coreutils/tail.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * Mini tail implementation for busybox
   4  *
   5  * Copyright (C) 2001 by Matt Kraai <kraai@alumni.carnegiemellon.edu>
   6  *
   7  * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
   8  */
   9
  10 /* BB_AUDIT SUSv3 compliant (need fancy for -c) */
  11 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  12 /* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
  13
  14 /* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
  15  *
  16  * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
  17  * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
  18  * 1) mixing printf/write without fflush()ing stdout
  19  * 2) no check that any open files are present
  20  * 3) optstring had -q taking an arg
  21  * 4) no error checking on write in some cases, and a warning even then
  22  * 5) q and s interaction bug
  23  * 6) no check for lseek error
  24  * 7) lseek attempted when count==0 even if arg was +0 (from top)
  25  */
  26
  27 #include "busybox.h"
  28
  29 static const struct suffix_mult tail_suffixes[] = {
  30         { "b", 512 },
  31         { "k", 1024 },
  32         { "m", 1048576 },
  33         { NULL, 0 }
  34 };
  35
  36 static int status;
  37
  38 static void tail_xbb_full_write(const char *buf, size_t len)
  39 {
  40         /* If we get a write error, there is really no sense in continuing. */
  41         if (full_write(STDOUT_FILENO, buf, len) < 0)
  42                 bb_perror_nomsg_and_die();
  43 }
  44
  45 static void tail_xprint_header(const char *fmt, const char *filename)
  46 {
  47 #if defined __GLIBC__
  48         if (dprintf(STDOUT_FILENO, fmt, filename) < 0) {
  49                 bb_perror_nomsg_and_die();
  50         }
  51 #else
  52         int hdr_len = strlen(fmt) + strlen(filename);
  53         char *hdr = xzalloc(hdr_len);
  54         sprintf(hdr, filename, filename);
  55         tail_xbb_full_write(hdr, hdr_len);
  56 #endif
  57 }
  58
  59 static ssize_t tail_read(int fd, char *buf, size_t count)
  60 {
  61         ssize_t r;
  62         off_t current,end;
  63         struct stat sbuf;
  64
  65         end = current = lseek(fd, 0, SEEK_CUR);
  66         if (!fstat(fd, &sbuf))
  67                 end = sbuf.st_size;
  68         lseek(fd, end < current ? 0 : current, SEEK_SET);
  69         if ((r = safe_read(fd, buf, count)) < 0) {
  70                 bb_perror_msg(bb_msg_read_error);
  71                 status = EXIT_FAILURE;
  72         }
  73
  74         return r;
  75 }
  76
  77 static const char tail_opts[] =
  78         "fn:c:"
  79 #if ENABLE_FEATURE_FANCY_TAIL
  80         "qs:v"
  81 #endif
  82         ;
  83
  84 static const char header_fmt[] = "\n==> %s <==\n";
  85
  86 int tail_main(int argc, char **argv)
  87 {
  88         long count = 10;
  89         unsigned sleep_period = 1;
  90         int from_top = 0;
  91         int follow = 0;
  92         int header_threshhold = 1;
  93         int count_bytes = 0;
  94
  95         char *tailbuf;
  96         size_t tailbufsize;
  97         int taillen = 0;
  98         int newline = 0;
  99
 100         int *fds, nfiles, nread, nwrite, seen, i, opt;
 101         char *s, *buf;
 102         const char *fmt;
 103
 104 #if !ENABLE_DEBUG_YANK_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 105         /* Allow legacy syntax of an initial numeric option without -n. */
 106         if (argc >= 2 && (argv[1][0] == '+' || argv[1][0] == '-')
 107          && isdigit(argv[1][1])
 108         ) {
 109                 optind = 2;
 110                 optarg = argv[1];
 111                 goto GET_COUNT;
 112         }
 113 #endif
 114
 115         while ((opt = getopt(argc, argv, tail_opts)) > 0) {
 116                 switch (opt) {
 117                         case 'f':
 118                                 follow = 1;
 119                                 break;
 120                         case 'c':
 121                                 count_bytes = 1;
 122                                 /* FALLS THROUGH */
 123                         case 'n':
 124 #if !ENABLE_DEBUG_YANK_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 125  GET_COUNT:
 126 #endif
 127                                 from_top = 0;
 128                                 if (*optarg == '+') {
 129                                         ++optarg;
 130                                         from_top = 1;
 131                                 }
 132                                 count = xatol_sfx(optarg, tail_suffixes);
 133                                 /* Note: Leading whitespace is an error trapped above. */
 134                                 if (count < 0) {
 135                                         count = -count;
 136                                 }
 137                                 break;
 138 #if ENABLE_FEATURE_FANCY_TAIL
 139                         case 'q':
 140                                 header_threshhold = INT_MAX;
 141                                 break;
 142                         case 's':
 143                                 sleep_period = xatou(optarg);
 144                                 break;
 145                         case 'v':
 146                                 header_threshhold = 0;
 147                                 break;
 148 #endif
 149                         default:
 150                                 bb_show_usage();
 151                 }
 152         }
 153         argc -= optind;
 154         argv += optind;
 155
 156         /* open all the files */
 157         fds = xmalloc(sizeof(int) * (argc + 1));
 158         nfiles = i = 0;
 159         if (argc == 0) {
 160                 struct stat statbuf;
 161
 162                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 163                         follow = 0;
 164                 }
 165                 *argv = (char *) bb_msg_standard_input;
 166                 goto DO_STDIN;
 167         }
 168
 169         do {
 170                 if (LONE_DASH(argv[i])) {
 171  DO_STDIN:
 172                         fds[nfiles] = STDIN_FILENO;
 173                 } else if ((fds[nfiles] = open(argv[i], O_RDONLY)) < 0) {
 174                         bb_perror_msg("%s", argv[i]);
 175                         status = EXIT_FAILURE;
 176                         continue;
 177                 }
 178                 argv[nfiles] = argv[i];
 179                 ++nfiles;
 180         } while (++i < argc);
 181
 182         if (!nfiles) {
 183                 bb_error_msg_and_die("no files");
 184         }
 185
 186         tailbufsize = BUFSIZ;
 187
 188         /* tail the files */
 189         if (from_top < count_bytes) {   /* Each is 0 or 1, so true iff 0 < 1. */
 190                 /* Hence, !from_top && count_bytes */
 191                 if (tailbufsize < count) {
 192                         tailbufsize = count + BUFSIZ;
 193                 }
 194         }
 195
 196         buf = tailbuf = xmalloc(tailbufsize);
 197
 198         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 199         i = 0;
 200         do {
 201                 /* Be careful.  It would be possible to optimize the count-bytes
 202                  * case if the file is seekable.  If you do though, remember that
 203                  * starting file position may not be the beginning of the file.
 204                  * Beware of backing up too far.  See example in wc.c.
 205                  */
 206                 if ((!(count|from_top)) && (lseek(fds[i], 0, SEEK_END) >= 0)) {
 207                         continue;
 208                 }
 209
 210                 if (nfiles > header_threshhold) {
 211                         tail_xprint_header(fmt, argv[i]);
 212                         fmt = header_fmt;
 213                 }
 214
 215                 buf = tailbuf;
 216                 taillen = 0;
 217                 seen = 1;
 218                 newline = 0;
 219
 220                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 221                         if (from_top) {
 222                                 nwrite = nread;
 223                                 if (seen < count) {
 224                                         if (count_bytes) {
 225                                                 nwrite -= (count - seen);
 226                                                 seen = count;
 227                                         } else {
 228                                                 s = buf;
 229                                                 do {
 230                                                         --nwrite;
 231                                                         if ((*s++ == '\n') && (++seen == count)) {
 232                                                                 break;
 233                                                         }
 234                                                 } while (nwrite);
 235                                         }
 236                                 }
 237                                 tail_xbb_full_write(buf + nread - nwrite, nwrite);
 238                         } else if (count) {
 239                                 if (count_bytes) {
 240                                         taillen += nread;
 241                                         if (taillen > count) {
 242                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 243                                                 taillen = count;
 244                                         }
 245                                 } else {
 246                                         int k = nread;
 247                                         int nbuf = 0;
 248
 249                                         while (k) {
 250                                                 --k;
 251                                                 if (buf[k] == '\n') {
 252                                                         ++nbuf;
 253                                                 }
 254                                         }
 255
 256                                         if (newline + nbuf < count) {
 257                                                 newline += nbuf;
 258                                                 taillen += nread;
 259
 260                                         } else {
 261                                                 int extra = 0;
 262                                                 if (buf[nread-1] != '\n') {
 263                                                         extra = 1;
 264                                                 }
 265
 266                                                 k = newline + nbuf + extra - count;
 267                                                 s = tailbuf;
 268                                                 while (k) {
 269                                                         if (*s == '\n') {
 270                                                                 --k;
 271                                                         }
 272                                                         ++s;
 273                                                 }
 274
 275                                                 taillen += nread - (s - tailbuf);
 276                                                 memmove(tailbuf, s, taillen);
 277                                                 newline = count - extra;
 278                                         }
 279                                         if (tailbufsize < taillen + BUFSIZ) {
 280                                                 tailbufsize = taillen + BUFSIZ;
 281                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 282                                         }
 283                                 }
 284                                 buf = tailbuf + taillen;
 285                         }
 286                 }
 287
 288                 if (!from_top) {
 289                         tail_xbb_full_write(tailbuf, taillen);
 290                 }
 291
 292                 taillen = 0;
 293         } while (++i < nfiles);
 294
 295         buf = xrealloc(tailbuf, BUFSIZ);
 296
 297         fmt = NULL;
 298
 299         while (follow) {
 300                 sleep(sleep_period);
 301                 i = 0;
 302                 do {
 303                         if (nfiles > header_threshhold) {
 304                                 fmt = header_fmt;
 305                         }
 306                         while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
 307                                 if (fmt) {
 308                                         tail_xprint_header(fmt, argv[i]);
 309                                         fmt = NULL;
 310                                 }
 311                                 tail_xbb_full_write(buf, nread);
 312                         }
 313                 } while (++i < nfiles);
 314         }
 315
 316         return status;
 317 }