Interprets EXPR as a hex string and returns the corresponding numeric value. If EXPR is omitted, uses
print hex '0xAf'; # prints '175' print hex 'aF'; # same $valid_input =~ /\A(?:0?[xX])?(?:_?[0-9a-fA-F])*\z/
A hex string consists of hex digits and an optional
x prefix. Each hex digit may be preceded by a single underscore, which will be ignored. Any other character triggers a warning and causes the rest of the string to be ignored (even leading whitespace, unlike "oct"). Only integers can be represented, and integer overflow triggers a warning.