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 /* Mar 16, 2003      Manuel Novoa III   (mjn3@codepoet.org)
  10  *
  11  * Pretty much rewritten to fix numerous bugs and reduce realloc() calls.
  12  * Bugs fixed (although I may have forgotten one or two... it was pretty bad)
  13  * 1) mixing printf/write without fflush()ing stdout
  14  * 2) no check that any open files are present
  15  * 3) optstring had -q taking an arg
  16  * 4) no error checking on write in some cases, and a warning even then
  17  * 5) q and s interaction bug
  18  * 6) no check for lseek error
  19  * 7) lseek attempted when count==0 even if arg was +0 (from top)
  20  */
  21 //config:config TAIL
  22 //config:       bool "tail"
  23 //config:       default y
  24 //config:       help
  25 //config:         tail is used to print the last specified number of lines
  26 //config:         from files.
  27 //config:
  28 //config:config FEATURE_FANCY_TAIL
  29 //config:       bool "Enable -q, -s, -v, and -F options"
  30 //config:       default y
  31 //config:       depends on TAIL
  32 //config:       help
  33 //config:         These options are provided by GNU tail, but
  34 //config:         are not specific in the SUSv3 standard:
  35 //config:           -q      Never output headers giving file names
  36 //config:           -s SEC  Wait SEC seconds between reads with -f
  37 //config:           -v      Always output headers giving file names
  38 //config:           -F      Same as -f, but keep retrying
  39
  40 //applet:IF_TAIL(APPLET(tail, BB_DIR_USR_BIN, BB_SUID_DROP))
  41
  42 //kbuild:lib-$(CONFIG_TAIL) += tail.o
  43
  44 /* BB_AUDIT SUSv3 compliant (need fancy for -c) */
  45 /* BB_AUDIT GNU compatible -c, -q, and -v options in 'fancy' configuration. */
  46 /* http://www.opengroup.org/onlinepubs/007904975/utilities/tail.html */
  47
  48 //usage:#define tail_trivial_usage
  49 //usage:       "[OPTIONS] [FILE]..."
  50 //usage:#define tail_full_usage "\n\n"
  51 //usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
  52 //usage:       "With more than one FILE, precede each with a filename header.\n"
  53 //usage:     "\n        -f              Print data as file grows"
  54 //usage:     "\n        -c [+]N[kbm]    Print last N bytes"
  55 //usage:     "\n        -n N[kbm]       Print last N lines"
  56 //usage:     "\n        -n +N[kbm]      Start on Nth line and print the rest"
  57 //usage:        IF_FEATURE_FANCY_TAIL(
  58 //usage:     "\n        -q              Never print headers"
  59 //usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  60 //usage:     "\n        -v              Always print headers"
  61 //usage:     "\n        -F              Same as -f, but keep retrying"
  62 //usage:     "\n"
  63 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  64 //usage:        )
  65 //usage:
  66 //usage:#define tail_example_usage
  67 //usage:       "$ tail -n 1 /etc/resolv.conf\n"
  68 //usage:       "nameserver 10.0.0.1\n"
  69
  70 #include "libbb.h"
  71 #include "common_bufsiz.h"
  72
  73 struct globals {
  74         bool from_top;
  75         bool exitcode;
  76 } FIX_ALIASING;
  77 #define G (*(struct globals*)bb_common_bufsiz1)
  78 #define INIT_G() do { setup_common_bufsiz(); } while (0)
  79
  80 static void tail_xprint_header(const char *fmt, const char *filename)
  81 {
  82         if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  83                 bb_perror_nomsg_and_die();
  84 }
  85
  86 static ssize_t tail_read(int fd, char *buf, size_t count)
  87 {
  88         ssize_t r;
  89
  90         r = full_read(fd, buf, count);
  91         if (r < 0) {
  92                 bb_perror_msg(bb_msg_read_error);
  93                 G.exitcode = EXIT_FAILURE;
  94         }
  95
  96         return r;
  97 }
  98
  99 #define header_fmt_str "\n==> %s <==\n"
 100
 101 static unsigned eat_num(const char *p)
 102 {
 103         if (*p == '-')
 104                 p++;
 105         else if (*p == '+') {
 106                 p++;
 107                 G.from_top = 1;
 108         }
 109         return xatou_sfx(p, bkm_suffixes);
 110 }
 111
 112 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 113 int tail_main(int argc, char **argv)
 114 {
 115         unsigned count = 10;
 116         unsigned sleep_period = 1;
 117         const char *str_c, *str_n;
 118
 119         char *tailbuf;
 120         size_t tailbufsize;
 121         unsigned header_threshhold = 1;
 122         unsigned nfiles;
 123         int i, opt;
 124
 125         int *fds;
 126         const char *fmt;
 127         int prev_fd;
 128
 129         INIT_G();
 130
 131 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 132         /* Allow legacy syntax of an initial numeric option without -n. */
 133         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 134          && isdigit(argv[1][1])
 135         ) {
 136                 count = eat_num(argv[1]);
 137                 argv++;
 138                 argc--;
 139         }
 140 #endif
 141
 142         /* -s NUM, -F imlies -f */
 143         IF_FEATURE_FANCY_TAIL(opt_complementary = "Ff";)
 144         opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:+vF"),
 145                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 146 #define FOLLOW (opt & 0x1)
 147 #define COUNT_BYTES (opt & 0x2)
 148         //if (opt & 0x1) // -f
 149         if (opt & 0x2) count = eat_num(str_c); // -c
 150         if (opt & 0x4) count = eat_num(str_n); // -n
 151 #if ENABLE_FEATURE_FANCY_TAIL
 152         /* q: make it impossible for nfiles to be > header_threshhold */
 153         if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 154         //if (opt & 0x10) // -s
 155         if (opt & 0x20) header_threshhold = 0; // -v
 156 # define FOLLOW_RETRY (opt & 0x40)
 157 #else
 158 # define FOLLOW_RETRY 0
 159 #endif
 160         argc -= optind;
 161         argv += optind;
 162
 163         /* open all the files */
 164         fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 165         if (!argv[0]) {
 166                 struct stat statbuf;
 167
 168                 if (fstat(STDIN_FILENO, &statbuf) == 0
 169                  && S_ISFIFO(statbuf.st_mode)
 170                 ) {
 171                         opt &= ~1; /* clear FOLLOW */
 172                 }
 173                 argv[0] = (char *) bb_msg_standard_input;
 174         }
 175         nfiles = i = 0;
 176         do {
 177                 int fd = open_or_warn_stdin(argv[i]);
 178                 if (fd < 0 && !FOLLOW_RETRY) {
 179                         G.exitcode = EXIT_FAILURE;
 180                         continue;
 181                 }
 182                 fds[nfiles] = fd;
 183                 argv[nfiles++] = argv[i];
 184         } while (++i < argc);
 185
 186         if (!nfiles)
 187                 bb_error_msg_and_die("no files");
 188
 189         /* prepare the buffer */
 190         tailbufsize = BUFSIZ;
 191         if (!G.from_top && COUNT_BYTES) {
 192                 if (tailbufsize < count + BUFSIZ) {
 193                         tailbufsize = count + BUFSIZ;
 194                 }
 195         }
 196         /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 197          * (In fact, it doesn't need ANY memory). So delay allocation.
 198          */
 199         tailbuf = NULL;
 200
 201         /* tail the files */
 202
 203         fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 204         i = 0;
 205         do {
 206                 char *buf;
 207                 int taillen;
 208                 int newlines_seen;
 209                 unsigned seen;
 210                 int nread;
 211                 int fd = fds[i];
 212
 213                 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 214                         continue; /* may happen with -F */
 215
 216                 if (nfiles > header_threshhold) {
 217                         tail_xprint_header(fmt, argv[i]);
 218                         fmt = header_fmt_str;
 219                 }
 220
 221                 if (!G.from_top) {
 222                         off_t current = lseek(fd, 0, SEEK_END);
 223                         if (current > 0) {
 224                                 unsigned off;
 225                                 if (COUNT_BYTES) {
 226                                 /* Optimizing count-bytes case if the file is seekable.
 227                                  * Beware of backing up too far.
 228                                  * Also we exclude files with size 0 (because of /proc/xxx) */
 229                                         if (count == 0)
 230                                                 continue; /* showing zero bytes is easy :) */
 231                                         current -= count;
 232                                         if (current < 0)
 233                                                 current = 0;
 234                                         xlseek(fd, current, SEEK_SET);
 235                                         bb_copyfd_size(fd, STDOUT_FILENO, count);
 236                                         continue;
 237                                 }
 238 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 239                                 /* Optimizing count-lines case if the file is seekable.
 240                                  * We assume the lines are <64k.
 241                                  * (Users complain that tail takes too long
 242                                  * on multi-gigabyte files) */
 243                                 off = (count | 0xf); /* for small counts, be more paranoid */
 244                                 if (off > (INT_MAX / (64*1024)))
 245                                         off = (INT_MAX / (64*1024));
 246                                 current -= off * (64*1024);
 247                                 if (current < 0)
 248                                         current = 0;
 249                                 xlseek(fd, current, SEEK_SET);
 250 #endif
 251                         }
 252                 }
 253
 254                 if (!tailbuf)
 255                         tailbuf = xmalloc(tailbufsize);
 256
 257                 buf = tailbuf;
 258                 taillen = 0;
 259                 /* "We saw 1st line/byte".
 260                  * Used only by +N code ("start from Nth", 1-based): */
 261                 seen = 1;
 262                 newlines_seen = 0;
 263                 while ((nread = tail_read(fd, buf, tailbufsize - taillen)) > 0) {
 264                         if (G.from_top) {
 265                                 int nwrite = nread;
 266                                 if (seen < count) {
 267                                         /* We need to skip a few more bytes/lines */
 268                                         if (COUNT_BYTES) {
 269                                                 nwrite -= (count - seen);
 270                                                 seen += nread;
 271                                         } else {
 272                                                 char *s = buf;
 273                                                 do {
 274                                                         --nwrite;
 275                                                         if (*s++ == '\n' && ++seen == count) {
 276                                                                 break;
 277                                                         }
 278                                                 } while (nwrite);
 279                                         }
 280                                 }
 281                                 if (nwrite > 0)
 282                                         xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 283                         } else if (count) {
 284                                 if (COUNT_BYTES) {
 285                                         taillen += nread;
 286                                         if (taillen > (int)count) {
 287                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 288                                                 taillen = count;
 289                                         }
 290                                 } else {
 291                                         int k = nread;
 292                                         int newlines_in_buf = 0;
 293
 294                                         do { /* count '\n' in last read */
 295                                                 k--;
 296                                                 if (buf[k] == '\n') {
 297                                                         newlines_in_buf++;
 298                                                 }
 299                                         } while (k);
 300
 301                                         if (newlines_seen + newlines_in_buf < (int)count) {
 302                                                 newlines_seen += newlines_in_buf;
 303                                                 taillen += nread;
 304                                         } else {
 305                                                 int extra = (buf[nread-1] != '\n');
 306                                                 char *s;
 307
 308                                                 k = newlines_seen + newlines_in_buf + extra - count;
 309                                                 s = tailbuf;
 310                                                 while (k) {
 311                                                         if (*s == '\n') {
 312                                                                 k--;
 313                                                         }
 314                                                         s++;
 315                                                 }
 316                                                 taillen += nread - (s - tailbuf);
 317                                                 memmove(tailbuf, s, taillen);
 318                                                 newlines_seen = count - extra;
 319                                         }
 320                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 321                                                 tailbufsize = taillen + BUFSIZ;
 322                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 323                                         }
 324                                 }
 325                                 buf = tailbuf + taillen;
 326                         }
 327                 } /* while (tail_read() > 0) */
 328                 if (!G.from_top) {
 329                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 330                 }
 331         } while (++i < nfiles);
 332         prev_fd = fds[i-1];
 333
 334         tailbuf = xrealloc(tailbuf, BUFSIZ);
 335
 336         fmt = NULL;
 337
 338         if (FOLLOW) while (1) {
 339                 sleep(sleep_period);
 340
 341                 i = 0;
 342                 do {
 343                         int nread;
 344                         const char *filename = argv[i];
 345                         int fd = fds[i];
 346
 347                         if (FOLLOW_RETRY) {
 348                                 struct stat sbuf, fsbuf;
 349
 350                                 if (fd < 0
 351                                  || fstat(fd, &fsbuf) < 0
 352                                  || stat(filename, &sbuf) < 0
 353                                  || fsbuf.st_dev != sbuf.st_dev
 354                                  || fsbuf.st_ino != sbuf.st_ino
 355                                 ) {
 356                                         int new_fd;
 357
 358                                         if (fd >= 0)
 359                                                 close(fd);
 360                                         new_fd = open(filename, O_RDONLY);
 361                                         if (new_fd >= 0) {
 362                                                 bb_error_msg("%s has %s; following end of new file",
 363                                                         filename, (fd < 0) ? "appeared" : "been replaced"
 364                                                 );
 365                                         } else if (fd >= 0) {
 366                                                 bb_perror_msg("%s has become inaccessible", filename);
 367                                         }
 368                                         fds[i] = fd = new_fd;
 369                                 }
 370                         }
 371                         if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 372                                 continue;
 373                         if (nfiles > header_threshhold) {
 374                                 fmt = header_fmt_str;
 375                         }
 376                         for (;;) {
 377                                 /* tail -f keeps following files even if they are truncated */
 378                                 struct stat sbuf;
 379                                 /* /proc files report zero st_size, don't lseek them */
 380                                 if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
 381                                         off_t current = lseek(fd, 0, SEEK_CUR);
 382                                         if (sbuf.st_size < current)
 383                                                 xlseek(fd, 0, SEEK_SET);
 384                                 }
 385
 386                                 nread = tail_read(fd, tailbuf, BUFSIZ);
 387                                 if (nread <= 0)
 388                                         break;
 389                                 if (fmt && (fd != prev_fd)) {
 390                                         tail_xprint_header(fmt, filename);
 391                                         fmt = NULL;
 392                                         prev_fd = fd;
 393                                 }
 394                                 xwrite(STDOUT_FILENO, tailbuf, nread);
 395                         }
 396                 } while (++i < nfiles);
 397         } /* while (1) */
 398
 399         if (ENABLE_FEATURE_CLEAN_UP) {
 400                 free(fds);
 401                 free(tailbuf);
 402         }
 403         return G.exitcode;
 404 }