This bit looks fishy:

foreach (@numbers)
{
  unless ($_ == $1)
  { push @numbers,$1; }
}
[download]

This would push $1 onto @numbers multiple times (once for each existing element that didn't match) except that it never runs at all since @numbers starts out empty. You could use the grep() function to check whether a value occurs in the array, but a better approach would be to use a hash instead and check with exists().

Also, your subroutine doesn't explicitly return a value.