hex
hex EXPR
This function interprets EXPR as a hexadecimal string and returns the equivalent decimal value. (To interpret strings that might start with or x see oct.) If EXPR is omitted, it interprets $_. The following code sets $number to 4,294,906,560:
$number = hex("ffff12c0");
To do the inverse function, use:
sprintf "%lx", $number; # (That's an ell, not a one.)