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_xbb_full_write(const char *buf, size_t len)
  46 {
  47         /* If we get a write error, there is really no sense in continuing. */
  48         if (full_write(STDOUT_FILENO, buf, len) < 0)
  49                 bb_perror_nomsg_and_die();
  50 }
  51
  52 static void tail_xprint_header(const char *fmt, const char *filename)
  53 {
  54 #if defined __GLIBC__
  55         if (dprintf(STDOUT_FILENO, fmt, filename) < 0) {
  56                 bb_perror_nomsg_and_die();
  57         }
  58 #else
  59         int hdr_len = strlen(fmt) + strlen(filename);
  60         char *hdr = xzalloc(hdr_len);
  61         sprintf(hdr, filename, filename);
  62         tail_xbb_full_write(hdr, hdr_len);
  63 #endif
  64 }
  65
  66 static ssize_t tail_read(int fd, char *buf, size_t count)
  67 {
  68         ssize_t r;
  69         off_t current,end;
  70         struct stat sbuf;
  71
  72         end = current = lseek(fd, 0, SEEK_CUR);
  73         if (!fstat(fd, &sbuf))
  74                 end = sbuf.st_size;
  75         lseek(fd, end < current ? 0 : current, SEEK_SET);
  76         if ((r = safe_read(fd, buf, count)) < 0) {
  77                 bb_perror_msg(bb_msg_read_error);
  78                 status = EXIT_FAILURE;
  79         }
  80
  81         return r;
  82 }
  83
  84 static const char tail_opts[] =
  85         "fn:c:"
  86 #if ENABLE_FEATURE_FANCY_TAIL
  87         "qs:v"
  88 #endif
  89         ;
  90
  91 static const char header_fmt[] = "\n==> %s <==\n";
  92
  93 int tail_main(int argc, char **argv)
  94 {
  95         long count = 10;
  96         unsigned int sleep_period = 1;
  97         int from_top = 0;
  98         int follow = 0;
  99         int header_threshhold = 1;
 100         int count_bytes = 0;
 101
 102         char *tailbuf;
 103         size_t tailbufsize;
 104         int taillen = 0;
 105         int newline = 0;
 106
 107         int *fds, nfiles, nread, nwrite, seen, i, opt;
 108         char *s, *buf;
 109         const char *fmt;
 110
 111 #if !ENABLE_DEBUG_YANK_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 112         /* Allow legacy syntax of an initial numeric option without -n. */
 113         if (argc >=2 && ((argv[1][0] == '+') || ((argv[1][0] == '-')
 114                         /* && (isdigit)(argv[1][1]) */
 115                         && (((unsigned int)(argv[1][1] - '0')) <= 9))))
 116         {
 117                 optind = 2;
 118                 optarg = argv[1];
 119                 goto GET_COUNT;
 120         }
 121 #endif
 122
 123         while ((opt = getopt(argc, argv, tail_opts)) > 0) {
 124                 switch (opt) {
 125                         case 'f':
 126                                 follow = 1;
 127                                 break;
 128                         case 'c':
 129                                 count_bytes = 1;
 130                                 /* FALLS THROUGH */
 131                         case 'n':
 132 #if !ENABLE_DEBUG_YANK_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 133                         GET_COUNT:
 134 #endif
 135                                 count = xatol_sfx(optarg, tail_suffixes);
 136                                 /* Note: Leading whitespace is an error trapped above. */
 137                                 if (*optarg == '+') {
 138                                         from_top = 1;
 139                                 } else {
 140                                         from_top = 0;
 141                                 }
 142                                 if (count < 0) {
 143                                         count = -count;
 144                                 }
 145                                 break;
 146 #if ENABLE_FEATURE_FANCY_TAIL
 147                         case 'q':
 148                                 header_threshhold = INT_MAX;
 149                                 break;
 150                         case 's':
 151                                 sleep_period = xatou(optarg);
 152                                 break;
 153                         case 'v':
 154                                 header_threshhold = 0;
 155                                 break;
 156 #endif
 157                         default:
 158                                 bb_show_usage();
 159                 }
 160         }
 161
 162         /* open all the files */
 163         fds = (int *)xmalloc(sizeof(int) * (argc - optind + 1));
 164
 165         argv += optind;
 166         nfiles = i = 0;
 167
 168         if ((argc -= optind) == 0) {
 169                 struct stat statbuf;
 170
 171                 if (!fstat(STDIN_FILENO, &statbuf) && S_ISFIFO(statbuf.st_mode)) {
 172                         follow = 0;
 173                 }
 174                 /* --argv; */
 175                 *argv = (char *) bb_msg_standard_input;
 176                 goto DO_STDIN;
 177         }
 178
 179         do {
 180                 if ((argv[i][0] == '-') && !argv[i][1]) {
 181                 DO_STDIN:
 182                         fds[nfiles] = STDIN_FILENO;
 183                 } else if ((fds[nfiles] = open(argv[i], O_RDONLY)) < 0) {
 184                         bb_perror_msg("%s", argv[i]);
 185                         status = EXIT_FAILURE;
 186                         continue;
 187                 }
 188                 argv[nfiles] = argv[i];
 189                 ++nfiles;
 190         } while (++i < argc);
 191
 192         if (!nfiles) {
 193                 bb_error_msg_and_die("no files");
 194         }
 195
 196         tailbufsize = BUFSIZ;
 197
 198         /* tail the files */
 199         if (from_top < count_bytes) {   /* Each is 0 or 1, so true iff 0 < 1. */
 200                 /* Hence, !from_top && count_bytes */
 201                 if (tailbufsize < count) {
 202                         tailbufsize = count + BUFSIZ;
 203                 }
 204         }
 205
 206         buf = tailbuf = xmalloc(tailbufsize);
 207
 208         fmt = header_fmt + 1;   /* Skip header leading newline on first output. */
 209         i = 0;
 210         do {
 211                 /* Be careful.  It would be possible to optimize the count-bytes
 212                  * case if the file is seekable.  If you do though, remember that
 213                  * starting file position may not be the beginning of the file.
 214                  * Beware of backing up too far.  See example in wc.c.
 215                  */
 216                 if ((!(count|from_top)) && (lseek(fds[i], 0, SEEK_END) >= 0)) {
 217                         continue;
 218                 }
 219
 220                 if (nfiles > header_threshhold) {
 221                         tail_xprint_header(fmt, argv[i]);
 222                         fmt = header_fmt;
 223                 }
 224
 225                 buf = tailbuf;
 226                 taillen = 0;
 227                 seen = 1;
 228                 newline = 0;
 229
 230                 while ((nread = tail_read(fds[i], buf, tailbufsize-taillen)) > 0) {
 231                         if (from_top) {
 232                                 nwrite = nread;
 233                                 if (seen < count) {
 234                                         if (count_bytes) {
 235                                                 nwrite -= (count - seen);
 236                                                 seen = count;
 237                                         } else {
 238                                                 s = buf;
 239                                                 do {
 240                                                         --nwrite;
 241                                                         if ((*s++ == '\n') && (++seen == count)) {
 242                                                                 break;
 243                                                         }
 244                                                 } while (nwrite);
 245                                         }
 246                                 }
 247                                 tail_xbb_full_write(buf + nread - nwrite, nwrite);
 248                         } else if (count) {
 249                                 if (count_bytes) {
 250                                         taillen += nread;
 251                                         if (taillen > count) {
 252                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 253                                                 taillen = count;
 254                                         }
 255                                 } else {
 256                                         int k = nread;
 257                                         int nbuf = 0;
 258
 259                                         while (k) {
 260                                                 --k;
 261                                                 if (buf[k] == '\n') {
 262                                                         ++nbuf;
 263                                                 }
 264                                         }
 265
 266                                         if (newline + nbuf < count) {
 267                                                 newline += nbuf;
 268                                                 taillen += nread;
 269
 270                                         } else {
 271                                                 int extra = 0;
 272                                                 if (buf[nread-1] != '\n') {
 273                                                         extra = 1;
 274                                                 }
 275
 276                                                 k = newline + nbuf + extra - count;
 277                                                 s = tailbuf;
 278                                                 while (k) {
 279                                                         if (*s == '\n') {
 280                                                                 --k;
 281                                                         }
 282                                                         ++s;
 283                                                 }
 284
 285                                                 taillen += nread - (s - tailbuf);
 286                                                 memmove(tailbuf, s, taillen);
 287                                                 newline = count - extra;
 288                                         }
 289                                         if (tailbufsize < taillen + BUFSIZ) {
 290                                                 tailbufsize = taillen + BUFSIZ;
 291                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 292                                         }
 293                                 }
 294                                 buf = tailbuf + taillen;
 295                         }
 296                 }
 297
 298                 if (!from_top) {
 299                         tail_xbb_full_write(tailbuf, taillen);
 300                 }
 301
 302                 taillen = 0;
 303         } while (++i < nfiles);
 304
 305         buf = xrealloc(tailbuf, BUFSIZ);
 306
 307         fmt = NULL;
 308
 309         while (follow) {
 310                 sleep(sleep_period);
 311                 i = 0;
 312                 do {
 313                         if (nfiles > header_threshhold) {
 314                                 fmt = header_fmt;
 315                         }
 316                         while ((nread = tail_read(fds[i], buf, sizeof(buf))) > 0) {
 317                                 if (fmt) {
 318                                         tail_xprint_header(fmt, argv[i]);
 319                                         fmt = NULL;
 320                                 }
 321                                 tail_xbb_full_write(buf, nread);
 322                         }
 323                 } while (++i < nfiles);
 324         }
 325
 326         return status;
 327 }