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