while (<F2>) {
    $ptfkey = $_; # you can skip this using above suggestion
    $ptfpn = $ptfkey; # don't need this if just matching

    $ptfpn =~ m/^(\w+)/; # if only letters and numbers
    $ptfpn =~ m/^([\d\-\.]+)/; # if it's a float
    $F1hash{$1} = 1;
    }