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.

1 files changed, 3 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 1ee2c17a8..e4472dfac 100644
--- a/NEWS
+++ b/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.