If you're going to be doing something with each element the following 'for' idiom is useful:

for (grep /.*P.*\.0912\.ama\.gz/, @sourcefiles) {
    # $_ contains each matching name
}
[download]

As sauoq pointed out, though, this does iterate over the list. It's hard to search through a list without iterating :) But grep is your friend. Learn it, love it.
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"I hate it when I think myself into a corner."
Matt Mitchell