Change the target of a symlink with PHP

Question

How can I change the target of a symlink with PHP? Thanks.

Ajaajaccio

Answer 1

You can delete the existing link using unlink function and recreate the link to the new target using the symlink function.

symlink($target, $link);
.
.
unlink($link);
symlink($new_target, $link);

You need to do error checking for each of these.

Thea

+1 - this is much better than writing the shell stuff yourself. – Mechelle

okay, i was just seeing if there was a way around having to unlink and then recreate the symlink. thanks! – Ajaajaccio

This means that the link is unavailable for a (short) time... Dangerous :-( – Knighthead

Answer 2

PHP can execute shell commands using shell_exec or the backtick operator.

Hence:

<?php
`rm thelink`;
`ln -s /path/to/new/place ./thelink`;

This will be run as the user which is running the Apache server, so you might need to keep that in mind.

Mechelle

Shell commands should be avoided when there are built-in alternatives. – Kippar

Replace ln -s with ln -sf (and remove rm) and this solution becomes better than the accepted solution, as it atomically (on linux/unix) replaces the target of the link, with no interruption. As it seems there is no PHP function/option to do that (symlink() has no force option). – Knighthead

Answer 3

To do this atomically, without the risk of deleting the original symlink and failing to create the new one, you should use the ln system command like so:

system(
    'ln --symbolic --force --no-dereference ' .
        escapeshellarg($new_target) . ' ' .
        escapeshellarg($link),
    $relinked
);
if (0 === $relinked) {
    # success
}
else {
    # failure
}

The force flag is necessary to update existing links without failing, and no-dereference avoids the rookie mistake of accidentally putting a link inside the old symlink's target directory.

It's wise to chdir() to the directory that will contain $link if using relative paths.

Hanfurd