realpath: a new program to print the resolved path

This program is compatible with other realpath(1)
implementations, and also incorporates relpath like support,
through the --relative options.  The relpath support
was suggested by Peng Yu, who also provided an initial
implemenation of that functionality.

* AUTHORS: Add my name.
* NEWS: Mention the new command.
* README: Likewise.
* doc/coreutils.texi (realpath invocation): Add realpath info.
* man/Makefile.am (realpath.1): Add dependency.
* man/realpath.x: New template.
* man/.gitignore: Ignore generated man page.
* po/POTFILES.in: Add src/realpath.c.
* src/.gitignore: Exclude realpath.
* src/Makefile.am (EXTRA_PROGRAMS): Add realpath.
* src/realpath.c: New file.
* scripts/git-hooks/commit-msg: Add realpath to the list of prefixes.
* tests/Makefile.am (TESTS): Add misc/realpath.
* tests/misc/realpath: New file.

3 files changed, 333 insertions, 0 deletions

diff --git a/src/.gitignore b/src/.gitignore
index d25a8e57b..9c4c9b717 100644
--- a/src/.gitignore
+++ b/src/.gitignore
@@ -68,6 +68,7 @@ printf
 ptx
 pwd
 readlink
+realpath
 rm
 rmdir
 runcon
diff --git a/src/Makefile.am b/src/Makefile.am
index 6e0b3ae2d..db3159f7d 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -97,6 +97,7 @@ EXTRA_PROGRAMS = \
   ptx		\
   pwd		\
   readlink	\
+  realpath	\
   rm		\
   rmdir		\
   runcon	\
@@ -248,6 +249,7 @@ printf_LDADD = $(LDADD)
 ptx_LDADD = $(LDADD)
 pwd_LDADD = $(LDADD)
 readlink_LDADD = $(LDADD)
+realpath_LDADD = $(LDADD)
 rm_LDADD = $(LDADD)
 rmdir_LDADD = $(LDADD)
 runcon_LDADD = $(LDADD)
@@ -373,6 +375,7 @@ du_LDADD += $(LIBICONV)
 getlimits_LDADD += $(LIBICONV)
 printf_LDADD += $(LIBICONV)
 ptx_LDADD += $(LIBICONV)
+realpath_LDADD += $(LIBICONV)
 split_LDADD += $(LIBICONV)
 stdbuf_LDADD += $(LIBICONV)
 timeout_LDADD += $(LIBICONV)
diff --git a/src/realpath.c b/src/realpath.c
new file mode 100644
index 000000000..cb0ef2f1f
--- /dev/null
+++ b/src/realpath.c
@@ -0,0 +1,329 @@
+/* realpath - print the resolved path
+   Copyright (C) 2011-2012 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/>.  */
+
+/* Written by Pádraig Brady.  */
+
+#include <config.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <sys/types.h>
+
+#include "system.h"
+#include "canonicalize.h"
+#include "error.h"
+#include "quote.h"
+
+/* The official name of this program (e.g., no `g' prefix).  */
+#define PROGRAM_NAME "realpath"
+
+#define AUTHORS proper_name_utf8 ("Padraig Brady", "P\303\241draig Brady")
+
+enum
+{
+  RELATIVE_TO_OPTION = CHAR_MAX + 1,
+  RELATIVE_BASE_OPTION
+};
+
+static bool verbose = true;
+static bool logical;
+static bool use_nuls;
+static const char *can_relative_to;
+static const char *can_relative_base;
+
+static struct option const longopts[] =
+{
+  {"canonicalize-existing", no_argument, NULL, 'e'},
+  {"canonicalize-missing", no_argument, NULL, 'm'},
+  {"relative-to", required_argument, NULL, RELATIVE_TO_OPTION},
+  {"relative-base", required_argument, NULL, RELATIVE_BASE_OPTION},
+  {"quiet", no_argument, NULL, 'q'},
+  {"strip", no_argument, NULL, 's' /* FIXME: deprecate in 2013 or so */},
+  {"no-symlinks", no_argument, NULL, 's'},
+  {"zero", no_argument, NULL, 'z'},
+  {"logical", no_argument, NULL, 'L'},
+  {"physical", no_argument, NULL, 'P'},
+  {GETOPT_HELP_OPTION_DECL},
+  {GETOPT_VERSION_OPTION_DECL},
+  {NULL, 0, NULL, 0}
+};
+
+void
+usage (int status)
+{
+  if (status != EXIT_SUCCESS)
+    fprintf (stderr, _("Try `%s --help' for more information.\n"),
+             program_name);
+  else
+    {
+      printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
+      fputs (_("\
+Print the resolved absolute file name;\n\
+all but the last component must exist\n\
+\n\
+"), stdout);
+      fputs (_("\
+  -e, --canonicalize-existing  all components of the path must exist\n\
+  -m, --canonicalize-missing   no components of the path need exist\n\
+  -L, --logical                resolve `..' components before symlinks\n\
+  -P, --physical               resolve symlinks as encountered (default)\n\
+  -q, --quiet                  suppress most error messages\n\
+      --relative-to=FILE       print the resolved path relative to FILE\n\
+      --relative-base=FILE     print absolute paths unless paths below FILE\n\
+  -s, --strip, --no-symlinks   don't expand symlinks\n\
+  -z, --zero                   separate output with NUL rather than newline\n\
+\n\
+"), stdout);
+      fputs (HELP_OPTION_DESCRIPTION, stdout);
+      fputs (VERSION_OPTION_DESCRIPTION, stdout);
+      emit_ancillary_info ();
+    }
+  exit (status);
+}
+
+/* A wrapper around canonicalize_filename_mode(),
+   to call it twice when in LOGICAL mode.  */
+static char *
+realpath_canon (const char *fname, int can_mode)
+{
+  char *can_fname = canonicalize_filename_mode (fname, can_mode);
+  if (logical && can_fname)  /* canonicalize again to resolve symlinks.  */
+    {
+      can_mode &= ~CAN_NOLINKS;
+      char *can_fname2 = canonicalize_filename_mode (can_fname, can_mode);
+      free (can_fname);
+      return can_fname2;
+    }
+  return can_fname;
+}
+
+/* Test whether prefix is parent or match of path.  */
+static bool _GL_ATTRIBUTE_PURE
+path_prefix (const char *prefix, const char *path)
+{
+  while (*prefix && *path)
+    {
+      if (*prefix != *path)
+        break;
+      prefix++;
+      path++;
+    }
+  return (!*prefix && (*path == '/' || !*path));
+}
+
+/* Return the length of the longest common prefix
+   of PATH1 and PATH2, ensuring only full path components
+   are matched.  Return 0 on no match.  */
+static int _GL_ATTRIBUTE_PURE
+path_common_prefix (const char *path1, const char *path2)
+{
+  int i = 0;
+  int ret = 0;
+
+  while (*path1 && *path2)
+    {
+      if (*path1 != *path2)
+        break;
+      if (*path1 == '/')
+        ret = i;
+      path1++;
+      path2++;
+      i++;
+    }
+
+  if (!*path1 && !*path2)
+    ret = i;
+  if (!*path1 && *path2 == '/')
+    ret = i;
+  if (!*path2 && *path1 == '/')
+    ret = i;
+
+  return ret;
+}
+
+/* Output the relative representation if requested.  */
+static bool
+relpath (const char *can_fname)
+{
+  if (can_relative_to)
+    {
+      /* Enforce --relative-base.  */
+      if (can_relative_base)
+        {
+          if (!path_prefix (can_relative_base, can_fname)
+              || !path_prefix (can_relative_base, can_relative_to))
+            return false;
+        }
+
+      /* Skip the prefix common to --relative-to and path.  */
+      int common_index = path_common_prefix (can_relative_to, can_fname);
+      const char *relto_suffix = can_relative_to + common_index;
+      const char *fname_suffix = can_fname + common_index;
+
+      /* Replace remaining components of --relative-to with '..', to get
+         to a common directory.  Then output the remainder of fname.  */
+      if (*relto_suffix)
+        {
+          ++relto_suffix;
+          printf ("%s", "..");
+          for (; *relto_suffix; ++relto_suffix)
+            {
+              if (*relto_suffix == '/')
+                printf ("%s", "/..");
+            }
+
+          printf ("%s", fname_suffix);
+        }
+      else
+        {
+          if (*fname_suffix)
+            printf ("%s", ++fname_suffix);
+          else
+            printf ("%c", '.');
+        }
+
+      putchar (use_nuls ? '\0' : '\n');
+
+      return true;
+    }
+
+  return false;
+}
+
+static bool
+isdir (const char *path)
+{
+  struct stat sb;
+  if (stat (path, &sb) != 0)
+    error (EXIT_FAILURE, errno, _("cannot stat %s"), quote (path));
+  return S_ISDIR (sb.st_mode);
+}
+
+static bool
+process_path (const char *fname, int can_mode)
+{
+  char *can_fname = realpath_canon (fname, can_mode);
+  if (!can_fname)
+    {
+      if (verbose)
+        error (0, errno, "%s", quote (fname));
+      return false;
+    }
+
+  if (!relpath (can_fname))
+    printf ("%s%c", can_fname, (use_nuls ? '\0' : '\n'));
+
+  free (can_fname);
+
+  return true;
+}
+
+int
+main (int argc, char **argv)
+{
+  bool ok = true;
+  int can_mode = CAN_ALL_BUT_LAST;
+  const char *relative_to = NULL;
+  const char *relative_base = NULL;
+
+  initialize_main (&argc, &argv);
+  set_program_name (argv[0]);
+  setlocale (LC_ALL, "");
+  bindtextdomain (PACKAGE, LOCALEDIR);
+  textdomain (PACKAGE);
+
+  atexit (close_stdout);
+
+  while (1)
+    {
+      int c = getopt_long (argc, argv, "eLmPqsz", longopts, NULL);
+      if (c == -1)
+        break;
+      switch (c)
+        {
+        case 'e':
+          can_mode &= ~CAN_MODE_MASK;
+          can_mode |= CAN_EXISTING;
+          break;
+        case 'm':
+          can_mode &= ~CAN_MODE_MASK;
+          can_mode |= CAN_MISSING;
+          break;
+        case 'L':
+          can_mode |= CAN_NOLINKS;
+          logical = true;
+          break;
+        case 's':
+          can_mode |= CAN_NOLINKS;
+          logical = false;
+          break;
+        case 'P':
+          can_mode &= ~CAN_NOLINKS;
+          logical = false;
+          break;
+        case 'q':
+          verbose = false;
+          break;
+        case 'z':
+          use_nuls = true;
+          break;
+        case RELATIVE_TO_OPTION:
+          relative_to = optarg;
+          break;
+        case RELATIVE_BASE_OPTION:
+          relative_base = optarg;
+          break;
+        case_GETOPT_HELP_CHAR;
+        case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
+        default:
+          usage (EXIT_FAILURE);
+        }
+    }
+
+  if (optind >= argc)
+    {
+      error (0, 0, _("missing operand"));
+      usage (EXIT_FAILURE);
+    }
+
+  if (relative_base && !relative_to)
+    {
+      error (0, 0, _("--relative-base requires --relative-to"));
+      usage (EXIT_FAILURE);
+    }
+
+  bool need_dir = (can_mode & CAN_MODE_MASK) == CAN_EXISTING;
+  if (relative_to)
+    {
+      can_relative_to = realpath_canon (relative_to, can_mode);
+      if (!can_relative_to)
+        error (EXIT_FAILURE, errno, "%s", quote (relative_to));
+      if (need_dir && !isdir (can_relative_to))
+        error (EXIT_FAILURE, ENOTDIR, "%s", quote (relative_to));
+    }
+  if (relative_base)
+    {
+      can_relative_base = realpath_canon (relative_base, can_mode);
+      if (!can_relative_base)
+        error (EXIT_FAILURE, errno, "%s", quote (relative_base));
+      if (need_dir && !isdir (can_relative_base))
+        error (EXIT_FAILURE, ENOTDIR, "%s", quote (relative_base));
+    }
+
+  for (; optind < argc; ++optind)
+    ok &= process_path (argv[optind], can_mode);
+
+  exit (ok ? EXIT_SUCCESS : EXIT_FAILURE);
+}