hex
See the current Perl documentation for hex.
Here is our local, out-dated (pre-5.6) version:
hex - convert a string to a hexadecimal number
hex EXPR
hex
Interprets
EXPR as a hex string and returns the corresponding
value. (To convert strings that might start with either 0 or 0x see oct.) If
EXPR is omitted, uses $_.
print hex '0xAf'; # prints '175'
print hex 'aF'; # same