Hi Eric,
You said:
> Among other things, I can see the following changes that coreutils
> will need to make to become compliant, or else we need to push back on
> the POSIX folks if we have strong reasons to complain that their
> specification will break things:
>
> POSIX wants 'readlink non-symlink' to output a diagnostic; that is, it
> looks like POSIX wants us to behave like '-v' is enabled by default
> (our current behavior of -q by default will be non-compliant).
I have attached a patch that I think is correct for readlink.
It is a bit more complex than just behaving the same as 'readlink -v'
previously would. This is because the behavior of non-POSIX
options. Here are some commands:
$ touch file
$ ln -s symlink file
# Example 1
$ readlink -v file
readlink: file: Invalid argument
# Example 2
$ readlink -v -f file
/home/collin/file
If 'readlink -v' where 'POSIXLY_CORRECT=1 readlink' then example 1 would
conform. I think that example 2 would violate POSIX.
So, when POSIXLY_CORRECT is enabled we can call 'readlink', check for
errors, and then canonicalize if it is successful.
Collin
>From 49d32775db13eb3f272853eb1c7124fff17b93f8 Mon Sep 17 00:00:00 2001
Message-ID: <49d32775db13eb3f272853eb1c7124fff17b93f8.1754194901.git.collin.fu...@gmail.com>
From: Collin Funk <collin.fu...@gmail.com>
Date: Sat, 2 Aug 2025 20:51:30 -0700
Subject: [PATCH] readlink: emit errors when POSIXLY_CORRECT is set
* src/readlink.c (main): Set verbose if the POSIXLY_CORRECT environment
variable is set. Check if the file is a symbolic link if POSIXLY_CORRECT
is set.
* tests/readlink/readlink-posix.sh: New file.
* tests/local.mk (all_tests): Add it.
* NEWS: Mention the change.
* doc/coreutils.texi (readlink invocation): Document the behavior of
POSIXLY_CORRECT.
---
NEWS | 6 ++++
doc/coreutils.texi | 5 ++++
src/readlink.c | 24 ++++++++++++++--
tests/local.mk | 1 +
tests/readlink/readlink-posix.sh | 48 ++++++++++++++++++++++++++++++++
5 files changed, 81 insertions(+), 3 deletions(-)
create mode 100755 tests/readlink/readlink-posix.sh
diff --git a/NEWS b/NEWS
index 110e688b1..e79067bb4 100644
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,12 @@ GNU coreutils NEWS -*- outline -*-
'factor' is now much faster at identifying large prime numbers,
and significantly faster on composite numbers greater than 2^128.
+** New Features
+
+ readlink will print a diagnostic message to standard error and exit
+ with a non-zero status when given a file that is not a symbolic link
+ if the POSIXLY_CORRECT environment variable is defined.
+
** Bug fixes
cksum was not compilable by Apple LLVM 10.0.0 x86-64, which
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 40ecf3126..15a231bc3 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -11474,6 +11474,11 @@ @node readlink invocation
@end table
+@vindex POSIXLY_CORRECT
+If the @env{POSIXLY_CORRECT} environment variable is set and
+@var{file} is not a symbolic link, @command{readlink} will emit a
+diagnostic message to standard error and exit with a nonzero status.
+
The @command{readlink} utility first appeared in OpenBSD 2.1.
The @command{realpath} command without options, operates like
diff --git a/src/readlink.c b/src/readlink.c
index 44def1dbb..4586e5820 100644
--- a/src/readlink.c
+++ b/src/readlink.c
@@ -97,6 +97,7 @@ main (int argc, char **argv)
int status = EXIT_SUCCESS;
int optc;
bool use_nuls = false;
+ bool posixly_correct = (getenv ("POSIXLY_CORRECT") != nullptr);
initialize_main (&argc, &argv);
set_program_name (argv[0]);
@@ -152,12 +153,29 @@ main (int argc, char **argv)
no_newline = false;
}
+ /* POSIX requires a diagnostic message written to standard error and a
+ non-zero exit status when given a file that is not a symbolic link. */
+ if (posixly_correct)
+ verbose = true;
+
for (; optind < argc; ++optind)
{
char const *fname = argv[optind];
- char *value = (can_mode != -1
- ? canonicalize_filename_mode (fname, can_mode)
- : areadlink_with_size (fname, 63));
+ char *value;
+
+ if (! posixly_correct)
+ value = (can_mode != -1
+ ? canonicalize_filename_mode (fname, can_mode)
+ : areadlink_with_size (fname, 63));
+ else
+ {
+ /* We have to check if the file is a symbolic link before
+ canonicalizing. */
+ value = areadlink_with_size (fname, 63);
+ if (value && can_mode != -1)
+ value = canonicalize_filename_mode (value, can_mode);
+ }
+
if (value)
{
fputs (value, stdout);
diff --git a/tests/local.mk b/tests/local.mk
index 6b527f108..7364ec89f 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -365,6 +365,7 @@ all_tests = \
tests/printf/printf-quote.sh \
tests/pwd/pwd-long.sh \
tests/readlink/readlink-fp-loop.sh \
+ tests/readlink/readlink-posix.sh \
tests/readlink/readlink-root.sh \
tests/misc/realpath.sh \
tests/runcon/runcon-compute.sh \
diff --git a/tests/readlink/readlink-posix.sh b/tests/readlink/readlink-posix.sh
new file mode 100755
index 000000000..a301545cf
--- /dev/null
+++ b/tests/readlink/readlink-posix.sh
@@ -0,0 +1,48 @@
+#!/bin/sh
+# Test readlink with POSIXLY_CORRECT defined.
+
+# Copyright (C) 2025 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 <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ readlink
+
+touch file || framework_failure_
+ln -s file link1 || framework_failure_
+
+# POSIX requires a diagnostic error and non-zero exit status if the file is not
+# a symbolic link.
+cat <<\EOF > exp || framework_failure_
+readlink: file: Invalid argument
+EOF
+returns_ 1 env POSIXLY_CORRECT=1 readlink file 2>err || fail=1
+compare exp err || fail=1
+returns_ 1 env POSIXLY_CORRECT=1 readlink -f file 2>err || fail=1
+compare exp err || fail=1
+returns_ 1 env POSIXLY_CORRECT=1 readlink -e file 2>err || fail=1
+compare exp err || fail=1
+returns_ 1 env POSIXLY_CORRECT=1 readlink -m file 2>err || fail=1
+
+# Check on a symbolic link.
+cat <<\EOF > exp || framework_failure_
+file
+EOF
+POSIXLY_CORRECT=1 readlink link1 >out || fail=1
+compare exp out || fail=1
+POSIXLY_CORRECT=1 readlink -f link1 || fail=1
+POSIXLY_CORRECT=1 readlink -e link1 || fail=1
+POSIXLY_CORRECT=1 readlink -m link1 || fail=1
+
+Exit $fail
--
2.50.1
