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 <stdio.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <ctype.h>
  31 #include <unistd.h>
  32 #include <fcntl.h>
  33 #include <sys/stat.h>
  34 #include "busybox.h"
  35
  36 static const struct suffix_mult tail_suffixes[] = {
  37         { "b", 512 },
  38         { "k", 1024 },
  39         { "m", 1048576 },
  40         { NULL, 0 }
  41 };
  42
  43 static int status;
  44
  45 static void tail_xprint_header(const char *fmt, const char *filename)
  46 {
  47         /* If we get an output error, there is really no sense in continuing. */
  48         if (dprintf(STDOUT_FILENO, fmt, filename) < 0) {
  49                 bb_perror_nomsg_and_die();
  50         }
  51 }
  52
  53 /* len should probably be size_t */
  54 static void tail_xbb_full_write(const char *buf, size_t len)
  55 {
  56         /* If we get a write error, there is really no sense in continuing. */
  57         if (bb_full_write(STDOUT_FILENO, buf, len) < 0) {
  58                 bb_perror_nomsg_and_die();
  59         }
  60 }
  61
  62 static ssize_t tail_read(int fd, char *buf, size_t count)
  63 {
  64         ssize_t r;
  65         off_t current,end;
  66         struct stat sbuf;
  67
  68         end = current = lseek(fd, 0, SEEK_CUR);
  69         if (!fstat(fd, &sbuf))
  70                 end = sbuf.st_size;
  71         lseek(fd, end < current ? 0 : current, SEEK_SET);
  72         if ((r = safe_read(fd, buf, count)) < 0) {
  73                 bb_perror_msg("read");
  74                 status = EXIT_FAILURE;
  75         }
  76
  77         return r;
  78 }
  79
  80 static const char tail_opts[] =
  81         "fn:c:"
  82 #if ENABLE_FEATURE_FANCY_TAIL
  83         "qs:v"
  84 #endif
  85         ;
  86
  87 static const char header_fmt[] = "\n==> %s <==\n";
  88
  89 int tail_main(int argc, char **argv)
  90 {
  91         long count = 10;
  92         unsigned int sleep_period = 1;
  93         int from_top = 0;
  94         int follow = 0;
  95         int header_threshhold = 1;
  96         int count_bytes = 0;
  97
  98         char *tailbuf;
  99         size_t tailbufsize;
 100         int taillen = 0;
 101         int newline = 0;
 102
 103         int *fds, nfiles, nread, nwrite, seen, i, opt;
 104         char *s, *buf;
 105         const char *fmt;
 106
 107 #if !ENABLE_DEBUG_YANK_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 108         /* Allow legacy syntax of an initial numeric option without -n. */
 109         if (argc >=2 && ((argv[1][0] == '+') || ((argv[1][0] == '-')
 110                         /* && (isdigit)(argv[1][1]) */
 111                         && (((unsigned int)(argv[1][1] - '0')) <= 9))))
 112         {
 113                 optind = 2;
 114                 optarg = argv[1];
 115                 goto GET_COUNT;
 116         }
 117 #endif
 118
 119         while ((opt = getopt(argc, argv, tail_opts)) > 0) {
 120                 switch (opt) {
 121                         case 'f':
 122                                 follow = 1;
 123                                 break;
 124                         case 'c':
 125                                 count_bytes = 1;
 126                                 /* FALLS THROUGH */
 127                         case 'n':
 128 #if !ENABLE_DEBUG_YANK_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 129                         GET_COUNT:
 130 #endif
 131                                 count = bb_xgetlarg10_sfx(optarg, tail_suffixes);
 132                                 /* Note: Leading whitespace is an error trapped above. */
 133                                 if (*optarg == '+') {
 134                                         from_top = 1;
 135                                 } else {
 136                                         from_top = 0;
 137                                 }
 138                                 if (count < 0) {
 139                                         count = -count;
 140                                 }
 141                                 break;
 142 #if ENABLE_FEATURE_FANCY_TAIL
 143                         case 'q':
 144                                 header_threshhold = INT_MAX;
 145                                 break;
 146                         case 's':
 147                                 sleep_period =bb_xgetularg10_bnd(optarg, 0, UINT_MAX);
 148                                 break;
 149                         case 'v':
 150                                 header_threshhold = 0;
 151                                 break;
 152 #endif
 153                         default:
 154                                 bb_show_usage();
 155                 }
 156         }
 157
 158         /* open all the files */
 159         fds = (int *)xmalloc(sizeof(int) * (argc - optind + 1));
 160
 161         argv += optind;
 162         nfiles = i = 0;
 163
 164         if ((argc -= optind) == 0) {
 165                 struct stat statbuf;
 166
 167                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 168                         follow = 0;
 169                 }
 170                 /* --argv; */
 171                 *argv = (char *) bb_msg_standard_input;
 172                 goto DO_STDIN;
 173         }
 174
 175         do {
 176                 if ((argv[i][0] == '-') && !argv[i][1]) {
 177                 DO_STDIN:
 178                         fds[nfiles] = STDIN_FILENO;
 179                 } else if ((fds[nfiles] = open(argv[i], O_RDONLY)) < 0) {
 180                         bb_perror_msg("%s", argv[i]);
 181                         status = EXIT_FAILURE;
 182                         continue;
 183                 }
 184                 argv[nfiles] = argv[i];
 185                 ++nfiles;
 186         } while (++i < argc);
 187
 188         if (!nfiles) {
 189                 bb_error_msg_and_die("no files");
 190         }
 191
 192         tailbufsize = BUFSIZ;
 193
 194         /* tail the files */
 195         if (from_top < count_bytes) {   /* Each is 0 or 1, so true iff 0 < 1. */
 196                 /* Hence, !from_top && count_bytes */
 197                 if (tailbufsize < count) {
 198                         tailbufsize = count + BUFSIZ;
 199                 }
 200         }
 201
 202         buf = tailbuf = xmalloc(tailbufsize);
 203
 204         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 205         i = 0;
 206         do {
 207                 /* Be careful.  It would be possible to optimize the count-bytes
 208                  * case if the file is seekable.  If you do though, remember that
 209                  * starting file position may not be the beginning of the file.
 210                  * Beware of backing up too far.  See example in wc.c.
 211                  */
 212                 if ((!(count|from_top)) && (lseek(fds[i], 0, SEEK_END) >= 0)) {
 213                         continue;
 214                 }
 215
 216                 if (nfiles > header_threshhold) {
 217                         tail_xprint_header(fmt, argv[i]);
 218                         fmt = header_fmt;
 219                 }
 220
 221                 buf = tailbuf;
 222                 taillen = 0;
 223                 seen = 1;
 224                 newline = 0;
 225
 226                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 227                         if (from_top) {
 228                                 nwrite = nread;
 229                                 if (seen < count) {
 230                                         if (count_bytes) {
 231                                                 nwrite -= (count - seen);
 232                                                 seen = count;
 233                                         } else {
 234                                                 s = buf;
 235                                                 do {
 236                                                         --nwrite;
 237                                                         if ((*s++ == '\n') && (++seen == count)) {
 238                                                                 break;
 239                                                         }
 240                                                 } while (nwrite);
 241                                         }
 242                                 }
 243                                 tail_xbb_full_write(buf + nread - nwrite, nwrite);
 244                         } else if (count) {
 245                                 if (count_bytes) {
 246                                         taillen += nread;
 247                                         if (taillen > count) {
 248                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 249                                                 taillen = count;
 250                                         }
 251                                 } else {
 252                                         int k = nread;
 253                                         int nbuf = 0;
 254
 255                                         while (k) {
 256                                                 --k;
 257                                                 if (buf[k] == '\n') {
 258                                                         ++nbuf;
 259                                                 }
 260                                         }
 261
 262                                         if (newline + nbuf < count) {
 263                                                 newline += nbuf;
 264                                                 taillen += nread;
 265
 266                                         } else {
 267                                                 int extra = 0;
 268                                                 if (buf[nread-1] != '\n') {
 269                                                         extra = 1;
 270                                                 }
 271
 272                                                 k = newline + nbuf + extra - count;
 273                                                 s = tailbuf;
 274                                                 while (k) {
 275                                                         if (*s == '\n') {
 276                                                                 --k;
 277                                                         }
 278                                                         ++s;
 279                                                 }
 280
 281                                                 taillen += nread - (s - tailbuf);
 282                                                 memmove(tailbuf, s, taillen);
 283                                                 newline = count - extra;
 284                                         }
 285                                         if (tailbufsize < taillen + BUFSIZ) {
 286                                                 tailbufsize = taillen + BUFSIZ;
 287                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 288                                         }
 289                                 }
 290                                 buf = tailbuf + taillen;
 291                         }
 292                 }
 293
 294                 if (!from_top) {
 295                         tail_xbb_full_write(tailbuf, taillen);
 296                 }
 297
 298                 taillen = 0;
 299         } while (++i < nfiles);
 300
 301         buf = xrealloc(tailbuf, BUFSIZ);
 302
 303         fmt = NULL;
 304
 305         while (follow) {
 306                 sleep(sleep_period);
 307                 i = 0;
 308                 do {
 309                         if (nfiles > header_threshhold) {
 310                                 fmt = header_fmt;
 311                         }
 312                         while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
 313                                 if (fmt) {
 314                                         tail_xprint_header(fmt, argv[i]);
 315                                         fmt = NULL;
 316                                 }
 317                                 tail_xbb_full_write(buf, nread);
 318                         }
 319                 } while (++i < nfiles);
 320         }
 321
 322         return status;
 323 }