perl-esque data parsing for hex post variables

I can't get the php to convert audio data to nicely formed binary wav format. For instance, in perl you simply do a $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg; and you're done with it. In php, there are two problems: 1. no existence of a handy builtin hex2bin() function (though many have been written, such as function hex2bin($hex_str) for ($i = 0; $i < strlen($hex_str); $i += 2) $bin_str .= chr(hexdec(substr($hex_str, $i, 2))); } return $bin_str; } which seems to get the case done, 2. But the real problem is that doing a straight hex2bin conversion is not what that beautiful little perl script does. The part that confuses me is the hash oriented piece /%([a-fA-F0-9][a-fA-F0-9])/ -- what exactly is it doing? Is it just stepping through the string two characters at a time and comparing them? Or is it doing something more ambitious and arcane that I'm not really grasping. I tried to emulate it with the following php workaround, but come up short... for ($i = 0; $i < strlen($hex_str); $i += 2) $newdata =. preg_replace("/[a-fA-F0-9][a-fA-F0-9]/",pack("C",hexdec(substr($hex_str, $i, 2))),$hex_str); } Any help?