Bash – Is it possible to notify/warn that current path isn’t a valid symlink anymore

bashsymlink

Let's say we have ./a and ./b directories. Then we create a symlink using ln -s a x and entering it cd x The pwd would be x

Then in another terminal we change the x so that it pointed to b. But the first one would still return x for pwd which is not consistent anymore.

So is there a way for current terminal (bash) to alert/warn if the current path is the obsolete symlink?

Best Answer

Here's an approach which uses the fact that bash does command expansion on $PS1 to test to see if . and $PWD have the same inode in the prompt:

PS1='$([[ $(stat -Lc%i $PWD 2>/dev/null) == $(stat -c%i .) ]] || echo "\[\e[1;31m\]PWD invalid or changed \[\e[m\]")'"$PS1"

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Linux – How to make a variable symlink ? (or something similar)

For those people viewing this more recently, I've written a small FUSE filesystem called HomeFS that forwards calls to a directory relative to the calling users' home directories.

That is, if you have a user Tyler and a user Sarah with a HomeFS mountpoint at /usr/share/bigsoft/config and a relative directory of .config/bigsoft, when Tyler does ls /usr/share/bigsoft he will see the contents of /home/tyler/.config/bigsoft and Sarah will see the contents of /home/sarah/.config/bigsoft.

Primarily, this is to work around proprietary software which insists its variable files be in some 'install directory', like how some Windows software tends to work.

Shell Symlinks – Understanding Directory Symlink Traversals and Parent Directory

bash "knows" about symlinks and tracks this info when you use a symlink to enter a directory.

You can check this by doing the following in your example:

$ cd /dir2
$ cd linked
$ pwd
/dir2/linked
$ PWD='' bash -c pwd
/dir1

You need to start the bash with an empty PWD variable, otherwise it uses that trick to display the "fake" path.

Note that ls is a separate program and as such doesn't have bash's knowledge of how you arrived at the current directory, so ls .. will just show the contents of the real parent directory, not relative to the symlink you followed.

Most programs will not depend on the environment variable CWD as there are many ways of starting programs, via the bash shell is just one so it's not reliable to expect CWD to contain the correct value (try setting CWD to something wrong before doing bash -c pwd, you can see it checks the value for sanity).

Best Answer

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Linux – How to make a variable symlink ? (or something similar)

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