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:     "\nOptions:"
  33 //usage:     "\n        -f              Print data as file grows"
  34 //usage:        IF_FEATURE_FANCY_TAIL(
  35 //usage:     "\n        -s SECONDS      Wait SECONDS between reads with -f"
  36 //usage:        )
  37 //usage:     "\n        -n N[kbm]       Print last N lines"
  38 //usage:        IF_FEATURE_FANCY_TAIL(
  39 //usage:     "\n        -c N[kbm]       Print last N bytes"
  40 //usage:     "\n        -q              Never print headers"
  41 //usage:     "\n        -v              Always print headers"
  42 //usage:     "\n"
  43 //usage:     "\nN may be suffixed by k (x1024), b (x512), or m (x1024^2)."
  44 //usage:     "\nIf N starts with a '+', output begins with the Nth item from the start"
  45 //usage:     "\nof each file, not from the end."
  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 static const struct suffix_mult tail_suffixes[] = {
  55         { "b", 512 },
  56         { "k", 1024 },
  57         { "m", 1024*1024 },
  58         { "", 0 }
  59 };
  60
  61 struct globals {
  62         bool status;
  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.status = 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.status = 1; /* mark that we saw "+" */
 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         bool from_top;
 113         const char *str_c, *str_n;
 114
 115         char *tailbuf;
 116         size_t tailbufsize;
 117         unsigned header_threshhold = 1;
 118         unsigned nfiles;
 119         int i, opt;
 120
 121         int *fds;
 122         const char *fmt;
 123
 124 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 125         /* Allow legacy syntax of an initial numeric option without -n. */
 126         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 127          && isdigit(argv[1][1])
 128         ) {
 129                 count = eat_num(argv[1]);
 130                 argv++;
 131                 argc--;
 132         }
 133 #endif
 134
 135         /* -s NUM, -F imlies -f */
 136         IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 137         opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 138                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 139 #define FOLLOW (opt & 0x1)
 140 #define COUNT_BYTES (opt & 0x2)
 141         //if (opt & 0x1) // -f
 142         if (opt & 0x2) count = eat_num(str_c); // -c
 143         if (opt & 0x4) count = eat_num(str_n); // -n
 144 #if ENABLE_FEATURE_FANCY_TAIL
 145         /* q: make it impossible for nfiles to be > header_threshhold */
 146         if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 147         //if (opt & 0x10) // -s
 148         if (opt & 0x20) header_threshhold = 0; // -v
 149 # define FOLLOW_RETRY (opt & 0x40)
 150 #else
 151 # define FOLLOW_RETRY 0
 152 #endif
 153         argc -= optind;
 154         argv += optind;
 155         from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */
 156         G.status = EXIT_SUCCESS;
 157
 158         /* open all the files */
 159         fds = xmalloc(sizeof(fds[0]) * (argc + 1));
 160         if (!argv[0]) {
 161                 struct stat statbuf;
 162
 163                 if (fstat(STDIN_FILENO, &statbuf) == 0
 164                  && S_ISFIFO(statbuf.st_mode)
 165                 ) {
 166                         opt &= ~1; /* clear FOLLOW */
 167                 }
 168                 argv[0] = (char *) bb_msg_standard_input;
 169         }
 170         nfiles = i = 0;
 171         do {
 172                 int fd = open_or_warn_stdin(argv[i]);
 173                 if (fd < 0 && !FOLLOW_RETRY) {
 174                         G.status = EXIT_FAILURE;
 175                         continue;
 176                 }
 177                 fds[nfiles] = fd;
 178                 argv[nfiles++] = argv[i];
 179         } while (++i < argc);
 180
 181         if (!nfiles)
 182                 bb_error_msg_and_die("no files");
 183
 184         /* prepare the buffer */
 185         tailbufsize = BUFSIZ;
 186         if (!from_top && COUNT_BYTES) {
 187                 if (tailbufsize < count + BUFSIZ) {
 188                         tailbufsize = count + BUFSIZ;
 189                 }
 190         }
 191         tailbuf = xmalloc(tailbufsize);
 192
 193         /* tail the files */
 194         fmt = header_fmt_str + 1; /* skip header leading newline on 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 -E */
 206
 207                 if (nfiles > header_threshhold) {
 208                         tail_xprint_header(fmt, argv[i]);
 209                         fmt = header_fmt_str;
 210                 }
 211
 212                 if (!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                 buf = tailbuf;
 246                 taillen = 0;
 247                 /* "We saw 1st line/byte".
 248                  * Used only by +N code ("start from Nth", 1-based): */
 249                 seen = 1;
 250                 newlines_seen = 0;
 251                 while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) {
 252                         if (from_top) {
 253                                 int nwrite = nread;
 254                                 if (seen < count) {
 255                                         /* We need to skip a few more bytes/lines */
 256                                         if (COUNT_BYTES) {
 257                                                 nwrite -= (count - seen);
 258                                                 seen = count;
 259                                         } else {
 260                                                 char *s = buf;
 261                                                 do {
 262                                                         --nwrite;
 263                                                         if (*s++ == '\n' && ++seen == count) {
 264                                                                 break;
 265                                                         }
 266                                                 } while (nwrite);
 267                                         }
 268                                 }
 269                                 if (nwrite > 0)
 270                                         xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 271                         } else if (count) {
 272                                 if (COUNT_BYTES) {
 273                                         taillen += nread;
 274                                         if (taillen > (int)count) {
 275                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 276                                                 taillen = count;
 277                                         }
 278                                 } else {
 279                                         int k = nread;
 280                                         int newlines_in_buf = 0;
 281
 282                                         do { /* count '\n' in last read */
 283                                                 k--;
 284                                                 if (buf[k] == '\n') {
 285                                                         newlines_in_buf++;
 286                                                 }
 287                                         } while (k);
 288
 289                                         if (newlines_seen + newlines_in_buf < (int)count) {
 290                                                 newlines_seen += newlines_in_buf;
 291                                                 taillen += nread;
 292                                         } else {
 293                                                 int extra = (buf[nread-1] != '\n');
 294                                                 char *s;
 295
 296                                                 k = newlines_seen + newlines_in_buf + extra - count;
 297                                                 s = tailbuf;
 298                                                 while (k) {
 299                                                         if (*s == '\n') {
 300                                                                 k--;
 301                                                         }
 302                                                         s++;
 303                                                 }
 304                                                 taillen += nread - (s - tailbuf);
 305                                                 memmove(tailbuf, s, taillen);
 306                                                 newlines_seen = count - extra;
 307                                         }
 308                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 309                                                 tailbufsize = taillen + BUFSIZ;
 310                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 311                                         }
 312                                 }
 313                                 buf = tailbuf + taillen;
 314                         }
 315                 } /* while (tail_read() > 0) */
 316                 if (!from_top) {
 317                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 318                 }
 319         } while (++i < nfiles);
 320
 321         tailbuf = xrealloc(tailbuf, BUFSIZ);
 322
 323         fmt = NULL;
 324
 325         if (FOLLOW) while (1) {
 326                 sleep(sleep_period);
 327
 328                 i = 0;
 329                 do {
 330                         int nread;
 331                         const char *filename = argv[i];
 332                         int fd = fds[i];
 333
 334                         if (FOLLOW_RETRY) {
 335                                 struct stat sbuf, fsbuf;
 336
 337                                 if (fd < 0
 338                                  || fstat(fd, &fsbuf) < 0
 339                                  || stat(filename, &sbuf) < 0
 340                                  || fsbuf.st_dev != sbuf.st_dev
 341                                  || fsbuf.st_ino != sbuf.st_ino
 342                                 ) {
 343                                         int new_fd;
 344
 345                                         if (fd >= 0)
 346                                                 close(fd);
 347                                         new_fd = open(filename, O_RDONLY);
 348                                         if (new_fd >= 0) {
 349                                                 bb_error_msg("%s has %s; following end of new file",
 350                                                         filename, (fd < 0) ? "appeared" : "been replaced"
 351                                                 );
 352                                         } else if (fd >= 0) {
 353                                                 bb_perror_msg("%s has become inaccessible", filename);
 354                                         }
 355                                         fds[i] = fd = new_fd;
 356                                 }
 357                         }
 358                         if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 359                                 continue;
 360                         if (nfiles > header_threshhold) {
 361                                 fmt = header_fmt_str;
 362                         }
 363                         while ((nread = tail_read(fd, tailbuf, BUFSIZ)) > 0) {
 364                                 if (fmt) {
 365                                         tail_xprint_header(fmt, filename);
 366                                         fmt = NULL;
 367                                 }
 368                                 xwrite(STDOUT_FILENO, tailbuf, nread);
 369                         }
 370                 } while (++i < nfiles);
 371         }
 372         if (ENABLE_FEATURE_CLEAN_UP) {
 373                 free(fds);
 374                 free(tailbuf);
 375         }
 376         return G.status;
 377 }