Re: readlink(1) of more than one file?

[Pádraig Brady]

On 12/16/2012 12:29 AM, Pádraig Brady wrote:
> On 12/15/2012 11:10 PM, Dmitry V. Levin wrote:
> > On Sat, Dec 15, 2012 at 03:40:36PM +0000, Pádraig Brady wrote:
> > > On 12/15/2012 03:09 PM, Bernhard Voelker wrote:
> > [...]
> > > > And finally: -n is pretty much useless now with multiple arguments,
> > > > because the output is just concatenated together:
> > > >
> > > >    $ src/readlink --no /user /user
> > > >    homehome
> > >
> > > > Wouldn't it be better to allow -n only for single-argument calls,
> > > > or use a blank " " as delimiter between the output for multiple
> > > > args, or warn?
> > >
> > > Since -n is a largely redundant option anyway,
> > > I was just keeping it around for compat reasons.
> > > BSD operates like above, so why diverge?
> >
> > If BSD readlink -n does something totally useless, it's not a reason
> > to follow and introduce that useless behaviour in GNU readlink.
> >
> > I've tried to construct an example where readlink -n with multiple
> > arguments could be used harmlessly, and the only case I have so far
> > is when readlink's output does not matter (e.g. grep -q ^.) or discarded
> > completely.
> >
> > So, please do not add multiple arguments support to readlink -n unless
> > you can also add a usage example for that feature.
>
> Ok fair enough.
> I'll adjust to that -n suppresses only the trailing delimiter.

Pushing with this adjustment.

thanks,
Pádraig.

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index d393063..0646f82 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -9789,7 +9789,8 @@ as a directory.
 @itemx --no-newline
 @opindex -n
 @opindex --no-newline
-Do not print the output delimiter.
+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
diff --git a/src/readlink.c b/src/readlink.c
index de8211f..ff7d67f 100644
--- a/src/readlink.c
+++ b/src/readlink.c
@@ -77,7 +77,7 @@ usage (int status)
                                 every component of the given name recursively,\
 \n\
                                 without requirements on components existence\n\
-  -n, --no-newline              do not output a delimiter after each item\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\
@@ -146,6 +146,13 @@ main (int argc, char **argv)
       usage (EXIT_FAILURE);
     }

+  if (argc - optind > 1)
+    {
+      if (no_newline)
+        error (0, 0, _("ignoring --no-newline with multiple arguments"));
+      no_newline = false;
+    }
+
   for (; optind < argc; ++optind)
     {
       const char *fname = argv[optind];
diff --git a/tests/readlink/multi.sh b/tests/readlink/multi.sh
index 9f22791..9a853e1 100755
--- a/tests/readlink/multi.sh
+++ b/tests/readlink/multi.sh
@@ -27,16 +27,20 @@ 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_
+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 kept around for mainly compatibility reasons,
-# so we behave like BSD here and don't output
-# delimiters, even if handling multiple arguments.
-printf "/1/1" > exp || framework_failure_
+# 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

+# Noting 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