sub test {
    my $s = shift;
    my $l = length $s;
    if ($s =~ /[xyz]{$l}/) {
        print "$s matches\n";
        return;
    }
    print "$s doesn't match\n";
}

##</code><code>##

sub test {
    my $s = shift;
    if ( $s =~ /^[xyz]+$/ ) {
        print "$s matches\n";
        return;
    }
    print "$s doesn't match\n";
}

##</code><code>##

sub test {
    my $s = shift;
    if ( $s =~ /[^xyz]/ ) {
        print "$s contains non-xyz characters.\n";
        return;
    }
    print "$s does not contain non-xyz characters.\n";
}