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 source tree.
   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 //kbuild:lib-$(CONFIG_TAIL) += tail.o
  28
  29 //usage:#define tail_trivial_usage
  30 //usage:       "[OPTIONS] [FILE]..."
  31 //usage:#define tail_full_usage "\n\n"
  32 //usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
  33 //usage:       "With more than one FILE, precede each with a filename header.\n"
  34 //usage:     "\n        -f              Print data as file grows"
  35 //usage:        IF_FEATURE_FANCY_TAIL(
  36 //usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  37 //usage:        )
  38 //usage:     "\n        -n N[kbm]       Print last N lines"
  39 //usage:     "\n        -n +N[kbm]      Start on Nth line and print the rest"
  40 //usage:        IF_FEATURE_FANCY_TAIL(
  41 //usage:     "\n        -c [+]N[kbm]    Print last N bytes"
  42 //usage:     "\n        -q              Never print headers"
  43 //usage:     "\n        -v              Always print headers"
  44 //usage:     "\n"
  45 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  46 //usage:        )
  47 //usage:
  48 //usage:#define tail_example_usage
  49 //usage:       "$ tail -n 1 /etc/resolv.conf\n"
  50 //usage:       "nameserver 10.0.0.1\n"
  51
  52 #include "libbb.h"
  53
  54 struct globals {
  55         bool from_top;
  56         bool exitcode;
  57 } FIX_ALIASING;
  58 #define G (*(struct globals*)&bb_common_bufsiz1)
  59 #define INIT_G() do { } while (0)
  60
  61 static void tail_xprint_header(const char *fmt, const char *filename)
  62 {
  63         if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  64                 bb_perror_nomsg_and_die();
  65 }
  66
  67 static ssize_t tail_read(int fd, char *buf, size_t count)
  68 {
  69         ssize_t r;
  70
  71         r = full_read(fd, buf, count);
  72         if (r < 0) {
  73                 bb_perror_msg(bb_msg_read_error);
  74                 G.exitcode = EXIT_FAILURE;
  75         }
  76
  77         return r;
  78 }
  79
  80 #define header_fmt_str "\n==> %s <==\n"
  81
  82 static unsigned eat_num(const char *p)
  83 {
  84         if (*p == '-')
  85                 p++;
  86         else if (*p == '+') {
  87                 p++;
  88                 G.from_top = 1;
  89         }
  90         return xatou_sfx(p, bkm_suffixes);
  91 }
  92
  93 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  94 int tail_main(int argc, char **argv)
  95 {
  96         unsigned count = 10;
  97         unsigned sleep_period = 1;
  98         const char *str_c, *str_n;
  99
 100         char *tailbuf;
 101         size_t tailbufsize;
 102         unsigned header_threshhold = 1;
 103         unsigned nfiles;
 104         int i, opt;
 105
 106         int *fds;
 107         const char *fmt;
 108
 109         INIT_G();
 110
 111 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 112         /* Allow legacy syntax of an initial numeric option without -n. */
 113         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 114          && isdigit(argv[1][1])
 115         ) {
 116                 count = eat_num(argv[1]);
 117                 argv++;
 118                 argc--;
 119         }
 120 #endif
 121
 122         /* -s NUM, -F imlies -f */
 123         IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 124         opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 125                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 126 #define FOLLOW (opt & 0x1)
 127 #define COUNT_BYTES (opt & 0x2)
 128         //if (opt & 0x1) // -f
 129         if (opt & 0x2) count = eat_num(str_c); // -c
 130         if (opt & 0x4) count = eat_num(str_n); // -n
 131 #if ENABLE_FEATURE_FANCY_TAIL
 132         /* q: make it impossible for nfiles to be > header_threshhold */
 133         if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 134         //if (opt & 0x10) // -s
 135         if (opt & 0x20) header_threshhold = 0; // -v
 136 # define FOLLOW_RETRY (opt & 0x40)
 137 #else
 138 # define FOLLOW_RETRY 0
 139 #endif
 140         argc -= optind;
 141         argv += optind;
 142
 143         /* open all the files */
 144         fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 145         if (!argv[0]) {
 146                 struct stat statbuf;
 147
 148                 if (fstat(STDIN_FILENO, &statbuf) == 0
 149                  && S_ISFIFO(statbuf.st_mode)
 150                 ) {
 151                         opt &= ~1; /* clear FOLLOW */
 152                 }
 153                 argv[0] = (char *) bb_msg_standard_input;
 154         }
 155         nfiles = i = 0;
 156         do {
 157                 int fd = open_or_warn_stdin(argv[i]);
 158                 if (fd < 0 && !FOLLOW_RETRY) {
 159                         G.exitcode = EXIT_FAILURE;
 160                         continue;
 161                 }
 162                 fds[nfiles] = fd;
 163                 argv[nfiles++] = argv[i];
 164         } while (++i < argc);
 165
 166         if (!nfiles)
 167                 bb_error_msg_and_die("no files");
 168
 169         /* prepare the buffer */
 170         tailbufsize = BUFSIZ;
 171         if (!G.from_top && COUNT_BYTES) {
 172                 if (tailbufsize < count + BUFSIZ) {
 173                         tailbufsize = count + BUFSIZ;
 174                 }
 175         }
 176         /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 177          * (In fact, it doesn't need ANY memory). So delay allocation.
 178          */
 179         tailbuf = NULL;
 180
 181         /* tail the files */
 182
 183         fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 184         i = 0;
 185         do {
 186                 char *buf;
 187                 int taillen;
 188                 int newlines_seen;
 189                 unsigned seen;
 190                 int nread;
 191                 int fd = fds[i];
 192
 193                 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 194                         continue; /* may happen with -F */
 195
 196                 if (nfiles > header_threshhold) {
 197                         tail_xprint_header(fmt, argv[i]);
 198                         fmt = header_fmt_str;
 199                 }
 200
 201                 if (!G.from_top) {
 202                         off_t current = lseek(fd, 0, SEEK_END);
 203                         if (current > 0) {
 204                                 unsigned off;
 205                                 if (COUNT_BYTES) {
 206                                 /* Optimizing count-bytes case if the file is seekable.
 207                                  * Beware of backing up too far.
 208                                  * Also we exclude files with size 0 (because of /proc/xxx) */
 209                                         if (count == 0)
 210                                                 continue; /* showing zero bytes is easy :) */
 211                                         current -= count;
 212                                         if (current < 0)
 213                                                 current = 0;
 214                                         xlseek(fd, current, SEEK_SET);
 215                                         bb_copyfd_size(fd, STDOUT_FILENO, count);
 216                                         continue;
 217                                 }
 218 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 219                                 /* Optimizing count-lines case if the file is seekable.
 220                                  * We assume the lines are <64k.
 221                                  * (Users complain that tail takes too long
 222                                  * on multi-gigabyte files) */
 223                                 off = (count | 0xf); /* for small counts, be more paranoid */
 224                                 if (off > (INT_MAX / (64*1024)))
 225                                         off = (INT_MAX / (64*1024));
 226                                 current -= off * (64*1024);
 227                                 if (current < 0)
 228                                         current = 0;
 229                                 xlseek(fd, current, SEEK_SET);
 230 #endif
 231                         }
 232                 }
 233
 234                 if (!tailbuf)
 235                         tailbuf = xmalloc(tailbufsize);
 236
 237                 buf = tailbuf;
 238                 taillen = 0;
 239                 /* "We saw 1st line/byte".
 240                  * Used only by +N code ("start from Nth", 1-based): */
 241                 seen = 1;
 242                 newlines_seen = 0;
 243                 while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
 244                         if (G.from_top) {
 245                                 int nwrite = nread;
 246                                 if (seen < count) {
 247                                         /* We need to skip a few more bytes/lines */
 248                                         if (COUNT_BYTES) {
 249                                                 nwrite -= (count - seen);
 250                                                 seen += nread;
 251                                         } else {
 252                                                 char *s = buf;
 253                                                 do {
 254                                                         --nwrite;
 255                                                         if (*s++ == '\n' && ++seen == count) {
 256                                                                 break;
 257                                                         }
 258                                                 } while (nwrite);
 259                                         }
 260                                 }
 261                                 if (nwrite > 0)
 262                                         xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 263                         } else if (count) {
 264                                 if (COUNT_BYTES) {
 265                                         taillen += nread;
 266                                         if (taillen > (int)count) {
 267                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 268                                                 taillen = count;
 269                                         }
 270                                 } else {
 271                                         int k = nread;
 272                                         int newlines_in_buf = 0;
 273
 274                                         do { /* count '\n' in last read */
 275                                                 k--;
 276                                                 if (buf[k] == '\n') {
 277                                                         newlines_in_buf++;
 278                                                 }
 279                                         } while (k);
 280
 281                                         if (newlines_seen + newlines_in_buf < (int)count) {
 282                                                 newlines_seen += newlines_in_buf;
 283                                                 taillen += nread;
 284                                         } else {
 285                                                 int extra = (buf[nread-1] != '\n');
 286                                                 char *s;
 287
 288                                                 k = newlines_seen + newlines_in_buf + extra - count;
 289                                                 s = tailbuf;
 290                                                 while (k) {
 291                                                         if (*s == '\n') {
 292                                                                 k--;
 293                                                         }
 294                                                         s++;
 295                                                 }
 296                                                 taillen += nread - (s - tailbuf);
 297                                                 memmove(tailbuf, s, taillen);
 298                                                 newlines_seen = count - extra;
 299                                         }
 300                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 301                                                 tailbufsize = taillen + BUFSIZ;
 302                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 303                                         }
 304                                 }
 305                                 buf = tailbuf + taillen;
 306                         }
 307                 } /* while (tail_read() > 0) */
 308                 if (!G.from_top) {
 309                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 310                 }
 311         } while (++i < nfiles);
 312
 313         tailbuf = xrealloc(tailbuf, BUFSIZ);
 314
 315         fmt = NULL;
 316
 317         if (FOLLOW) while (1) {
 318                 sleep(sleep_period);
 319
 320                 i = 0;
 321                 do {
 322                         int nread;
 323                         const char *filename = argv[i];
 324                         int fd = fds[i];
 325
 326                         if (FOLLOW_RETRY) {
 327                                 struct stat sbuf, fsbuf;
 328
 329                                 if (fd < 0
 330                                  || fstat(fd, &fsbuf) < 0
 331                                  || stat(filename, &sbuf) < 0
 332                                  || fsbuf.st_dev != sbuf.st_dev
 333                                  || fsbuf.st_ino != sbuf.st_ino
 334                                 ) {
 335                                         int new_fd;
 336
 337                                         if (fd >= 0)
 338                                                 close(fd);
 339                                         new_fd = open(filename, O_RDONLY);
 340                                         if (new_fd >= 0) {
 341                                                 bb_error_msg("%s has %s; following end of new file",
 342                                                         filename, (fd < 0) ? "appeared" : "been replaced"
 343                                                 );
 344                                         } else if (fd >= 0) {
 345                                                 bb_perror_msg("%s has become inaccessible", filename);
 346                                         }
 347                                         fds[i] = fd = new_fd;
 348                                 }
 349                         }
 350                         if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 351                                 continue;
 352                         if (nfiles > header_threshhold) {
 353                                 fmt = header_fmt_str;
 354                         }
 355                         for (;;) {
 356                                 /* tail -f keeps following files even if they are truncated */
 357                                 struct stat sbuf;
 358                                 /* /proc files report zero st_size, don't lseek them */
 359                                 if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
 360                                         off_t current = lseek(fd, 0, SEEK_CUR);
 361                                         if (sbuf.st_size < current)
 362                                                 xlseek(fd, 0, SEEK_SET);
 363                                 }
 364
 365                                 nread = tail_read(fd, tailbuf, BUFSIZ);
 366                                 if (nread <= 0)
 367                                         break;
 368                                 if (fmt) {
 369                                         tail_xprint_header(fmt, filename);
 370                                         fmt = NULL;
 371                                 }
 372                                 xwrite(STDOUT_FILENO, tailbuf, nread);
 373                         }
 374                 } while (++i < nfiles);
 375         } /* while (1) */
 376
 377         if (ENABLE_FEATURE_CLEAN_UP) {
 378                 free(fds);
 379                 free(tailbuf);
 380         }
 381         return G.exitcode;
 382 }