...
my $oshort_line = substr( $oline, 0, 49 );
...
my $nshort_line = substr( $nline, 0, 49 );
...

##</code><code>##

$ perl -E 'my $x = "X" x 49 . "Y" x 49; say substr $x, 0, 49'
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
$ perl -E 'my $x = "X" x 49 . "Y" x 49; say substr $x, 0, 50'
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXY