so, effectively you want to see if one file has a different hash to another file?

you go thru' the list of files, create the hash and store it against the filename.

the next pass, you go get the filename and the hash, then using the retrieved filename generate another hash into a different variable, then compare the old and new hashes...

If your script is a deamon, use a config file to store the files you want to hash, and an $oldhash and $newhash variable to compare any difference between the two values. Make sure you suck in the config file over every iteration so you can pick up any addition/deletions rather than restarting the daemon each time.

that sounds way too simple an answer, perhaps i dont understand your question properly