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 2, or (at your option)
   7    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, write to the Free Software Foundation,
  16    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.  */
  17
  18 /* Written by Jay Lepreau (lepreau@cs.utah.edu).
  19    GNU enhancements by David MacKenzie (djm@gnu.ai.mit.edu). */
  20
  21 /* Copy each FILE, or the standard input if none are given or when a
  22    FILE name of "-" is encountered, to the standard output with the
  23    order of the records reversed.  The records are separated by
  24    instances of a string, or a newline if none is given.  By default, the
  25    separator string is attached to the end of the record that it
  26    follows in the file.
  27
  28    Options:
  29    -b, --before                 The separator is attached to the beginning
  30                                 of the record that it precedes in the file.
  31    -r, --regex                  The separator is a regular expression.
  32    -s, --separator=separator    Use SEPARATOR as the record separator.
  33
  34    To reverse a file byte by byte, use (in bash, ksh, or sh):
  35 tac -r -s '.\|
  36 ' file */
  37
  38 #include <config.h>
  39
  40 #include <stdio.h>
  41 #include <getopt.h>
  42 #include <sys/types.h>
  43 #include "system.h"
  44
  45 #include <regex.h>
  46
  47 #include "error.h"
  48 #include "quote.h"
  49 #include "quotearg.h"
  50 #include "safe-read.h"
  51 #include "stdlib--.h"
  52
  53 /* The official name of this program (e.g., no `g' prefix).  */
  54 #define PROGRAM_NAME "tac"
  55
  56 #define AUTHORS "Jay Lepreau", "David MacKenzie"
  57
  58 #if defined __MSDOS__ || defined _WIN32
  59 /* Define this to non-zero on systems for which the regular mechanism
  60    (of unlinking an open file and expecting to be able to write, seek
  61    back to the beginning, then reread it) doesn't work.  E.g., on Windows
  62    and DOS systems.  */
  63 # define DONT_UNLINK_WHILE_OPEN 1
  64 #endif
  65
  66
  67 #ifndef DEFAULT_TMPDIR
  68 # define DEFAULT_TMPDIR "/tmp"
  69 #endif
  70
  71 /* The number of bytes per atomic read. */
  72 #define INITIAL_READSIZE 8192
  73
  74 /* The number of bytes per atomic write. */
  75 #define WRITESIZE 8192
  76
  77 /* The name this program was run with. */
  78 char *program_name;
  79
  80 /* The string that separates the records of the file. */
  81 static char *separator;
  82
  83 /* True if we have ever read standard input.  */
  84 static bool have_read_stdin = false;
  85
  86 /* If true, print `separator' along with the record preceding it
  87    in the file; otherwise with the record following it. */
  88 static bool separator_ends_record;
  89
  90 /* 0 if `separator' is to be matched as a regular expression;
  91    otherwise, the length of `separator', used as a sentinel to
  92    stop the search. */
  93 static size_t sentinel_length;
  94
  95 /* The length of a match with `separator'.  If `sentinel_length' is 0,
  96    `match_length' is computed every time a match succeeds;
  97    otherwise, it is simply the length of `separator'. */
  98 static size_t match_length;
  99
 100 /* The input buffer. */
 101 static char *G_buffer;
 102
 103 /* The number of bytes to read at once into `buffer'. */
 104 static size_t read_size;
 105
 106 /* The size of `buffer'.  This is read_size * 2 + sentinel_length + 2.
 107    The extra 2 bytes allow `past_end' to have a value beyond the
 108    end of `G_buffer' and `match_start' to run off the front of `G_buffer'. */
 109 static size_t G_buffer_size;
 110
 111 /* The compiled regular expression representing `separator'. */
 112 static struct re_pattern_buffer compiled_separator;
 113 static char compiled_separator_fastmap[UCHAR_MAX + 1];
 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       printf (_("\nReport bugs to <%s>.\n"), PACKAGE_BUGREPORT);
 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 *separator1 = separator + 1; /* Speed optimization, non-regexp. */
 215   size_t match_length1 = match_length - 1; /* Speed optimization, non-regexp. */
 216   struct re_registers regs;
 217
 218   /* Find the size of the input file. */
 219   file_pos = lseek (input_fd, (off_t) 0, SEEK_END);
 220   if (file_pos < 1)
 221     return true;                        /* It's an empty file. */
 222
 223   /* Arrange for the first read to lop off enough to leave the rest of the
 224      file a multiple of `read_size'.  Since `read_size' can change, this may
 225      not always hold during the program run, but since it usually will, leave
 226      it here for i/o efficiency (page/sector boundaries and all that).
 227      Note: the efficiency gain has not been verified. */
 228   saved_record_size = file_pos % read_size;
 229   if (saved_record_size == 0)
 230     saved_record_size = read_size;
 231   file_pos -= saved_record_size;
 232   /* `file_pos' now points to the start of the last (probably partial) block
 233      in the input file. */
 234
 235   if (lseek (input_fd, file_pos, SEEK_SET) < 0)
 236     error (0, errno, _("%s: seek failed"), quotearg_colon (file));
 237
 238   if (safe_read (input_fd, G_buffer, saved_record_size) != saved_record_size)
 239     {
 240       error (0, errno, _("%s: read error"), quotearg_colon (file));
 241       return false;
 242     }
 243
 244   match_start = past_end = G_buffer + saved_record_size;
 245   /* For non-regexp search, move past impossible positions for a match. */
 246   if (sentinel_length)
 247     match_start -= match_length1;
 248
 249   for (;;)
 250     {
 251       /* Search backward from `match_start' - 1 to `G_buffer' for a match
 252          with `separator'; for speed, use strncmp if `separator' contains no
 253          metacharacters.
 254          If the match succeeds, set `match_start' to point to the start of
 255          the match and `match_length' to the length of the match.
 256          Otherwise, make `match_start' < `G_buffer'. */
 257       if (sentinel_length == 0)
 258         {
 259           size_t i = match_start - G_buffer;
 260           regoff_t ri = i;
 261           regoff_t range = 1 - ri;
 262           regoff_t ret;
 263
 264           if (1 < range)
 265             error (EXIT_FAILURE, 0, _("record too large"));
 266
 267           if (range == 1
 268               || ((ret = re_search (&compiled_separator, G_buffer,
 269                                     i, i - 1, range, &regs))
 270                   == -1))
 271             match_start = G_buffer - 1;
 272           else if (ret == -2)
 273             {
 274               error (EXIT_FAILURE, 0,
 275                      _("error in regular expression search"));
 276             }
 277           else
 278             {
 279               match_start = G_buffer + regs.start[0];
 280               match_length = regs.end[0] - regs.start[0];
 281             }
 282         }
 283       else
 284         {
 285           /* `match_length' is constant for non-regexp boundaries. */
 286           while (*--match_start != first_char
 287                  || (match_length1 && strncmp (match_start + 1, separator1,
 288                                                match_length1)))
 289             /* Do nothing. */ ;
 290         }
 291
 292       /* Check whether we backed off the front of `G_buffer' without finding
 293          a match for `separator'. */
 294       if (match_start < G_buffer)
 295         {
 296           if (file_pos == 0)
 297             {
 298               /* Hit the beginning of the file; print the remaining record. */
 299               output (G_buffer, past_end);
 300               return true;
 301             }
 302
 303           saved_record_size = past_end - G_buffer;
 304           if (saved_record_size > read_size)
 305             {
 306               /* `G_buffer_size' is about twice `read_size', so since
 307                  we want to read in another `read_size' bytes before
 308                  the data already in `G_buffer', we need to increase
 309                  `G_buffer_size'. */
 310               char *newbuffer;
 311               size_t offset = sentinel_length ? sentinel_length : 1;
 312               ptrdiff_t match_start_offset = match_start - G_buffer;
 313               ptrdiff_t past_end_offset = past_end - G_buffer;
 314               size_t old_G_buffer_size = G_buffer_size;
 315
 316               read_size *= 2;
 317               G_buffer_size = read_size * 2 + sentinel_length + 2;
 318               if (G_buffer_size < old_G_buffer_size)
 319                 xalloc_die ();
 320               newbuffer = xrealloc (G_buffer - offset, G_buffer_size);
 321               newbuffer += offset;
 322               /* Adjust the pointers for the new buffer location.  */
 323               match_start = newbuffer + match_start_offset;
 324               past_end = newbuffer + past_end_offset;
 325               G_buffer = newbuffer;
 326             }
 327
 328           /* Back up to the start of the next bufferfull of the file.  */
 329           if (file_pos >= read_size)
 330             file_pos -= read_size;
 331           else
 332             {
 333               read_size = file_pos;
 334               file_pos = 0;
 335             }
 336           if (lseek (input_fd, file_pos, SEEK_SET) < 0)
 337             error (0, errno, _("%s: seek failed"), quotearg_colon (file));
 338
 339           /* Shift the pending record data right to make room for the new.
 340              The source and destination regions probably overlap.  */
 341           memmove (G_buffer + read_size, G_buffer, saved_record_size);
 342           past_end = G_buffer + read_size + saved_record_size;
 343           /* For non-regexp searches, avoid unneccessary scanning. */
 344           if (sentinel_length)
 345             match_start = G_buffer + read_size;
 346           else
 347             match_start = past_end;
 348
 349           if (safe_read (input_fd, G_buffer, read_size) != read_size)
 350             {
 351               error (0, errno, _("%s: read error"), quotearg_colon (file));
 352               return false;
 353             }
 354         }
 355       else
 356         {
 357           /* Found a match of `separator'. */
 358           if (separator_ends_record)
 359             {
 360               char *match_end = match_start + match_length;
 361
 362               /* If this match of `separator' isn't at the end of the
 363                  file, print the record. */
 364               if (!first_time || match_end != past_end)
 365                 output (match_end, past_end);
 366               past_end = match_end;
 367               first_time = false;
 368             }
 369           else
 370             {
 371               output (match_start, past_end);
 372               past_end = match_start;
 373             }
 374
 375           /* For non-regex matching, we can back up.  */
 376           if (sentinel_length > 0)
 377             match_start -= match_length - 1;
 378         }
 379     }
 380 }
 381
 382 #if DONT_UNLINK_WHILE_OPEN
 383
 384 /* FIXME-someday: remove all of this DONT_UNLINK_WHILE_OPEN junk.
 385    Using atexit like this is wrong, since it can fail
 386    when called e.g. 32 or more times.
 387    But this isn't a big deal, since the code is used only on WOE/DOS
 388    systems, and few people invoke tac on that many nonseekable files.  */
 389
 390 static const char *file_to_remove;
 391 static FILE *fp_to_close;
 392
 393 static void
 394 unlink_tempfile (void)
 395 {
 396   fclose (fp_to_close);
 397   unlink (file_to_remove);
 398 }
 399
 400 static void
 401 record_or_unlink_tempfile (char const *fn, FILE *fp)
 402 {
 403   if (!file_to_remove)
 404     {
 405       file_to_remove = fn;
 406       fp_to_close = fp;
 407       atexit (unlink_tempfile);
 408     }
 409 }
 410
 411 #else
 412
 413 static void
 414 record_or_unlink_tempfile (char const *fn, FILE *fp ATTRIBUTE_UNUSED)
 415 {
 416   unlink (fn);
 417 }
 418
 419 #endif
 420
 421 /* Copy from file descriptor INPUT_FD (corresponding to the named FILE) to
 422    a temporary file, and set *G_TMP and *G_TEMPFILE to the resulting stream
 423    and file name.  Return true if successful.  */
 424
 425 static bool
 426 copy_to_temp (FILE **g_tmp, char **g_tempfile, int input_fd, char const *file)
 427 {
 428   static char *template = NULL;
 429   static char *tempdir;
 430   char *tempfile;
 431   FILE *tmp;
 432   int fd;
 433
 434   if (template == NULL)
 435     {
 436       char const * const Template = "%s/tacXXXXXX";
 437       tempdir = getenv ("TMPDIR");
 438       if (tempdir == NULL)
 439         tempdir = DEFAULT_TMPDIR;
 440
 441       /* Subtract 2 for `%s' and add 1 for the trailing NUL byte.  */
 442       template = xmalloc (strlen (tempdir) + strlen (Template) - 2 + 1);
 443       sprintf (template, Template, tempdir);
 444     }
 445
 446   /* FIXME: there's a small window between a successful mkstemp call
 447      and the unlink that's performed by record_or_unlink_tempfile.
 448      If we're interrupted in that interval, this code fails to remove
 449      the temporary file.  On systems that define DONT_UNLINK_WHILE_OPEN,
 450      the window is much larger -- it extends to the atexit-called
 451      unlink_tempfile.
 452      FIXME: clean up upon fatal signal.  Don't block them, in case
 453      $TMPFILE is a remote file system.  */
 454
 455   tempfile = template;
 456   fd = mkstemp (template);
 457   if (fd < 0)
 458     {
 459       error (0, errno, _("cannot create temporary file %s"), quote (tempfile));
 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         freopen (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   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     freopen (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     error (EXIT_FAILURE, errno, "-");
 665   exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
 666 }