src/tac.c

   1 /* tac - concatenate and print files in reverse
   2    Copyright (C) 1988-1991, 1995-2006 Free Software Foundation, Inc.
   3
   4    This program is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU General Public License as published by
   6    the Free Software Foundation, either version 3 of the License, or
   7    (at your option) any later version.
   8
   9    This program is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU General Public License for more details.
  13
  14    You should have received a copy of the GNU General Public License
  15    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Jay Lepreau (lepreau@cs.utah.edu).
  18    GNU enhancements by David MacKenzie (djm@gnu.ai.mit.edu). */
  19
  20 /* Copy each FILE, or the standard input if none are given or when a
  21    FILE name of "-" is encountered, to the standard output with the
  22    order of the records reversed.  The records are separated by
  23    instances of a string, or a newline if none is given.  By default, the
  24    separator string is attached to the end of the record that it
  25    follows in the file.
  26
  27    Options:
  28    -b, --before                 The separator is attached to the beginning
  29                                 of the record that it precedes in the file.
  30    -r, --regex                  The separator is a regular expression.
  31    -s, --separator=separator    Use SEPARATOR as the record separator.
  32
  33    To reverse a file byte by byte, use (in bash, ksh, or sh):
  34 tac -r -s '.\|
  35 ' file */
  36
  37 #include <config.h>
  38
  39 #include <stdio.h>
  40 #include <getopt.h>
  41 #include <sys/types.h>
  42 #include "system.h"
  43
  44 #include <regex.h>
  45
  46 #include "error.h"
  47 #include "quote.h"
  48 #include "quotearg.h"
  49 #include "safe-read.h"
  50 #include "stdlib--.h"
  51
  52 /* The official name of this program (e.g., no `g' prefix).  */
  53 #define PROGRAM_NAME "tac"
  54
  55 #define AUTHORS "Jay Lepreau", "David MacKenzie"
  56
  57 #if defined __MSDOS__ || defined _WIN32
  58 /* Define this to non-zero on systems for which the regular mechanism
  59    (of unlinking an open file and expecting to be able to write, seek
  60    back to the beginning, then reread it) doesn't work.  E.g., on Windows
  61    and DOS systems.  */
  62 # define DONT_UNLINK_WHILE_OPEN 1
  63 #endif
  64
  65
  66 #ifndef DEFAULT_TMPDIR
  67 # define DEFAULT_TMPDIR "/tmp"
  68 #endif
  69
  70 /* The number of bytes per atomic read. */
  71 #define INITIAL_READSIZE 8192
  72
  73 /* The number of bytes per atomic write. */
  74 #define WRITESIZE 8192
  75
  76 /* The name this program was run with. */
  77 char *program_name;
  78
  79 /* The string that separates the records of the file. */
  80 static char const *separator;
  81
  82 /* True if we have ever read standard input.  */
  83 static bool have_read_stdin = false;
  84
  85 /* If true, print `separator' along with the record preceding it
  86    in the file; otherwise with the record following it. */
  87 static bool separator_ends_record;
  88
  89 /* 0 if `separator' is to be matched as a regular expression;
  90    otherwise, the length of `separator', used as a sentinel to
  91    stop the search. */
  92 static size_t sentinel_length;
  93
  94 /* The length of a match with `separator'.  If `sentinel_length' is 0,
  95    `match_length' is computed every time a match succeeds;
  96    otherwise, it is simply the length of `separator'. */
  97 static size_t match_length;
  98
  99 /* The input buffer. */
 100 static char *G_buffer;
 101
 102 /* The number of bytes to read at once into `buffer'. */
 103 static size_t read_size;
 104
 105 /* The size of `buffer'.  This is read_size * 2 + sentinel_length + 2.
 106    The extra 2 bytes allow `past_end' to have a value beyond the
 107    end of `G_buffer' and `match_start' to run off the front of `G_buffer'. */
 108 static size_t G_buffer_size;
 109
 110 /* The compiled regular expression representing `separator'. */
 111 static struct re_pattern_buffer compiled_separator;
 112 static char compiled_separator_fastmap[UCHAR_MAX + 1];
 113
 114 static struct option const longopts[] =
 115 {
 116   {"before", no_argument, NULL, 'b'},
 117   {"regex", no_argument, NULL, 'r'},
 118   {"separator", required_argument, NULL, 's'},
 119   {GETOPT_HELP_OPTION_DECL},
 120   {GETOPT_VERSION_OPTION_DECL},
 121   {NULL, 0, NULL, 0}
 122 };
 123
 124 void
 125 usage (int status)
 126 {
 127   if (status != EXIT_SUCCESS)
 128     fprintf (stderr, _("Try `%s --help' for more information.\n"),
 129              program_name);
 130   else
 131     {
 132       printf (_("\
 133 Usage: %s [OPTION]... [FILE]...\n\
 134 "),
 135               program_name);
 136       fputs (_("\
 137 Write each FILE to standard output, last line first.\n\
 138 With no FILE, or when FILE is -, read standard input.\n\
 139 \n\
 140 "), stdout);
 141       fputs (_("\
 142 Mandatory arguments to long options are mandatory for short options too.\n\
 143 "), stdout);
 144       fputs (_("\
 145   -b, --before             attach the separator before instead of after\n\
 146   -r, --regex              interpret the separator as a regular expression\n\
 147   -s, --separator=STRING   use STRING as the separator instead of newline\n\
 148 "), stdout);
 149       fputs (HELP_OPTION_DESCRIPTION, stdout);
 150       fputs (VERSION_OPTION_DESCRIPTION, stdout);
 151       emit_bug_reporting_address ();
 152     }
 153   exit (status);
 154 }
 155
 156 /* Print the characters from START to PAST_END - 1.
 157    If START is NULL, just flush the buffer. */
 158
 159 static void
 160 output (const char *start, const char *past_end)
 161 {
 162   static char buffer[WRITESIZE];
 163   static size_t bytes_in_buffer = 0;
 164   size_t bytes_to_add = past_end - start;
 165   size_t bytes_available = WRITESIZE - bytes_in_buffer;
 166
 167   if (start == 0)
 168     {
 169       fwrite (buffer, 1, bytes_in_buffer, stdout);
 170       bytes_in_buffer = 0;
 171       return;
 172     }
 173
 174   /* Write out as many full buffers as possible. */
 175   while (bytes_to_add >= bytes_available)
 176     {
 177       memcpy (buffer + bytes_in_buffer, start, bytes_available);
 178       bytes_to_add -= bytes_available;
 179       start += bytes_available;
 180       fwrite (buffer, 1, WRITESIZE, stdout);
 181       bytes_in_buffer = 0;
 182       bytes_available = WRITESIZE;
 183     }
 184
 185   memcpy (buffer + bytes_in_buffer, start, bytes_to_add);
 186   bytes_in_buffer += bytes_to_add;
 187 }
 188
 189 /* Print in reverse the file open on descriptor FD for reading FILE.
 190    Return true if successful.  */
 191
 192 static bool
 193 tac_seekable (int input_fd, const char *file)
 194 {
 195   /* Pointer to the location in `G_buffer' where the search for
 196      the next separator will begin. */
 197   char *match_start;
 198
 199   /* Pointer to one past the rightmost character in `G_buffer' that
 200      has not been printed yet. */
 201   char *past_end;
 202
 203   /* Length of the record growing in `G_buffer'. */
 204   size_t saved_record_size;
 205
 206   /* Offset in the file of the next read. */
 207   off_t file_pos;
 208
 209   /* True if `output' has not been called yet for any file.
 210      Only used when the separator is attached to the preceding record. */
 211   bool first_time = true;
 212   char first_char = *separator; /* Speed optimization, non-regexp. */
 213   char const *separator1 = separator + 1; /* Speed optimization, non-regexp. */
 214   size_t match_length1 = match_length - 1; /* Speed optimization, non-regexp. */
 215   struct re_registers regs;
 216
 217   /* Find the size of the input file. */
 218   file_pos = lseek (input_fd, (off_t) 0, SEEK_END);
 219   if (file_pos < 1)
 220     return true;                        /* It's an empty file. */
 221
 222   /* Arrange for the first read to lop off enough to leave the rest of the
 223      file a multiple of `read_size'.  Since `read_size' can change, this may
 224      not always hold during the program run, but since it usually will, leave
 225      it here for i/o efficiency (page/sector boundaries and all that).
 226      Note: the efficiency gain has not been verified. */
 227   saved_record_size = file_pos % read_size;
 228   if (saved_record_size == 0)
 229     saved_record_size = read_size;
 230   file_pos -= saved_record_size;
 231   /* `file_pos' now points to the start of the last (probably partial) block
 232      in the input file. */
 233
 234   if (lseek (input_fd, file_pos, SEEK_SET) < 0)
 235     error (0, errno, _("%s: seek failed"), quotearg_colon (file));
 236
 237   if (safe_read (input_fd, G_buffer, saved_record_size) != saved_record_size)
 238     {
 239       error (0, errno, _("%s: read error"), quotearg_colon (file));
 240       return false;
 241     }
 242
 243   match_start = past_end = G_buffer + saved_record_size;
 244   /* For non-regexp search, move past impossible positions for a match. */
 245   if (sentinel_length)
 246     match_start -= match_length1;
 247
 248   for (;;)
 249     {
 250       /* Search backward from `match_start' - 1 to `G_buffer' for a match
 251          with `separator'; for speed, use strncmp if `separator' contains no
 252          metacharacters.
 253          If the match succeeds, set `match_start' to point to the start of
 254          the match and `match_length' to the length of the match.
 255          Otherwise, make `match_start' < `G_buffer'. */
 256       if (sentinel_length == 0)
 257         {
 258           size_t i = match_start - G_buffer;
 259           regoff_t ri = i;
 260           regoff_t range = 1 - ri;
 261           regoff_t ret;
 262
 263           if (1 < range)
 264             error (EXIT_FAILURE, 0, _("record too large"));
 265
 266           if (range == 1
 267               || ((ret = re_search (&compiled_separator, G_buffer,
 268                                     i, i - 1, range, &regs))
 269                   == -1))
 270             match_start = G_buffer - 1;
 271           else if (ret == -2)
 272             {
 273               error (EXIT_FAILURE, 0,
 274                      _("error in regular expression search"));
 275             }
 276           else
 277             {
 278               match_start = G_buffer + regs.start[0];
 279               match_length = regs.end[0] - regs.start[0];
 280             }
 281         }
 282       else
 283         {
 284           /* `match_length' is constant for non-regexp boundaries. */
 285           while (*--match_start != first_char
 286                  || (match_length1 && strncmp (match_start + 1, separator1,
 287                                                match_length1)))
 288             /* Do nothing. */ ;
 289         }
 290
 291       /* Check whether we backed off the front of `G_buffer' without finding
 292          a match for `separator'. */
 293       if (match_start < G_buffer)
 294         {
 295           if (file_pos == 0)
 296             {
 297               /* Hit the beginning of the file; print the remaining record. */
 298               output (G_buffer, past_end);
 299               return true;
 300             }
 301
 302           saved_record_size = past_end - G_buffer;
 303           if (saved_record_size > read_size)
 304             {
 305               /* `G_buffer_size' is about twice `read_size', so since
 306                  we want to read in another `read_size' bytes before
 307                  the data already in `G_buffer', we need to increase
 308                  `G_buffer_size'. */
 309               char *newbuffer;
 310               size_t offset = sentinel_length ? sentinel_length : 1;
 311               ptrdiff_t match_start_offset = match_start - G_buffer;
 312               ptrdiff_t past_end_offset = past_end - G_buffer;
 313               size_t old_G_buffer_size = G_buffer_size;
 314
 315               read_size *= 2;
 316               G_buffer_size = read_size * 2 + sentinel_length + 2;
 317               if (G_buffer_size < old_G_buffer_size)
 318                 xalloc_die ();
 319               newbuffer = xrealloc (G_buffer - offset, G_buffer_size);
 320               newbuffer += offset;
 321               /* Adjust the pointers for the new buffer location.  */
 322               match_start = newbuffer + match_start_offset;
 323               past_end = newbuffer + past_end_offset;
 324               G_buffer = newbuffer;
 325             }
 326
 327           /* Back up to the start of the next bufferfull of the file.  */
 328           if (file_pos >= read_size)
 329             file_pos -= read_size;
 330           else
 331             {
 332               read_size = file_pos;
 333               file_pos = 0;
 334             }
 335           if (lseek (input_fd, file_pos, SEEK_SET) < 0)
 336             error (0, errno, _("%s: seek failed"), quotearg_colon (file));
 337
 338           /* Shift the pending record data right to make room for the new.
 339              The source and destination regions probably overlap.  */
 340           memmove (G_buffer + read_size, G_buffer, saved_record_size);
 341           past_end = G_buffer + read_size + saved_record_size;
 342           /* For non-regexp searches, avoid unneccessary scanning. */
 343           if (sentinel_length)
 344             match_start = G_buffer + read_size;
 345           else
 346             match_start = past_end;
 347
 348           if (safe_read (input_fd, G_buffer, read_size) != read_size)
 349             {
 350               error (0, errno, _("%s: read error"), quotearg_colon (file));
 351               return false;
 352             }
 353         }
 354       else
 355         {
 356           /* Found a match of `separator'. */
 357           if (separator_ends_record)
 358             {
 359               char *match_end = match_start + match_length;
 360
 361               /* If this match of `separator' isn't at the end of the
 362                  file, print the record. */
 363               if (!first_time || match_end != past_end)
 364                 output (match_end, past_end);
 365               past_end = match_end;
 366               first_time = false;
 367             }
 368           else
 369             {
 370               output (match_start, past_end);
 371               past_end = match_start;
 372             }
 373
 374           /* For non-regex matching, we can back up.  */
 375           if (sentinel_length > 0)
 376             match_start -= match_length - 1;
 377         }
 378     }
 379 }
 380
 381 #if DONT_UNLINK_WHILE_OPEN
 382
 383 /* FIXME-someday: remove all of this DONT_UNLINK_WHILE_OPEN junk.
 384    Using atexit like this is wrong, since it can fail
 385    when called e.g. 32 or more times.
 386    But this isn't a big deal, since the code is used only on WOE/DOS
 387    systems, and few people invoke tac on that many nonseekable files.  */
 388
 389 static const char *file_to_remove;
 390 static FILE *fp_to_close;
 391
 392 static void
 393 unlink_tempfile (void)
 394 {
 395   fclose (fp_to_close);
 396   unlink (file_to_remove);
 397 }
 398
 399 static void
 400 record_or_unlink_tempfile (char const *fn, FILE *fp)
 401 {
 402   if (!file_to_remove)
 403     {
 404       file_to_remove = fn;
 405       fp_to_close = fp;
 406       atexit (unlink_tempfile);
 407     }
 408 }
 409
 410 #else
 411
 412 static void
 413 record_or_unlink_tempfile (char const *fn, FILE *fp ATTRIBUTE_UNUSED)
 414 {
 415   unlink (fn);
 416 }
 417
 418 #endif
 419
 420 /* Copy from file descriptor INPUT_FD (corresponding to the named FILE) to
 421    a temporary file, and set *G_TMP and *G_TEMPFILE to the resulting stream
 422    and file name.  Return true if successful.  */
 423
 424 static bool
 425 copy_to_temp (FILE **g_tmp, char **g_tempfile, int input_fd, char const *file)
 426 {
 427   static char *template = NULL;
 428   static char const *tempdir;
 429   char *tempfile;
 430   FILE *tmp;
 431   int fd;
 432
 433   if (template == NULL)
 434     {
 435       char const * const Template = "%s/tacXXXXXX";
 436       tempdir = getenv ("TMPDIR");
 437       if (tempdir == NULL)
 438         tempdir = DEFAULT_TMPDIR;
 439
 440       /* Subtract 2 for `%s' and add 1 for the trailing NUL byte.  */
 441       template = xmalloc (strlen (tempdir) + strlen (Template) - 2 + 1);
 442       sprintf (template, Template, tempdir);
 443     }
 444
 445   /* FIXME: there's a small window between a successful mkstemp call
 446      and the unlink that's performed by record_or_unlink_tempfile.
 447      If we're interrupted in that interval, this code fails to remove
 448      the temporary file.  On systems that define DONT_UNLINK_WHILE_OPEN,
 449      the window is much larger -- it extends to the atexit-called
 450      unlink_tempfile.
 451      FIXME: clean up upon fatal signal.  Don't block them, in case
 452      $TMPFILE is a remote file system.  */
 453
 454   tempfile = template;
 455   fd = mkstemp (template);
 456   if (fd < 0)
 457     {
 458       error (0, errno, _("cannot create temporary file %s"), quote (tempfile));
 459       return false;
 460     }
 461
 462   tmp = fdopen (fd, (O_BINARY ? "w+b" : "w+"));
 463   if (! tmp)
 464     {
 465       error (0, errno, _("cannot open %s for writing"), quote (tempfile));
 466       close (fd);
 467       unlink (tempfile);
 468       return false;
 469     }
 470
 471   record_or_unlink_tempfile (tempfile, tmp);
 472
 473   while (1)
 474     {
 475       size_t bytes_read = safe_read (input_fd, G_buffer, read_size);
 476       if (bytes_read == 0)
 477         break;
 478       if (bytes_read == SAFE_READ_ERROR)
 479         {
 480           error (0, errno, _("%s: read error"), quotearg_colon (file));
 481           goto Fail;
 482         }
 483
 484       if (fwrite (G_buffer, 1, bytes_read, tmp) != bytes_read)
 485         {
 486           error (0, errno, _("%s: write error"), quotearg_colon (tempfile));
 487           goto Fail;
 488         }
 489     }
 490
 491   if (fflush (tmp) != 0)
 492     {
 493       error (0, errno, _("%s: write error"), quotearg_colon (tempfile));
 494       goto Fail;
 495     }
 496
 497   *g_tmp = tmp;
 498   *g_tempfile = tempfile;
 499   return true;
 500
 501  Fail:
 502   fclose (tmp);
 503   return false;
 504 }
 505
 506 /* Copy INPUT_FD to a temporary, then tac that file.
 507    Return true if successful.  */
 508
 509 static bool
 510 tac_nonseekable (int input_fd, const char *file)
 511 {
 512   FILE *tmp_stream;
 513   char *tmp_file;
 514   return (copy_to_temp (&tmp_stream, &tmp_file, input_fd, file)
 515           && tac_seekable (fileno (tmp_stream), tmp_file));
 516 }
 517
 518 /* Print FILE in reverse, copying it to a temporary
 519    file first if it is not seekable.
 520    Return true if successful.  */
 521
 522 static bool
 523 tac_file (const char *filename)
 524 {
 525   bool ok;
 526   off_t file_size;
 527   int fd;
 528   bool is_stdin = STREQ (filename, "-");
 529
 530   if (is_stdin)
 531     {
 532       have_read_stdin = true;
 533       fd = STDIN_FILENO;
 534       filename = _("standard input");
 535       if (O_BINARY && ! isatty (STDIN_FILENO))
 536         freopen (NULL, "rb", stdin);
 537     }
 538   else
 539     {
 540       fd = open (filename, O_RDONLY | O_BINARY);
 541       if (fd < 0)
 542         {
 543           error (0, errno, _("cannot open %s for reading"), quote (filename));
 544           return false;
 545         }
 546     }
 547
 548   file_size = lseek (fd, (off_t) 0, SEEK_END);
 549
 550   ok = (file_size < 0 || isatty (fd)
 551         ? tac_nonseekable (fd, filename)
 552         : tac_seekable (fd, filename));
 553
 554   if (!is_stdin && close (fd) != 0)
 555     {
 556       error (0, errno, _("%s: read error"), quotearg_colon (filename));
 557       ok = false;
 558     }
 559   return ok;
 560 }
 561
 562 int
 563 main (int argc, char **argv)
 564 {
 565   const char *error_message;    /* Return value from re_compile_pattern. */
 566   int optc;
 567   bool ok;
 568   size_t half_buffer_size;
 569
 570   /* Initializer for file_list if no file-arguments
 571      were specified on the command line.  */
 572   static char const *const default_file_list[] = {"-", NULL};
 573   char const *const *file;
 574
 575   initialize_main (&argc, &argv);
 576   program_name = argv[0];
 577   setlocale (LC_ALL, "");
 578   bindtextdomain (PACKAGE, LOCALEDIR);
 579   textdomain (PACKAGE);
 580
 581   atexit (close_stdout);
 582
 583   separator = "\n";
 584   sentinel_length = 1;
 585   separator_ends_record = true;
 586
 587   while ((optc = getopt_long (argc, argv, "brs:", longopts, NULL)) != -1)
 588     {
 589       switch (optc)
 590         {
 591         case 'b':
 592           separator_ends_record = false;
 593           break;
 594         case 'r':
 595           sentinel_length = 0;
 596           break;
 597         case 's':
 598           separator = optarg;
 599           if (*separator == 0)
 600             error (EXIT_FAILURE, 0, _("separator cannot be empty"));
 601           break;
 602         case_GETOPT_HELP_CHAR;
 603         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 604         default:
 605           usage (EXIT_FAILURE);
 606         }
 607     }
 608
 609   if (sentinel_length == 0)
 610     {
 611       compiled_separator.buffer = NULL;
 612       compiled_separator.allocated = 0;
 613       compiled_separator.fastmap = compiled_separator_fastmap;
 614       compiled_separator.translate = NULL;
 615       error_message = re_compile_pattern (separator, strlen (separator),
 616                                           &compiled_separator);
 617       if (error_message)
 618         error (EXIT_FAILURE, 0, "%s", error_message);
 619     }
 620   else
 621     match_length = sentinel_length = strlen (separator);
 622
 623   read_size = INITIAL_READSIZE;
 624   while (sentinel_length >= read_size / 2)
 625     {
 626       if (SIZE_MAX / 2 < read_size)
 627         xalloc_die ();
 628       read_size *= 2;
 629     }
 630   half_buffer_size = read_size + sentinel_length + 1;
 631   G_buffer_size = 2 * half_buffer_size;
 632   if (! (read_size < half_buffer_size && half_buffer_size < G_buffer_size))
 633     xalloc_die ();
 634   G_buffer = xmalloc (G_buffer_size);
 635   if (sentinel_length)
 636     {
 637       strcpy (G_buffer, separator);
 638       G_buffer += sentinel_length;
 639     }
 640   else
 641     {
 642       ++G_buffer;
 643     }
 644
 645   file = (optind < argc
 646           ? (char const *const *) &argv[optind]
 647           : default_file_list);
 648
 649   if (O_BINARY && ! isatty (STDOUT_FILENO))
 650     freopen (NULL, "wb", stdout);
 651
 652   {
 653     size_t i;
 654     ok = true;
 655     for (i = 0; file[i]; ++i)
 656       ok &= tac_file (file[i]);
 657   }
 658
 659   /* Flush the output buffer. */
 660   output ((char *) NULL, (char *) NULL);
 661
 662   if (have_read_stdin && close (STDIN_FILENO) < 0)
 663     error (EXIT_FAILURE, errno, "-");
 664   exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
 665 }