Since you are assinging variables from a hash, it's difficult to tell if you've misspelled the keys. One way to find out is to print the names of the params and visually compare each one to your hash keys. (Since you're already printing them out, you should have no problem with that.)

Another method is to keep breaking your print line in two to perform a binary search for the variable giving you the uninitialized warning.

Yet another idea would be to use the hash directly rather than the variables. I'm not sure why you're copying the data to new variables since you are not untainting anything (though I realize this could be a simplified example.)