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