Re: [bug #24949] coreutils pwd not implementing latest POSIX features

[Eric Blake]

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According to Eric Blake on 3/23/2009 2:53 PM:
> Follow-up Comment #3, bug #24949 (project coreutils):
> 
> How about the attached patch?

To make it easier to review, this is my proposed patch to make pwd
understand -L and -P, per POSIX.  I made the choice of having the behavior
depend on POSIXLY_CORRECT, because I disagree with POSIX' choice of
mandating the -L option as the default (too many scripts expect /bin/pwd
to behave differently from pwd).

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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From 596f7e825631434335477be3370724b1702810dd Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Mon, 23 Mar 2009 14:48:19 -0600
Subject: [PATCH] pwd: support -L and -P

* src/pwd.c (longopts): New variable.
(logical_getcwd): New function.
(main): Use it.
(usage): Document new options.
* doc/coreutils.texi (pwd invocation): Likewise.
* NEWS: Likewise.
* tests/misc/pwd-option: New file.
* tests/Makefile.am (TESTS): Add test.
* THANKS: Update.
Reported by Paul D. Smith, in savannah bug 24949.
---
 NEWS                  |    6 +++
 THANKS                |    1 +
 doc/coreutils.texi    |   38 ++++++++++++++++++---
 src/pwd.c             |   86 +++++++++++++++++++++++++++++++++++++++++++++---
 tests/Makefile.am     |    1 +
 tests/misc/pwd-option |   64 ++++++++++++++++++++++++++++++++++++
 6 files changed, 184 insertions(+), 12 deletions(-)
 create mode 100755 tests/misc/pwd-option

diff --git a/NEWS b/NEWS
index 766f271..3d64d87 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,12 @@ GNU coreutils NEWS                                    -*- 
outline -*-

 * Noteworthy changes in release ?.? (????-??-??) [?]

+** New features
+
+  pwd now accepts the options --logical (-L) and --physical (-P).  For
+  compatibility with existing scripts, -P is the default behavior
+  unless POSIXLY_CORRECT is requested.
+
 ** Bug fixes

   cat once again immediately outputs data it has processed.
diff --git a/THANKS b/THANKS
index d4b2d61..665a9ef 100644
--- a/THANKS
+++ b/THANKS
@@ -437,6 +437,7 @@ Oliver Kiddle                       address@hidden
 Oskar Liljeblad                     address@hidden
 Pádraig Brady                       address@hidden
 Patrick Mauritz                     address@hidden
+Paul D. Smith                       address@hidden
 Paul Eggert                         address@hidden
 Paul Ghaleb                         address@hidden
 Paul Jarc                           address@hidden
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 04db676..55f601f 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -11872,13 +11872,39 @@ pwd invocation
 @cindex current working directory, printing
 @cindex working directory, printing

address@hidden symbolic links and @command{pwd}
address@hidden prints the fully resolved name of the current directory.
-That is, all components of the printed name will be actual directory
-names---none will be symbolic links.

-The only options are a lone @option{--help} or
address@hidden  @xref{Common options}.
address@hidden prints the name of the current directory.  Synopsis:
+
address@hidden
+pwd address@hidden@dots{}
address@hidden example
+
+The program accepts the following options.  Also see @ref{Common options}.
+
address@hidden @samp
address@hidden -L
address@hidden --logical
address@hidden -L
address@hidden --logical
+If the contents of the environment variable @env{PWD} provide an
+absolute name of the current directory with no @samp{.} or @samp{..}
+components, but possibly with symbolic links, then output those
+contents.  Otherwise, fall back to default @option{-P} handling.
+
address@hidden -P
address@hidden --physical
address@hidden -P
address@hidden --physical
+Print a fully resolved name for the current directory.  That is, all
+components of the printed name will be actual directory names---none
+will be symbolic links.
address@hidden table
+
address@hidden symbolic links and @command{pwd}
+If @option{-L} and @option{-P} are both given, the last one takes
+precedence.  If neither option is given, then this implementation uses
address@hidden as the default unless the @env{POSIXLY_CORRECT}
+environment variable is set.

 @mayConflictWithShellBuiltIn{pwd}

diff --git a/src/pwd.c b/src/pwd.c
index ac59155..21bb3d7 100644
--- a/src/pwd.c
+++ b/src/pwd.c
@@ -1,5 +1,5 @@
 /* pwd - print current directory
-   Copyright (C) 1994-1997, 1999-2008 Free Software Foundation, Inc.
+   Copyright (C) 1994-1997, 1999-2009 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
@@ -38,6 +38,15 @@ struct file_name
   char *start;
 };

+static struct option const longopts[] =
+{
+  {"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)
 {
@@ -46,11 +55,15 @@ usage (int status)
             program_name);
   else
     {
-      printf (_("Usage: %s [OPTION]\n"), program_name);
+      printf (_("Usage: %s [OPTION]...\n"), program_name);
       fputs (_("\
 Print the full filename of the current working directory.\n\
 \n\
 "), stdout);
+      fputs (_("\
+  -L, --logical   use PWD from environment, even if it contains symlinks\n\
+  -P, --physical  avoid all symlinks\n\
+"), stdout);
       fputs (HELP_OPTION_DESCRIPTION, stdout);
       fputs (VERSION_OPTION_DESCRIPTION, stdout);
       printf (USAGE_BUILTIN_WARNING, PROGRAM_NAME);
@@ -279,10 +292,43 @@ robust_getcwd (struct file_name *file_name)
     file_name_prepend (file_name, "", 0);
 }

+
+/* Return PWD from the environment if it is acceptable for 'pwd -L'
+   output, otherwise NULL.  */
+static char *
+logical_getcwd (void)
+{
+  struct stat st1;
+  struct stat st2;
+  char *wd = getenv ("PWD");
+  char *p;
+
+  /* Textual validation first.  */
+  if (!wd || wd[0] != '/')
+    return NULL;
+  p = wd;
+  while ((p = strstr (p, "/.")))
+    {
+      if (!p[2] || p[2] == '/'
+          || (p[2] == '.' && (!p[3] || p[3] == '/')))
+        return NULL;
+      p++;
+    }
+
+  /* System call validation.  */
+  if (stat (wd, &st1) == 0 && stat (".", &st2) == 0
+      && st1.st_dev == st2.st_dev && st1.st_ino == st2.st_ino)
+    return wd;
+  return NULL;
+}
+
+
 int
 main (int argc, char **argv)
 {
   char *wd;
+  /* POSIX requires a default of -L, but most scripts expect -P.  */
+  bool logical = (getenv ("POSIXLY_CORRECT") != NULL);

   initialize_main (&argc, &argv);
   set_program_name (argv[0]);
@@ -292,14 +338,42 @@ main (int argc, char **argv)

   atexit (close_stdout);

-  parse_long_options (argc, argv, PROGRAM_NAME, PACKAGE_NAME, Version,
-                     usage, AUTHORS, (char const *) NULL);
-  if (getopt_long (argc, argv, "", NULL, NULL) != -1)
-    usage (EXIT_FAILURE);
+  while (1)
+    {
+      int c = getopt_long (argc, argv, "LP", longopts, NULL);
+      if (c == -1)
+        break;
+      switch (c)
+        {
+        case 'L':
+          logical = true;
+          break;
+        case 'P':
+          logical = false;
+          break;
+
+        case_GETOPT_HELP_CHAR;
+
+       case_GETOPT_VERSION_CHAR (PROGRAM_NAME, AUTHORS);
+
+       default:
+         usage (EXIT_FAILURE);
+        }
+    }

   if (optind < argc)
     error (0, 0, _("ignoring non-option arguments"));

+  if (logical)
+    {
+      wd = logical_getcwd ();
+      if (wd)
+        {
+          puts (wd);
+          exit (EXIT_SUCCESS);
+        }
+    }
+
   wd = xgetcwd ();
   if (wd != NULL)
     {
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 3a15a87..5f150ad 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -142,6 +142,7 @@ TESTS =                                             \
   misc/join                                    \
   pr/pr-tests                                  \
   misc/df-P                                    \
+  misc/pwd-option                              \
   misc/pwd-unreadable-parent                   \
   misc/chcon-fail                              \
   misc/cut                                     \
diff --git a/tests/misc/pwd-option b/tests/misc/pwd-option
new file mode 100755
index 0000000..d6f0e41
--- /dev/null
+++ b/tests/misc/pwd-option
@@ -0,0 +1,64 @@
+#!/bin/sh
+# Ensure that pwd options work.
+
+# Copyright (C) 2009 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/>.
+
+if test "$VERBOSE" = yes; then
+  set -x
+  env -- pwd --version
+fi
+
+. $srcdir/test-lib.sh
+
+mkdir -p a/b || framework_failure
+ln -s a/b c || framework_failure
+base=`env -- pwd`
+
+# Remove any logical paths from $PWD.
+cd "$base" || framework_failure
+test "x$PWD" = "x$base" || framework_failure
+
+# Enter a logical directory.
+cd c || fail=1
+test "x$PWD" = "x$base/c" || skip_test_ "cd does not properly update \$PWD"
+
+fail=0
+env -- pwd -L > out || fail=1
+printf %s\\n "$base/c" > exp || fail=1
+
+env -- pwd --logical -P >> out || fail=1
+printf %s\\n "$base/a/b" >> exp || fail=1
+
+env -- pwd --physical >> out || fail=1
+printf %s\\n "$base/a/b" >> exp || fail=1
+
+# By default, we use -P unless POSIXLY_CORRECT.
+env -- pwd >> out || fail=1
+printf %s\\n "$base/a/b" >> exp || fail=1
+
+env -- POSIXLY_CORRECT=1 pwd >> out || fail=1
+printf %s\\n "$base/c" >> exp || fail=1
+
+# Make sure we reject bogus values, and silently fall back to -P.
+env -- PWD=$PWD/. pwd >> out || fail=1
+printf %s\\n "$base/a/b" >> exp || fail=1
+
+env -- PWD=bogus pwd >> out || fail=1
+printf %s\\n "$base/a/b" >> exp || fail=1
+
+compare out exp || fail=1
+
+Exit $fail
-- 
1.6.1.2