for (1 .. 4) {
    if ($_ % 2) {print "odd"}   # Assume 'once only blocks'
    else {print "even"}
}

##</code><code>##

    {
        FIRST {
            ...
        }
    }

##</code><code>##

    my $flag = 1;
    ...
    if ($flag && CONDITION) {
        $flag = 0;
        ...
    }