How do I find the percentage of similarity between strings?

Superman has asked for the wisdom of the Perl Monks concerning the following question: ⭐ (strings)

I have 2 strings which should be identical:

$PDBline;
$XMLline;
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and I test for this normally:

if ($PDBline eq $XMLline){etc...}
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However in the event that they dont match I want to do a percentage comparison where I match each word in $PDBline against the words in $XMLline.

So say I want a 75 % similarity between the 2 strings...

my $threshold = 0.75;

my $counter = 0;

foreach my $word ( split ' ', $PDBline ) {
  $counter++ if $XMLline =~ /$word/;
}
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Does this seem right or is there an easier way to do this??

Originally posted as a Categorized Question.