src/tac.c

   1 /* tac - concatenate and print files in reverse
   2    Copyright (C) 1988-1991, 1995-2006, 2008-2010 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 #include "xfreopen.h"
  52
  53 /* The official name of this program (e.g., no `g' prefix).  */
  54 #define PROGRAM_NAME "tac"
  55
  56 #define AUTHORS \
  57   proper_name ("Jay Lepreau"), \
  58   proper_name ("David MacKenzie")
  59
  60 #if defined __MSDOS__ || defined _WIN32
  61 /* Define this to non-zero on systems for which the regular mechanism
  62    (of unlinking an open file and expecting to be able to write, seek
  63    back to the beginning, then reread it) doesn't work.  E.g., on Windows
  64    and DOS systems.  */
  65 # define DONT_UNLINK_WHILE_OPEN 1
  66 #endif
  67
  68
  69 #ifndef DEFAULT_TMPDIR
  70 # define DEFAULT_TMPDIR "/tmp"
  71 #endif
  72
  73 /* The number of bytes per atomic read. */
  74 #define INITIAL_READSIZE 8192
  75
  76 /* The number of bytes per atomic write. */
  77 #define WRITESIZE 8192
  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 static struct re_registers regs;
 114
 115 static struct option const longopts[] =
 116 {
 117   {"before", no_argument, NULL, 'b'},
 118   {"regex", no_argument, NULL, 'r'},
 119   {"separator", required_argument, NULL, 's'},
 120   {GETOPT_HELP_OPTION_DECL},
 121   {GETOPT_VERSION_OPTION_DECL},
 122   {NULL, 0, NULL, 0}
 123 };
 124
 125 void
 126 usage (int status)
 127 {
 128   if (status != EXIT_SUCCESS)
 129     fprintf (stderr, _("Try `%s --help' for more information.\n"),
 130              program_name);
 131   else
 132     {
 133       printf (_("\
 134 Usage: %s [OPTION]... [FILE]...\n\
 135 "),
 136               program_name);
 137       fputs (_("\
 138 Write each FILE to standard output, last line first.\n\
 139 With no FILE, or when FILE is -, read standard input.\n\
 140 \n\
 141 "), stdout);
 142       fputs (_("\
 143 Mandatory arguments to long options are mandatory for short options too.\n\
 144 "), stdout);
 145       fputs (_("\
 146   -b, --before             attach the separator before instead of after\n\
 147   -r, --regex              interpret the separator as a regular expression\n\
 148   -s, --separator=STRING   use STRING as the separator instead of newline\n\
 149 "), stdout);
 150       fputs (HELP_OPTION_DESCRIPTION, stdout);
 151       fputs (VERSION_OPTION_DESCRIPTION, stdout);
 152       emit_ancillary_info ();
 153     }
 154   exit (status);
 155 }
 156
 157 /* Print the characters from START to PAST_END - 1.
 158    If START is NULL, just flush the buffer. */
 159
 160 static void
 161 output (const char *start, const char *past_end)
 162 {
 163   static char buffer[WRITESIZE];
 164   static size_t bytes_in_buffer = 0;
 165   size_t bytes_to_add = past_end - start;
 166   size_t bytes_available = WRITESIZE - bytes_in_buffer;
 167
 168   if (start == 0)
 169     {
 170       fwrite (buffer, 1, bytes_in_buffer, stdout);
 171       bytes_in_buffer = 0;
 172       return;
 173     }
 174
 175   /* Write out as many full buffers as possible. */
 176   while (bytes_to_add >= bytes_available)
 177     {
 178       memcpy (buffer + bytes_in_buffer, start, bytes_available);
 179       bytes_to_add -= bytes_available;
 180       start += bytes_available;
 181       fwrite (buffer, 1, WRITESIZE, stdout);
 182       bytes_in_buffer = 0;
 183       bytes_available = WRITESIZE;
 184     }
 185
 186   memcpy (buffer + bytes_in_buffer, start, bytes_to_add);
 187   bytes_in_buffer += bytes_to_add;
 188 }
 189
 190 /* Print in reverse the file open on descriptor FD for reading FILE.
 191    Return true if successful.  */
 192
 193 static bool
 194 tac_seekable (int input_fd, const char *file)
 195 {
 196   /* Pointer to the location in `G_buffer' where the search for
 197      the next separator will begin. */
 198   char *match_start;
 199
 200   /* Pointer to one past the rightmost character in `G_buffer' that
 201      has not been printed yet. */
 202   char *past_end;
 203
 204   /* Length of the record growing in `G_buffer'. */
 205   size_t saved_record_size;
 206
 207   /* Offset in the file of the next read. */
 208   off_t file_pos;
 209
 210   /* True if `output' has not been called yet for any file.
 211      Only used when the separator is attached to the preceding record. */
 212   bool first_time = true;
 213   char first_char = *separator; /* Speed optimization, non-regexp. */
 214   char const *separator1 = separator + 1; /* Speed optimization, non-regexp. */
 215   size_t match_length1 = match_length - 1; /* Speed optimization, non-regexp. */
 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   while (true)
 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 in %s"),
 459              quote (tempdir));
 460       return false;
 461     }
 462
 463   tmp = fdopen (fd, (O_BINARY ? "w+b" : "w+"));
 464   if (! tmp)
 465     {
 466       error (0, errno, _("cannot open %s for writing"), quote (tempfile));
 467       close (fd);
 468       unlink (tempfile);
 469       return false;
 470     }
 471
 472   record_or_unlink_tempfile (tempfile, tmp);
 473
 474   while (1)
 475     {
 476       size_t bytes_read = safe_read (input_fd, G_buffer, read_size);
 477       if (bytes_read == 0)
 478         break;
 479       if (bytes_read == SAFE_READ_ERROR)
 480         {
 481           error (0, errno, _("%s: read error"), quotearg_colon (file));
 482           goto Fail;
 483         }
 484
 485       if (fwrite (G_buffer, 1, bytes_read, tmp) != bytes_read)
 486         {
 487           error (0, errno, _("%s: write error"), quotearg_colon (tempfile));
 488           goto Fail;
 489         }
 490     }
 491
 492   if (fflush (tmp) != 0)
 493     {
 494       error (0, errno, _("%s: write error"), quotearg_colon (tempfile));
 495       goto Fail;
 496     }
 497
 498   *g_tmp = tmp;
 499   *g_tempfile = tempfile;
 500   return true;
 501
 502  Fail:
 503   fclose (tmp);
 504   return false;
 505 }
 506
 507 /* Copy INPUT_FD to a temporary, then tac that file.
 508    Return true if successful.  */
 509
 510 static bool
 511 tac_nonseekable (int input_fd, const char *file)
 512 {
 513   FILE *tmp_stream;
 514   char *tmp_file;
 515   return (copy_to_temp (&tmp_stream, &tmp_file, input_fd, file)
 516           && tac_seekable (fileno (tmp_stream), tmp_file));
 517 }
 518
 519 /* Print FILE in reverse, copying it to a temporary
 520    file first if it is not seekable.
 521    Return true if successful.  */
 522
 523 static bool
 524 tac_file (const char *filename)
 525 {
 526   bool ok;
 527   off_t file_size;
 528   int fd;
 529   bool is_stdin = STREQ (filename, "-");
 530
 531   if (is_stdin)
 532     {
 533       have_read_stdin = true;
 534       fd = STDIN_FILENO;
 535       filename = _("standard input");
 536       if (O_BINARY && ! isatty (STDIN_FILENO))
 537         xfreopen (NULL, "rb", stdin);
 538     }
 539   else
 540     {
 541       fd = open (filename, O_RDONLY | O_BINARY);
 542       if (fd < 0)
 543         {
 544           error (0, errno, _("cannot open %s for reading"), quote (filename));
 545           return false;
 546         }
 547     }
 548
 549   file_size = lseek (fd, (off_t) 0, SEEK_END);
 550
 551   ok = (file_size < 0 || isatty (fd)
 552         ? tac_nonseekable (fd, filename)
 553         : tac_seekable (fd, filename));
 554
 555   if (!is_stdin && close (fd) != 0)
 556     {
 557       error (0, errno, _("%s: read error"), quotearg_colon (filename));
 558       ok = false;
 559     }
 560   return ok;
 561 }
 562
 563 int
 564 main (int argc, char **argv)
 565 {
 566   const char *error_message;    /* Return value from re_compile_pattern. */
 567   int optc;
 568   bool ok;
 569   size_t half_buffer_size;
 570
 571   /* Initializer for file_list if no file-arguments
 572      were specified on the command line.  */
 573   static char const *const default_file_list[] = {"-", NULL};
 574   char const *const *file;
 575
 576   initialize_main (&argc, &argv);
 577   set_program_name (argv[0]);
 578   setlocale (LC_ALL, "");
 579   bindtextdomain (PACKAGE, LOCALEDIR);
 580   textdomain (PACKAGE);
 581
 582   atexit (close_stdout);
 583
 584   separator = "\n";
 585   sentinel_length = 1;
 586   separator_ends_record = true;
 587
 588   while ((optc = getopt_long (argc, argv, "brs:", longopts, NULL)) != -1)
 589     {
 590       switch (optc)
 591         {
 592         case 'b':
 593           separator_ends_record = false;
 594           break;
 595         case 'r':
 596           sentinel_length = 0;
 597           break;
 598         case 's':
 599           separator = optarg;
 600           if (*separator == 0)
 601             error (EXIT_FAILURE, 0, _("separator cannot be empty"));
 602           break;
 603         case_GETOPT_HELP_CHAR;
 604         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 605         default:
 606           usage (EXIT_FAILURE);
 607         }
 608     }
 609
 610   if (sentinel_length == 0)
 611     {
 612       compiled_separator.buffer = NULL;
 613       compiled_separator.allocated = 0;
 614       compiled_separator.fastmap = compiled_separator_fastmap;
 615       compiled_separator.translate = NULL;
 616       error_message = re_compile_pattern (separator, strlen (separator),
 617                                           &compiled_separator);
 618       if (error_message)
 619         error (EXIT_FAILURE, 0, "%s", error_message);
 620     }
 621   else
 622     match_length = sentinel_length = strlen (separator);
 623
 624   read_size = INITIAL_READSIZE;
 625   while (sentinel_length >= read_size / 2)
 626     {
 627       if (SIZE_MAX / 2 < read_size)
 628         xalloc_die ();
 629       read_size *= 2;
 630     }
 631   half_buffer_size = read_size + sentinel_length + 1;
 632   G_buffer_size = 2 * half_buffer_size;
 633   if (! (read_size < half_buffer_size && half_buffer_size < G_buffer_size))
 634     xalloc_die ();
 635   G_buffer = xmalloc (G_buffer_size);
 636   if (sentinel_length)
 637     {
 638       strcpy (G_buffer, separator);
 639       G_buffer += sentinel_length;
 640     }
 641   else
 642     {
 643       ++G_buffer;
 644     }
 645
 646   file = (optind < argc
 647           ? (char const *const *) &argv[optind]
 648           : default_file_list);
 649
 650   if (O_BINARY && ! isatty (STDOUT_FILENO))
 651     xfreopen (NULL, "wb", stdout);
 652
 653   {
 654     size_t i;
 655     ok = true;
 656     for (i = 0; file[i]; ++i)
 657       ok &= tac_file (file[i]);
 658   }
 659
 660   /* Flush the output buffer. */
 661   output ((char *) NULL, (char *) NULL);
 662
 663   if (have_read_stdin && close (STDIN_FILENO) < 0)
 664     {
 665       error (0, errno, "-");
 666       ok = false;
 667     }
 668
 669 #ifdef lint
 670   size_t offset = sentinel_length ? sentinel_length : 1;
 671   free (G_buffer - offset);
 672 #endif
 673
 674   exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
 675 }