http://www.perlmonks.org?node_id=11110217

Skeeve has asked for the wisdom of the Perl Monks concerning the following question:

I'm wondering how I could create a relative symlink in perl.

Currently I'm using symlink in a perl script running in a docker container. The created link is an absolute link - for the container. On the docker host otoh this link is a broken link.

Now I'm wondering whether or not it's possible to create relative links in perl. I fear this can only be done by changing to the directory where the original file resides or by relying on a systemcall invoking ln -rs …, right?

But maybe someone here has another good idea?

s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
+.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e

Replies are listed 'Best First'.
Re: create a relative symlink
by dave_the_m (Monsignor) on Dec 16, 2019 at 08:15 UTC
    It's not clear to me what your issue is. If the target of the symlink is specified as a relative path, then then the symlink will be relative. Can you give a concrete example of your issue?

    Dave.

[reply]

      Thanks for asking, Dave.

      The issue here is, that my script is not running in the directory where the target is. Currently the linking looks something like this 

      my $newname="/home/script/data/archive/currentfile";
my $targetfile="/home/script/data/archive/infofile-2019-12-16";
symlink $targetfile, $newname;

      In order for the link to become relative I think I will have to do a chdir to the directory of $newname and make the path of $targetfile be relative to that.

      As both are in my case, in the same directory, the relative-path part is easy, but would it be different directories, it would be a bit more complicated.

      As the script is not running in the /home/script/data/archive directory, I think for symlink to create a working relative link, I need to do a chdir first. But then I need to change directory back as well.

      As the ln command has a "make a relative link" option, I thought there might be something available in perl as well. So in order not to reinvent the wheel, I'm asking…

      s$$([},&%#}/&/]+}%&{})*;#$&&s&&$^X.($'^"%]=\&(|?*{%
      +.+=%;.#_}\&"^"-+%*).}%:##%}={~=~:.")&e&&s""`$''`"e
[reply]
[d/l]
[select]
        my $newname="/home/script/data/archive/currentfile";
my $targetfile="infofile-2019-12-16";
symlink $targetfile, $newname;

        [download]
[reply]
[d/l]
        to create a working relative link, I need to do a chdir first
        That would be the easiest way. However, it seems that you simply need to calculate the relative link (relative to the folder/directory where the symlink-to-be shall reside), e.g. with Path::Tiny->relative()
        my $newname="/home/script/data/archive/currentfile";
my $targetfile="/home/script/data/archive/infofile-2019-12-16";

# untested
use Path::Tiny 'path';
my $newdir = path($newfile)->parent();
my $linktarget = path($targetfile)->relative($newdir);
print ":$linktarget:\n";
symlink $linktarget, $newname;

        [download]
[reply]
[d/l]
Re: create a relative symlink
by Anonymous Monk on Dec 18, 2019 at 03:24 UTC
    Does any operating system actually support a relative symlink?
[reply]
      Yes. In linux, you can easily create one: 
      ln -s .. parent

      [download]

      If you then move the link somewhere else, e.g. with 

      mv parent ..

      [download]

      it will now point to its new parent directory.

      map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]
[reply]
[d/l]
[select]
        Yes. In linux,

        Make that any POSIX-compatible system. A limit is the filesystem: The respective native filesystems generally support symlinks, but e.g. FAT does not.

        Alexander

        --
        Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)
[reply]

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