using Text::Levenshtein's distance function, I get source1 as the best match. 
use Text::Levenshtein qw(distance);

$target = 'source';
$best=undef;
for (qw(donor_dedupe_source indicted_video_source source1)) {
    $dist = distance($target,$_);
    if ($best == undef || $dist < $best) {
        $best = $dist;
        $bestword = $_;
    }
}
print "Best word was $bestword with an edit distance of $best\n";

[download]
output: Best word was source1 with an edit distance of 1

update: changed default value of $best to prevent perfect matches from being lost

In reply to Re: Tuning an approximate match to prefer closer lengths by bageler
in thread Tuning an approximate match to prefer closer lengths by samtregar

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