{
    last unless (my $once = $condition1) and $condition2;
    while(1) {
        # ...
        # ...
        last if $once or not $condition3;
    }
}

##</code><code>##

{
    last unless (my $once = $condition1) and $condition2;
    do {
        # ...
        # ...
    } while not $once and $condition3;
}