Perhaps take a look at Algorithm::Diff? You could split up your strings, then pass those sequences to the diff function, which should return the diffs. Perhaps you can use that array returned to determine how different the original strings were?

Here's some code:

    use Algorithm::Diff qw/diff/;

    my $ref1 = [ split //, "foo bar" ];
    my $ref2 = [ split //, "foo baz" ];

    my @diffs = diff $ref1, $ref2;
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