symlink problems with mac os

[Björn Raupach]

On 22. Oct 2017, at 14:53, Per Bothner <per@bothner.com<mailto:per@bothner.com>> wrote:

On 10/22/2017 05:00 AM, Björn Raupach wrote:
The readlink version of macOS isn’t the same as GNU/Linux one. The latter version does follow symlinks with -f. The macOS one does not support this feature.
I stumbled upon this while working on a port for MacPorts<https://www.macports.org>  Should make kawa easier to install and upgrade on macOS. (Of course it is already simple enough being a jar file and such…)

There is a Homebrew port fof Kawa which avoids the problem by patching
bin/kawa before installing it:

https://github.com/Homebrew/homebrew-core/blob/master/Formula/kawa.rb

Agreed. I would do a patch like this in MacPorts, too. Was just raising awareness of this minor issue if it was unnoticed before.


Another option is to install GNU readlink.

I considered replacing readlink -f by realpath, but as Mac OS doesn't
have readlink either, I don't see how that would help.

We could make the script more complicated, so it can work with plain readlink,
perhaps based on https://github.com/mkropat/sh-realpath/blob/master/realpath.sh .
I'm not thrilled to complicate the script that much, but it may be better
than adding a dependency.

Apache Maven does nice bash scripting to work around this issue. I am not much of a Bash programmer so I would need some time to figure this out. Here is the snippet:

## resolve links - $0 may be a link to Maven's home
PRG="$0"

# need this for relative symlinks
while [ -h "$PRG" ] ; do
  ls=`ls -ld "$PRG"`
  link=`expr "$ls" : '.*-> \(.*\)$'`
  if expr "$link" : '/.*' > /dev/null; then
    PRG="$link"
  else
    PRG="`dirname "$PRG"`/$link"
  fi
done


The reason for the readlink to handle the case that you install kawa
as a symlink for example /usr/local/bin/kawa -> /opt/kawa-3.0/bin/kawa .
I think that is useful to support - and it doesn't work without the -f.

The maven snippet above handles that case. I can link a link and still get maven to run. Would make it portable and doesn’t need any dependency.

Looking for patches? I have time to look at that and now I am curious enough to try and solve this. ;)

--
--Per Bothner
per@bothner.com<mailto:per@bothner.com>   http://per.bothner.com/