Unindenting computeroutput in DocBook

I had quite a bit docbook lying around in which the programlistings and computeroutputs were indented. Excessive indentation is not a good idea in such whitespace-preserving environments, so I took a look at the “Fancy Patterns” section of the Perl CookBook and wrote this little Perl snippet to unindent them (after saying M-x untabify in Emacs of course):

	    
#!/usr/bin/perl

use strict;

local $/=undef;
open FILE, "/home/jurjen/ApprenticesNotes.xml" or die "Couldn't open Appnotes";
my $string = <FILE>;
close FILE;

# Other modifications, they have nothing to do with indentation
$string =~ s/<literallayout>[[:space:]]+<computeroutput>/<literallayout><computeroutput>/g;
$string =~ s%</computeroutput>[[:space:]]+</literallayout>%</computeroutput></literallayout>%g;
$string =~ s/<command>[[:space:]]+/<command>/g;
$string =~ s%[[:space:]]+</command>%</command>%g;
$string =~ s/<computeroutput>[[:space:]]+/<computeroutput>/g;
$string =~ s%\n +</computeroutput>%</computeroutput>%g;

# T
sub unindent
{
    my ($input) = @_;
    my $minLength = length($input);
    my $spaceFound = 0;
    while ($input =~ m/(\n +)/gs) {
	my $thisLength = length($&) - 1;
	if ($thisLength < $minLength){
	    $minLength = $thisLength;
	}
	$spaceFound = 1;
    }
    if ($spaceFound && $minLength > 0){
	my $re = '\n'.(' ' x $minLength);
	$input =~ s/$re/\n/g;
    }
    return $input;
}

# Note the 'e' modifier that executes the substitution
$string =~ s%(<computeroutput>.*?</computeroutput>)%{unindent($1)}%gse;
$string =~ s%(<programlisting>.*?</programlisting>)%{unindent($1)}%gse;

print $string;