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
  10 /* BB_AUDIT SUSv3 compliant */
  11 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  12 /* http://www.opengroup.org/onlinepubs/007904975/utilities/head.html */
  13
  14 //usage:#define head_trivial_usage
  15 //usage:       "[OPTIONS] [FILE]..."
  16 //usage:#define head_full_usage "\n\n"
  17 //usage:       "Print first 10 lines of each FILE (or stdin) to stdout.\n"
  18 //usage:       "With more than one FILE, precede each with a filename header.\n"
  19 //usage:     "\nOptions:"
  20 //usage:     "\n        -n N[kbm]       Print first N lines"
  21 //usage:        IF_FEATURE_FANCY_HEAD(
  22 //usage:     "\n        -c N[kbm]       Print first N bytes"
  23 //usage:     "\n        -q              Never print headers"
  24 //usage:     "\n        -v              Always print headers"
  25 //usage:        )
  26 //usage:     "\n"
  27 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  28 //usage:
  29 //usage:#define head_example_usage
  30 //usage:       "$ head -n 2 /etc/passwd\n"
  31 //usage:       "root:x:0:0:root:/root:/bin/bash\n"
  32 //usage:       "daemon:x:1:1:daemon:/usr/sbin:/bin/sh\n"
  33
  34 #include "libbb.h"
  35
  36 /* This is a NOEXEC applet. Be very careful! */
  37
  38 static const char head_opts[] ALIGN1 =
  39         "n:"
  40 #if ENABLE_FEATURE_FANCY_HEAD
  41         "c:qv"
  42 #endif
  43         ;
  44
  45 static const struct suffix_mult head_suffixes[] = {
  46         { "b", 512 },
  47         { "k", 1024 },
  48         { "m", 1024*1024 },
  49         { "", 0 }
  50 };
  51
  52 #define header_fmt_str "\n==> %s <==\n"
  53
  54 int head_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  55 int head_main(int argc, char **argv)
  56 {
  57         unsigned long count = 10;
  58         unsigned long i;
  59 #if ENABLE_FEATURE_FANCY_HEAD
  60         int count_bytes = 0;
  61         int header_threshhold = 1;
  62 #endif
  63         FILE *fp;
  64         const char *fmt;
  65         char *p;
  66         int opt;
  67         int c;
  68         int retval = EXIT_SUCCESS;
  69
  70 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
  71         /* Allow legacy syntax of an initial numeric option without -n. */
  72         if (argv[1] && argv[1][0] == '-'
  73          && isdigit(argv[1][1])
  74         ) {
  75                 --argc;
  76                 ++argv;
  77                 p = (*argv) + 1;
  78                 goto GET_COUNT;
  79         }
  80 #endif
  81
  82         /* No size benefit in converting this to getopt32 */
  83         while ((opt = getopt(argc, argv, head_opts)) > 0) {
  84                 switch (opt) {
  85 #if ENABLE_FEATURE_FANCY_HEAD
  86                 case 'q':
  87                         header_threshhold = INT_MAX;
  88                         break;
  89                 case 'v':
  90                         header_threshhold = -1;
  91                         break;
  92                 case 'c':
  93                         count_bytes = 1;
  94                         /* fall through */
  95 #endif
  96                 case 'n':
  97                         p = optarg;
  98 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_HEAD
  99  GET_COUNT:
 100 #endif
 101                         count = xatoul_sfx(p, head_suffixes);
 102                         break;
 103                 default:
 104                         bb_show_usage();
 105                 }
 106         }
 107
 108         argc -= optind;
 109         argv += optind;
 110         if (!*argv)
 111                 *--argv = (char*)"-";
 112
 113         fmt = header_fmt_str + 1;
 114 #if ENABLE_FEATURE_FANCY_HEAD
 115         if (argc <= header_threshhold) {
 116                 header_threshhold = 0;
 117         }
 118 #else
 119         if (argc <= 1) {
 120                 fmt += 11; /* "" */
 121         }
 122         /* Now define some things here to avoid #ifdefs in the code below.
 123          * These should optimize out of the if conditions below. */
 124 #define header_threshhold   1
 125 #define count_bytes         0
 126 #endif
 127
 128         do {
 129                 fp = fopen_or_warn_stdin(*argv);
 130                 if (fp) {
 131                         if (fp == stdin) {
 132                                 *argv = (char *) bb_msg_standard_input;
 133                         }
 134                         if (header_threshhold) {
 135                                 printf(fmt, *argv);
 136                         }
 137                         i = count;
 138                         while (i && ((c = getc(fp)) != EOF)) {
 139                                 if (count_bytes || (c == '\n')) {
 140                                         --i;
 141                                 }
 142                                 putchar(c);
 143                         }
 144                         if (fclose_if_not_stdin(fp)) {
 145                                 bb_simple_perror_msg(*argv);
 146                                 retval = EXIT_FAILURE;
 147                         }
 148                         die_if_ferror_stdout();
 149                 } else {
 150                         retval = EXIT_FAILURE;
 151                 }
 152                 fmt = header_fmt_str;
 153         } while (*++argv);
 154
 155         fflush_stdout_and_exit(retval);
 156 }