src/readlink.c

   1 /* readlink -- display value of a symbolic link.
   2    Copyright (C) 2002-2023 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 <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Dmitry V. Levin */
  18
  19 #include <config.h>
  20 #include <stdio.h>
  21 #include <getopt.h>
  22 #include <sys/types.h>
  23
  24 #include "system.h"
  25 #include "canonicalize.h"
  26 #include "areadlink.h"
  27
  28 /* The official name of this program (e.g., no 'g' prefix).  */
  29 #define PROGRAM_NAME "readlink"
  30
  31 #define AUTHORS proper_name ("Dmitry V. Levin")
  32
  33 /* If true, do not output the trailing newline.  */
  34 static bool no_newline;
  35
  36 /* If true, report error messages.  */
  37 static bool verbose;
  38
  39 static struct option const longopts[] =
  40 {
  41   {"canonicalize", no_argument, nullptr, 'f'},
  42   {"canonicalize-existing", no_argument, nullptr, 'e'},
  43   {"canonicalize-missing", no_argument, nullptr, 'm'},
  44   {"no-newline", no_argument, nullptr, 'n'},
  45   {"quiet", no_argument, nullptr, 'q'},
  46   {"silent", no_argument, nullptr, 's'},
  47   {"verbose", no_argument, nullptr, 'v'},
  48   {"zero", no_argument, nullptr, 'z'},
  49   {GETOPT_HELP_OPTION_DECL},
  50   {GETOPT_VERSION_OPTION_DECL},
  51   {nullptr, 0, nullptr, 0}
  52 };
  53
  54 void
  55 usage (int status)
  56 {
  57   if (status != EXIT_SUCCESS)
  58     emit_try_help ();
  59   else
  60     {
  61       printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
  62       fputs (_("Print value of a symbolic link or canonical file name\n\n"),
  63              stdout);
  64       fputs (_("\
  65   -f, --canonicalize            canonicalize by following every symlink in\n\
  66                                 every component of the given name recursively;\
  67 \n\
  68                                 all but the last component must exist\n\
  69   -e, --canonicalize-existing   canonicalize by following every symlink in\n\
  70                                 every component of the given name recursively,\
  71 \n\
  72                                 all components must exist\n\
  73 "), stdout);
  74       fputs (_("\
  75   -m, --canonicalize-missing    canonicalize by following every symlink in\n\
  76                                 every component of the given name recursively,\
  77 \n\
  78                                 without requirements on components existence\n\
  79   -n, --no-newline              do not output the trailing delimiter\n\
  80   -q, --quiet\n\
  81   -s, --silent                  suppress most error messages (on by default)\n\
  82   -v, --verbose                 report error messages\n\
  83   -z, --zero                    end each output line with NUL, not newline\n\
  84 "), stdout);
  85       fputs (HELP_OPTION_DESCRIPTION, stdout);
  86       fputs (VERSION_OPTION_DESCRIPTION, stdout);
  87       emit_ancillary_info (PROGRAM_NAME);
  88     }
  89   exit (status);
  90 }
  91
  92 int
  93 main (int argc, char **argv)
  94 {
  95   /* If not -1, use this method to canonicalize.  */
  96   int can_mode = -1;
  97   int status = EXIT_SUCCESS;
  98   int optc;
  99   bool use_nuls = false;
 100
 101   initialize_main (&argc, &argv);
 102   set_program_name (argv[0]);
 103   setlocale (LC_ALL, "");
 104   bindtextdomain (PACKAGE, LOCALEDIR);
 105   textdomain (PACKAGE);
 106
 107   atexit (close_stdout);
 108
 109   while ((optc = getopt_long (argc, argv, "efmnqsvz", longopts, nullptr)) != -1)
 110     {
 111       switch (optc)
 112         {
 113         case 'e':
 114           can_mode = CAN_EXISTING;
 115           break;
 116         case 'f':
 117           can_mode = CAN_ALL_BUT_LAST;
 118           break;
 119         case 'm':
 120           can_mode = CAN_MISSING;
 121           break;
 122         case 'n':
 123           no_newline = true;
 124           break;
 125         case 'q':
 126         case 's':
 127           verbose = false;
 128           break;
 129         case 'v':
 130           verbose = true;
 131           break;
 132         case 'z':
 133           use_nuls = true;
 134           break;
 135         case_GETOPT_HELP_CHAR;
 136         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
 137         default:
 138           usage (EXIT_FAILURE);
 139         }
 140     }
 141
 142   if (optind >= argc)
 143     {
 144       error (0, 0, _("missing operand"));
 145       usage (EXIT_FAILURE);
 146     }
 147
 148   if (argc - optind > 1)
 149     {
 150       if (no_newline)
 151         error (0, 0, _("ignoring --no-newline with multiple arguments"));
 152       no_newline = false;
 153     }
 154
 155   for (; optind < argc; ++optind)
 156     {
 157       char const *fname = argv[optind];
 158       char *value = (can_mode != -1
 159                      ? canonicalize_filename_mode (fname, can_mode)
 160                      : areadlink_with_size (fname, 63));
 161       if (value)
 162         {
 163           fputs (value, stdout);
 164           if (! no_newline)
 165             putchar (use_nuls ? '\0' : '\n');
 166           free (value);
 167         }
 168       else
 169         {
 170           status = EXIT_FAILURE;
 171           if (verbose)
 172             error (0, errno, "%s", quotef (fname));
 173         }
 174     }
 175
 176   return status;
 177 }