open INPUT, "name_of_input_file" or die: $!; open GOOD_OUTPUT, ">good_data.csv" or die $!; open BAD_OUTPUT, ">discarded_data.csv" or die $!; while(my $line = ){ chomp $line; if(data_meets_good_condition){ print GOOD_OUTPUT "$line\n"; }else{ print BAD_OUTPUT "$line\n"; } }