Shell Scripting – How to Get Relative Links Between Two Paths

filesshellsymlinkzsh

Say I have two paths: <source_path> and <target_path>. I would like my shell (zsh) to automatically find out if there is a way to represent <target_path> from <source_path> as a relative path.

E.g. Let's assume

<source_path> is /foo/bar/something
<target_path> is /foo/hello/world

The result would be ../../hello/world

Why I need this:

I need like to create a symbolic link from <source_path> to <target_path> using a relative symbolic link whenever possible, since otherwise our samba server does not show the file properly when I access these files on the network from Windows (I am not the sys admin, and don't have control over this setting)

Assuming that <target_path> and <source_path> are absolute paths, the following creates a symbolic link pointing to an absolute path.

ln -s <target_path> <source_path>

so it does not work for my needs. I need to do this for hundreds of files, so I can't just manually fix it.

Any shell built-ins that take care of this?

Best Answer

You could use the symlinks command to convert absolute paths to relative:

/tmp$ mkdir -p 1/{a,b,c} 2
/tmp$ cd 2
/tmp/2$ ln -s /tmp/1/* .
/tmp/2$ ls -l
total 0
lrwxrwxrwx 1 stephane stephane 8 Jul 31 16:32 a -> /tmp/1/a/
lrwxrwxrwx 1 stephane stephane 8 Jul 31 16:32 b -> /tmp/1/b/
lrwxrwxrwx 1 stephane stephane 8 Jul 31 16:32 c -> /tmp/1/c/

We've got absolute links, let's convert them to relative:

/tmp/2$ symlinks -cr .
absolute: /tmp/2/a -> /tmp/1/a
changed:  /tmp/2/a -> ../1/a
absolute: /tmp/2/b -> /tmp/1/b
changed:  /tmp/2/b -> ../1/b
absolute: /tmp/2/c -> /tmp/1/c
changed:  /tmp/2/c -> ../1/c
/tmp/2$ ls -l
total 0
lrwxrwxrwx 1 stephane stephane 6 Jul 31 16:32 a -> ../1/a/
lrwxrwxrwx 1 stephane stephane 6 Jul 31 16:32 b -> ../1/b/
lrwxrwxrwx 1 stephane stephane 6 Jul 31 16:32 c -> ../1/c/

References

symlinks man page

Related Solutions

Bash Symlink – Using ‘ln -s’ with a Path Relative to PWD

The easiest way to link to the current directory as an absolute path, without typing the whole path string would be

ln -s "$(pwd)/foo" ~/bin/foo_link

The target (first) argument for the ln -s command works relative to the symbolic link's location, not your current directory. It helps to know that, essentially, the created symlink (the second argument) simply holds the text you provide for the first argument.

Therefore, if you do the following:

cd some_directory
ln -s foo foo_link

and then move that link around

mv foo_link ../some_other_directory
ls -l ../some_other_directory

you will see that foo_link tries to point to foo in the directory it is residing in. This also works with symbolic links pointing to relative paths. If you do the following:

ln -s ../foo yet_another_link

and then move yet_another_link to another directory and check where it points to, you'll see that it always points to ../foo. This is the intended behaviour, since many times symbolic links might be part of a directory structure that can reside in various absolute paths.

In your case, when you create the link by typing

ln -s foo ~/bin/foo_link

foo_link just holds a link to foo, relative to its location. Putting $(pwd) in front of the target argument's name simply adds the current working directory's absolute path, so that the link is created with an absolute target.

Symlink – How to Find All Symbolic Links in a Directory

You can find all the symbolic links using:

find / -type l

you might want to run this as root in order to get to every place on the disc.

You can expand these using readlink -f to get the full path of the link and you should be able to grep the output against the target directory that you are considering for deletion:

find / -type l -exec readlink -f {} + | grep -F /dir2

Using find / -type l -printf '%l\n' doesn't work as you get relative links like ../tmp/xyz which might be pointing to your target dir, but are not matched because they are not fully expanded.