You need to pack the hex representation into a binary string, so if you have '112233' you need to create the bytes "\x11\x22\x33". Then you can use the bitwise operators on these byte strings to do what you want.

Here's a nice way to do the conversions:

use strict;
use warnings;
use 5.010;  # just needed for say()

sub unascii {   pack 'h*', $_[0]; }
sub   ascii { unpack 'h*', $_[0]; }


say ascii unascii('aabbcc') ^ unascii('112233');
# output: bb99ff
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See pack, unpack and perlpacktut for more details.