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, int follow)
  70 {
  71         ssize_t r;
  72
  73         if (follow) {
  74                 /* tail -f keeps following files even if they are truncated */
  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
  86         r = full_read(fd, buf, count);
  87         if (r < 0) {
  88                 bb_perror_msg(bb_msg_read_error);
  89                 G.exitcode = EXIT_FAILURE;
  90         }
  91
  92         return r;
  93 }
  94
  95 #define header_fmt_str "\n==> %s <==\n"
  96
  97 static unsigned eat_num(const char *p)
  98 {
  99         if (*p == '-')
 100                 p++;
 101         else if (*p == '+') {
 102                 p++;
 103                 G.from_top = 1;
 104         }
 105         return xatou_sfx(p, head_tail_suffixes);
 106 }
 107
 108 int tail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 109 int tail_main(int argc, char **argv)
 110 {
 111         unsigned count = 10;
 112         unsigned sleep_period = 1;
 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         INIT_G();
 125
 126 #if ENABLE_INCLUDE_SUSv2 || ENABLE_FEATURE_FANCY_TAIL
 127         /* Allow legacy syntax of an initial numeric option without -n. */
 128         if (argv[1] && (argv[1][0] == '+' || argv[1][0] == '-')
 129          && isdigit(argv[1][1])
 130         ) {
 131                 count = eat_num(argv[1]);
 132                 argv++;
 133                 argc--;
 134         }
 135 #endif
 136
 137         /* -s NUM, -F imlies -f */
 138         IF_FEATURE_FANCY_TAIL(opt_complementary = "s+:Ff";)
 139         opt = getopt32(argv, "fc:n:" IF_FEATURE_FANCY_TAIL("qs:vF"),
 140                         &str_c, &str_n IF_FEATURE_FANCY_TAIL(,&sleep_period));
 141 #define FOLLOW (opt & 0x1)
 142 #define COUNT_BYTES (opt & 0x2)
 143         //if (opt & 0x1) // -f
 144         if (opt & 0x2) count = eat_num(str_c); // -c
 145         if (opt & 0x4) count = eat_num(str_n); // -n
 146 #if ENABLE_FEATURE_FANCY_TAIL
 147         /* q: make it impossible for nfiles to be > header_threshhold */
 148         if (opt & 0x8) header_threshhold = UINT_MAX; // -q
 149         //if (opt & 0x10) // -s
 150         if (opt & 0x20) header_threshhold = 0; // -v
 151 # define FOLLOW_RETRY (opt & 0x40)
 152 #else
 153 # define FOLLOW_RETRY 0
 154 #endif
 155         argc -= optind;
 156         argv += optind;
 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.exitcode = 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 (!G.from_top && COUNT_BYTES) {
 187                 if (tailbufsize < count + BUFSIZ) {
 188                         tailbufsize = count + BUFSIZ;
 189                 }
 190         }
 191         /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block.
 192          * (In fact, it doesn't need ANY memory). So delay allocation.
 193          */
 194         tailbuf = NULL;
 195
 196         /* tail the files */
 197
 198         fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */
 199         i = 0;
 200         do {
 201                 char *buf;
 202                 int taillen;
 203                 int newlines_seen;
 204                 unsigned seen;
 205                 int nread;
 206                 int fd = fds[i];
 207
 208                 if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 209                         continue; /* may happen with -F */
 210
 211                 if (nfiles > header_threshhold) {
 212                         tail_xprint_header(fmt, argv[i]);
 213                         fmt = header_fmt_str;
 214                 }
 215
 216                 if (!G.from_top) {
 217                         off_t current = lseek(fd, 0, SEEK_END);
 218                         if (current > 0) {
 219                                 unsigned off;
 220                                 if (COUNT_BYTES) {
 221                                 /* Optimizing count-bytes case if the file is seekable.
 222                                  * Beware of backing up too far.
 223                                  * Also we exclude files with size 0 (because of /proc/xxx) */
 224                                         if (count == 0)
 225                                                 continue; /* showing zero bytes is easy :) */
 226                                         current -= count;
 227                                         if (current < 0)
 228                                                 current = 0;
 229                                         xlseek(fd, current, SEEK_SET);
 230                                         bb_copyfd_size(fd, STDOUT_FILENO, count);
 231                                         continue;
 232                                 }
 233 #if 1 /* This is technically incorrect for *LONG* strings, but very useful */
 234                                 /* Optimizing count-lines case if the file is seekable.
 235                                  * We assume the lines are <64k.
 236                                  * (Users complain that tail takes too long
 237                                  * on multi-gigabyte files) */
 238                                 off = (count | 0xf); /* for small counts, be more paranoid */
 239                                 if (off > (INT_MAX / (64*1024)))
 240                                         off = (INT_MAX / (64*1024));
 241                                 current -= off * (64*1024);
 242                                 if (current < 0)
 243                                         current = 0;
 244                                 xlseek(fd, current, SEEK_SET);
 245 #endif
 246                         }
 247                 }
 248
 249                 if (!tailbuf)
 250                         tailbuf = xmalloc(tailbufsize);
 251
 252                 buf = tailbuf;
 253                 taillen = 0;
 254                 /* "We saw 1st line/byte".
 255                  * Used only by +N code ("start from Nth", 1-based): */
 256                 seen = 1;
 257                 newlines_seen = 0;
 258                 while ((nread = tail_read(fd, buf, tailbufsize - taillen, /*follow:*/ 0)) > 0) {
 259                         if (G.from_top) {
 260                                 int nwrite = nread;
 261                                 if (seen < count) {
 262                                         /* We need to skip a few more bytes/lines */
 263                                         if (COUNT_BYTES) {
 264                                                 nwrite -= (count - seen);
 265                                                 seen += nread;
 266                                         } else {
 267                                                 char *s = buf;
 268                                                 do {
 269                                                         --nwrite;
 270                                                         if (*s++ == '\n' && ++seen == count) {
 271                                                                 break;
 272                                                         }
 273                                                 } while (nwrite);
 274                                         }
 275                                 }
 276                                 if (nwrite > 0)
 277                                         xwrite(STDOUT_FILENO, buf + nread - nwrite, nwrite);
 278                         } else if (count) {
 279                                 if (COUNT_BYTES) {
 280                                         taillen += nread;
 281                                         if (taillen > (int)count) {
 282                                                 memmove(tailbuf, tailbuf + taillen - count, count);
 283                                                 taillen = count;
 284                                         }
 285                                 } else {
 286                                         int k = nread;
 287                                         int newlines_in_buf = 0;
 288
 289                                         do { /* count '\n' in last read */
 290                                                 k--;
 291                                                 if (buf[k] == '\n') {
 292                                                         newlines_in_buf++;
 293                                                 }
 294                                         } while (k);
 295
 296                                         if (newlines_seen + newlines_in_buf < (int)count) {
 297                                                 newlines_seen += newlines_in_buf;
 298                                                 taillen += nread;
 299                                         } else {
 300                                                 int extra = (buf[nread-1] != '\n');
 301                                                 char *s;
 302
 303                                                 k = newlines_seen + newlines_in_buf + extra - count;
 304                                                 s = tailbuf;
 305                                                 while (k) {
 306                                                         if (*s == '\n') {
 307                                                                 k--;
 308                                                         }
 309                                                         s++;
 310                                                 }
 311                                                 taillen += nread - (s - tailbuf);
 312                                                 memmove(tailbuf, s, taillen);
 313                                                 newlines_seen = count - extra;
 314                                         }
 315                                         if (tailbufsize < (size_t)taillen + BUFSIZ) {
 316                                                 tailbufsize = taillen + BUFSIZ;
 317                                                 tailbuf = xrealloc(tailbuf, tailbufsize);
 318                                         }
 319                                 }
 320                                 buf = tailbuf + taillen;
 321                         }
 322                 } /* while (tail_read() > 0) */
 323                 if (!G.from_top) {
 324                         xwrite(STDOUT_FILENO, tailbuf, taillen);
 325                 }
 326         } while (++i < nfiles);
 327
 328         tailbuf = xrealloc(tailbuf, BUFSIZ);
 329
 330         fmt = NULL;
 331
 332         if (FOLLOW) while (1) {
 333                 sleep(sleep_period);
 334
 335                 i = 0;
 336                 do {
 337                         int nread;
 338                         const char *filename = argv[i];
 339                         int fd = fds[i];
 340
 341                         if (FOLLOW_RETRY) {
 342                                 struct stat sbuf, fsbuf;
 343
 344                                 if (fd < 0
 345                                  || fstat(fd, &fsbuf) < 0
 346                                  || stat(filename, &sbuf) < 0
 347                                  || fsbuf.st_dev != sbuf.st_dev
 348                                  || fsbuf.st_ino != sbuf.st_ino
 349                                 ) {
 350                                         int new_fd;
 351
 352                                         if (fd >= 0)
 353                                                 close(fd);
 354                                         new_fd = open(filename, O_RDONLY);
 355                                         if (new_fd >= 0) {
 356                                                 bb_error_msg("%s has %s; following end of new file",
 357                                                         filename, (fd < 0) ? "appeared" : "been replaced"
 358                                                 );
 359                                         } else if (fd >= 0) {
 360                                                 bb_perror_msg("%s has become inaccessible", filename);
 361                                         }
 362                                         fds[i] = fd = new_fd;
 363                                 }
 364                         }
 365                         if (ENABLE_FEATURE_FANCY_TAIL && fd < 0)
 366                                 continue;
 367                         if (nfiles > header_threshhold) {
 368                                 fmt = header_fmt_str;
 369                         }
 370                         while ((nread = tail_read(fd, tailbuf, BUFSIZ, /*follow:*/ 1)) > 0) {
 371                                 if (fmt) {
 372                                         tail_xprint_header(fmt, filename);
 373                                         fmt = NULL;
 374                                 }
 375                                 xwrite(STDOUT_FILENO, tailbuf, nread);
 376                         }
 377                 } while (++i < nfiles);
 378         } /* while (1) */
 379
 380         if (ENABLE_FEATURE_CLEAN_UP) {
 381                 free(fds);
 382                 free(tailbuf);
 383         }
 384         return G.exitcode;
 385 }