Hex editing in PHP

[Mgccl]

I have some exe files, and I want to add patches to them by using the PHP way...
Suppose there are only 2 things I want to do, that is
Find HEX String $hex1 in offset $offset (a offset is where the $hex1 located)
in a file file.exe
and replace it by string $hex2

ok, this seems easy... but....
I thought when we read file in PHP, it uses it as text files, but how can I let PHP read it as HEX files? and replace things in it?

[bogu]

U may read the file binary and convert binary to hex: bin2hex