Besides the good advice you've received above, you should also investigate regex anchors ^ and $, for example: 
s/^$file$/something goes here/

[download]

Search for "anchor" in perlretut#Simple word matching.

-QM
--
Quantum Mechanics: The dreams stuff is made of

In reply to Re: How to handle metacharacters in input file for Perl one-liner code by QM
in thread How to handle metacharacters in input file for Perl one-liner code by debug

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