It was a typo. Instead of $testword should have been $testWord

Normally such typos are caught by the use strict pragma so that made me wonder why it did not pick this up here.

And then I saw that you declare two different lexical variables:

while (my $testWord = <$listWord>){ ...
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and a bit later (but still within the same scope)

main(my $testword);
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Obviously, use strict did not complain as all variables are "properly" declared, but obviously it serves no purpose to hand a freshly minted (and therefore undef) lexical variable to a subroutine.

I saw that you did it again in

my($bigramSuccess, $distanceSuccess, ) = main(my $testword, $r
+ightWord);
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