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 //usage:#define tail_trivial_usage
  28 //usage:       "[OPTIONS] [FILE]..."
  29 //usage:#define tail_full_usage "\n\n"
  30 //usage:       "Print last 10 lines of each FILE (or stdin) to stdout.\n"
  31 //usage:       "With more than one FILE, precede each with a filename header.\n"
  32 //usage:     "\n        -f              Print data as file grows"
  33 //usage:        IF_FEATURE_FANCY_TAIL(
  34 //usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  35 //usage:        )
  36 //usage:     "\n        -n N[kbm]       Print last N lines"
  37 //usage:        IF_FEATURE_FANCY_TAIL(
  38 //usage:     "\n        -c N[kbm]       Print last N bytes"
  39 //usage:     "\n        -q              Never print headers"
  40 //usage:     "\n        -v              Always print headers"
  41 //usage:     "\n"
  42 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  43 //usage:     "\nIf N starts with a '+', output begins with the Nth item from the start"
  44 //usage:     "\nof each file, not from the end."
  45 //usage:        )
  46 //usage:
  47 //usage:#define tail_example_usage
  48 //usage:       "$ tail -n 1 /etc/resolv.conf\n"
  49 //usage:       "nameserver 10.0.0.1\n"
  50
  51 #include "libbb.h"
  52
  53 static const struct suffix_mult tail_suffixes[] = {
  54         { "b", 512 },
  55         { "k", 1024 },
  56         { "m", 1024*1024 },
  57         { "", 0 }
  58 };
  59
  60 struct globals {
  61         bool from_top;
  62         bool exitcode;
  63 } FIX_ALIASING;
  64 #define G (*(struct globals*)&bb_common_bufsiz1)
  65
  66 static void tail_xprint_header(const char *fmt, const char *filename)
  67 {
  68         if (fdprintf(STDOUT_FILENO, fmt, filename) < 0)
  69                 bb_perror_nomsg_and_die();
  70 }
  71
  72 static ssize_t tail_read(int fd, char *buf, size_t count)
  73 {
  74         ssize_t r;
  75         off_t current;
  76         struct stat sbuf;
  77
  78         /* /proc files report zero st_size, don't lseek them. */
  79         if (fstat(fd, &sbuf) == 0 && sbuf.st_size > 0) {
  80                 current = lseek(fd, 0, SEEK_CUR);
  81                 if (sbuf.st_size < current)
  82                         xlseek(fd, 0, SEEK_SET);
  83         }
  84
  85         r = full_read(fd, buf, count);
  86         if (r < 0) {
  87                 bb_perror_msg(bb_msg_read_error);
  88                 G.exitcode = EXIT_FAILURE;
  89         }
  90
  91         return r;
  92 }
  93
  94 #define header_fmt_str "\n==> %s <==\n"
  95
  96 static unsigned eat_num(const char *p)
  97 {
  98         if (*p == '-')
  99                 p++;
 100         else if (*p == '+') {
 101                 p++;
 102                 G.from_top = 1;
 103         }
 104         return xatou_sfx(p, tail_suffixes);
 105 }
 106
 107 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 108 int tail_main(int argc, char **argv)
 109 {
 110         unsigned count = 10;
 111         unsigned sleep_period = 1;
 112         const char *str_c, *str_n;
 113
 114         char *tailbuf;
 115         size_t tailbufsize;
 116         unsigned header_threshhold = 1;
 117         unsigned nfiles;
 118         int i, opt;
 119
 120         int *fds;
 121         const char *fmt;
 122
 123 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 124         /* Allow legacy syntax of an initial numeric option without -n. */
 125         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 126          && isdigit(argv[1][1])
 127         ) {
 128                 count = eat_num(argv[1]);
 129                 argv++;
 130                 argc--;
 131         }
 132 #endif
 133
 134         /* -s NUM, -F imlies -f */
 135         IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 136         opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 137                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 138 #define FOLLOW (opt & 0x1)
 139 #define COUNT_BYTES (opt & 0x2)
 140         //if (opt & 0x1) // -f
 141         if (opt & 0x2) count = eat_num(str_c); // -c
 142         if (opt & 0x4) count = eat_num(str_n); // -n
 143 #if ENABLE_FEATURE_FANCY_TAIL
 144         /* q: make it impossible for nfiles to be > header_threshhold */
 145         if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 146         //if (opt & 0x10) // -s
 147         if (opt & 0x20) header_threshhold = 0; // -v
 148 # define FOLLOW_RETRY (opt & 0x40)
 149 #else
 150 # define FOLLOW_RETRY 0
 151 #endif
 152         argc -= optind;
 153         argv += optind;
 154
 155         /* open all the files */
 156         fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 157         if (!argv[0]) {
 158                 struct stat statbuf;
 159
 160                 if (fstat(STDIN_FILENO, &statbuf) == 0
 161                  && S_ISFIFO(statbuf.st_mode)
 162                 ) {
 163                         opt &= ~1; /* clear FOLLOW */
 164                 }
 165                 argv[0] = (char *) bb_msg_standard_input;
 166         }
 167         nfiles = i = 0;
 168         do {
 169                 int fd = open_or_warn_stdin(argv[i]);
 170                 if (fd < 0 && !FOLLOW_RETRY) {
 171                         G.exitcode = EXIT_FAILURE;
 172                         continue;
 173                 }
 174                 fds[nfiles] = fd;
 175                 argv[nfiles++] = argv[i];
 176         } while (++i < argc);
 177
 178         if (!nfiles)
 179                 bb_error_msg_and_die("no files");
 180
 181         /* prepare the buffer */
 182         tailbufsize = BUFSIZ;
 183         if (!G.from_top && COUNT_BYTES) {
 184                 if (tailbufsize < count + BUFSIZ) {
 185                         tailbufsize = count + BUFSIZ;
 186                 }
 187         }
 188         /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 189          * (In fact, it doesn't need ANY memory). So delay allocation.
 190          */
 191         tailbuf = NULL;
 192
 193         /* tail the files */
 194
 195         fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 196         i = 0;
 197         do {
 198                 char *buf;
 199                 int taillen;
 200                 int newlines_seen;
 201                 unsigned seen;
 202                 int nread;
 203                 int fd = fds[i];
 204
 205                 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 206                         continue; /* may happen with -E */
 207
 208                 if (nfiles > header_threshhold) {
 209                         tail_xprint_header(fmt, argv[i]);
 210                         fmt = header_fmt_str;
 211                 }
 212
 213                 if (!G.from_top) {
 214                         off_t current = lseek(fd, 0, SEEK_END);
 215                         if (current > 0) {
 216                                 unsigned off;
 217                                 if (COUNT_BYTES) {
 218                                 /* Optimizing count-bytes case if the file is seekable.
 219                                  * Beware of backing up too far.
 220                                  * Also we exclude files with size 0 (because of /proc/xxx) */
 221                                         if (count == 0)
 222                                                 continue; /* showing zero bytes is easy :) */
 223                                         current -= count;
 224                                         if (current < 0)
 225                                                 current = 0;
 226                                         xlseek(fd, current, SEEK_SET);
 227                                         bb_copyfd_size(fd, STDOUT_FILENO, count);
 228                                         continue;
 229                                 }
 230 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 231                                 /* Optimizing count-lines case if the file is seekable.
 232                                  * We assume the lines are <64k.
 233                                  * (Users complain that tail takes too long
 234                                  * on multi-gigabyte files) */
 235                                 off = (count | 0xf); /* for small counts, be more paranoid */
 236                                 if (off > (INT_MAX / (64*1024)))
 237                                         off = (INT_MAX / (64*1024));
 238                                 current -= off * (64*1024);
 239                                 if (current < 0)
 240                                         current = 0;
 241                                 xlseek(fd, current, SEEK_SET);
 242 #endif
 243                         }
 244                 }
 245
 246                 if (!tailbuf)
 247                         tailbuf = xmalloc(tailbufsize);
 248
 249                 buf = tailbuf;
 250                 taillen = 0;
 251                 /* "We saw 1st line/byte".
 252                  * Used only by +N code ("start from Nth", 1-based): */
 253                 seen = 1;
 254                 newlines_seen = 0;
 255                 while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
 256                         if (G.from_top) {
 257                                 int nwrite = nread;
 258                                 if (seen < count) {
 259                                         /* We need to skip a few more bytes/lines */
 260                                         if (COUNT_BYTES) {
 261                                                 nwrite -= (count - seen);
 262                                                 seen = count;
 263                                         } else {
 264                                                 char *s = buf;
 265                                                 do {
 266                                                         --nwrite;
 267                                                         if (*s++ == '\n' && ++seen == count) {
 268                                                                 break;
 269                                                         }
 270                                                 } while (nwrite);
 271                                         }
 272                                 }
 273                                 if (nwrite > 0)
 274                                         xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 275                         } else if (count) {
 276                                 if (COUNT_BYTES) {
 277                                         taillen += nread;
 278                                         if (taillen > (int)count) {
 279                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 280                                                 taillen = count;
 281                                         }
 282                                 } else {
 283                                         int k = nread;
 284                                         int newlines_in_buf = 0;
 285
 286                                         do { /* count '\n' in last read */
 287                                                 k--;
 288                                                 if (buf[k] == '\n') {
 289                                                         newlines_in_buf++;
 290                                                 }
 291                                         } while (k);
 292
 293                                         if (newlines_seen + newlines_in_buf < (int)count) {
 294                                                 newlines_seen += newlines_in_buf;
 295                                                 taillen += nread;
 296                                         } else {
 297                                                 int extra = (buf[nread-1] != '\n');
 298                                                 char *s;
 299
 300                                                 k = newlines_seen + newlines_in_buf + extra - count;
 301                                                 s = tailbuf;
 302                                                 while (k) {
 303                                                         if (*s == '\n') {
 304                                                                 k--;
 305                                                         }
 306                                                         s++;
 307                                                 }
 308                                                 taillen += nread - (s - tailbuf);
 309                                                 memmove(tailbuf, s, taillen);
 310                                                 newlines_seen = count - extra;
 311                                         }
 312                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 313                                                 tailbufsize = taillen + BUFSIZ;
 314                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 315                                         }
 316                                 }
 317                                 buf = tailbuf + taillen;
 318                         }
 319                 } /* while (tail_read() > 0) */
 320                 if (!G.from_top) {
 321                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 322                 }
 323         } while (++i < nfiles);
 324
 325         tailbuf = xrealloc(tailbuf, BUFSIZ);
 326
 327         fmt = NULL;
 328
 329         if (FOLLOW) while (1) {
 330                 sleep(sleep_period);
 331
 332                 i = 0;
 333                 do {
 334                         int nread;
 335                         const char *filename = argv[i];
 336                         int fd = fds[i];
 337
 338                         if (FOLLOW_RETRY) {
 339                                 struct stat sbuf, fsbuf;
 340
 341                                 if (fd < 0
 342                                  || fstat(fd, &fsbuf) < 0
 343                                  || stat(filename, &sbuf) < 0
 344                                  || fsbuf.st_dev != sbuf.st_dev
 345                                  || fsbuf.st_ino != sbuf.st_ino
 346                                 ) {
 347                                         int new_fd;
 348
 349                                         if (fd >= 0)
 350                                                 close(fd);
 351                                         new_fd = open(filename, O_RDONLY);
 352                                         if (new_fd >= 0) {
 353                                                 bb_error_msg("%s has %s; following end of new file",
 354                                                         filename, (fd < 0) ? "appeared" : "been replaced"
 355                                                 );
 356                                         } else if (fd >= 0) {
 357                                                 bb_perror_msg("%s has become inaccessible", filename);
 358                                         }
 359                                         fds[i] = fd = new_fd;
 360                                 }
 361                         }
 362                         if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 363                                 continue;
 364                         if (nfiles > header_threshhold) {
 365                                 fmt = header_fmt_str;
 366                         }
 367                         while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
 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 }