use strict;
use warnings;

my %baseball = (
    orioles   =>   "baltimore",
    twins     =>   "minnesota"
);

if ($baseball{yankees} .= $baseball{mets})  {
    foreach $_ (keys %baseball) {
        print "$_ => $baseball{$_}\n";
    }
}

__END__
Use of uninitialized value in concatenation (.) or string at test.pl line 10.