i finally ended up with something similar...

print &popline("passcodes.txt",10,7);
sub popline {
    my ($file, $lineswanted, $linelength) = @_;

    open     DATA, "+< $file";
    my @fileinfo = stat DATA;
    my %records = ();
        $records{filesize} = $fileinfo[7];
        $records{wanted_bytes} = $lineswanted * $linelength;
        $records{readpoint} = $records{filesize} - $records{wanted_byt
+es};

    # seek (DATA, -$records{wanted_bytes},2);     # reads from the end
+ of file, readpoint computation not necessary
    seek (DATA, $records{readpoint},0);            # reads from beginn
+ing, used b/c readpoint computation needed for truncate

    my @lines = <DATA>;
    truncate(DATA,$records{readpoint});
    
    return @lines;
}
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i'll add in flocking etc tonight.
short of filling up a database w/20k possible keys + status tags, what i did was create a flat.txt of possible keys. this function is for 'activating' a key -- 50-100 will be pulled off the file, inserted into a db with a status flag (active/used), and merged w/documentation is this the most secure method? probably not. but if someone is going to hack my machine and grab the file -- well, i'm just going to assume that they're talented enough to hack into mysql and alter the db as they see fit.