while (<>) {
    next unless /first check/;
    next unless /second one/;
    my @foo = split /delimiter/;
    next if @foo != 5; # or whatever
    
    ...
}

<p><font color=green><code>
2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$