Can you rephrase the question? i.e. "I want to check for matches in a file without using an 'open' on the file"..
Is something like
any help? (which can be run like: perl_script < a_file.txt
and will iterate over the lines in a_file.txt)
<update>It also occurs to me that you might be asking "how do I grep a file that I don't have read-access to?" - in which case you are up the proverbial creek..</update>
Tom Melly, firstname.lastname@example.org