I noticed this lines gives an error when there are no words of a given length:

$size[$_] = @{ $list[ $_ ] } for 1..$phrase_length;
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The error is:

Can't use an undefined value as an ARRAY reference at anagram.pl line 
+34.
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I fixed it with this:

for my $length ( 1..$phrase_length )
{
    my $ref = ref $list[ $length ];
    $size[$length] 
          = ( $ref =~ /ARRAY/ ? @{ $list[ $length ] } : 0 );
}
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(I didn't find an easier way, though I didn't look too hard.)

I'd be interested in seeing any improvements you (or anyone else) has made to this offline.