oldlinks: Find Unconnected Symbolic Links (Unix Power Tools, 3rd Edition)

8.16. oldlinks: Find Unconnected Symbolic Links

One problem with symbolic links is that they're relatively "fragile" (Section 10.6). The link and the file itself are different kinds of entities; the link only stores the name of the "real" file. Therefore, if you delete or rename the real file, you can be left with a "dead" or "old" link: a link that points to a file that doesn't exist.

This causes no end of confusion, particularly for new users. For example, you'll see things like this:

% ls -l nolink
lrwxrwxrwx   1 mikel     users    12 Nov  2 13:57 nolink -> /u/joe/afile
% cat nolink
cat: nolink: No such file or directory

The file's obviously there, but cat tells you that it doesn't exist.

There's no real solution to this problem, except to be careful. Try writing a script that checks links to see whether they exist. Here's one such script from Tom Christiansen; it uses find to track down all links and then uses perl to print the names of links that point to nonexistent files. (If you're a Perl hacker and you'll be using this script often, you could replace the Unix find utility with the Perl File::Find module.)

#!/bin/sh
find . -type l -print | perl -nle '-e || print'

The script only lists "dead" links; it doesn't try to delete them or do anything drastic. If you want to take some other action (such as deleting these links automatically), you can use the output of the script in backquotes (Section 28.14). For example:

% rm `oldlinks`

-- ML