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

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

##</code><code>##

Use of uninitialized value in concatenation(.)or string at /test.pl line 13.
orioles => baltimore
yankees => new york
twins => minnesota
mets => new york