Try this case:

use strict;
use warnings;

my $vmstr = "-1";
my $ymmv = "Mileage ";
my ($opstr) = $vmstr =~ /-(\d\d)$/;

print "$ymmv'$opstr'\n";
[download]

What do you expect should happen. What actually happens. How does it relate to your issue?

You might like to try without strictures first (comment out the first two lines).