my $state=0; #state 0 you expect a card id or comments
while ( my $line = <$FILE> ) {
    if ($state==0) {
        if ($line=~/.../) {
            dosemthing;
            $state=1;
        }
        elsif ($line=~/.../) {
            dosemthingelse;
            $state=4;
        else {
            print "error in datafile";
            $state=0;
        }
    }
    elsif ($state==1) {
        if ($line=~/.../) {
            ...