How do I cd up and down again with symlinks in bash?

Question

Structure:

/base/
   +- somedir/
   +- symlink/  -> /some_other_dir

This command (in addition to my Makefiles) fails:

cd /base/symlink
ls ../somedir

Bash complains that ../somedir does not exist. Likewise, my makefiles in some_other_dir that reference ../somedir fail. However, cd .. works just as expected. Can I have my shell act with regards to the logical structure?

Answer 1

.. is a directory entry in the current directory. It is a hardlink to the directory one level up. /base/symlink/.. is actually the same file as /some_other_dir/.., and it is / (unless some_other_dir is itself also a symlink to somewhere else).

In most shells, cd treats .. specially, that is instead of treating it as the .. directory entry, occurrences of .. are interpreted by cd (and not by the system's pathname resolution) as removing one level of directory.

As an example, in cd a/b/.., the shell does a chdir("a") instead of doing a chdir("a/b/.."). To get the latter, you need to do cd -P a/b/...

It's important to realise that it only applies to cd (and only in some shells), (IMO, a misfeature), not to ls or vi or anything else (unless that anything else is a script written with those shells).

In those shells where cd does that logical interpretation of .., the pwd builtin and the $PWD variable contain the logical current directory instead of the real (physical) one, that is one with possibly symlink directory components. Similarly, you can use pwd -P to get the physical working directory.

Now, if you want to do

cd /A/b
anything-but-cd ../c

And actually mean:

anything-but-cd /A/c

Regardless of whether /A/b was a symlink or not, you could do instead:

anything-but-cd "$(dirname -- "$PWD")/c"

or

anything-but-cd "${PWD%/*}/c"