Environment variables in symbolic links

Question

Can we use $HOME or other environment variable in symbolic links?

I know about using relative paths ../../.config but sometimes are to many ../ :) something like ~/.config would be more comfortable, or use of $HOME.

Edit:

habbie 's answer with psmears 's comment is the answer, sorry my question was incomplete.

While (as other answers show) you can use environment variables when creating symbolic links (as with any shell command!), you can't actually have environment variable (or '~') references in the symlink itself

Answer 1

Symbolic links are handled by the kernel, and the kernel does not care about environment variables. So, no.

Answer 2

Even though the symbolic links are resolved by the kernel, you could still do a LD_PRELOAD trick, wrapping all libc functions that take pathnames and expand any $XYZ components in the string returned by 'readlink' (parameter expansion). Then feed the expanded path to the wrapped function. You have to escape the target path from shell expansion when creating the link, as jaztik suggests.

As the injected library has full access to the users' environment, this will fulfill all expectations of the OP.

Answer 3

yes. no problem. actually you won't actually be using the $HOME variable in your link, so it won't work with smart solutions for groups of users for example. The variable is translated by the shell when executing the command, and the content of the variable is used in the link.

ln -s ~/test /tmp/test 

is expaned to

/<path>/<to>/home/test -> /tmp/test

Ah. and only the environment variables of the person calling ln will work. You can't store other peoples environment variables in the link. The variables are expanded before calling the command.

Answer 4

If you don't want to expand the variable in the link you can put single quotes around it,

ln -s '$HOME/file/or/folder' newname

This would give,

newname -> $HOME/file/or/folder

rather than have it expand to your locally set $HOME. As described in other answers it will not expand it at all. So you can eg use it to symlink to a file inside the literal $HOME folder.

[Note this is system dependent - not all systems support variant symlinks]

Answer 5

The closest I've been able to come is using a FUSE filesystem. It's pretty simple to use fusepy to write a custom passthrough filesystem, which can read environment variables when determining what real file to give. Of course, it only gets the environment variables of the process which mounted the passthrough system, so it's not as useful as it could be.

Answer 6

Yes you can.

ln -s $HOME/file/or/folder newname

You can set your own variables and use them, too. Add in your .bashrc (or .bash_profile):

export $MYPATH=/your/path