#! perl -slw use strict; use Data::Dumper; my $needle = 'the lazy cat'; my $haystack = 'the quick brown fox jumps over the lazy dog'; my @matches; for my $start (0..length $needle) { for my $len ($start+1 .. length $needle) { my $substr = substr($needle, $start, $len); push @matches, $haystack =~ m[($substr)]g; } } my ($len, $longest) = 0; length > $len and ($longest, $len) = ($_, length) for @matches; print "The longest common substring between\n", $needle, "\nand\n", $haystack, "\nis '$longest'"; __END__ C:\test>249239.pl The longest common substring between the lazy cat and the quick brown fox jumps over the lazy dog is 'the lazy ' C:\test>