readlink: support multiple command line arguments

This allows efficient processing of multiple files,
while also increasing compatibility with BSD's readlink(1).
We also add the -z, --zero option to delimit output items
with the NUL character which disambiguates output in the
presence of '\n' characters.

* src/readlink.c (usage): Add the --zero description,
and also adjust the description of --no-newline accordingly.
(main): Handle the -z option and iterate over multiple arguments.
Also as in commit v8.15-24-g9d46b25 we use fputs() and putchar()
rather than printf() for performance reasons.
* doc/coreutils.texi (readlink invocation): Document the
new --zero option, adjust the --no-newline description, and
tweak the general info to indicate multiple files are supported.
* tests/readlink/multi.sh: A new test for the new functionality.
* tests/local.mk: Reference the new test.
* man/readlink.x: Adjust the summary and also reference realpath.
* NEWS: Mention the improvement.
* THANKS.in: Suggested by Aaron Davies.

NEWS

@@ -61,6 +61,9 @@ GNU coreutils NEWS                                    -*- outline -*-
 
 ** Improvements
 
+  readlink now supports multiple arguments, and a complementary
+  -z, --zero option to delimit output items with the NUL character.
+
   stat and tail now know about CEPH.  stat -f --format=%T now reports the file
   system type, and tail -f uses polling for files on CEPH file systems.
 

THANKS.in

@@ -14,6 +14,7 @@ note to the bug-report mailing list (as seen at end of e.g., cp --help).
 
 ???                                 kytek@cybercomm.net
 A Costa                             agcosta@gis.net
+Aaron Davies                        aaron.davies@gmail.com
 Aaron Hawley                        ashawley@uvm.edu
 Achim Blumensath                    blume@corona.oche.de
 Adam Jimerson                       vendion@charter.net

doc/coreutils.texi

@@ -9737,20 +9737,20 @@ Set the default SELinux security context to be used for created files.
 
 @item Readlink mode
 
-@command{readlink} outputs the value of the given symbolic link.
+@command{readlink} outputs the value of the given symbolic links.
 If @command{readlink} is invoked with an argument other than the name
 of a symbolic link, it produces no output and exits with a nonzero exit code.
 
 @item Canonicalize mode
 
-@command{readlink} outputs the absolute name of the given file which contains
+@command{readlink} outputs the absolute name of the given files which contain
 no @file{.}, @file{..} components nor any repeated separators
 (@file{/}) or symbolic links.
 
 @end table
 
 @example
-readlink [@var{option}] @var{file}
+readlink [@var{option}]@dots{} @var{file}@dots{}
 @end example
 
 By default, @command{readlink} operates in readlink mode.
@@ -9789,7 +9789,8 @@ as a directory.
 @itemx --no-newline
 @opindex -n
 @opindex --no-newline
-Do not output the trailing newline.
+Do not print the output delimiter, when a single @var{file} is specified.
+Print a warning if specified along with multiple @var{file}s.
 
 @item -s
 @itemx -q
@@ -9807,6 +9808,12 @@ Suppress most error messages.
 @opindex --verbose
 Report error messages.
 
+@item -z
+@itemx --zero
+@opindex -z
+@opindex --zero
+Separate output items with @sc{nul} characters.
+
 @end table
 
 The @command{readlink} utility first appeared in OpenBSD 2.1.

man/readlink.x

@@ -1,6 +1,6 @@
 [NAME]
-readlink \- print value of a symbolic link or canonical file name
+readlink \- print resolved symbolic links or canonical file names
 [DESCRIPTION]
 .\" Add any additional description here
 [SEE ALSO]
-readlink(2)
+readlink(2), realpath(1), realpath(3)

src/readlink.c

@@ -25,7 +25,6 @@
 #include "canonicalize.h"
 #include "error.h"
 #include "areadlink.h"
-#include "quote.h"
 
 /* The official name of this program (e.g., no 'g' prefix).  */
 #define PROGRAM_NAME "readlink"
@@ -47,6 +46,7 @@ static struct option const longopts[] =
   {"quiet", no_argument, NULL, 'q'},
   {"silent", no_argument, NULL, 's'},
   {"verbose", no_argument, NULL, 'v'},
+  {"zero", no_argument, NULL, 'z'},
   {GETOPT_HELP_OPTION_DECL},
   {GETOPT_VERSION_OPTION_DECL},
   {NULL, 0, NULL, 0}
@@ -59,7 +59,7 @@ usage (int status)
     emit_try_help ();
   else
     {
-      printf (_("Usage: %s [OPTION]... FILE\n"), program_name);
+      printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
       fputs (_("Print value of a symbolic link or canonical file name\n\n"),
              stdout);
       fputs (_("\
@@ -77,10 +77,11 @@ usage (int status)
                                 every component of the given name recursively,\
 \n\
                                 without requirements on components existence\n\
-  -n, --no-newline              do not output the trailing newline\n\
+  -n, --no-newline              do not output the trailing delimiter\n\
   -q, --quiet,\n\
   -s, --silent                  suppress most error messages\n\
   -v, --verbose                 report error messages\n\
+  -z, --zero                    separate output with NUL rather than newline\n\
 "), stdout);
       fputs (HELP_OPTION_DESCRIPTION, stdout);
       fputs (VERSION_OPTION_DESCRIPTION, stdout);
@@ -94,14 +95,9 @@ main (int argc, char **argv)
 {
   /* If not -1, use this method to canonicalize.  */
   int can_mode = -1;
-
-  /* File name to canonicalize.  */
-  const char *fname;
-
-  /* Result of canonicalize.  */
-  char *value;
-
+  int status = EXIT_SUCCESS;
   int optc;
+  bool use_nuls = false;
 
   initialize_main (&argc, &argv);
   set_program_name (argv[0]);
@@ -111,7 +107,7 @@ main (int argc, char **argv)
 
   atexit (close_stdout);
 
-  while ((optc = getopt_long (argc, argv, "efmnqsv", longopts, NULL)) != -1)
+  while ((optc = getopt_long (argc, argv, "efmnqsvz", longopts, NULL)) != -1)
     {
       switch (optc)
         {
@@ -134,6 +130,9 @@ main (int argc, char **argv)
         case 'v':
           verbose = true;
           break;
+        case 'z':
+          use_nuls = true;
+          break;
         case_GETOPT_HELP_CHAR;
         case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
         default:
@@ -147,26 +146,33 @@ main (int argc, char **argv)
       usage (EXIT_FAILURE);
     }
 
-  fname = argv[optind++];
-
-  if (optind < argc)
+  if (argc - optind > 1)
     {
-      error (0, 0, _("extra operand %s"), quote (argv[optind]));
-      usage (EXIT_FAILURE);
+      if (no_newline)
+        error (0, 0, _("ignoring --no-newline with multiple arguments"));
+      no_newline = false;
     }
 
-  value = (can_mode != -1
-           ? canonicalize_filename_mode (fname, can_mode)
-           : areadlink_with_size (fname, 63));
-  if (value)
+  for (; optind < argc; ++optind)
     {
-      printf ("%s%s", value, (no_newline ? "" : "\n"));
-      free (value);
-      return EXIT_SUCCESS;
+      const char *fname = argv[optind];
+      char *value = (can_mode != -1
+                     ? canonicalize_filename_mode (fname, can_mode)
+                     : areadlink_with_size (fname, 63));
+      if (value)
+        {
+          fputs (value, stdout);
+          if (! no_newline)
+            putchar (use_nuls ? '\0' : '\n');
+          free (value);
+        }
+      else
+        {
+          status = EXIT_FAILURE;
+          if (verbose)
+            error (0, errno, "%s", fname);
+        }
     }
 
-  if (verbose)
-    error (EXIT_FAILURE, errno, "%s", fname);
-
-  return EXIT_FAILURE;
+  return status;
 }

tests/local.mk

@@ -602,6 +602,7 @@ all_tests =					\
   tests/readlink/can-e.sh			\
   tests/readlink/can-f.sh			\
   tests/readlink/can-m.sh			\
+  tests/readlink/multi.sh			\
   tests/readlink/rl-1.sh			\
   tests/rmdir/fail-perm.sh			\
   tests/rmdir/ignore.sh				\

tests/readlink/multi.sh

@@ -0,0 +1,46 @@
+#!/bin/sh
+# test multiple argument handling.
+
+# Copyright (C) 2012 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ readlink
+
+touch regfile || framework_failure_
+ln -s regfile link1 || framework_failure_
+
+readlink link1 link1 || fail=1
+readlink link1 link2 && fail=1
+readlink link1 link2 link1 && fail=1
+readlink -m link1 link2 || fail=1
+
+printf '/1\0/1\0' > exp || framework_failure_
+readlink -m --zero /1 /1 > out || fail=1
+compare exp out || fail=1
+
+# The largely redundant --no-newline option is ignored with multiple args.
+# Note BSD's readlink suppresses all delimiters, even with multiple args,
+# but that functionality was not thought useful.
+readlink -n -m --zero /1 /1 > out || fail=1
+compare exp out || fail=1
+
+# Note the edge case that the last xargs run may not have a delimiter
+rm out || framework_failure_
+printf '/1\0/1\0/1' > exp || framework_failure_
+printf '/1 /1 /1' | xargs -n2 readlink -n -m --zero >> out || fail=1
+compare exp out || fail=1
+
+Exit $fail