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