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 head options (-c, -q, and -v)"
  18 //config:       default y
  19 //config:       depends on HEAD
  20 //config:       help
  21 //config:         This enables the head options (-c, -q, and -v).
  22
  23 //applet:IF_HEAD(APPLET_NOEXEC(head, head, BB_DIR_USR_BIN, BB_SUID_DROP, head))
  24
  25 //kbuild:lib-$(CONFIG_HEAD) += head.o
  26
  27 /* BB_AUDIT SUSv3 compliant */
  28 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  29 /* http://www.opengroup.org/onlinepubs/007904975/utilities/head.html */
  30
  31 //usage:#define head_trivial_usage
  32 //usage:       "[OPTIONS] [FILE]..."
  33 //usage:#define head_full_usage "\n\n"
  34 //usage:       "Print first 10 lines of each FILE (or stdin) to stdout.\n"
  35 //usage:       "With more than one FILE, precede each with a filename header.\n"
  36 //usage:     "\n        -n N[kbm]       Print first N lines"
  37 //usage:        IF_FEATURE_FANCY_HEAD(
  38 //usage:     "\n        -n -N[kbm]      Print all except N last lines"
  39 //usage:     "\n        -c [-]N[kbm]    Print first N bytes"
  40 //usage:     "\n        -q              Never print headers"
  41 //usage:     "\n        -v              Always print headers"
  42 //usage:        )
  43 //usage:     "\n"
  44 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  45 //usage:
  46 //usage:#define head_example_usage
  47 //usage:       "$ head -n 2 /etc/passwd\n"
  48 //usage:       "root:x:0:0:root:/root:/bin/bash\n"
  49 //usage:       "daemon:x:1:1:daemon:/usr/sbin:/bin/sh\n"
  50
  51 #include "libbb.h"
  52
  53 /* This is a NOEXEC applet. Be very careful! */
  54
  55 #if !ENABLE_FEATURE_FANCY_HEAD
  56 # define print_first_N(fp,count,bytes) print_first_N(fp,count)
  57 #endif
  58 static void
  59 print_first_N(FILE *fp, unsigned long count, bool count_bytes)
  60 {
  61 #if !ENABLE_FEATURE_FANCY_HEAD
  62         const int count_bytes = 0;
  63 #endif
  64         while (count) {
  65                 int c = getc(fp);
  66                 if (c == EOF)
  67                         break;
  68                 if (count_bytes || (c == '\n'))
  69                         --count;
  70                 putchar(c);
  71         }
  72 }
  73
  74 #if ENABLE_FEATURE_FANCY_HEAD
  75 static void
  76 print_except_N_last_bytes(FILE *fp, unsigned count)
  77 {
  78         unsigned char *circle = xmalloc(++count);
  79         unsigned head = 0;
  80         for(;;) {
  81                 int c;
  82                 c = getc(fp);
  83                 if (c == EOF)
  84                         goto ret;
  85                 circle[head++] = c;
  86                 if (head == count)
  87                         break;
  88         }
  89         for (;;) {
  90                 int c;
  91                 if (head == count)
  92                         head = 0;
  93                 putchar(circle[head]);
  94                 c = getc(fp);
  95                 if (c == EOF)
  96                         goto ret;
  97                 circle[head] = c;
  98                 head++;
  99         }
 100  ret:
 101         free(circle);
 102 }
 103
 104 static void
 105 print_except_N_last_lines(FILE *fp, unsigned count)
 106 {
 107         char **circle = xzalloc((++count) * sizeof(circle[0]));
 108         unsigned head = 0;
 109         for(;;) {
 110                 char *c;
 111                 c = xmalloc_fgets(fp);
 112                 if (!c)
 113                         goto ret;
 114                 circle[head++] = c;
 115                 if (head == count)
 116                         break;
 117         }
 118         for (;;) {
 119                 char *c;
 120                 if (head == count)
 121                         head = 0;
 122                 fputs(circle[head], stdout);
 123                 c = xmalloc_fgets(fp);
 124                 if (!c)
 125                         goto ret;
 126                 free(circle[head]);
 127                 circle[head++] = c;
 128         }
 129  ret:
 130         head = 0;
 131         for(;;) {
 132                 free(circle[head++]);
 133                 if (head == count)
 134                         break;
 135         }
 136         free(circle);
 137 }
 138 #else
 139 /* Must never be called */
 140 void print_except_N_last_bytes(FILE *fp, unsigned count);
 141 void print_except_N_last_lines(FILE *fp, unsigned count);
 142 #endif
 143
 144 #if !ENABLE_FEATURE_FANCY_HEAD
 145 # define eat_num(negative_N,p) eat_num(p)
 146 #endif
 147 static unsigned long
 148 eat_num(bool *negative_N, const char *p)
 149 {
 150 #if ENABLE_FEATURE_FANCY_HEAD
 151         if (*p == '-') {
 152                 *negative_N = 1;
 153                 p++;
 154         }
 155 #endif
 156         return xatoul_sfx(p, bkm_suffixes);
 157 }
 158
 159 static const char head_opts[] ALIGN1 =
 160         "n:"
 161 #if ENABLE_FEATURE_FANCY_HEAD
 162         "c:qv"
 163 #endif
 164         ;
 165
 166 #define header_fmt_str "\n==> %s <==\n"
 167
 168 int head_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 169 int head_main(int argc, char **argv)
 170 {
 171         unsigned long count = 10;
 172 #if ENABLE_FEATURE_FANCY_HEAD
 173         int header_threshhold = 1;
 174         bool count_bytes = 0;
 175         bool negative_N = 0;
 176 #else
 177 # define header_threshhold 1
 178 # define count_bytes       0
 179 # define negative_N        0
 180 #endif
 181         FILE *fp;
 182         const char *fmt;
 183         char *p;
 184         int opt;
 185         int retval = EXIT_SUCCESS;
 186
 187 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
 188         /* Allow legacy syntax of an initial numeric option without -n. */
 189         if (argv[1] && argv[1][0] == '-'
 190          && isdigit(argv[1][1])
 191         ) {
 192                 --argc;
 193                 ++argv;
 194                 p = argv[0] + 1;
 195                 goto GET_COUNT;
 196         }
 197 #endif
 198
 199         /* No size benefit in converting this to getopt32 */
 200         while ((opt = getopt(argc, argv, head_opts)) > 0) {
 201                 switch (opt) {
 202 #if ENABLE_FEATURE_FANCY_HEAD
 203                 case 'q':
 204                         header_threshhold = INT_MAX;
 205                         break;
 206                 case 'v':
 207                         header_threshhold = -1;
 208                         break;
 209                 case 'c':
 210                         count_bytes = 1;
 211                         /* fall through */
 212 #endif
 213                 case 'n':
 214                         p = optarg;
 215 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
 216  GET_COUNT:
 217 #endif
 218                         count = eat_num(&negative_N, p);
 219                         break;
 220                 default:
 221                         bb_show_usage();
 222                 }
 223         }
 224
 225         argc -= optind;
 226         argv += optind;
 227         if (!*argv)
 228                 *--argv = (char*)"-";
 229
 230         fmt = header_fmt_str + 1;
 231         if (argc <= header_threshhold) {
 232 #if ENABLE_FEATURE_FANCY_HEAD
 233                 header_threshhold = 0;
 234 #else
 235                 fmt += 11; /* "" */
 236 #endif
 237         }
 238         if (negative_N) {
 239                 if (count >= INT_MAX / sizeof(char*))
 240                         bb_error_msg("count is too big: %lu", count);
 241         }
 242
 243         do {
 244                 fp = fopen_or_warn_stdin(*argv);
 245                 if (fp) {
 246                         if (fp == stdin) {
 247                                 *argv = (char *) bb_msg_standard_input;
 248                         }
 249                         if (header_threshhold) {
 250                                 printf(fmt, *argv);
 251                         }
 252                         if (negative_N) {
 253                                 if (count_bytes) {
 254                                         print_except_N_last_bytes(fp, count);
 255                                 } else {
 256                                         print_except_N_last_lines(fp, count);
 257                                 }
 258                         } else {
 259                                 print_first_N(fp, count, count_bytes);
 260                         }
 261                         die_if_ferror_stdout();
 262                         if (fclose_if_not_stdin(fp)) {
 263                                 bb_simple_perror_msg(*argv);
 264                                 retval = EXIT_FAILURE;
 265                         }
 266                 } else {
 267                         retval = EXIT_FAILURE;
 268                 }
 269                 fmt = header_fmt_str;
 270         } while (*++argv);
 271
 272         fflush_stdout_and_exit(retval);
 273 }