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