7f) {
                /* Highest bit in first_ch indicates that var is double-quoted */
                case '*':
                case '@': {
                        int i;
                        if (!G.global_argv[1])
                                break;
                        i = 1;
                        cant_be_null |= first_ch; /* do it for "$@" _now_, when we know it's not empty */
                        if (!(first_ch & 0x80)) { /* unquoted $* or $@ */
                                while (G.global_argv[i]) {
                                        n = expand_on_ifs(output, n, G.global_argv[i]);
                                        debug_printf_expand("expand_vars_to_list: argv %d (last %d)\n", i, G.global_argc - 1);
                                        if (G.global_argv[i++][0] && G.global_argv[i]) {
                                                /* this argv[] is not empty and not last:
                                                 * put terminating NUL, start new word */
                                                o_addchr(output, '\0');
                                                debug_print_list("expand_vars_to_list[2]", output, n);
                                                n = o_save_ptr(output, n);
                                                debug_print_list("expand_vars_to_list[3]", output, n);
                                        }
                                }
                        } else
                        /* If EXP_FLAG_SINGLEWORD, we handle assignment 'a=....$@.....'
                         * and in this case should treat it like '$*' - see 'else...' below */
                        if (first_ch == ('@'|0x80)  /* quoted $@ */
                         && !(output->o_expflags & EXP_FLAG_SINGLEWORD) /* not v="$@" case */
                        ) {
                                while (1) {
                                        o_addQstr(output, G.global_argv[i]);
                                        if (++i >= G.global_argc)
                                                break;
                                        o_addchr(output, '\0');
                                        debug_print_list("expand_vars_to_list[4]", output, n);
                                        n = o_save_ptr(output, n);
                                }
                        } else { /* quoted $* (or v="$@" case): add as one word */
                                while (1) {
                                        o_addQstr(output, G.global_argv[i]);
                                        if (!G.global_argv[++i])
                                                break;
                                        if (G.ifs[0])
                                                o_addchr(output, G.ifs[0]);
                                }
                        }
                        break;
                }
                case SPECIAL_VAR_SYMBOL: /* <SPECIAL_VAR_SYMBOL><SPECIAL_VAR_SYMBOL> */
                        /* "Empty variable", used to make "" etc to not disappear */
                        arg++;
                        cant_be_null = 0x80;
                        break;
#if ENABLE_HUSH_TICK
                case '`': /* <SPECIAL_VAR_SYMBOL>`cmd<SPECIAL_VAR_SYMBOL> */
                        *p = '\0'; /* replace trailing <SPECIAL_VAR_SYMBOL> */
                        arg++;
                        /* Can't just stuff it into output o_string,
                         * expanded result may need to be globbed
                         * and $IFS-splitted */
                        debug_printf_subst("SUBST '%s' first_ch %x\n", arg, first_ch);
                        G.last_exitcode = process_command_subs(&subst_result, arg);
                        debug_printf_subst("SUBST RES:%d '%s'\n", G.last_exitcode, subst_result.data);
                        val = subst_result.data;
                        goto store_val;
#endif
#if ENABLE_SH_MATH_SUPPORT
                case '+': { /* <SPECIAL_VAR_SYMBOL>+cmd<SPECIAL_VAR_SYMBOL> */
                        arith_t res;

                        arg++; /* skip '+' */
                        *p = '\0'; /* replace trailing <SPECIAL_VAR_SYMBOL> */
                        debug_printf_subst("ARITH '%s' first_ch %x\n", arg, first_ch);
                        res = expand_and_evaluate_arith(arg, NULL);
                        debug_printf_subst("ARITH RES '"ARITH_FMT"'\n", res);
                        sprintf(arith_buf, ARITH_FMT, res);
                        val = arith_buf;
                        break;
                }
#endif
                default:
                        val = expand_one_var(&to_be_freed, arg, &p);
 IF_HUSH_TICK(store_val:)
                        if (!(first_ch & 0x80)) { /* unquoted $VAR */
                                debug_printf_expand("unquoted '%s', output->o_escape:%d\n", val,
                                                !!(output->o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
                                if (val && val[0]) {
                                        n = expand_on_ifs(output, n, val);
                                        val = NULL;
                                }
                        } else { /* quoted $VAR, val will be appended below */
                                debug_printf_expand("quoted '%s', output->o_escape:%d\n", val,
                                                !!(output->o_expflags & EXP_FLAG_ESC_GLOB_CHARS));
                        }
                        break;

                } /* switch (char after <SPECIAL_VAR_SYMBOL>) */

                if (val && val[0]) {
                        o_addQstr(output, val);
                }
                free(to_be_freed);

                /* Restore NULL'ed SPECIAL_VAR_SYMBOL.
                 * Do the check to avoid writing to a const string. */
                if (*p != SPECIAL_VAR_SYMBOL)
                        *p = SPECIAL_VAR_SYMBOL;

#if ENABLE_HUSH_TICK
                o_free(&subst_result);
#endif
                arg = ++p;
        } /* end of "while (SPECIAL_VAR_SYMBOL is found) ..." */

        if (arg[0]) {
                debug_print_list("expand_vars_to_list[a]", output, n);
                /* this part is literal, and it was already pre-quoted
                 * if needed (much earlier), do not use o_addQstr here! */
                o_addstr_with_NUL(output, arg);
                debug_print_list("expand_vars_to_list[b]", output, n);
        } else if (output->length == o_get_last_ptr(output, n) /* expansion is empty */
         && !(cant_be_null & 0x80) /* and all vars were not quoted. */
        ) {
                n--;
                /* allow to reuse list[n] later without re-growth */
                output->has_empty_slot = 1;
        } else {
                o_addchr(output, '\0');
        }

        return n;
}

static char **expand_variables(char **argv, unsigned expflags)
{
        int n;
        char **list;
        o_string output = NULL_O_STRING;

        output.o_expflags = expflags;

        n = 0;
        while (*argv) {
                n = expand_vars_to_list(&output, n, *argv);
                argv++;
        }
        debug_print_list("expand_variables", &output, n);

        /* output.data (malloced in one block) gets returned in "list" */
        list = o_finalize_list(&output, n);
        debug_print_strings("expand_variables[1]", list);
        return list;
}

static char **expand_strvec_to_strvec(char **argv)
{
        return expand_variables(argv, EXP_FLAG_GLOB | EXP_FLAG_ESC_GLOB_CHARS);
}

#if ENABLE_HUSH_BASH_COMPAT
static char **expand_strvec_to_strvec_singleword_noglob(char **argv)
{
        return expand_variables(argv, EXP_FLAG_SINGLEWORD);
}
#endif

/* Used for expansion of right hand of assignments,
 * $((...)), heredocs, variable espansion parts.
 *
 * NB: should NOT do globbing!
 * "export v=/bin/c*; env | grep ^v=" outputs "v=/bin/c*"
 */
static char *expand_string_to_string(const char *str, int do_unbackslash)
{
#if !ENABLE_HUSH_BASH_COMPAT
        const int do_unbackslash = 1;
#endif
        char *argv[2], **list;

        debug_printf_expand("string_to_string<='%s'\n", str);
        /* This is generally an optimization, but it also
         * handles "", which otherwise trips over !list[0] check below.
         * (is this ever happens that we actually get str="" here?)
         */
        if (!strchr(str, SPECIAL_VAR_SYMBOL) && !strchr(str, '\\')) {
                //TODO: Can use on strings with \ too, just unbackslash() them?
                debug_printf_expand("string_to_string(fast)=>'%s'\n", str);
                return xstrdup(str);
        }

        argv[0] = (char*)str;
        argv[1] = NULL;
        list = expand_variables(argv, do_unbackslash
                        ? EXP_FLAG_ESC_GLOB_CHARS | EXP_FLAG_SINGLEWORD
                        : EXP_FLAG_SINGLEWORD
        );
        if (HUSH_DEBUG)
                if (!list[0] || list[1])
                        bb_error_msg_and_die("BUG in varexp2");
        /* actually, just move string 2*sizeof(char*) bytes back */
        overlapping_strcpy((char*)list, list[0]);
        if (do_unbackslash)
                unbackslash((char*)list);
        debug_printf_expand("string_to_string=>'%s'\n", (char*)list);
        return (char*)list;
}

/* Used for "eval" builtin */
static char* expand_strvec_to_string(char **argv)
{
        char **list;

        list = expand_variables(argv, EXP_FLAG_SINGLEWORD);
        /* Convert all NULs to spaces */
        if (list[0]) {
                int n = 1;
                while (list[n]) {
                        if (HUSH_DEBUG)
                                if (list[n-1] + strlen(list[n-1]) + 1 != list[n])
                                        bb_error_msg_and_die("BUG in varexp3");
                        /* bash uses ' ' regardless of $IFS contents */
                        list[n][-1] = ' ';
                        n++;
                }
        }
        overlapping_strcpy((char*)list, list[0]);
        debug_printf_expand("strvec_to_string='%s'\n", (char*)list);
        return (char*)list;
}

static char **expand_assignments(char **argv, int count)
{
        int i;
        char **p;

        G.expanded_assignments = p = NULL;
        /* Expand assignments into one string each */
        for (i = 0; i < count; i++) {
                G.expanded_assignments = p = add_string_to_strings(p, expand_string_to_string(argv[i], /*unbackslash:*/ 1));
        }
        G.expanded_assignments = NULL;
        return p;
}


#if BB_MMU
/* never called */
void re_execute_shell(char ***to_free, const char *s,
                char *g_argv0, char **g_argv,
                char **builtin_argv) NORETURN;

static void reset_traps_to_defaults(void)
{
        /* This function is always called in a child shell
         * after fork (not vfork, NOMMU doesn't use this function).
         */
        unsigned sig;
        unsigned mask;

        /* Child shells are not interactive.
         * SIGTTIN/SIGTTOU/SIGTSTP should not have special handling.
         * Testcase: (while :; do :; done) + ^Z should background.
         * Same goes for SIGTERM, SIGHUP, SIGINT.
         */
        if (!G.traps && !(G.non_DFL_mask & SPECIAL_INTERACTIVE_SIGS))
                return; /* already no traps and no SPECIAL_INTERACTIVE_SIGS */

        /* Switching off SPECIAL_INTERACTIVE_SIGS.
         * Stupid. It can be done with *single* &= op, but we can't use
         * the fact that G.blocked_set is implemented as a bitmask
         * in libc... */
        mask = (SPECIAL_INTERACTIVE_SIGS >> 1);
        sig = 1;
        while (1) {
                if (mask & 1) {
                        /* Careful. Only if no trap or trap is not "" */
                        if (!G.traps || !G.traps[sig] || G.traps[sig][0])
                                sigdelset(&G.blocked_set, sig);
                }
                mask >>= 1;
                if (!mask)
                        break;
                sig++;
        }
        /* Our homegrown sig mask is saner to work with :) */
        G.non_DFL_mask &= ~SPECIAL_INTERACTIVE_SIGS;

        /* Resetting all traps to default except empty ones */
        mask = G.non_DFL_mask;
        if (G.traps) for (sig = 0; sig < NSIG; sig++, mask >>= 1) {
                if (!G.traps[sig] || !G.traps[sig][0])
                        continue;
                free(G.traps[sig]);
                G.traps[sig] = NULL;
                /* There is no signal for 0 (EXIT) */
                if (sig == 0)
                        continue;
                /* There was a trap handler, we just removed it.
                 * But if sig still has non-DFL handling,
                 * we should not unblock the sig. */
                if (mask & 1)
                        continue;
                sigdelset(&G.blocked_set, sig);
        }
        sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
}

#else /* !BB_MMU */

static void re_execute_shell(char ***to_free, const char *s,
                char *g_argv0, char **g_argv,
                char **builtin_argv) NORETURN;
static void re_execute_shell(char ***to_free, const char *s,
                char *g_argv0, char **g_argv,
                char **builtin_argv)
{
# define NOMMU_HACK_FMT ("-$%x:%x:%x:%x:%x:%llx" IF_HUSH_LOOPS(":%x"))
        /* delims + 2 * (number of bytes in printed hex numbers) */
        char param_buf[sizeof(NOMMU_HACK_FMT) + 2 * (sizeof(int)*6 + sizeof(long long)*1)];
        char *heredoc_argv[4];
        struct variable *cur;
# if ENABLE_HUSH_FUNCTIONS
        struct function *funcp;
# endif
        char **argv, **pp;
        unsigned cnt;
        unsigned long long empty_trap_mask;

        if (!g_argv0) { /* heredoc */
                argv = heredoc_argv;
                argv[0] = (char *) G.argv0_for_re_execing;
                argv[1] = (char *) "-<";
                argv[2] = (char *) s;
                argv[3] = NULL;
                pp = &argv[3]; /* used as pointer to empty environment */
                goto do_exec;
        }

        cnt = 0;
        pp = builtin_argv;
        if (pp) while (*pp++)
                cnt++;

        empty_trap_mask = 0;
        if (G.traps) {
                int sig;
                for (sig = 1; sig < NSIG; sig++) {
                        if (G.traps[sig] && !G.traps[sig][0])
                                empty_trap_mask |= 1LL << sig;
                }
        }

        sprintf(param_buf, NOMMU_HACK_FMT
                        , (unsigned) G.root_pid
                        , (unsigned) G.root_ppid
                        , (unsigned) G.last_bg_pid
                        , (unsigned) G.last_exitcode
                        , cnt
                        , empty_trap_mask
                        IF_HUSH_LOOPS(, G.depth_of_loop)
                        );
# undef NOMMU_HACK_FMT
        /* 1:hush 2:-$<pid>:<pid>:<exitcode>:<etc...> <vars...> <funcs...>
         * 3:-c 4:<cmd> 5:<arg0> <argN...> 6:NULL
         */
        cnt += 6;
        for (cur = G.top_var; cur; cur = cur->next) {
                if (!cur->flg_export || cur->flg_read_only)
                        cnt += 2;
        }
# if ENABLE_HUSH_FUNCTIONS
        for (funcp = G.top_func; funcp; funcp = funcp->next)
                cnt += 3;
# endif
        pp = g_argv;
        while (*pp++)
                cnt++;
        *to_free = argv = pp = xzalloc(sizeof(argv[0]) * cnt);
        *pp++ = (char *) G.argv0_for_re_execing;
        *pp++ = param_buf;
        for (cur = G.top_var; cur; cur = cur->next) {
                if (strcmp(cur->varstr, hush_version_str) == 0)
                        continue;
                if (cur->flg_read_only) {
                        *pp++ = (char *) "-R";
                        *pp++ = cur->varstr;
                } else if (!cur->flg_export) {
                        *pp++ = (char *) "-V";
                        *pp++ = cur->varstr;
                }
        }
# if ENABLE_HUSH_FUNCTIONS
        for (funcp = G.top_func; funcp; funcp = funcp->next) {
                *pp++ = (char *) "-F";
                *pp++ = funcp->name;
                *pp++ = funcp->body_as_string;
        }
# endif
        /* We can pass activated traps here. Say, -Tnn:trap_string
         *
         * However, POSIX says that subshells reset signals with traps
         * to SIG_DFL.
         * I tested bash-3.2 and it not only does that with true subshells
         * of the form ( list ), but with any forked children shells.
         * I set trap "echo W" WINCH; and then tried:
         *
         * { echo 1; sleep 20; echo 2; } &
         * while true; do echo 1; sleep 20; echo 2; break; done &
         * true | { echo 1; sleep 20; echo 2; } | cat
         *
         * In all these cases sending SIGWINCH to the child shell
         * did not run the trap. If I add trap "echo V" WINCH;
         * _inside_ group (just before echo 1), it works.
         *
         * I conclude it means we don't need to pass active traps here.
         * Even if we would use signal handlers instead of signal masking
         * in order to implement trap handling,
         * exec syscall below resets signals to SIG_DFL for us.
         */
        *pp++ = (char *) "-c";
        *pp++ = (char *) s;
        if (builtin_argv) {
                while (*++builtin_argv)
                        *pp++ = *builtin_argv;
                *pp++ = (char *) "";
        }
        *pp++ = g_argv0;
        while (*g_argv)
                *pp++ = *g_argv++;
        /* *pp = NULL; - is already there */
        pp = environ;

 do_exec:
        debug_printf_exec("re_execute_shell pid:%d cmd:'%s'\n", getpid(), s);
        sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
        execve(bb_busybox_exec_path, argv, pp);
        /* Fallback. Useful for init=/bin/hush usage etc */
        if (argv[0][0] == '/')
                execve(argv[0], argv, pp);
        xfunc_error_retval = 127;
        bb_error_msg_and_die("can't re-execute the shell");
}
#endif  /* !BB_MMU */


static int run_and_free_list(struct pipe *pi);

/* Executing from string: eval, sh -c '...'
 *          or from file: /etc/profile, . file, sh <script>, sh (intereactive)
 * end_trigger controls how often we stop parsing
 * NUL: parse all, execute, return
 * ';': parse till ';' or newline, execute, repeat till EOF
 */
static void parse_and_run_stream(struct in_str *inp, int end_trigger)
{
        /* Why we need empty flag?
         * An obscure corner case "false; ``; echo $?":
         * empty command in `` should still set $? to 0.
         * But we can't just set $? to 0 at the start,
         * this breaks "false; echo `echo $?`" case.
         */
        bool empty = 1;
        while (1) {
                struct pipe *pipe_list;

                pipe_list = parse_stream(NULL, inp, end_trigger);
                if (!pipe_list) { /* EOF */
                        if (empty)
                                G.last_exitcode = 0;
                        break;
                }
                debug_print_tree(pipe_list, 0);
                debug_printf_exec("parse_and_run_stream: run_and_free_list\n");
                run_and_free_list(pipe_list);
                empty = 0;
        }
}

static void parse_and_run_string(const char *s)
{
        struct in_str input;
        setup_string_in_str(&input, s);
        parse_and_run_stream(&input, '\0');
}

static void parse_and_run_file(FILE *f)
{
        struct in_str input;
        setup_file_in_str(&input, f);
        parse_and_run_stream(&input, ';');
}

#if ENABLE_HUSH_TICK
static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
{
        pid_t pid;
        int channel[2];
# if !BB_MMU
        char **to_free = NULL;
# endif

        xpipe(channel);
        pid = BB_MMU ? xfork() : xvfork();
        if (pid == 0) { /* child */
                disable_restore_tty_pgrp_on_exit();
                /* Process substitution is not considered to be usual
                 * 'command execution'.
                 * SUSv3 says ctrl-Z should be ignored, ctrl-C should not.
                 */
                bb_signals(0
                        + (1 << SIGTSTP)
                        + (1 << SIGTTIN)
                        + (1 << SIGTTOU)
                        , SIG_IGN);
                CLEAR_RANDOM_T(&G.random_gen); /* or else $RANDOM repeats in child */
                close(channel[0]); /* NB: close _first_, then move fd! */
                xmove_fd(channel[1], 1);
                /* Prevent it from trying to handle ctrl-z etc */
                IF_HUSH_JOB(G.run_list_level = 1;)
                /* Awful hack for `trap` or $(trap).
                 *
                 * http://www.opengroup.org/onlinepubs/009695399/utilities/trap.html
                 * contains an example where "trap" is executed in a subshell:
                 *
                 * save_traps=$(trap)
                 * ...
                 * eval "$save_traps"
                 *
                 * Standard does not say that "trap" in subshell shall print
                 * parent shell's traps. It only says that its output
                 * must have suitable form, but then, in the above example
                 * (which is not supposed to be normative), it implies that.
                 *
                 * bash (and probably other shell) does implement it
                 * (traps are reset to defaults, but "trap" still shows them),
                 * but as a result, "trap" logic is hopelessly messed up:
                 *
                 * # trap
                 * trap -- 'echo Ho' SIGWINCH  <--- we have a handler
                 * # (trap)        <--- trap is in subshell - no output (correct, traps are reset)
                 * # true | trap   <--- trap is in subshell - no output (ditto)
                 * # echo `true | trap`    <--- in subshell - output (but traps are reset!)
                 * trap -- 'echo Ho' SIGWINCH
                 * # echo `(trap)`         <--- in subshell in subshell - output
                 * trap -- 'echo Ho' SIGWINCH
                 * # echo `true | (trap)`  <--- in subshell in subshell in subshell - output!
                 * trap -- 'echo Ho' SIGWINCH
                 *
                 * The rules when to forget and when to not forget traps
                 * get really complex and nonsensical.
                 *
                 * Our solution: ONLY bare $(trap) or `trap` is special.
                 */
                s = skip_whitespace(s);
                if (strncmp(s, "trap", 4) == 0
                 && skip_whitespace(s + 4)[0] == '\0'
                ) {
                        static const char *const argv[] = { NULL, NULL };
                        builtin_trap((char**)argv);
                        exit(0); /* not _exit() - we need to fflush */
                }
# if BB_MMU
                reset_traps_to_defaults();
                parse_and_run_string(s);
                _exit(G.last_exitcode);
# else
        /* We re-execute after vfork on NOMMU. This makes this script safe:
         * yes "0123456789012345678901234567890" | dd bs=32 count=64k >BIG
         * huge=`cat BIG` # was blocking here forever
         * echo OK
         */
                re_execute_shell(&to_free,
                                s,
                                G.global_argv[0],
                                G.global_argv + 1,
                                NULL);
# endif
        }

        /* parent */
        *pid_p = pid;
# if ENABLE_HUSH_FAST
        G.count_SIGCHLD++;
//bb_error_msg("[%d] fork in generate_stream_from_string:"
//              " G.count_SIGCHLD:%d G.handled_SIGCHLD:%d",
//              getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
# endif
        enable_restore_tty_pgrp_on_exit();
# if !BB_MMU
        free(to_free);
# endif
        close(channel[1]);
        close_on_exec_on(channel[0]);
        return xfdopen_for_read(channel[0]);
}

/* Return code is exit status of the process that is run. */
static int process_command_subs(o_string *dest, const char *s)
{
        FILE *fp;
        struct in_str pipe_str;
        pid_t pid;
        int status, ch, eol_cnt;

        fp = generate_stream_from_string(s, &pid);

        /* Now send results of command back into original context */
        setup_file_in_str(&pipe_str, fp);
        eol_cnt = 0;
        while ((ch = i_getch(&pipe_str)) != EOF) {
                if (ch == '\n') {
                        eol_cnt++;
                        continue;
                }
                while (eol_cnt) {
                        o_addchr(dest, '\n');
                        eol_cnt--;
                }
                o_addQchr(dest, ch);
        }

        debug_printf("done reading from `cmd` pipe, closing it\n");
        fclose(fp);
        /* We need to extract exitcode. Test case
         * "true; echo `sleep 1; false` $?"
         * should print 1 */
        safe_waitpid(pid, &status, 0);
        debug_printf("child exited. returning its exitcode:%d\n", WEXITSTATUS(status));
        return WEXITSTATUS(status);
}
#endif /* ENABLE_HUSH_TICK */


static void setup_heredoc(struct redir_struct *redir)
{
        struct fd_pair pair;
        pid_t pid;
        int len, written;
        /* the _body_ of heredoc (misleading field name) */
        const char *heredoc = redir->rd_filename;
        char *expanded;
#if !BB_MMU
        char **to_free;
#endif

        expanded = NULL;
        if (!(redir->rd_dup & HEREDOC_QUOTED)) {
                expanded = encode_then_expand_string(heredoc, /*process_bkslash:*/ 1, /*unbackslash:*/ 1);
                if (expanded)
                        heredoc = expanded;
        }
        len = strlen(heredoc);

        close(redir->rd_fd); /* often saves dup2+close in xmove_fd */
        xpiped_pair(pair);
        xmove_fd(pair.rd, redir->rd_fd);

        /* Try writing without forking. Newer kernels have
         * dynamically growing pipes. Must use non-blocking write! */
        ndelay_on(pair.wr);
        while (1) {
                written = write(pair.wr, heredoc, len);
                if (written <= 0)
                        break;
                len -= written;
                if (len == 0) {
                        close(pair.wr);
                        free(expanded);
                        return;
                }
                heredoc += written;
        }
        ndelay_off(pair.wr);

        /* Okay, pipe buffer was not big enough */
        /* Note: we must not create a stray child (bastard? :)
         * for the unsuspecting parent process. Child creates a grandchild
         * and exits before parent execs the process which consumes heredoc
         * (that exec happens after we return from this function) */
#if !BB_MMU
        to_free = NULL;
#endif
        pid = xvfork();
        if (pid == 0) {
                /* child */
                disable_restore_tty_pgrp_on_exit();
                pid = BB_MMU ? xfork() : xvfork();
                if (pid != 0)
                        _exit(0);
                /* grandchild */
                close(redir->rd_fd); /* read side of the pipe */
#if BB_MMU
                full_write(pair.wr, heredoc, len); /* may loop or block */
                _exit(0);
#else
                /* Delegate blocking writes to another process */
                xmove_fd(pair.wr, STDOUT_FILENO);
                re_execute_shell(&to_free, heredoc, NULL, NULL, NULL);
#endif
        }
        /* parent */
#if ENABLE_HUSH_FAST
        G.count_SIGCHLD++;
//bb_error_msg("[%d] fork in setup_heredoc: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
#endif
        enable_restore_tty_pgrp_on_exit();
#if !BB_MMU
        free(to_free);
#endif
        close(pair.wr);
        free(expanded);
        wait(NULL); /* wait till child has died */
}

/* squirrel != NULL means we squirrel away copies of stdin, stdout,
 * and stderr if they are redirected. */
static int setup_redirects(struct command *prog, int squirrel[])
{
        int openfd, mode;
        struct redir_struct *redir;

        for (redir = prog->redirects; redir; redir = redir->next) {
                if (redir->rd_type == REDIRECT_HEREDOC2) {
                        /* rd_fd<<HERE case */
                        if (squirrel && redir->rd_fd < 3
                         && squirrel[redir->rd_fd] < 0
                        ) {
                                squirrel[redir->rd_fd] = dup(redir->rd_fd);
                        }
                        /* for REDIRECT_HEREDOC2, rd_filename holds _contents_
                         * of the heredoc */
                        debug_printf_parse("set heredoc '%s'\n",
                                        redir->rd_filename);
                        setup_heredoc(redir);
                        continue;
                }

                if (redir->rd_dup == REDIRFD_TO_FILE) {
                        /* rd_fd<*>file case (<*> is <,>,>>,<>) */
                        char *p;
                        if (redir->rd_filename == NULL) {
                                /* Something went wrong in the parse.
                                 * Pretend it didn't happen */
                                bb_error_msg("bug in redirect parse");
                                continue;
                        }
                        mode = redir_table[redir->rd_type].mode;
                        p = expand_string_to_string(redir->rd_filename, /*unbackslash:*/ 1);
                        openfd = open_or_warn(p, mode);
                        free(p);
                        if (openfd < 0) {
                        /* this could get lost if stderr has been redirected, but
                         * bash and ash both lose it as well (though zsh doesn't!) */
//what the above comment tries to say?
                                return 1;
                        }
                } else {
                        /* rd_fd<*>rd_dup or rd_fd<*>- cases */
                        openfd = redir->rd_dup;
                }

                if (openfd != redir->rd_fd) {
                        if (squirrel && redir->rd_fd < 3
                         && squirrel[redir->rd_fd] < 0
                        ) {
                                squirrel[redir->rd_fd] = dup(redir->rd_fd);
                        }
                        if (openfd == REDIRFD_CLOSE) {
                                /* "n>-" means "close me" */
                                close(redir->rd_fd);
                        } else {
                                xdup2(openfd, redir->rd_fd);
                                if (redir->rd_dup == REDIRFD_TO_FILE)
                                        close(openfd);
                        }
                }
        }
        return 0;
}

static void restore_redirects(int squirrel[])
{
        int i, fd;
        for (i = 0; i < 3; i++) {
                fd = squirrel[i];
                if (fd != -1) {
                        /* We simply die on error */
                        xmove_fd(fd, i);
                }
        }
}

static char *find_in_path(const char *arg)
{
        char *ret = NULL;
        const char *PATH = get_local_var_value("PATH");

        if (!PATH)
                return NULL;

        while (1) {
                const char *end = strchrnul(PATH, ':');
                int sz = end - PATH; /* must be int! */

                free(ret);
                if (sz != 0) {
                        ret = xasprintf("%.*s/%s", sz, PATH, arg);
                } else {
                        /* We have xxx::yyyy in $PATH,
                         * it means "use current dir" */
                        ret = xstrdup(arg);
                }
                if (access(ret, F_OK) == 0)
                        break;

                if (*end == '\0') {
                        free(ret);
                        return NULL;
                }
                PATH = end + 1;
        }

        return ret;
}

static const struct built_in_command *find_builtin_helper(const char *name,
                const struct built_in_command *x,
                const struct built_in_command *end)
{
        while (x != end) {
                if (strcmp(name, x->b_cmd) != 0) {
                        x++;
                        continue;
                }
                debug_printf_exec("found builtin '%s'\n", name);
                return x;
        }
        return NULL;
}
static const struct built_in_command *find_builtin1(const char *name)
{
        return find_builtin_helper(name, bltins1, &bltins1[ARRAY_SIZE(bltins1)]);
}
static const struct built_in_command *find_builtin(const char *name)
{
        const struct built_in_command *x = find_builtin1(name);
        if (x)
                return x;
        return find_builtin_helper(name, bltins2, &bltins2[ARRAY_SIZE(bltins2)]);
}

#if ENABLE_HUSH_FUNCTIONS
static struct function **find_function_slot(const char *name)
{
        struct function **funcpp = &G.top_func;
        while (*funcpp) {
                if (strcmp(name, (*funcpp)->name) == 0) {
                        break;
                }
                funcpp = &(*funcpp)->next;
        }
        return funcpp;
}

static const struct function *find_function(const char *name)
{
        const struct function *funcp = *find_function_slot(name);
        if (funcp)
                debug_printf_exec("found function '%s'\n", name);
        return funcp;
}

/* Note: takes ownership on name ptr */
static struct function *new_function(char *name)
{
        struct function **funcpp = find_function_slot(name);
        struct function *funcp = *funcpp;

        if (funcp != NULL) {
                struct command *cmd = funcp->parent_cmd;
                debug_printf_exec("func %p parent_cmd %p\n", funcp, cmd);
                if (!cmd) {
                        debug_printf_exec("freeing & replacing function '%s'\n", funcp->name);
                        free(funcp->name);
                        /* Note: if !funcp->body, do not free body_as_string!
                         * This is a special case of "-F name body" function:
                         * body_as_string was not malloced! */
                        if (funcp->body) {
                                free_pipe_list(funcp->body);
# if !BB_MMU
                                free(funcp->body_as_string);
# endif
                        }
                } else {
                        debug_printf_exec("reinserting in tree & replacing function '%s'\n", funcp->name);
                        cmd->argv[0] = funcp->name;
                        cmd->group = funcp->body;
# if !BB_MMU
                        cmd->group_as_string = funcp->body_as_string;
# endif
                }
        } else {
                debug_printf_exec("remembering new function '%s'\n", name);
                funcp = *funcpp = xzalloc(sizeof(*funcp));
                /*funcp->next = NULL;*/
        }

        funcp->name = name;
        return funcp;
}

static void unset_func(const char *name)
{
        struct function **funcpp = find_function_slot(name);
        struct function *funcp = *funcpp;

        if (funcp != NULL) {
                debug_printf_exec("freeing function '%s'\n", funcp->name);
                *funcpp = funcp->next;
                /* funcp is unlinked now, deleting it.
                 * Note: if !funcp->body, the function was created by
                 * "-F name body", do not free ->body_as_string
                 * and ->name as they were not malloced. */
                if (funcp->body) {
                        free_pipe_list(funcp->body);
                        free(funcp->name);
# if !BB_MMU
                        free(funcp->body_as_string);
# endif
                }
                free(funcp);
        }
}

# if BB_MMU
#define exec_function(to_free, funcp, argv) \
        exec_function(funcp, argv)
# endif
static void exec_function(char ***to_free,
                const struct function *funcp,
                char **argv) NORETURN;
static void exec_function(char ***to_free,
                const struct function *funcp,
                char **argv)
{
# if BB_MMU
        int n = 1;

        argv[0] = G.global_argv[0];
        G.global_argv = argv;
        while (*++argv)
                n++;
        G.global_argc = n;
        /* On MMU, funcp->body is always non-NULL */
        n = run_list(funcp->body);
        fflush_all();
        _exit(n);
# else
        re_execute_shell(to_free,
                        funcp->body_as_string,
                        G.global_argv[0],
                        argv + 1,
                        NULL);
# endif
}

static int run_function(const struct function *funcp, char **argv)
{
        int rc;
        save_arg_t sv;
        smallint sv_flg;

        save_and_replace_G_args(&sv, argv);

        /* "we are in function, ok to use return" */
        sv_flg = G.flag_return_in_progress;
        G.flag_return_in_progress = -1;
# if ENABLE_HUSH_LOCAL
        G.func_nest_level++;
# endif

        /* On MMU, funcp->body is always non-NULL */
# if !BB_MMU
        if (!funcp->body) {
                /* Function defined by -F */
                parse_and_run_string(funcp->body_as_string);
                rc = G.last_exitcode;
        } else
# endif
        {
                rc = run_list(funcp->body);
        }

# if ENABLE_HUSH_LOCAL
        {
                struct variable *var;
                struct variable **var_pp;

                var_pp = &G.top_var;
                while ((var = *var_pp) != NULL) {
                        if (var->func_nest_level < G.func_nest_level) {
                                var_pp = &var->next;
                                continue;
                        }
                        /* Unexport */
                        if (var->flg_export)
                                bb_unsetenv(var->varstr);
                        /* Remove from global list */
                        *var_pp = var->next;
                        /* Free */
                        if (!var->max_len)
                                free(var->varstr);
                        free(var);
                }
                G.func_nest_level--;
        }
# endif
        G.flag_return_in_progress = sv_flg;

        restore_G_args(&sv, argv);

        return rc;
}
#endif /* ENABLE_HUSH_FUNCTIONS */


#if BB_MMU
#define exec_builtin(to_free, x, argv) \
        exec_builtin(x, argv)
#else
#define exec_builtin(to_free, x, argv) \
        exec_builtin(to_free, argv)
#endif
static void exec_builtin(char ***to_free,
                const struct built_in_command *x,
                char **argv) NORETURN;
static void exec_builtin(char ***to_free,
                const struct built_in_command *x,
                char **argv)
{
#if BB_MMU
        int rcode = x->b_function(argv);
        fflush_all();
        _exit(rcode);
#else
        /* On NOMMU, we must never block!
         * Example: { sleep 99 | read line; } & echo Ok
         */
        re_execute_shell(to_free,
                        argv[0],
                        G.global_argv[0],
                        G.global_argv + 1,
                        argv);
#endif
}


static void execvp_or_die(char **argv) NORETURN;
static void execvp_or_die(char **argv)
{
        debug_printf_exec("execing '%s'\n", argv[0]);
        sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
        execvp(argv[0], argv);
        bb_perror_msg("can't execute '%s'", argv[0]);
        _exit(127); /* bash compat */
}

#if ENABLE_HUSH_MODE_X
static void dump_cmd_in_x_mode(char **argv)
{
        if (G_x_mode && argv) {
                /* We want to output the line in one write op */
                char *buf, *p;
                int len;
                int n;

                len = 3;
                n = 0;
                while (argv[n])
                        len += strlen(argv[n++]) + 1;
                buf = xmalloc(len);
                buf[0] = '+';
                p = buf + 1;
                n = 0;
                while (argv[n])
                        p += sprintf(p, " %s", argv[n++]);
                *p++ = '\n';
                *p = '\0';
                fputs(buf, stderr);
                free(buf);
        }
}
#else
# define dump_cmd_in_x_mode(argv) ((void)0)
#endif

#if BB_MMU
#define pseudo_exec_argv(nommu_save, argv, assignment_cnt, argv_expanded) \
        pseudo_exec_argv(argv, assignment_cnt, argv_expanded)
#define pseudo_exec(nommu_save, command, argv_expanded) \
        pseudo_exec(command, argv_expanded)
#endif

/* Called after [v]fork() in run_pipe, or from builtin_exec.
 * Never returns.
 * Don't exit() here.  If you don't exec, use _exit instead.
 * The at_exit handlers apparently confuse the calling process,
 * in particular stdin handling.  Not sure why? -- because of vfork! (vda) */
static void pseudo_exec_argv(nommu_save_t *nommu_save,
                char **argv, int assignment_cnt,
                char **argv_expanded) NORETURN;
static NOINLINE void pseudo_exec_argv(nommu_save_t *nommu_save,
                char **argv, int assignment_cnt,
                char **argv_expanded)
{
        char **new_env;

        new_env = expand_assignments(argv, assignment_cnt);
        dump_cmd_in_x_mode(new_env);

        if (!argv[assignment_cnt]) {
                /* Case when we are here: ... | var=val | ...
                 * (note that we do not exit early, i.e., do not optimize out
                 * expand_assignments(): think about ... | var=`sleep 1` | ...
                 */
                free_strings(new_env);
                _exit(EXIT_SUCCESS);
        }

#if BB_MMU
        set_vars_and_save_old(new_env);
        free(new_env); /* optional */
        /* we can also destroy set_vars_and_save_old's return value,
         * to save memory */
#else
        nommu_save->new_env = new_env;
        nommu_save->old_vars = set_vars_and_save_old(new_env);
#endif

        if (argv_expanded) {
                argv = argv_expanded;
        } else {
                argv = expand_strvec_to_strvec(argv + assignment_cnt);
#if !BB_MMU
                nommu_save->argv = argv;
#endif
        }
        dump_cmd_in_x_mode(argv);

#if ENABLE_FEATURE_SH_STANDALONE || BB_MMU
        if (strchr(argv[0], '/') != NULL)
                goto skip;
#endif

        /* Check if the command matches any of the builtins.
         * Depending on context, this might be redundant.  But it's
         * easier to waste a few CPU cycles than it is to figure out
         * if this is one of those cases.
         */
        {
                /* On NOMMU, it is more expensive to re-execute shell
                 * just in order to run echo or test builtin.
                 * It's better to skip it here and run corresponding
                 * non-builtin later. */
                const struct built_in_command *x;
                x = BB_MMU ? find_builtin(argv[0]) : find_builtin1(argv[0]);
                if (x) {
                        exec_builtin(&nommu_save->argv_from_re_execing, x, argv);
                }
        }
#if ENABLE_HUSH_FUNCTIONS
        /* Check if the command matches any functions */
        {
                const struct function *funcp = find_function(argv[0]);
                if (funcp) {
                        exec_function(&nommu_save->argv_from_re_execing, funcp, argv);
                }
        }
#endif

#if ENABLE_FEATURE_SH_STANDALONE
        /* Check if the command matches any busybox applets */
        {
                int a = find_applet_by_name(argv[0]);
                if (a >= 0) {
# if BB_MMU /* see above why on NOMMU it is not allowed */
                        if (APPLET_IS_NOEXEC(a)) {
                                debug_printf_exec("running applet '%s'\n", argv[0]);
                                run_applet_no_and_exit(a, argv);
                        }
# endif
                        /* Re-exec ourselves */
                        debug_printf_exec("re-execing applet '%s'\n", argv[0]);
                        sigprocmask(SIG_SETMASK, &G.inherited_set, NULL);
                        execv(bb_busybox_exec_path, argv);
                        /* If they called chroot or otherwise made the binary no longer
                         * executable, fall through */
                }
        }
#endif

#if ENABLE_FEATURE_SH_STANDALONE || BB_MMU
 skip:
#endif
        execvp_or_die(argv);
}

/* Called after [v]fork() in run_pipe
 */
static void pseudo_exec(nommu_save_t *nommu_save,
                struct command *command,
                char **argv_expanded) NORETURN;
static void pseudo_exec(nommu_save_t *nommu_save,
                struct command *command,
                char **argv_expanded)
{
        if (command->argv) {
                pseudo_exec_argv(nommu_save, command->argv,
                                command->assignment_cnt, argv_expanded);
        }

        if (command->group) {
                /* Cases when we are here:
                 * ( list )
                 * { list } &
                 * ... | ( list ) | ...
                 * ... | { list } | ...
                 */
#if BB_MMU
                int rcode;
                debug_printf_exec("pseudo_exec: run_list\n");
                reset_traps_to_defaults();
                rcode = run_list(command->group);
                /* OK to leak memory by not calling free_pipe_list,
                 * since this process is about to exit */
                _exit(rcode);
#else
                re_execute_shell(&nommu_save->argv_from_re_execing,
                                command->group_as_string,
                                G.global_argv[0],
                                G.global_argv + 1,
                                NULL);
#endif
        }

        /* Case when we are here: ... | >file */
        debug_printf_exec("pseudo_exec'ed null command\n");
        _exit(EXIT_SUCCESS);
}

#if ENABLE_HUSH_JOB
static const char *get_cmdtext(struct pipe *pi)
{
        char **argv;
        char *p;
        int len;

        /* This is subtle. ->cmdtext is created only on first backgrounding.
         * (Think "cat, <ctrl-z>, fg, <ctrl-z>, fg, <ctrl-z>...." here...)
         * On subsequent bg argv is trashed, but we won't use it */
        if (pi->cmdtext)
                return pi->cmdtext;
        argv = pi->cmds[0].argv;
        if (!argv || !argv[0]) {
                pi->cmdtext = xzalloc(1);
                return pi->cmdtext;
        }

        len = 0;
        do {
                len += strlen(*argv) + 1;
        } while (*++argv);
        p = xmalloc(len);
        pi->cmdtext = p;
        argv = pi->cmds[0].argv;
        do {
                len = strlen(*argv);
                memcpy(p, *argv, len);
                p += len;
                *p++ = ' ';
        } while (*++argv);
        p[-1] = '\0';
        return pi->cmdtext;
}

static void insert_bg_job(struct pipe *pi)
{
        struct pipe *job, **jobp;
        int i;

        /* Linear search for the ID of the job to use */
        pi->jobid = 1;
        for (job = G.job_list; job; job = job->next)
                if (job->jobid >= pi->jobid)
                        pi->jobid = job->jobid + 1;

        /* Add job to the list of running jobs */
        jobp = &G.job_list;
        while ((job = *jobp) != NULL)
                jobp = &job->next;
        job = *jobp = xmalloc(sizeof(*job));

        *job = *pi; /* physical copy */
        job->next = NULL;
        job->cmds = xzalloc(sizeof(pi->cmds[0]) * pi->num_cmds);
        /* Cannot copy entire pi->cmds[] vector! This causes double frees */
        for (i = 0; i < pi->num_cmds; i++) {
                job->cmds[i].pid = pi->cmds[i].pid;
                /* all other fields are not used and stay zero */
        }
        job->cmdtext = xstrdup(get_cmdtext(pi));

        if (G_interactive_fd)
                printf("[%d] %d %s\n", job->jobid, job->cmds[0].pid, job->cmdtext);
        G.last_jobid = job->jobid;
}

static void remove_bg_job(struct pipe *pi)
{
        struct pipe *prev_pipe;

        if (pi == G.job_list) {
                G.job_list = pi->next;
        } else {
                prev_pipe = G.job_list;
                while (prev_pipe->next != pi)
                        prev_pipe = prev_pipe->next;
                prev_pipe->next = pi->next;
        }
        if (G.job_list)
                G.last_jobid = G.job_list->jobid;
        else
                G.last_jobid = 0;
}

/* Remove a backgrounded job */
static void delete_finished_bg_job(struct pipe *pi)
{
        remove_bg_job(pi);
        free_pipe(pi);
}
#endif /* JOB */

/* Check to see if any processes have exited -- if they
 * have, figure out why and see if a job has completed */
static int checkjobs(struct pipe *fg_pipe)
{
        int attributes;
        int status;
#if ENABLE_HUSH_JOB
        struct pipe *pi;
#endif
        pid_t childpid;
        int rcode = 0;

        debug_printf_jobs("checkjobs %p\n", fg_pipe);

        attributes = WUNTRACED;
        if (fg_pipe == NULL)
                attributes |= WNOHANG;

        errno = 0;
#if ENABLE_HUSH_FAST
        if (G.handled_SIGCHLD == G.count_SIGCHLD) {
//bb_error_msg("[%d] checkjobs: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d children?:%d fg_pipe:%p",
//getpid(), G.count_SIGCHLD, G.handled_SIGCHLD, G.we_have_children, fg_pipe);
                /* There was neither fork nor SIGCHLD since last waitpid */
                /* Avoid doing waitpid syscall if possible */
                if (!G.we_have_children) {
                        errno = ECHILD;
                        return -1;
                }
                if (fg_pipe == NULL) { /* is WNOHANG set? */
                        /* We have children, but they did not exit
                         * or stop yet (we saw no SIGCHLD) */
                        return 0;
                }
                /* else: !WNOHANG, waitpid will block, can't short-circuit */
        }
#endif

/* Do we do this right?
 * bash-3.00# sleep 20 | false
 * <ctrl-Z pressed>
 * [3]+  Stopped          sleep 20 | false
 * bash-3.00# echo $?
 * 1   <========== bg pipe is not fully done, but exitcode is already known!
 * [hush 1.14.0: yes we do it right]
 */
 wait_more:
        while (1) {
                int i;
                int dead;

#if ENABLE_HUSH_FAST
                i = G.count_SIGCHLD;
#endif
                childpid = waitpid(-1, &status, attributes);
                if (childpid <= 0) {
                        if (childpid && errno != ECHILD)
                                bb_perror_msg("waitpid");
#if ENABLE_HUSH_FAST
                        else { /* Until next SIGCHLD, waitpid's are useless */
                                G.we_have_children = (childpid == 0);
                                G.handled_SIGCHLD = i;
//bb_error_msg("[%d] checkjobs: waitpid returned <= 0, G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
                        }
#endif
                        break;
                }
                dead = WIFEXITED(status) || WIFSIGNALED(status);

#if DEBUG_JOBS
                if (WIFSTOPPED(status))
                        debug_printf_jobs("pid %d stopped by sig %d (exitcode %d)\n",
                                        childpid, WSTOPSIG(status), WEXITSTATUS(status));
                if (WIFSIGNALED(status))
                        debug_printf_jobs("pid %d killed by sig %d (exitcode %d)\n",
                                        childpid, WTERMSIG(status), WEXITSTATUS(status));
                if (WIFEXITED(status))
                        debug_printf_jobs("pid %d exited, exitcode %d\n",
                                        childpid, WEXITSTATUS(status));
#endif
                /* Were we asked to wait for fg pipe? */
                if (fg_pipe) {
                        i = fg_pipe->num_cmds;
                        while (--i >= 0) {
                                debug_printf_jobs("check pid %d\n", fg_pipe->cmds[i].pid);
                                if (fg_pipe->cmds[i].pid != childpid)
                                        continue;
                                if (dead) {
                                        int ex;
                                        fg_pipe->cmds[i].pid = 0;
                                        fg_pipe->alive_cmds--;
                                        ex = WEXITSTATUS(status);
                                        /* bash prints killer signal's name for *last*
                                         * process in pipe (prints just newline for SIGINT).
                                         * Mimic this. Example: "sleep 5" + (^\ or kill -QUIT)
                                         */
                                        if (WIFSIGNALED(status)) {
                                                int sig = WTERMSIG(status);
                                                if (i == fg_pipe->num_cmds-1)
                                                        printf("%s\n", sig == SIGINT ? "" : get_signame(sig));
                                                /* TODO: MIPS has 128 sigs (1..128), what if sig==128 here?
                                                 * Maybe we need to use sig | 128? */
                                                ex = sig + 128;
                                        }
                                        fg_pipe->cmds[i].cmd_exitcode = ex;
                                } else {
                                        fg_pipe->cmds[i].is_stopped = 1;
                                        fg_pipe->stopped_cmds++;
                                }
                                debug_printf_jobs("fg_pipe: alive_cmds %d stopped_cmds %d\n",
                                                fg_pipe->alive_cmds, fg_pipe->stopped_cmds);
                                if (fg_pipe->alive_cmds == fg_pipe->stopped_cmds) {
                                        /* All processes in fg pipe have exited or stopped */
                                        i = fg_pipe->num_cmds;
                                        while (--i >= 0) {
                                                rcode = fg_pipe->cmds[i].cmd_exitcode;
                                                /* usually last process gives overall exitstatus,
                                                 * but with "set -o pipefail", last *failed* process does */
                                                if (G.o_opt[OPT_O_PIPEFAIL] == 0 || rcode != 0)
                                                        break;
                                        }
                                        IF_HAS_KEYWORDS(if (fg_pipe->pi_inverted) rcode = !rcode;)
/* Note: *non-interactive* bash does not continue if all processes in fg pipe
 * are stopped. Testcase: "cat | cat" in a script (not on command line!)
 * and "killall -STOP cat" */
                                        if (G_interactive_fd) {
#if ENABLE_HUSH_JOB
                                                if (fg_pipe->alive_cmds != 0)
                                                        insert_bg_job(fg_pipe);
#endif
                                                return rcode;
                                        }
                                        if (fg_pipe->alive_cmds == 0)
                                                return rcode;
                                }
                                /* There are still running processes in the fg pipe */
                                goto wait_more; /* do waitpid again */
                        }
                        /* it wasnt fg_pipe, look for process in bg pipes */
                }

#if ENABLE_HUSH_JOB
                /* We asked to wait for bg or orphaned children */
                /* No need to remember exitcode in this case */
                for (pi = G.job_list; pi; pi = pi->next) {
                        for (i = 0; i < pi->num_cmds; i++) {
                                if (pi->cmds[i].pid == childpid)
                                        goto found_pi_and_prognum;
                        }
                }
                /* Happens when shell is used as init process (init=/bin/sh) */
                debug_printf("checkjobs: pid %d was not in our list!\n", childpid);
                continue; /* do waitpid again */

 found_pi_and_prognum:
                if (dead) {
                        /* child exited */
                        pi->cmds[i].pid = 0;
                        pi->alive_cmds--;
                        if (!pi->alive_cmds) {
                                if (G_interactive_fd)
                                        printf(JOB_STATUS_FORMAT, pi->jobid,
                                                        "Done", pi->cmdtext);
                                delete_finished_bg_job(pi);
                        }
                } else {
                        /* child stopped */
                        pi->cmds[i].is_stopped = 1;
                        pi->stopped_cmds++;
                }
#endif
        } /* while (waitpid succeeds)... */

        return rcode;
}

#if ENABLE_HUSH_JOB
static int checkjobs_and_fg_shell(struct pipe *fg_pipe)
{
        pid_t p;
        int rcode = checkjobs(fg_pipe);
        if (G_saved_tty_pgrp) {
                /* Job finished, move the shell to the foreground */
                p = getpgrp(); /* our process group id */
                debug_printf_jobs("fg'ing ourself: getpgrp()=%d\n", (int)p);
                tcsetpgrp(G_interactive_fd, p);
        }
        return rcode;
}
#endif

/* Start all the jobs, but don't wait for anything to finish.
 * See checkjobs().
 *
 * Return code is normally -1, when the caller has to wait for children
 * to finish to determine the exit status of the pipe.  If the pipe
 * is a simple builtin command, however, the action is done by the
 * time run_pipe returns, and the exit code is provided as the
 * return value.
 *
 * Returns -1 only if started some children. IOW: we have to
 * mask out retvals of builtins etc with 0xff!
 *
 * The only case when we do not need to [v]fork is when the pipe
 * is single, non-backgrounded, non-subshell command. Examples:
 * cmd ; ...   { list } ; ...
 * cmd && ...  { list } && ...
 * cmd || ...  { list } || ...
 * If it is, then we can run cmd as a builtin, NOFORK [do we do this?],
 * or (if SH_STANDALONE) an applet, and we can run the { list }
 * with run_list. If it isn't one of these, we fork and exec cmd.
 *
 * Cases when we must fork:
 * non-single:   cmd | cmd
 * backgrounded: cmd &     { list } &
 * subshell:     ( list ) [&]
 */
#if !ENABLE_HUSH_MODE_X
#define redirect_and_varexp_helper(new_env_p, old_vars_p, command, squirrel, argv_expanded) \
        redirect_and_varexp_helper(new_env_p, old_vars_p, command, squirrel)
#endif
static int redirect_and_varexp_helper(char ***new_env_p,
                struct variable **old_vars_p,
                struct command *command,
                int squirrel[3],
                char **argv_expanded)
{
        /* setup_redirects acts on file descriptors, not FILEs.
         * This is perfect for work that comes after exec().
         * Is it really safe for inline use?  Experimentally,
         * things seem to work. */
        int rcode = setup_redirects(command, squirrel);
        if (rcode == 0) {
                char **new_env = expand_assignments(command->argv, command->assignment_cnt);
                *new_env_p = new_env;
                dump_cmd_in_x_mode(new_env);
                dump_cmd_in_x_mode(argv_expanded);
                if (old_vars_p)
                        *old_vars_p = set_vars_and_save_old(new_env);
        }
        return rcode;
}
static NOINLINE int run_pipe(struct pipe *pi)
{
        static const char *const null_ptr = NULL;

        int cmd_no;
        int next_infd;
        struct command *command;
        char **argv_expanded;
        char **argv;
        /* it is not always needed, but we aim to smaller code */
        int squirrel[] = { -1, -1, -1 };
        int rcode;

        debug_printf_exec("run_pipe start: members:%d\n", pi->num_cmds);
        debug_enter();

        /* Testcase: set -- q w e; (IFS='' echo "$*"; IFS=''; echo "$*"); echo "$*"
         * Result should be 3 lines: q w e, qwe, q w e
         */
        G.ifs = get_local_var_value("IFS");
        if (!G.ifs)
                G.ifs = defifs;

        IF_HUSH_JOB(pi->pgrp = -1;)
        pi->stopped_cmds = 0;
        command = &pi->cmds[0];
        argv_expanded = NULL;

        if (pi->num_cmds != 1
         || pi->followup == PIPE_BG
         || command->cmd_type == CMD_SUBSHELL
        ) {
                goto must_fork;
        }

        pi->alive_cmds = 1;

        debug_printf_exec(": group:%p argv:'%s'\n",
                command->group, command->argv ? command->argv[0] : "NONE");

        if (command->group) {
#if ENABLE_HUSH_FUNCTIONS
                if (command->cmd_type == CMD_FUNCDEF) {
                        /* "executing" func () { list } */
                        struct function *funcp;

                        funcp = new_function(command->argv[0]);
                        /* funcp->name is already set to argv[0] */
                        funcp->body = command->group;
# if !BB_MMU
                        funcp->body_as_string = command->group_as_string;
                        command->group_as_string = NULL;
# endif
                        command->group = NULL;
                        command->argv[0] = NULL;
                        debug_printf_exec("cmd %p has child func at %p\n", command, funcp);
                        funcp->parent_cmd = command;
                        command->child_func = funcp;

                        debug_printf_exec("run_pipe: return EXIT_SUCCESS\n");
                        debug_leave();
                        return EXIT_SUCCESS;
                }
#endif
                /* { list } */
                debug_printf("non-subshell group\n");
                rcode = 1; /* exitcode if redir failed */
                if (setup_redirects(command, squirrel) == 0) {
                        debug_printf_exec(": run_list\n");
                        rcode = run_list(command->group) & 0xff;
                }
                restore_redirects(squirrel);
                IF_HAS_KEYWORDS(if (pi->pi_inverted) rcode = !rcode;)
                debug_leave();
                debug_printf_exec("run_pipe: return %d\n", rcode);
                return rcode;
        }

        argv = command->argv ? command->argv : (char **) &null_ptr;
        {
                const struct built_in_command *x;
#if ENABLE_HUSH_FUNCTIONS
                const struct function *funcp;
#else
                enum { funcp = 0 };
#endif
                char **new_env = NULL;
                struct variable *old_vars = NULL;

                if (argv[command->assignment_cnt] == NULL) {
                        /* Assignments, but no command */
                        /* Ensure redirects take effect (that is, create files).
                         * Try "a=t >file" */
#if 0 /* A few cases in testsuite fail with this code. FIXME */
                        rcode = redirect_and_varexp_helper(&new_env, /*old_vars:*/ NULL, command, squirrel, /*argv_expanded:*/ NULL);
                        /* Set shell variables */
                        if (new_env) {
                                argv = new_env;
                                while (*argv) {
                                        set_local_var(*argv, /*exp:*/ 0, /*lvl:*/ 0, /*ro:*/ 0);
                                        /* Do we need to flag set_local_var() errors?
                                         * "assignment to readonly var" and "putenv error"
                                         */
                                        argv++;
                                }
                        }
                        /* Redirect error sets $? to 1. Otherwise,
                         * if evaluating assignment value set $?, retain it.
                         * Try "false; q=`exit 2`; echo $?" - should print 2: */
                        if (rcode == 0)
                                rcode = G.last_exitcode;
                        /* Exit, _skipping_ variable restoring code: */
                        goto clean_up_and_ret0;

#else /* Older, bigger, but more correct code */

                        rcode = setup_redirects(command, squirrel);
                        restore_redirects(squirrel);
                        /* Set shell variables */
                        if (G_x_mode)
                                bb_putchar_stderr('+');
                        while (*argv) {
                                char *p = expand_string_to_string(*argv, /*unbackslash:*/ 1);
                                if (G_x_mode)
                                        fprintf(stderr, " %s", p);
                                debug_printf_exec("set shell var:'%s'->'%s'\n",
                                                *argv, p);
                                set_local_var(p, /*exp:*/ 0, /*lvl:*/ 0, /*ro:*/ 0);
                                /* Do we need to flag set_local_var() errors?
                                 * "assignment to readonly var" and "putenv error"
                                 */
                                argv++;
                        }
                        if (G_x_mode)
                                bb_putchar_stderr('\n');
                        /* Redirect error sets $? to 1. Otherwise,
                         * if evaluating assignment value set $?, retain it.
                         * Try "false; q=`exit 2`; echo $?" - should print 2: */
                        if (rcode == 0)
                                rcode = G.last_exitcode;
                        IF_HAS_KEYWORDS(if (pi->pi_inverted) rcode = !rcode;)
                        debug_leave();
                        debug_printf_exec("run_pipe: return %d\n", rcode);
                        return rcode;
#endif
                }

                /* Expand the rest into (possibly) many strings each */
                if (0) {}
#if ENABLE_HUSH_BASH_COMPAT
                else if (command->cmd_type == CMD_SINGLEWORD_NOGLOB) {
                        argv_expanded = expand_strvec_to_strvec_singleword_noglob(argv + command->assignment_cnt);
                }
#endif
                else {
                        argv_expanded = expand_strvec_to_strvec(argv + command->assignment_cnt);
                }

                /* if someone gives us an empty string: `cmd with empty output` */
                if (!argv_expanded[0]) {
                        free(argv_expanded);
                        debug_leave();
                        return G.last_exitcode;
                }

                x = find_builtin(argv_expanded[0]);
#if ENABLE_HUSH_FUNCTIONS
                funcp = NULL;
                if (!x)
                        funcp = find_function(argv_expanded[0]);
#endif
                if (x || funcp) {
                        if (!funcp) {
                                if (x->b_function == builtin_exec && argv_expanded[1] == NULL) {
                                        debug_printf("exec with redirects only\n");
                                        rcode = setup_redirects(command, NULL);
                                        goto clean_up_and_ret1;
                                }
                        }
                        rcode = redirect_and_varexp_helper(&new_env, &old_vars, command, squirrel, argv_expanded);
                        if (rcode == 0) {
                                if (!funcp) {
                                        debug_printf_exec(": builtin '%s' '%s'...\n",
                                                x->b_cmd, argv_expanded[1]);
                                        rcode = x->b_function(argv_expanded) & 0xff;
                                        fflush_all();
                                }
#if ENABLE_HUSH_FUNCTIONS
                                else {
# if ENABLE_HUSH_LOCAL
                                        struct variable **sv;
                                        sv = G.shadowed_vars_pp;
                                        G.shadowed_vars_pp = &old_vars;
# endif
                                        debug_printf_exec(": function '%s' '%s'...\n",
                                                funcp->name, argv_expanded[1]);
                                        rcode = run_function(funcp, argv_expanded) & 0xff;
# if ENABLE_HUSH_LOCAL
                                        G.shadowed_vars_pp = sv;
# endif
                                }
#endif
                        }
 clean_up_and_ret:
                        unset_vars(new_env);
                        add_vars(old_vars);
/* clean_up_and_ret0: */
                        restore_redirects(squirrel);
 clean_up_and_ret1:
                        free(argv_expanded);
                        IF_HAS_KEYWORDS(if (pi->pi_inverted) rcode = !rcode;)
                        debug_leave();
                        debug_printf_exec("run_pipe return %d\n", rcode);
                        return rcode;
                }

                if (ENABLE_FEATURE_SH_STANDALONE) {
                        int n = find_applet_by_name(argv_expanded[0]);
                        if (n >= 0 && APPLET_IS_NOFORK(n)) {
                                rcode = redirect_and_varexp_helper(&new_env, &old_vars, command, squirrel, argv_expanded);
                                if (rcode == 0) {
                                        debug_printf_exec(": run_nofork_applet '%s' '%s'...\n",
                                                argv_expanded[0], argv_expanded[1]);
                                        rcode = run_nofork_applet(n, argv_expanded);
                                }
                                goto clean_up_and_ret;
                        }
                }
                /* It is neither builtin nor applet. We must fork. */
        }

 must_fork:
        /* NB: argv_expanded may already be created, and that
         * might include `cmd` runs! Do not rerun it! We *must*
         * use argv_expanded if it's non-NULL */

        /* Going to fork a child per each pipe member */
        pi->alive_cmds = 0;
        next_infd = 0;

        cmd_no = 0;
        while (cmd_no < pi->num_cmds) {
                struct fd_pair pipefds;
#if !BB_MMU
                volatile nommu_save_t nommu_save;
                nommu_save.new_env = NULL;
                nommu_save.old_vars = NULL;
                nommu_save.argv = NULL;
                nommu_save.argv_from_re_execing = NULL;
#endif
                command = &pi->cmds[cmd_no];
                cmd_no++;
                if (command->argv) {
                        debug_printf_exec(": pipe member '%s' '%s'...\n",
                                        command->argv[0], command->argv[1]);
                } else {
                        debug_printf_exec(": pipe member with no argv\n");
                }

                /* pipes are inserted between pairs of commands */
                pipefds.rd = 0;
                pipefds.wr = 1;
                if (cmd_no < pi->num_cmds)
                        xpiped_pair(pipefds);

                command->pid = BB_MMU ? fork() : vfork();
                if (!command->pid) { /* child */
#if ENABLE_HUSH_JOB
                        disable_restore_tty_pgrp_on_exit();
                        CLEAR_RANDOM_T(&G.random_gen); /* or else $RANDOM repeats in child */

                        /* Every child adds itself to new process group
                         * with pgid == pid_of_first_child_in_pipe */
                        if (G.run_list_level == 1 && G_interactive_fd) {
                                pid_t pgrp;
                                pgrp = pi->pgrp;
                                if (pgrp < 0) /* true for 1st process only */
                                        pgrp = getpid();
                                if (setpgid(0, pgrp) == 0
                                 && pi->followup != PIPE_BG
                                 && G_saved_tty_pgrp /* we have ctty */
                                ) {
                                        /* We do it in *every* child, not just first,
                                         * to avoid races */
                                        tcsetpgrp(G_interactive_fd, pgrp);
                                }
                        }
#endif
                        if (pi->alive_cmds == 0 && pi->followup == PIPE_BG) {
                                /* 1st cmd in backgrounded pipe
                                 * should have its stdin /dev/null'ed */
                                close(0);
                                if (open(bb_dev_null, O_RDONLY))
                                        xopen("/", O_RDONLY);
                        } else {
                                xmove_fd(next_infd, 0);
                        }
                        xmove_fd(pipefds.wr, 1);
                        if (pipefds.rd > 1)
                                close(pipefds.rd);
                        /* Like bash, explicit redirects override pipes,
                         * and the pipe fd is available for dup'ing. */
                        if (setup_redirects(command, NULL))
                                _exit(1);

                        /* Restore default handlers just prior to exec */
                        /*signal(SIGCHLD, SIG_DFL); - so far we don't have any handlers */

                        /* Stores to nommu_save list of env vars putenv'ed
                         * (NOMMU, on MMU we don't need that) */
                        /* cast away volatility... */
                        pseudo_exec((nommu_save_t*) &nommu_save, command, argv_expanded);
                        /* pseudo_exec() does not return */
                }

                /* parent or error */
#if ENABLE_HUSH_FAST
                G.count_SIGCHLD++;
//bb_error_msg("[%d] fork in run_pipe: G.count_SIGCHLD:%d G.handled_SIGCHLD:%d", getpid(), G.count_SIGCHLD, G.handled_SIGCHLD);
#endif
                enable_restore_tty_pgrp_on_exit();
#if !BB_MMU
                /* Clean up after vforked child */
                free(nommu_save.argv);
                free(nommu_save.argv_from_re_execing);
                unset_vars(nommu_save.new_env);
                add_vars(nommu_save.old_vars);
#endif
                free(argv_expanded);
                argv_expanded = NULL;
                if (command->pid < 0) { /* [v]fork failed */
                        /* Clearly indicate, was it fork or vfork */
                        bb_perror_msg(BB_MMU ? "vfork"+1 : "vfork");
                } else {
                        pi->alive_cmds++;
#if ENABLE_HUSH_JOB
                        /* Second and next children need to know pid of first one */
                        if (pi->pgrp < 0)
                                pi->pgrp = command->pid;
#endif
                }

                if (cmd_no > 1)
                        close(next_infd);
                if (cmd_no < pi->num_cmds)
                        close(pipefds.wr);
                /* Pass read (output) pipe end to next iteration */
                next_infd = pipefds.rd;
        }

        if (!pi->alive_cmds) {
                debug_leave();
                debug_printf_exec("run_pipe return 1 (all forks failed, no children)\n");
                return 1;
        }

        debug_leave();
        debug_printf_exec("run_pipe return -1 (%u children started)\n", pi->alive_cmds);
        return -1;
}

/* NB: called by pseudo_exec, and therefore must not modify any
 * global data until exec/_exit (we can be a child after vfork!) */
static int run_list(struct pipe *pi)
{
#if ENABLE_HUSH_CASE
        char *case_word = NULL;
#endif
#if ENABLE_HUSH_LOOPS
        struct pipe *loop_top = NULL;
        char **for_lcur = NULL;
        char **for_list = NULL;
#endif
        smallint last_followup;
        smalluint rcode;
#if ENABLE_HUSH_IF || ENABLE_HUSH_CASE
        smalluint cond_code = 0;
#else
        enum { cond_code = 0 };
#endif
#if HAS_KEYWORDS
        smallint rword;      /* RES_foo */
        smallint last_rword; /* ditto */
#endif

        debug_printf_exec("run_list start lvl %d\n", G.run_list_level);
        debug_enter();

#if ENABLE_HUSH_LOOPS
        /* Check syntax for "for" */
        {
                struct pipe *cpipe;
                for (cpipe = pi; cpipe; cpipe = cpipe->next) {
                        if (cpipe->res_word != RES_FOR && cpipe->res_word != RES_IN)
                                continue;
                        /* current word is FOR or IN (BOLD in comments below) */
                        if (cpipe->next == NULL) {
                                syntax_error("malformed for");
                                debug_leave();
                                debug_printf_exec("run_list lvl %d return 1\n", G.run_list_level);
                                return 1;
                        }
                        /* "FOR v; do ..." and "for v IN a b; do..." are ok */
                        if (cpipe->next->res_word == RES_DO)
                                continue;
                        /* next word is not "do". It must be "in" then ("FOR v in ...") */
                        if (cpipe->res_word == RES_IN /* "for v IN a b; not_do..."? */
                         || cpipe->next->res_word != RES_IN /* FOR v not_do_and_not_in..."? */
                        ) {
                                syntax_error("malformed for");
                                debug_leave();
                                debug_printf_exec("run_list lvl %d return 1\n", G.run_list_level);
                                return 1;
                        }
                }
        }
#endif

        /* Past this point, all code paths should jump to ret: label
         * in order to return, no direct "return" statements please.
         * This helps to ensure that no memory is leaked. */

#if ENABLE_HUSH_JOB
        G.run_list_level++;
#endif

#if HAS_KEYWORDS
        rword = RES_NONE;
        last_rword = RES_XXXX;
#endif
        last_followup = PIPE_SEQ;
        rcode = G.last_exitcode;

        /* Go through list of pipes, (maybe) executing them. */
        for (; pi; pi = IF_HUSH_LOOPS(rword == RES_DONE ? loop_top : ) pi->next) {
                if (G.flag_SIGINT)
                        break;

                IF_HAS_KEYWORDS(rword = pi->res_word;)
                debug_printf_exec(": rword=%d cond_code=%d last_rword=%d\n",
                                rword, cond_code, last_rword);
#if ENABLE_HUSH_LOOPS
                if ((rword == RES_WHILE || rword == RES_UNTIL || rword == RES_FOR)
                 && loop_top == NULL /* avoid bumping G.depth_of_loop twice */
                ) {
                        /* start of a loop: remember where loop starts */
                        loop_top = pi;
                        G.depth_of_loop++;
                }
#endif
                /* Still in the same "if...", "then..." or "do..." branch? */
                if (IF_HAS_KEYWORDS(rword == last_rword &&) 1) {
                        if ((rcode == 0 && last_followup == PIPE_OR)
                         || (rcode != 0 && last_followup == PIPE_AND)
                        ) {
                                /* It is "<true> || CMD" or "<false> && CMD"
                                 * and we should not execute CMD */
                                debug_printf_exec("skipped cmd because of || or &&\n");
                                last_followup = pi->followup;
                                continue;
                        }
                }
                last_followup = pi->followup;
                IF_HAS_KEYWORDS(last_rword = rword;)
#if ENABLE_HUSH_IF
                if (cond_code) {
                        if (rword == RES_THEN) {
                                /* if false; then ... fi has exitcode 0! */
                                G.last_exitcode = rcode = EXIT_SUCCESS;
                                /* "if <false> THEN cmd": skip cmd */
                                continue;
                        }
                } else {
                        if (rword == RES_ELSE || rword == RES_ELIF) {
                                /* "if <true> then ... ELSE/ELIF cmd":
                                 * skip cmd and all following ones */
                                break;
                        }
                }
#endif
#if ENABLE_HUSH_LOOPS
                if (rword == RES_FOR) { /* && pi->num_cmds - always == 1 */
                        if (!for_lcur) {
                                /* first loop through for */

                                static const char encoded_dollar_at[] ALIGN1 = {
                                        SPECIAL_VAR_SYMBOL, '@' | 0x80, SPECIAL_VAR_SYMBOL, '\0'
                                }; /* encoded representation of "$@" */
                                static const char *const encoded_dollar_at_argv[] = {
                                        encoded_dollar_at, NULL
                                }; /* argv list with one element: "$@" */
                                char **vals;

                                vals = (char**)encoded_dollar_at_argv;
                                if (pi->next->res_word == RES_IN) {
                                        /* if no variable values after "in" we skip "for" */
                                        if (!pi->next->cmds[0].argv) {
                                                G.last_exitcode = rcode = EXIT_SUCCESS;
                                                debug_printf_exec(": null FOR: exitcode EXIT_SUCCESS\n");
                                                break;
                                        }
                                        vals = pi->next->cmds[0].argv;
                                } /* else: "for var; do..." -> assume "$@" list */
                                /* create list of variable values */
                                debug_print_strings("for_list made from", vals);
                                for_list = expand_strvec_to_strvec(vals);
                                for_lcur = for_list;
                                debug_print_strings("for_list", for_list);
                        }
                        if (!*for_lcur) {
                                /* "for" loop is over, clean up */
                                free(for_list);
                                for_list = NULL;
                                for_lcur = NULL;
                                break;
                        }
                        /* Insert next value from for_lcur */
                        /* note: *for_lcur already has quotes removed, $var expanded, etc */
                        set_local_var(xasprintf("%s=%s", pi->cmds[0].argv[0], *for_lcur++), /*exp:*/ 0, /*lvl:*/ 0, /*ro:*/ 0);
                        continue;
                }
                if (rword == RES_IN) {
                        continue; /* "for v IN list;..." - "in" has no cmds anyway */
                }
                if (rword == RES_DONE) {
                        continue; /* "done" has no cmds too */
                }
#endif
#if ENABLE_HUSH_CASE
                if (rword == RES_CASE) {
                        case_word = expand_strvec_to_string(pi->cmds->argv);
                        continue;
                }
                if (rword == RES_MATCH) {
                        char **argv;

                        if (!case_word) /* "case ... matched_word) ... WORD)": we executed selected branch, stop */
                                break;
                        /* all prev words didn't match, does this one match? */
                        argv = pi->cmds->argv;
                        while (*argv) {
                                char *pattern = expand_string_to_string(*argv, /*unbackslash:*/ 1);
                                /* TODO: which FNM_xxx flags to use? */
                                cond_code = (fnmatch(pattern, case_word, /*flags:*/ 0) != 0);
                                free(pattern);
                                if (cond_code == 0) { /* match! we will execute this branch */
                                        free(case_word); /* make future "word)" stop */
                                        case_word = NULL;
                                        break;
                                }
                                argv++;
                        }
                        continue;
                }
                if (rword == RES_CASE_BODY) { /* inside of a case branch */
                        if (cond_code != 0)
                                continue; /* not matched yet, skip this pipe */
                }
#endif
                /* Just pressing <enter> in shell should check for jobs.
                 * OTOH, in non-interactive shell this is useless
                 * and only leads to extra job checks */
                if (pi->num_cmds == 0) {
                        if (G_interactive_fd)
                                goto check_jobs_and_continue;
                        continue;
                }

                /* After analyzing all keywords and conditions, we decided
                 * to execute this pipe. NB: have to do checkjobs(NULL)
                 * after run_pipe to collect any background children,
                 * even if list execution is to be stopped. */
                debug_printf_exec(": run_pipe with %d members\n", pi->num_cmds);
                {
                        int r;
#if ENABLE_HUSH_LOOPS
                        G.flag_break_continue = 0;
#endif
                        rcode = r = run_pipe(pi); /* NB: rcode is a smallint */
                        if (r != -1) {
                                /* We ran a builtin, function, or group.
                                 * rcode is already known
                                 * and we don't need to wait for anything. */
                                G.last_exitcode = rcode;
                                debug_printf_exec(": builtin/func exitcode %d\n", rcode);
                                check_and_run_traps(0);
#if ENABLE_HUSH_LOOPS
                                /* Was it "break" or "continue"? */
                                if (G.flag_break_continue) {
                                        smallint fbc = G.flag_break_continue;
                                        /* We might fall into outer *loop*,
                                         * don't want to break it too */
                                        if (loop_top) {
                                                G.depth_break_continue--;
                                                if (G.depth_break_continue == 0)
                                                        G.flag_break_continue = 0;
                                                /* else: e.g. "continue 2" should *break* once, *then* continue */
                                        } /* else: "while... do... { we are here (innermost list is not a loop!) };...done" */
                                        if (G.depth_break_continue != 0 || fbc == BC_BREAK)
                                                goto check_jobs_and_break;
                                        /* "continue": simulate end of loop */
                                        rword = RES_DONE;
                                        continue;
                                }
#endif
#if ENABLE_HUSH_FUNCTIONS
                                if (G.flag_return_in_progress == 1) {
                                        /* same as "goto check_jobs_and_break" */
                                        checkjobs(NULL);
                                        break;
                                }
#endif
                        } else if (pi->followup == PIPE_BG) {
                                /* What does bash do with attempts to background builtins? */
                                /* even bash 3.2 doesn't do that well with nested bg:
                                 * try "{ { sleep 10; echo DEEP; } & echo HERE; } &".
                                 * I'm NOT treating inner &'s as jobs */
                                check_and_run_traps(0);
#if ENABLE_HUSH_JOB
                                if (G.run_list_level == 1)
                                        insert_bg_job(pi);
#endif
                                /* Last command's pid goes to $! */
                                G.last_bg_pid = pi->cmds[pi->num_cmds - 1].pid;
                                G.last_exitcode = rcode = EXIT_SUCCESS;
                                debug_printf_exec(": cmd&: exitcode EXIT_SUCCESS\n");
                        } else {
#if ENABLE_HUSH_JOB
                                if (G.run_list_level == 1 && G_interactive_fd) {
                                        /* Waits for completion, then fg's main shell */
                                        rcode = checkjobs_and_fg_shell(pi);
                                        debug_printf_exec(": checkjobs_and_fg_shell exitcode %d\n", rcode);
                                        check_and_run_traps(0);
                                } else
#endif
                                { /* This one just waits for completion */
                                        rcode = checkjobs(pi);
                                        debug_printf_exec(": checkjobs exitcode %d\n", rcode);
                                        check_and_run_traps(0);
                                }
                                G.last_exitcode = rcode;
                        }
                }

                /* Analyze how result affects subsequent commands */
#if ENABLE_HUSH_IF
                if (rword == RES_IF || rword == RES_ELIF)
                        cond_code = rcode;
#endif
#if ENABLE_HUSH_LOOPS
                /* Beware of "while false; true; do ..."! */
                if (pi->next && pi->next->res_word == RES_DO) {
                        if (rword == RES_WHILE) {
                                if (rcode) {
                                        /* "while false; do...done" - exitcode 0 */
                                        G.last_exitcode = rcode = EXIT_SUCCESS;
                                        debug_printf_exec(": while expr is false: breaking (exitcode:EXIT_SUCCESS)\n");
                                        goto check_jobs_and_break;
                                }
                        }
                        if (rword == RES_UNTIL) {
                                if (!rcode) {
                                        debug_printf_exec(": until expr is true: breaking\n");
 check_jobs_and_break:
                                        checkjobs(NULL);
                                        break;
                                }
                        }
                }
#endif

 check_jobs_and_continue:
                checkjobs(NULL);
        } /* for (pi) */

#if ENABLE_HUSH_JOB
        G.run_list_level--;
#endif
#if ENABLE_HUSH_LOOPS
        if (loop_top)
                G.depth_of_loop--;
        free(for_list);
#endif
#if ENABLE_HUSH_CASE
        free(case_word);
#endif
        debug_leave();
        debug_printf_exec("run_list lvl %d return %d\n", G.run_list_level + 1, rcode);
        return rcode;
}

/* Select which version we will use */
static int run_and_free_list(struct pipe *pi)
{
        int rcode = 0;
        debug_printf_exec("run_and_free_list entered\n");
        if (!G.o_opt[OPT_O_NOEXEC]) {
                debug_printf_exec(": run_list: 1st pipe with %d cmds\n", pi->num_cmds);
                rcode = run_list(pi);
        }
        /* free_pipe_list has the side effect of clearing memory.
         * In the long run that function can be merged with run_list,
         * but doing that now would hobble the debugging effort. */
        free_pipe_list(pi);
        debug_printf_exec("run_and_free_list return %d\n", rcode);
        return rcode;
}


/* Called a few times only (or even once if "sh -c") */
static void init_sigmasks(void)
{
        unsigned sig;
        unsigned mask;
        sigset_t old_blocked_set;

        if (!G.inherited_set_is_saved) {
                sigprocmask(SIG_SETMASK, NULL, &G.blocked_set);
                G.inherited_set = G.blocked_set;
        }
        old_blocked_set = G.blocked_set;

        mask = (1 << SIGQUIT);
        if (G_interactive_fd) {
                mask = (1 << SIGQUIT) | SPECIAL_INTERACTIVE_SIGS;
                if (G_saved_tty_pgrp) /* we have ctty, job control sigs work */
                        mask |= SPECIAL_JOB_SIGS;
        }
        G.non_DFL_mask = mask;

        sig = 0;
        while (mask) {
                if (mask & 1)
                        sigaddset(&G.blocked_set, sig);
                mask >>= 1;
                sig++;
        }
        sigdelset(&G.blocked_set, SIGCHLD);

        if (memcmp(&old_blocked_set, &G.blocked_set, sizeof(old_blocked_set)) != 0)
                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);

        /* POSIX allows shell to re-enable SIGCHLD
         * even if it was SIG_IGN on entry */
#if ENABLE_HUSH_FAST
        G.count_SIGCHLD++; /* ensure it is != G.handled_SIGCHLD */
        if (!G.inherited_set_is_saved)
                signal(SIGCHLD, SIGCHLD_handler);
#else
        if (!G.inherited_set_is_saved)
                signal(SIGCHLD, SIG_DFL);
#endif

        G.inherited_set_is_saved = 1;
}

#if ENABLE_HUSH_JOB
/* helper */
static void maybe_set_to_sigexit(int sig)
{
        void (*handler)(int);
        /* non_DFL_mask'ed signals are, well, masked,
         * no need to set handler for them.
         */
        if (!((G.non_DFL_mask >> sig) & 1)) {
                handler = signal(sig, sigexit);
                if (handler == SIG_IGN) /* oops... restore back to IGN! */
                        signal(sig, handler);
        }
}
/* Set handlers to restore tty pgrp and exit */
static void set_fatal_handlers(void)
{
        /* We _must_ restore tty pgrp on fatal signals */
        if (HUSH_DEBUG) {
                maybe_set_to_sigexit(SIGILL );
                maybe_set_to_sigexit(SIGFPE );
                maybe_set_to_sigexit(SIGBUS );
                maybe_set_to_sigexit(SIGSEGV);
                maybe_set_to_sigexit(SIGTRAP);
        } /* else: hush is perfect. what SEGV? */
        maybe_set_to_sigexit(SIGABRT);
        /* bash 3.2 seems to handle these just like 'fatal' ones */
        maybe_set_to_sigexit(SIGPIPE);
        maybe_set_to_sigexit(SIGALRM);
        /* if we are interactive, SIGHUP, SIGTERM and SIGINT are masked.
         * if we aren't interactive... but in this case
         * we never want to restore pgrp on exit, and this fn is not called */
        /*maybe_set_to_sigexit(SIGHUP );*/
        /*maybe_set_to_sigexit(SIGTERM);*/
        /*maybe_set_to_sigexit(SIGINT );*/
}
#endif

static int set_mode(int state, char mode, const char *o_opt)
{
        int idx;
        switch (mode) {
        case 'n':
                G.o_opt[OPT_O_NOEXEC] = state;
                break;
        case 'x':
                IF_HUSH_MODE_X(G_x_mode = state;)
                break;
        case 'o':
                if (!o_opt) {
                        /* "set -+o" without parameter.
                         * in bash, set -o produces this output:
                         *  pipefail        off
                         * and set +o:
                         *  set +o pipefail
                         * We always use the second form.
                         */
                        const char *p = o_opt_strings;
                        idx = 0;
                        while (*p) {
                                printf("set %co %s\n", (G.o_opt[idx] ? '-' : '+'), p);
                                idx++;
                                p += strlen(p) + 1;
                        }
                        break;
                }
                idx = index_in_strings(o_opt_strings, o_opt);
                if (idx >= 0) {
                        G.o_opt[idx] = state;
                        break;
                }
        default:
                return EXIT_FAILURE;
        }
        return EXIT_SUCCESS;
}

int hush_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int hush_main(int argc, char **argv)
{
        int opt;
        unsigned builtin_argc;
        char **e;
        struct variable *cur_var;
        struct variable *shell_ver;

        INIT_G();
        if (EXIT_SUCCESS) /* if EXIT_SUCCESS == 0, it is already done */
                G.last_exitcode = EXIT_SUCCESS;
#if !BB_MMU
        G.argv0_for_re_execing = argv[0];
#endif
        /* Deal with HUSH_VERSION */
        shell_ver = xzalloc(sizeof(*shell_ver));
        shell_ver->flg_export = 1;
        shell_ver->flg_read_only = 1;
        /* Code which handles ${var<op>...} needs writable values for all variables,
         * therefore we xstrdup: */
        shell_ver->varstr = xstrdup(hush_version_str);
        /* Create shell local variables from the values
         * currently living in the environment */
        debug_printf_env("unsetenv '%s'\n", "HUSH_VERSION");
        unsetenv("HUSH_VERSION"); /* in case it exists in initial env */
        G.top_var = shell_ver;
        cur_var = G.top_var;
        e = environ;
        if (e) while (*e) {
                char *value = strchr(*e, '=');
                if (value) { /* paranoia */
                        cur_var->next = xzalloc(sizeof(*cur_var));
                        cur_var = cur_var->next;
                        cur_var->varstr = *e;
                        cur_var->max_len = strlen(*e);
                        cur_var->flg_export = 1;
                }
                e++;
        }
        /* (Re)insert HUSH_VERSION into env (AFTER we scanned the env!) */
        debug_printf_env("putenv '%s'\n", shell_ver->varstr);
        putenv(shell_ver->varstr);

        /* Export PWD */
        set_pwd_var(/*exp:*/ 1);
        /* bash also exports SHLVL and _,
         * and sets (but doesn't export) the following variables:
         * BASH=/bin/bash
         * BASH_VERSINFO=([0]="3" [1]="2" [2]="0" [3]="1" [4]="release" [5]="i386-pc-linux-gnu")
         * BASH_VERSION='3.2.0(1)-release'
         * HOSTTYPE=i386
         * MACHTYPE=i386-pc-linux-gnu
         * OSTYPE=linux-gnu
         * HOSTNAME=<xxxxxxxxxx>
         * PPID=<NNNNN> - we also do it elsewhere
         * EUID=<NNNNN>
         * UID=<NNNNN>
         * GROUPS=()
         * LINES=<NNN>
         * COLUMNS=<NNN>
         * BASH_ARGC=()
         * BASH_ARGV=()
         * BASH_LINENO=()
         * BASH_SOURCE=()
         * DIRSTACK=()
         * PIPESTATUS=([0]="0")
         * HISTFILE=/<xxx>/.bash_history
         * HISTFILESIZE=500
         * HISTSIZE=500
         * MAILCHECK=60
         * PATH=/usr/gnu/bin:/usr/local/bin:/bin:/usr/bin:.
         * SHELL=/bin/bash
         * SHELLOPTS=braceexpand:emacs:hashall:histexpand:history:interactive-comments:monitor
         * TERM=dumb
         * OPTERR=1
         * OPTIND=1
         * IFS=$' \t\n'
         * PS1='\s-\v\$ '
         * PS2='> '
         * PS4='+ '
         */

#if ENABLE_FEATURE_EDITING
        G.line_input_state = new_line_input_t(FOR_SHELL);
# if defined MAX_HISTORY && MAX_HISTORY > 0 && ENABLE_HUSH_SAVEHISTORY
        {
                const char *hp = get_local_var_value("HISTFILE");
                if (!hp) {
                        hp = get_local_var_value("HOME");
                        if (hp) {
                                G.line_input_state->hist_file = concat_path_file(hp, ".hush_history");
                                //set_local_var(xasprintf("HISTFILE=%s", ...));
                        }
                }
        }
# endif
#endif

        G.global_argc = argc;
        G.global_argv = argv;
        /* Initialize some more globals to non-zero values */
        cmdedit_update_prompt();

        if (setjmp(die_jmp)) {
                /* xfunc has failed! die die die */
                /* no EXIT traps, this is an escape hatch! */
                G.exiting = 1;
                hush_exit(xfunc_error_retval);
        }

        /* Shell is non-interactive at first. We need to call
         * init_sigmasks() if we are going to execute "sh <script>",
         * "sh -c <cmds>" or login shell's /etc/profile and friends.
         * If we later decide that we are interactive, we run init_sigmasks()
         * in order to intercept (more) signals.
         */

        /* Parse options */
        /* http://www.opengroup.org/onlinepubs/9699919799/utilities/sh.html */
        builtin_argc = 0;
        while (1) {
                opt = getopt(argc, argv, "+c:xins"
#if !BB_MMU
                                "<:$:R:V:"
# if ENABLE_HUSH_FUNCTIONS
                                "F:"
# endif
#endif
                );
                if (opt <= 0)
                        break;
                switch (opt) {
                case 'c':
                        /* Possibilities:
                         * sh ... -c 'script'
                         * sh ... -c 'script' ARG0 [ARG1...]
                         * On NOMMU, if builtin_argc != 0,
                         * sh ... -c 'builtin' BARGV... "" ARG0 [ARG1...]
                         * "" needs to be replaced with NULL
                         * and BARGV vector fed to builtin function.
                         * Note: the form without ARG0 never happens:
                         * sh ... -c 'builtin' BARGV... ""
                         */
                        if (!G.root_pid) {
                                G.root_pid = getpid();
                                G.root_ppid = getppid();
                        }
                        G.global_argv = argv + optind;
                        G.global_argc = argc - optind;
                        if (builtin_argc) {
                                /* -c 'builtin' [BARGV...] "" ARG0 [ARG1...] */
                                const struct built_in_command *x;

                                init_sigmasks();
                                x = find_builtin(optarg);
                                if (x) { /* paranoia */
                                        G.global_argc -= builtin_argc; /* skip [BARGV...] "" */
                                        G.global_argv += builtin_argc;
                                        G.global_argv[-1] = NULL; /* replace "" */
                                        G.last_exitcode = x->b_function(argv + optind - 1);
                                }
                                goto final_return;
                        }
                        if (!G.global_argv[0]) {
                                /* -c 'script' (no params): prevent empty $0 */
                                G.global_argv--; /* points to argv[i] of 'script' */
                                G.global_argv[0] = argv[0];
                                G.global_argc++;
                        } /* else -c 'script' ARG0 [ARG1...]: $0 is ARG0 */
                        init_sigmasks();
                        parse_and_run_string(optarg);
                        goto final_return;
                case 'i':
                        /* Well, we cannot just declare interactiveness,
                         * we have to have some stuff (ctty, etc) */
                        /* G_interactive_fd++; */
                        break;
                case 's':
                        /* "-s" means "read from stdin", but this is how we always
                         * operate, so simply do nothing here. */
                        break;
#if !BB_MMU
                case '<': /* "big heredoc" support */
                        full_write1_str(optarg);
                        _exit(0);
                case '$': {
                        unsigned long long empty_trap_mask;

                        G.root_pid = bb_strtou(optarg, &optarg, 16);
                        optarg++;
                        G.root_ppid = bb_strtou(optarg, &optarg, 16);
                        optarg++;
                        G.last_bg_pid = bb_strtou(optarg, &optarg, 16);
                        optarg++;
                        G.last_exitcode = bb_strtou(optarg, &optarg, 16);
                        optarg++;
                        builtin_argc = bb_strtou(optarg, &optarg, 16);
                        optarg++;
                        empty_trap_mask = bb_strtoull(optarg, &optarg, 16);
                        if (empty_trap_mask != 0) {
                                int sig;
                                init_sigmasks();
                                G.traps = xzalloc(sizeof(G.traps[0]) * NSIG);
                                for (sig = 1; sig < NSIG; sig++) {
                                        if (empty_trap_mask & (1LL << sig)) {
                                                G.traps[sig] = xzalloc(1); /* == xstrdup(""); */
                                                sigaddset(&G.blocked_set, sig);
                                        }
                                }
                                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
                        }
# if ENABLE_HUSH_LOOPS
                        optarg++;
                        G.depth_of_loop = bb_strtou(optarg, &optarg, 16);
# endif
                        break;
                }
                case 'R':
                case 'V':
                        set_local_var(xstrdup(optarg), /*exp:*/ 0, /*lvl:*/ 0, /*ro:*/ opt == 'R');
                        break;
# if ENABLE_HUSH_FUNCTIONS
                case 'F': {
                        struct function *funcp = new_function(optarg);
                        /* funcp->name is already set to optarg */
                        /* funcp->body is set to NULL. It's a special case. */
                        funcp->body_as_string = argv[optind];
                        optind++;
                        break;
                }
# endif
#endif
                case 'n':
                case 'x':
                        if (set_mode(1, opt, NULL) == 0) /* no error */
                                break;
                default:
#ifndef BB_VER
                        fprintf(stderr, "Usage: sh [FILE]...\n"
                                        "   or: sh -c command [args]...\n\n");
                        exit(EXIT_FAILURE);
#else
                        bb_show_usage();
#endif
                }
        } /* option parsing loop */

        if (!G.root_pid) {
                G.root_pid = getpid();
                G.root_ppid = getppid();
        }

        /* If we are login shell... */
        if (argv[0] && argv[0][0] == '-') {
                FILE *input;
                debug_printf("sourcing /etc/profile\n");
                input = fopen_for_read("/etc/profile");
                if (input != NULL) {
                        close_on_exec_on(fileno(input));
                        init_sigmasks();
                        parse_and_run_file(input);
                        fclose(input);
                }
                /* bash: after sourcing /etc/profile,
                 * tries to source (in the given order):
                 * ~/.bash_profile, ~/.bash_login, ~/.profile,
                 * stopping on first found. --noprofile turns this off.
                 * bash also sources ~/.bash_logout on exit.
                 * If called as sh, skips .bash_XXX files.
                 */
        }

        if (argv[optind]) {
                FILE *input;
                /*
                 * "bash <script>" (which is never interactive (unless -i?))
                 * sources $BASH_ENV here (without scanning $PATH).
                 * If called as sh, does the same but with $ENV.
                 */
                debug_printf("running script '%s'\n", argv[optind]);
                G.global_argv = argv + optind;
                G.global_argc = argc - optind;
                input = xfopen_for_read(argv[optind]);
                close_on_exec_on(fileno(input));
                init_sigmasks();
                parse_and_run_file(input);
#if ENABLE_FEATURE_CLEAN_UP
                fclose(input);
#endif
                goto final_return;
        }

        /* Up to here, shell was non-interactive. Now it may become one.
         * NB: don't forget to (re)run init_sigmasks() as needed.
         */

        /* A shell is interactive if the '-i' flag was given,
         * or if all of the following conditions are met:
         *    no -c command
         *    no arguments remaining or the -s flag given
         *    standard input is a terminal
         *    standard output is a terminal
         * Refer to Posix.2, the description of the 'sh' utility.
         */
#if ENABLE_HUSH_JOB
        if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)) {
                G_saved_tty_pgrp = tcgetpgrp(STDIN_FILENO);
                debug_printf("saved_tty_pgrp:%d\n", G_saved_tty_pgrp);
                if (G_saved_tty_pgrp < 0)
                        G_saved_tty_pgrp = 0;

                /* try to dup stdin to high fd#, >= 255 */
                G_interactive_fd = fcntl(STDIN_FILENO, F_DUPFD, 255);
                if (G_interactive_fd < 0) {
                        /* try to dup to any fd */
                        G_interactive_fd = dup(STDIN_FILENO);
                        if (G_interactive_fd < 0) {
                                /* give up */
                                G_interactive_fd = 0;
                                G_saved_tty_pgrp = 0;
                        }
                }
// TODO: track & disallow any attempts of user
// to (inadvertently) close/redirect G_interactive_fd
        }
        debug_printf("interactive_fd:%d\n", G_interactive_fd);
        if (G_interactive_fd) {
                close_on_exec_on(G_interactive_fd);

                if (G_saved_tty_pgrp) {
                        /* If we were run as 'hush &', sleep until we are
                         * in the foreground (tty pgrp == our pgrp).
                         * If we get started under a job aware app (like bash),
                         * make sure we are now in charge so we don't fight over
                         * who gets the foreground */
                        while (1) {
                                pid_t shell_pgrp = getpgrp();
                                G_saved_tty_pgrp = tcgetpgrp(G_interactive_fd);
                                if (G_saved_tty_pgrp == shell_pgrp)
                                        break;
                                /* send TTIN to ourself (should stop us) */
                                kill(- shell_pgrp, SIGTTIN);
                        }
                }

                /* Block some signals */
                init_sigmasks();

                if (G_saved_tty_pgrp) {
                        /* Set other signals to restore saved_tty_pgrp */
                        set_fatal_handlers();
                        /* Put ourselves in our own process group
                         * (bash, too, does this only if ctty is available) */
                        bb_setpgrp(); /* is the same as setpgid(our_pid, our_pid); */
                        /* Grab control of the terminal */
                        tcsetpgrp(G_interactive_fd, getpid());
                }
                /* -1 is special - makes xfuncs longjmp, not exit
                 * (we reset die_sleep = 0 whereever we [v]fork) */
                enable_restore_tty_pgrp_on_exit(); /* sets die_sleep = -1 */
        } else {
                init_sigmasks();
        }
#elif ENABLE_HUSH_INTERACTIVE
        /* No job control compiled in, only prompt/line editing */
        if (isatty(STDIN_FILENO) && isatty(STDOUT_FILENO)) {
                G_interactive_fd = fcntl(STDIN_FILENO, F_DUPFD, 255);
                if (G_interactive_fd < 0) {
                        /* try to dup to any fd */
                        G_interactive_fd = dup(STDIN_FILENO);
                        if (G_interactive_fd < 0)
                                /* give up */
                                G_interactive_fd = 0;
                }
        }
        if (G_interactive_fd) {
                close_on_exec_on(G_interactive_fd);
        }
        init_sigmasks();
#else
        /* We have interactiveness code disabled */
        init_sigmasks();
#endif
        /* bash:
         * if interactive but not a login shell, sources ~/.bashrc
         * (--norc turns this off, --rcfile <file> overrides)
         */

        if (!ENABLE_FEATURE_SH_EXTRA_QUIET && G_interactive_fd) {
                /* note: ash and hush share this string */
                printf("\n\n%s %s\n"
                        IF_HUSH_HELP("Enter 'help' for a list of built-in commands.\n")
                        "\n",
                        bb_banner,
                        "hush - the humble shell"
                );
        }

        parse_and_run_file(stdin);

 final_return:
        hush_exit(G.last_exitcode);
}


#if ENABLE_MSH
int msh_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int msh_main(int argc, char **argv)
{
        //bb_error_msg("msh is deprecated, please use hush instead");
        return hush_main(argc, argv);
}
#endif


/*
 * Built-ins
 */
static int FAST_FUNC builtin_true(char **argv UNUSED_PARAM)
{
        return 0;
}

static int run_applet_main(char **argv, int (*applet_main_func)(int argc, char **argv))
{
        int argc = 0;
        while (*argv) {
                argc++;
                argv++;
        }
        return applet_main_func(argc, argv - argc);
}

static int FAST_FUNC builtin_test(char **argv)
{
        return run_applet_main(argv, test_main);
}

static int FAST_FUNC builtin_echo(char **argv)
{
        return run_applet_main(argv, echo_main);
}

#if ENABLE_PRINTF
static int FAST_FUNC builtin_printf(char **argv)
{
        return run_applet_main(argv, printf_main);
}
#endif

static char **skip_dash_dash(char **argv)
{
        argv++;
        if (argv[0] && argv[0][0] == '-' && argv[0][1] == '-' && argv[0][2] == '\0')
                argv++;
        return argv;
}

static int FAST_FUNC builtin_eval(char **argv)
{
        int rcode = EXIT_SUCCESS;

        argv = skip_dash_dash(argv);
        if (*argv) {
                char *str = expand_strvec_to_string(argv);
                /* bash:
                 * eval "echo Hi; done" ("done" is syntax error):
                 * "echo Hi" will not execute too.
                 */
                parse_and_run_string(str);
                free(str);
                rcode = G.last_exitcode;
        }
        return rcode;
}

static int FAST_FUNC builtin_cd(char **argv)
{
        const char *newdir;

        argv = skip_dash_dash(argv);
        newdir = argv[0];
        if (newdir == NULL) {
                /* bash does nothing (exitcode 0) if HOME is ""; if it's unset,
                 * bash says "bash: cd: HOME not set" and does nothing
                 * (exitcode 1)
                 */
                const char *home = get_local_var_value("HOME");
                newdir = home ? home : "/";
        }
        if (chdir(newdir)) {
                /* Mimic bash message exactly */
                bb_perror_msg("cd: %s", newdir);
                return EXIT_FAILURE;
        }
        /* Read current dir (get_cwd(1) is inside) and set PWD.
         * Note: do not enforce exporting. If PWD was unset or unexported,
         * set it again, but do not export. bash does the same.
         */
        set_pwd_var(/*exp:*/ 0);
        return EXIT_SUCCESS;
}

static int FAST_FUNC builtin_exec(char **argv)
{
        argv = skip_dash_dash(argv);
        if (argv[0] == NULL)
                return EXIT_SUCCESS; /* bash does this */

        /* Careful: we can end up here after [v]fork. Do not restore
         * tty pgrp then, only top-level shell process does that */
        if (G_saved_tty_pgrp && getpid() == G.root_pid)
                tcsetpgrp(G_interactive_fd, G_saved_tty_pgrp);

        /* TODO: if exec fails, bash does NOT exit! We do.
         * We'll need to undo sigprocmask (it's inside execvp_or_die)
         * and tcsetpgrp, and this is inherently racy.
         */
        execvp_or_die(argv);
}

static int FAST_FUNC builtin_exit(char **argv)
{
        debug_printf_exec("%s()\n", __func__);

        /* interactive bash:
         * # trap "echo EEE" EXIT
         * # exit
         * exit
         * There are stopped jobs.
         * (if there are _stopped_ jobs, running ones don't count)
         * # exit
         * exit
         # EEE (then bash exits)
         *
         * TODO: we can use G.exiting = -1 as indicator "last cmd was exit"
         */

        /* note: EXIT trap is run by hush_exit */
        argv = skip_dash_dash(argv);
        if (argv[0] == NULL)
                hush_exit(G.last_exitcode);
        /* mimic bash: exit 123abc == exit 255 + error msg */
        xfunc_error_retval = 255;
        /* bash: exit -2 == exit 254, no error msg */
        hush_exit(xatoi(argv[0]) & 0xff);
}

static void print_escaped(const char *s)
{
        if (*s == '\'')
                goto squote;
        do {
                const char *p = strchrnul(s, '\'');
                /* print 'xxxx', possibly just '' */
                printf("'%.*s'", (int)(p - s), s);
                if (*p == '\0')
                        break;
                s = p;
 squote:
                /* s points to '; print "'''...'''" */
                putchar('"');
                do putchar('\''); while (*++s == '\'');
                putchar('"');
        } while (*s);
}

#if !ENABLE_HUSH_LOCAL
#define helper_export_local(argv, exp, lvl) \
        helper_export_local(argv, exp)
#endif
static void helper_export_local(char **argv, int exp, int lvl)
{
        do {
                char *name = *argv;
                char *name_end = strchrnul(name, '=');

                /* So far we do not check that name is valid (TODO?) */

                if (*name_end == '\0') {
                        struct variable *var, **vpp;

                        vpp = get_ptr_to_local_var(name, name_end - name);
                        var = vpp ? *vpp : NULL;

                        if (exp == -1) { /* unexporting? */
                                /* export -n NAME (without =VALUE) */
                                if (var) {
                                        var->flg_export = 0;
                                        debug_printf_env("%s: unsetenv '%s'\n", __func__, name);
                                        unsetenv(name);
                                } /* else: export -n NOT_EXISTING_VAR: no-op */
                                continue;
                        }
                        if (exp == 1) { /* exporting? */
                                /* export NAME (without =VALUE) */
                                if (var) {
                                        var->flg_export = 1;
                                        debug_printf_env("%s: putenv '%s'\n", __func__, var->varstr);
                                        putenv(var->varstr);
                                        continue;
                                }
                        }
                        /* Exporting non-existing variable.
                         * bash does not put it in environment,
                         * but remembers that it is exported,
                         * and does put it in env when it is set later.
                         * We just set it to "" and export. */
                        /* Or, it's "local NAME" (without =VALUE).
                         * bash sets the value to "". */
                        name = xasprintf("%s=", name);
                } else {
                        /* (Un)exporting/making local NAME=VALUE */
                        name = xstrdup(name);
                }
                set_local_var(name, /*exp:*/ exp, /*lvl:*/ lvl, /*ro:*/ 0);
        } while (*++argv);
}

static int FAST_FUNC builtin_export(char **argv)
{
        unsigned opt_unexport;

#if ENABLE_HUSH_EXPORT_N
        /* "!": do not abort on errors */
        opt_unexport = getopt32(argv, "!n");
        if (opt_unexport == (uint32_t)-1)
                return EXIT_FAILURE;
        argv += optind;
#else
        opt_unexport = 0;
        argv++;
#endif

        if (argv[0] == NULL) {
                char **e = environ;
                if (e) {
                        while (*e) {
#if 0
                                puts(*e++);
#else
                                /* ash emits: export VAR='VAL'
                                 * bash: declare -x VAR="VAL"
                                 * we follow ash example */
                                const char *s = *e++;
                                const char *p = strchr(s, '=');

                                if (!p) /* wtf? take next variable */
                                        continue;
                                /* export var= */
                                printf("export %.*s", (int)(p - s) + 1, s);
                                print_escaped(p + 1);
                                putchar('\n');
#endif
                        }
                        /*fflush_all(); - done after each builtin anyway */
                }
                return EXIT_SUCCESS;
        }

        helper_export_local(argv, (opt_unexport ? -1 : 1), 0);

        return EXIT_SUCCESS;
}

#if ENABLE_HUSH_LOCAL
static int FAST_FUNC builtin_local(char **argv)
{
        if (G.func_nest_level == 0) {
                bb_error_msg("%s: not in a function", argv[0]);
                return EXIT_FAILURE; /* bash compat */
        }
        helper_export_local(argv, 0, G.func_nest_level);
        return EXIT_SUCCESS;
}
#endif

static int FAST_FUNC builtin_trap(char **argv)
{
        int sig;
        char *new_cmd;

        if (!G.traps)
                G.traps = xzalloc(sizeof(G.traps[0]) * NSIG);

        argv++;
        if (!*argv) {
                int i;
                /* No args: print all trapped */
                for (i = 0; i < NSIG; ++i) {
                        if (G.traps[i]) {
                                printf("trap -- ");
                                print_escaped(G.traps[i]);
                                /* note: bash adds "SIG", but only if invoked
                                 * as "bash". If called as "sh", or if set -o posix,
                                 * then it prints short signal names.
                                 * We are printing short names: */
                                printf(" %s\n", get_signame(i));
                        }
                }
                /*fflush_all(); - done after each builtin anyway */
                return EXIT_SUCCESS;
        }

        new_cmd = NULL;
        /* If first arg is a number: reset all specified signals */
        sig = bb_strtou(*argv, NULL, 10);
        if (errno == 0) {
                int ret;
 process_sig_list:
                ret = EXIT_SUCCESS;
                while (*argv) {
                        sig = get_signum(*argv++);
                        if (sig < 0 || sig >= NSIG) {
                                ret = EXIT_FAILURE;
                                /* Mimic bash message exactly */
                                bb_perror_msg("trap: %s: invalid signal specification", argv[-1]);
                                continue;
                        }

                        free(G.traps[sig]);
                        G.traps[sig] = xstrdup(new_cmd);

                        debug_printf("trap: setting SIG%s (%i) to '%s'\n",
                                get_signame(sig), sig, G.traps[sig]);

                        /* There is no signal for 0 (EXIT) */
                        if (sig == 0)
                                continue;

                        if (new_cmd) {
                                sigaddset(&G.blocked_set, sig);
                        } else {
                                /* There was a trap handler, we are removing it
                                 * (if sig has non-DFL handling,
                                 * we don't need to do anything) */
                                if (sig < 32 && (G.non_DFL_mask & (1 << sig)))
                                        continue;
                                sigdelset(&G.blocked_set, sig);
                        }
                }
                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
                return ret;
        }

        if (!argv[1]) { /* no second arg */
                bb_error_msg("trap: invalid arguments");
                return EXIT_FAILURE;
        }

        /* First arg is "-": reset all specified to default */
        /* First arg is "--": skip it, the rest is "handler SIGs..." */
        /* Everything else: set arg as signal handler
         * (includes "" case, which ignores signal) */
        if (argv[0][0] == '-') {
                if (argv[0][1] == '\0') { /* "-" */
                        /* new_cmd remains NULL: "reset these sigs" */
                        goto reset_traps;
                }
                if (argv[0][1] == '-' && argv[0][2] == '\0') { /* "--" */
                        argv++;
                }
                /* else: "-something", no special meaning */
        }
        new_cmd = *argv;
 reset_traps:
        argv++;
        goto process_sig_list;
}

/* http://www.opengroup.org/onlinepubs/9699919799/utilities/type.html */
static int FAST_FUNC builtin_type(char **argv)
{
        int ret = EXIT_SUCCESS;

        while (*++argv) {
                const char *type;
                char *path = NULL;

                if (0) {} /* make conditional compile easier below */
                /*else if (find_alias(*argv))
                        type = "an alias";*/
#if ENABLE_HUSH_FUNCTIONS
                else if (find_function(*argv))
                        type = "a function";
#endif
                else if (find_builtin(*argv))
                        type = "a shell builtin";
                else if ((path = find_in_path(*argv)) != NULL)
                        type = path;
                else {
                        bb_error_msg("type: %s: not found", *argv);
                        ret = EXIT_FAILURE;
                        continue;
                }

                printf("%s is %s\n", *argv, type);
                free(path);
        }

        return ret;
}

#if ENABLE_HUSH_JOB
/* built-in 'fg' and 'bg' handler */
static int FAST_FUNC builtin_fg_bg(char **argv)
{
        int i, jobnum;
        struct pipe *pi;

        if (!G_interactive_fd)
                return EXIT_FAILURE;

        /* If they gave us no args, assume they want the last backgrounded task */
        if (!argv[1]) {
                for (pi = G.job_list; pi; pi = pi->next) {
                        if (pi->jobid == G.last_jobid) {
                                goto found;
                        }
                }
                bb_error_msg("%s: no current job", argv[0]);
                return EXIT_FAILURE;
        }
        if (sscanf(argv[1], "%%%d", &jobnum) != 1) {
                bb_error_msg("%s: bad argument '%s'", argv[0], argv[1]);
                return EXIT_FAILURE;
        }
        for (pi = G.job_list; pi; pi = pi->next) {
                if (pi->jobid == jobnum) {
                        goto found;
                }
        }
        bb_error_msg("%s: %d: no such job", argv[0], jobnum);
        return EXIT_FAILURE;
 found:
        /* TODO: bash prints a string representation
         * of job being foregrounded (like "sleep 1 | cat") */
        if (argv[0][0] == 'f' && G_saved_tty_pgrp) {
                /* Put the job into the foreground.  */
                tcsetpgrp(G_interactive_fd, pi->pgrp);
        }

        /* Restart the processes in the job */
        debug_printf_jobs("reviving %d procs, pgrp %d\n", pi->num_cmds, pi->pgrp);
        for (i = 0; i < pi->num_cmds; i++) {
                debug_printf_jobs("reviving pid %d\n", pi->cmds[i].pid);
                pi->cmds[i].is_stopped = 0;
        }
        pi->stopped_cmds = 0;

        i = kill(- pi->pgrp, SIGCONT);
        if (i < 0) {
                if (errno == ESRCH) {
                        delete_finished_bg_job(pi);
                        return EXIT_SUCCESS;
                }
                bb_perror_msg("kill (SIGCONT)");
        }

        if (argv[0][0] == 'f') {
                remove_bg_job(pi);
                return checkjobs_and_fg_shell(pi);
        }
        return EXIT_SUCCESS;
}
#endif

#if ENABLE_HUSH_HELP
static int FAST_FUNC builtin_help(char **argv UNUSED_PARAM)
{
        const struct built_in_command *x;

        printf(
                "Built-in commands:\n"
                "------------------\n");
        for (x = bltins1; x != &bltins1[ARRAY_SIZE(bltins1)]; x++) {
                if (x->b_descr)
                        printf("%-10s%s\n", x->b_cmd, x->b_descr);
        }
        bb_putchar('\n');
        return EXIT_SUCCESS;
}
#endif

#if ENABLE_HUSH_JOB
static int FAST_FUNC builtin_jobs(char **argv UNUSED_PARAM)
{
        struct pipe *job;
        const char *status_string;

        for (job = G.job_list; job; job = job->next) {
                if (job->alive_cmds == job->stopped_cmds)
                        status_string = "Stopped";
                else
                        status_string = "Running";

                printf(JOB_STATUS_FORMAT, job->jobid, status_string, job->cmdtext);
        }
        return EXIT_SUCCESS;
}
#endif

#if HUSH_DEBUG
static int FAST_FUNC builtin_memleak(char **argv UNUSED_PARAM)
{
        void *p;
        unsigned long l;

# ifdef M_TRIM_THRESHOLD
        /* Optional. Reduces probability of false positives */
        malloc_trim(0);
# endif
        /* Crude attempt to find where "free memory" starts,
         * sans fragmentation. */
        p = malloc(240);
        l = (unsigned long)p;
        free(p);
        p = malloc(3400);
        if (l < (unsigned long)p) l = (unsigned long)p;
        free(p);

        if (!G.memleak_value)
                G.memleak_value = l;

        l -= G.memleak_value;
        if ((long)l < 0)
                l = 0;
        l /= 1024;
        if (l > 127)
                l = 127;

        /* Exitcode is "how many kilobytes we leaked since 1st call" */
        return l;
}
#endif

static int FAST_FUNC builtin_pwd(char **argv UNUSED_PARAM)
{
        puts(get_cwd(0));
        return EXIT_SUCCESS;
}

static int FAST_FUNC builtin_read(char **argv)
{
        const char *r;
        char *opt_n = NULL;
        char *opt_p = NULL;
        char *opt_t = NULL;
        char *opt_u = NULL;
        int read_flags;

        /* "!": do not abort on errors.
         * Option string must start with "sr" to match BUILTIN_READ_xxx
         */
        read_flags = getopt32(argv, "!srn:p:t:u:", &opt_n, &opt_p, &opt_t, &opt_u);
        if (read_flags == (uint32_t)-1)
                return EXIT_FAILURE;
        argv += optind;

        r = shell_builtin_read(set_local_var_from_halves,
                argv,
                get_local_var_value("IFS"), /* can be NULL */
                read_flags,
                opt_n,
                opt_p,
                opt_t,
                opt_u
        );

        if ((uintptr_t)r > 1) {
                bb_error_msg("%s", r);
                r = (char*)(uintptr_t)1;
        }

        return (uintptr_t)r;
}

/* http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#set
 * built-in 'set' handler
 * SUSv3 says:
 * set [-abCefhmnuvx] [-o option] [argument...]
 * set [+abCefhmnuvx] [+o option] [argument...]
 * set -- [argument...]
 * set -o
 * set +o
 * Implementations shall support the options in both their hyphen and
 * plus-sign forms. These options can also be specified as options to sh.
 * Examples:
 * Write out all variables and their values: set
 * Set $1, $2, and $3 and set "$#" to 3: set c a b
 * Turn on the -x and -v options: set -xv
 * Unset all positional parameters: set --
 * Set $1 to the value of x, even if it begins with '-' or '+': set -- "$x"
 * Set the positional parameters to the expansion of x, even if x expands
 * with a leading '-' or '+': set -- $x
 *
 * So far, we only support "set -- [argument...]" and some of the short names.
 */
static int FAST_FUNC builtin_set(char **argv)
{
        int n;
        char **pp, **g_argv;
        char *arg = *++argv;

        if (arg == NULL) {
                struct variable *e;
                for (e = G.top_var; e; e = e->next)
                        puts(e->varstr);
                return EXIT_SUCCESS;
        }

        do {
                if (strcmp(arg, "--") == 0) {
                        ++argv;
                        goto set_argv;
                }
                if (arg[0] != '+' && arg[0] != '-')
                        break;
                for (n = 1; arg[n]; ++n) {
                        if (set_mode((arg[0] == '-'), arg[n], argv[1]))
                                goto error;
                        if (arg[n] == 'o' && argv[1])
                                argv++;
                }
        } while ((arg = *++argv) != NULL);
        /* Now argv[0] is 1st argument */

        if (arg == NULL)
                return EXIT_SUCCESS;
 set_argv:

        /* NB: G.global_argv[0] ($0) is never freed/changed */
        g_argv = G.global_argv;
        if (G.global_args_malloced) {
                pp = g_argv;
                while (*++pp)
                        free(*pp);
                g_argv[1] = NULL;
        } else {
                G.global_args_malloced = 1;
                pp = xzalloc(sizeof(pp[0]) * 2);
                pp[0] = g_argv[0]; /* retain $0 */
                g_argv = pp;
        }
        /* This realloc's G.global_argv */
        G.global_argv = pp = add_strings_to_strings(g_argv, argv, /*dup:*/ 1);

        n = 1;
        while (*++pp)
                n++;
        G.global_argc = n;

        return EXIT_SUCCESS;

        /* Nothing known, so abort */
 error:
        bb_error_msg("set: %s: invalid option", arg);
        return EXIT_FAILURE;
}

static int FAST_FUNC builtin_shift(char **argv)
{
        int n = 1;
        argv = skip_dash_dash(argv);
        if (argv[0]) {
                n = atoi(argv[0]);
        }
        if (n >= 0 && n < G.global_argc) {
                if (G.global_args_malloced) {
                        int m = 1;
                        while (m <= n)
                                free(G.global_argv[m++]);
                }
                G.global_argc -= n;
                memmove(&G.global_argv[1], &G.global_argv[n+1],
                                G.global_argc * sizeof(G.global_argv[0]));
                return EXIT_SUCCESS;
        }
        return EXIT_FAILURE;
}

static int FAST_FUNC builtin_source(char **argv)
{
        char *arg_path, *filename;
        FILE *input;
        save_arg_t sv;
#if ENABLE_HUSH_FUNCTIONS
        smallint sv_flg;
#endif

        argv = skip_dash_dash(argv);
        filename = argv[0];
        if (!filename) {
                /* bash says: "bash: .: filename argument required" */
                return 2; /* bash compat */
        }
        arg_path = NULL;
        if (!strchr(filename, '/')) {
                arg_path = find_in_path(filename);
                if (arg_path)
                        filename = arg_path;
        }
        input = fopen_or_warn(filename, "r");
        free(arg_path);
        if (!input) {
                /* bb_perror_msg("%s", *argv); - done by fopen_or_warn */
                return EXIT_FAILURE;
        }
        close_on_exec_on(fileno(input));

#if ENABLE_HUSH_FUNCTIONS
        sv_flg = G.flag_return_in_progress;
        /* "we are inside sourced file, ok to use return" */
        G.flag_return_in_progress = -1;
#endif
        save_and_replace_G_args(&sv, argv);

        parse_and_run_file(input);
        fclose(input);

        restore_G_args(&sv, argv);
#if ENABLE_HUSH_FUNCTIONS
        G.flag_return_in_progress = sv_flg;
#endif

        return G.last_exitcode;
}

static int FAST_FUNC builtin_umask(char **argv)
{
        int rc;
        mode_t mask;

        mask = umask(0);
        argv = skip_dash_dash(argv);
        if (argv[0]) {
                mode_t old_mask = mask;

                mask ^= 0777;
                rc = bb_parse_mode(argv[0], &mask);
                mask ^= 0777;
                if (rc == 0) {
                        mask = old_mask;
                        /* bash messages:
                         * bash: umask: 'q': invalid symbolic mode operator
                         * bash: umask: 999: octal number out of range
                         */
                        bb_error_msg("%s: invalid mode '%s'", "umask", argv[0]);
                }
        } else {
                rc = 1;
                /* Mimic bash */
                printf("%04o\n", (unsigned) mask);
                /* fall through and restore mask which we set to 0 */
        }
        umask(mask);

        return !rc; /* rc != 0 - success */
}

/* http://www.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#unset */
static int FAST_FUNC builtin_unset(char **argv)
{
        int ret;
        unsigned opts;

        /* "!": do not abort on errors */
        /* "+": stop at 1st non-option */
        opts = getopt32(argv, "!+vf");
        if (opts == (unsigned)-1)
                return EXIT_FAILURE;
        if (opts == 3) {
                bb_error_msg("unset: -v and -f are exclusive");
                return EXIT_FAILURE;
        }
        argv += optind;

        ret = EXIT_SUCCESS;
        while (*argv) {
                if (!(opts & 2)) { /* not -f */
                        if (unset_local_var(*argv)) {
                                /* unset <nonexistent_var> doesn't fail.
                                 * Error is when one tries to unset RO var.
                                 * Message was printed by unset_local_var. */
                                ret = EXIT_FAILURE;
                        }
                }
#if ENABLE_HUSH_FUNCTIONS
                else {
                        unset_func(*argv);
                }
#endif
                argv++;
        }
        return ret;
}

/* http://www.opengroup.org/onlinepubs/9699919799/utilities/wait.html */
static int FAST_FUNC builtin_wait(char **argv)
{
        int ret = EXIT_SUCCESS;
        int status, sig;

        argv = skip_dash_dash(argv);
        if (argv[0] == NULL) {
                /* Don't care about wait results */
                /* Note 1: must wait until there are no more children */
                /* Note 2: must be interruptible */
                /* Examples:
                 * $ sleep 3 & sleep 6 & wait
                 * [1] 30934 sleep 3
                 * [2] 30935 sleep 6
                 * [1] Done                   sleep 3
                 * [2] Done                   sleep 6
                 * $ sleep 3 & sleep 6 & wait
                 * [1] 30936 sleep 3
                 * [2] 30937 sleep 6
                 * [1] Done                   sleep 3
                 * ^C <-- after ~4 sec from keyboard
                 * $
                 */
                sigaddset(&G.blocked_set, SIGCHLD);
                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
                while (1) {
                        checkjobs(NULL);
                        if (errno == ECHILD)
                                break;
                        /* Wait for SIGCHLD or any other signal of interest */
                        /* sigtimedwait with infinite timeout: */
                        sig = sigwaitinfo(&G.blocked_set, NULL);
                        if (sig > 0) {
                                sig = check_and_run_traps(sig);
                                if (sig && sig != SIGCHLD) { /* see note 2 */
                                        ret = 128 + sig;
                                        break;
                                }
                        }
                }
                sigdelset(&G.blocked_set, SIGCHLD);
                sigprocmask(SIG_SETMASK, &G.blocked_set, NULL);
                return ret;
        }

        /* This is probably buggy wrt interruptible-ness */
        while (*argv) {
                pid_t pid = bb_strtou(*argv, NULL, 10);
                if (errno) {
                        /* mimic bash message */
                        bb_error_msg("wait: '%s': not a pid or valid job spec", *argv);
                        return EXIT_FAILURE;
                }
                if (waitpid(pid, &status, 0) == pid) {
                        if (WIFSIGNALED(status))
                                ret = 128 + WTERMSIG(status);
                        else if (WIFEXITED(status))
                                ret = WEXITSTATUS(status);
                        else /* wtf? */
                                ret = EXIT_FAILURE;
                } else {
                        bb_perror_msg("wait %s", *argv);
                        ret = 127;
                }
                argv++;
        }

        return ret;
}

#if ENABLE_HUSH_LOOPS || ENABLE_HUSH_FUNCTIONS
static unsigned parse_numeric_argv1(char **argv, unsigned def, unsigned def_min)
{
        if (argv[1]) {
                def = bb_strtou(argv[1], NULL, 10);
                if (errno || def < def_min || argv[2]) {
                        bb_error_msg("%s: bad arguments", argv[0]);
                        def = UINT_MAX;
                }
        }
        return def;
}
#endif

#if ENABLE_HUSH_LOOPS
static int FAST_FUNC builtin_break(char **argv)
{
        unsigned depth;
        if (G.depth_of_loop == 0) {
                bb_error_msg("%s: only meaningful in a loop", argv[0]);
                return EXIT_SUCCESS; /* bash compat */
        }
        G.flag_break_continue++; /* BC_BREAK = 1 */

        G.depth_break_continue = depth = parse_numeric_argv1(argv, 1, 1);
        if (depth == UINT_MAX)
                G.flag_break_continue = BC_BREAK;
        if (G.depth_of_loop < depth)
                G.depth_break_continue = G.depth_of_loop;

        return EXIT_SUCCESS;
}

static int FAST_FUNC builtin_continue(char **argv)
{
        G.flag_break_continue = 1; /* BC_CONTINUE = 2 = 1+1 */
        return builtin_break(argv);
}
#endif

#if ENABLE_HUSH_FUNCTIONS
static int FAST_FUNC builtin_return(char **argv)
{
        int rc;

        if (G.flag_return_in_progress != -1) {
                bb_error_msg("%s: not in a function or sourced script", argv[0]);
                return EXIT_FAILURE; /* bash compat */
        }

        G.flag_return_in_progress = 1;

        /* bash:
         * out of range: wraps around at 256, does not error out
         * non-numeric param:
         * f() { false; return qwe; }; f; echo $?
         * bash: return: qwe: numeric argument required  <== we do this
         * 255  <== we also do this
         */
        rc = parse_numeric_argv1(argv, G.last_exitcode, 0);
        return rc;
}
#endif