Where is my Broken Link

05 Feb 2015

Post first published in nixtip

This task bugs me quite often, there many methods to perform this job but want to share the options I consider safer.

Having this scenario:

$ touch a b c
$ ln -s a a.link
$ ln -s b b.link
$ ln -s c c.link
$ rm b

$ ll
total 0
-rw-r--r--   1 klashxx   klashxx   0 Feb 1 09:45 a
lrwxr-xr-x   1 klashxx   klashxx   1 Feb 1 09:45 a.link -> a
lrwxr-xr-x   1 klashxx   klashxx   1 Feb 1 09:45 b.link -> b
-rw-r--r--   1 klashxx   klashxx   0 Feb 1 09:45 c
lrwxr-xr-x   1 klashxx   klashxx   1 Feb 1 09:45 c.link -> c

Find

find . -type l -exec test ! -e {} \; -print

-type l True if is a symbolic link file type.

-exec test ! -e {} Test if the file where the link points DOES NOT exists.

-print Show the broken link

Outputs

./b.link

Perl + bash

for link in *.link; do
  perl -se 'exit 5 unless (-e readlink($link));' -- -link=$link
  [[ $? -eq 5 ]] && echo "broken link: $link"
done

Outputs

broken link: b.link

Let’s explain the mini Perl program that makes the trick.

-s

enables rudimentary switch parsing for switches on the command line after the program name but before any filename arguments (or before an argument of –). Any switch found there is removed from @ARGV and sets the corresponding variable in the Perl program. The following program prints “1” if the program is invoked with a -xyz switch, and “abc” if it is invoked with -xyz=abc.

-e commandline

may be used to enter one line of program. If -e is given, Perl will not look for a filename in the >argument list. Multiple -e commands may be given to build up a multi-line script. Make sure to use >semicolons where you would in a normal program.

So… we use –s to pick link parameter and –e to execute the program.

Program

exit 5 unless (-e readlink($link)) returns where is the symbolic link pointing.

Arguments

-- marks the end of options and disables further option processing. Any arguments after the —- are treated as filenames and arguments (bash man).

-link=$link pass link variable to Perl program (see –s flag)

-e test if the file exists.

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