in reply to Inserting a Value
I can't emphasize Ovid's advice enough. Assume your input is *EVIL*, produced by those with the blackest of hearts, bent on your destruction for no reason other than that they can do it. That said, your script had better be running under -T (known as "Taint Mode", read perlsec). More to the present practical matters, see the old classic How can I expand variables in text strings?, this question has been asked often enough to be a FAQ.
If not P, what? Q maybe?