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