coreutils/head.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * head implementation for busybox
   4  *
   5  * Copyright (C) 2003  Manuel Novoa III  <mjn3@codepoet.org>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   8  */
   9 //config:config HEAD
  10 //config:       bool "head"
  11 //config:       default y
  12 //config:       help
  13 //config:         head is used to print the first specified number of lines
  14 //config:         from files.
  15 //config:
  16 //config:config FEATURE_FANCY_HEAD
  17 //config:       bool "Enable -c, -q, and -v"
  18 //config:       default y
  19 //config:       depends on HEAD
  20
  21 //applet:IF_HEAD(APPLET_NOEXEC(head, head, BB_DIR_USR_BIN, BB_SUID_DROP, head))
  22
  23 //kbuild:lib-$(CONFIG_HEAD) += head.o
  24
  25 /* BB_AUDIT SUSv3 compliant */
  26 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  27 /* http://www.opengroup.org/onlinepubs/007904975/utilities/head.html */
  28
  29 //usage:#define head_trivial_usage
  30 //usage:       "[OPTIONS] [FILE]..."
  31 //usage:#define head_full_usage "\n\n"
  32 //usage:       "Print first 10 lines of each FILE (or stdin) to stdout.\n"
  33 //usage:       "With more than one FILE, precede each with a filename header.\n"
  34 //usage:     "\n        -n N[kbm]       Print first N lines"
  35 //usage:        IF_FEATURE_FANCY_HEAD(
  36 //usage:     "\n        -n -N[kbm]      Print all except N last lines"
  37 //usage:     "\n        -c [-]N[kbm]    Print first N bytes"
  38 //usage:     "\n        -q              Never print headers"
  39 //usage:     "\n        -v              Always print headers"
  40 //usage:        )
  41 //usage:     "\n"
  42 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  43 //usage:
  44 //usage:#define head_example_usage
  45 //usage:       "$ head -n 2 /etc/passwd\n"
  46 //usage:       "root:x:0:0:root:/root:/bin/bash\n"
  47 //usage:       "daemon:x:1:1:daemon:/usr/sbin:/bin/sh\n"
  48
  49 #include "libbb.h"
  50
  51 /* This is a NOEXEC applet. Be very careful! */
  52
  53 #if !ENABLE_FEATURE_FANCY_HEAD
  54 # define print_first_N(fp,count,bytes) print_first_N(fp,count)
  55 #endif
  56 static void
  57 print_first_N(FILE *fp, unsigned long count, bool count_bytes)
  58 {
  59 #if !ENABLE_FEATURE_FANCY_HEAD
  60         const int count_bytes = 0;
  61 #endif
  62         while (count) {
  63                 int c = getc(fp);
  64                 if (c == EOF)
  65                         break;
  66                 if (count_bytes || (c == '\n'))
  67                         --count;
  68                 putchar(c);
  69         }
  70 }
  71
  72 #if ENABLE_FEATURE_FANCY_HEAD
  73 static void
  74 print_except_N_last_bytes(FILE *fp, unsigned count)
  75 {
  76         unsigned char *circle = xmalloc(++count);
  77         unsigned head = 0;
  78         for(;;) {
  79                 int c;
  80                 c = getc(fp);
  81                 if (c == EOF)
  82                         goto ret;
  83                 circle[head++] = c;
  84                 if (head == count)
  85                         break;
  86         }
  87         for (;;) {
  88                 int c;
  89                 if (head == count)
  90                         head = 0;
  91                 putchar(circle[head]);
  92                 c = getc(fp);
  93                 if (c == EOF)
  94                         goto ret;
  95                 circle[head] = c;
  96                 head++;
  97         }
  98  ret:
  99         free(circle);
 100 }
 101
 102 static void
 103 print_except_N_last_lines(FILE *fp, unsigned count)
 104 {
 105         char **circle = xzalloc((++count) * sizeof(circle[0]));
 106         unsigned head = 0;
 107         for(;;) {
 108                 char *c;
 109                 c = xmalloc_fgets(fp);
 110                 if (!c)
 111                         goto ret;
 112                 circle[head++] = c;
 113                 if (head == count)
 114                         break;
 115         }
 116         for (;;) {
 117                 char *c;
 118                 if (head == count)
 119                         head = 0;
 120                 fputs(circle[head], stdout);
 121                 c = xmalloc_fgets(fp);
 122                 if (!c)
 123                         goto ret;
 124                 free(circle[head]);
 125                 circle[head++] = c;
 126         }
 127  ret:
 128         head = 0;
 129         for(;;) {
 130                 free(circle[head++]);
 131                 if (head == count)
 132                         break;
 133         }
 134         free(circle);
 135 }
 136 #else
 137 /* Must never be called */
 138 void print_except_N_last_bytes(FILE *fp, unsigned count);
 139 void print_except_N_last_lines(FILE *fp, unsigned count);
 140 #endif
 141
 142 #if !ENABLE_FEATURE_FANCY_HEAD
 143 # define eat_num(negative_N,p) eat_num(p)
 144 #endif
 145 static unsigned long
 146 eat_num(bool *negative_N, const char *p)
 147 {
 148 #if ENABLE_FEATURE_FANCY_HEAD
 149         if (*p == '-') {
 150                 *negative_N = 1;
 151                 p++;
 152         }
 153 #endif
 154         return xatoul_sfx(p, bkm_suffixes);
 155 }
 156
 157 static const char head_opts[] ALIGN1 =
 158         "n:"
 159 #if ENABLE_FEATURE_FANCY_HEAD
 160         "c:qv"
 161 #endif
 162         ;
 163
 164 #define header_fmt_str "\n==> %s <==\n"
 165
 166 int head_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 167 int head_main(int argc, char **argv)
 168 {
 169         unsigned long count = 10;
 170 #if ENABLE_FEATURE_FANCY_HEAD
 171         int header_threshhold = 1;
 172         bool count_bytes = 0;
 173         bool negative_N = 0;
 174 #else
 175 # define header_threshhold 1
 176 # define count_bytes       0
 177 # define negative_N        0
 178 #endif
 179         FILE *fp;
 180         const char *fmt;
 181         char *p;
 182         int opt;
 183         int retval = EXIT_SUCCESS;
 184
 185 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
 186         /* Allow legacy syntax of an initial numeric option without -n. */
 187         if (argv[1] && argv[1][0] == '-'
 188          && isdigit(argv[1][1])
 189         ) {
 190                 --argc;
 191                 ++argv;
 192                 p = argv[0] + 1;
 193                 goto GET_COUNT;
 194         }
 195 #endif
 196
 197         /* No size benefit in converting this to getopt32 */
 198         while ((opt = getopt(argc, argv, head_opts)) > 0) {
 199                 switch (opt) {
 200 #if ENABLE_FEATURE_FANCY_HEAD
 201                 case 'q':
 202                         header_threshhold = INT_MAX;
 203                         break;
 204                 case 'v':
 205                         header_threshhold = -1;
 206                         break;
 207                 case 'c':
 208                         count_bytes = 1;
 209                         /* fall through */
 210 #endif
 211                 case 'n':
 212                         p = optarg;
 213 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
 214  GET_COUNT:
 215 #endif
 216                         count = eat_num(&negative_N, p);
 217                         break;
 218                 default:
 219                         bb_show_usage();
 220                 }
 221         }
 222
 223         argc -= optind;
 224         argv += optind;
 225         if (!*argv)
 226                 *--argv = (char*)"-";
 227
 228         fmt = header_fmt_str + 1;
 229         if (argc <= header_threshhold) {
 230 #if ENABLE_FEATURE_FANCY_HEAD
 231                 header_threshhold = 0;
 232 #else
 233                 fmt += 11; /* "" */
 234 #endif
 235         }
 236         if (negative_N) {
 237                 if (count >= INT_MAX / sizeof(char*))
 238                         bb_error_msg("count is too big: %lu", count);
 239         }
 240
 241         do {
 242                 fp = fopen_or_warn_stdin(*argv);
 243                 if (fp) {
 244                         if (fp == stdin) {
 245                                 *argv = (char *) bb_msg_standard_input;
 246                         }
 247                         if (header_threshhold) {
 248                                 printf(fmt, *argv);
 249                         }
 250                         if (negative_N) {
 251                                 if (count_bytes) {
 252                                         print_except_N_last_bytes(fp, count);
 253                                 } else {
 254                                         print_except_N_last_lines(fp, count);
 255                                 }
 256                         } else {
 257                                 print_first_N(fp, count, count_bytes);
 258                         }
 259                         die_if_ferror_stdout();
 260                         if (fclose_if_not_stdin(fp)) {
 261                                 bb_simple_perror_msg(*argv);
 262                                 retval = EXIT_FAILURE;
 263                         }
 264                 } else {
 265                         retval = EXIT_FAILURE;
 266                 }
 267                 fmt = header_fmt_str;
 268         } while (*++argv);
 269
 270         fflush_stdout_and_exit(retval);
 271 }