a_file.txt sample:
http://www.ok.com/test_www.pdf       
http://www.ok.com/test_1234.html        
http://www.ok.com/test_part.pdf       
http://www.ok.com/test_345.pdf       
http://www.ok.com/test_error.html

##</code><code>##

b_file.txt sample:
http://www.ok.com/test_www.pdf              
http://www.ok.com/test_part.pdf       
http://www.ok.com/test_345.pdf

##</code><code>##

 
#!/usr/bin/perl

use strict; use warnings;

use Text::Diff;

my $diffs = diff 'a_file.txt' => 'b_file.txt';

print $diffs;