Short intro from the docs

       -P   NOTE: Use of -P is strongly discouraged because of its inh
+erent
            problems, including poor portability.

            This option causes your program to be run through the C pr
+eproces-
            sor before compilation by Perl.  Because both comments and
+ cpp
            directives begin with the # character, you should avoid st
+arting
            comments with any words recognized by the C preprocessor s
+uch as
            "if", "else", or "define".

            If you're considering using "-P", you might also want to l
+ook at
            the Filter::cpp module from CPAN.
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-- 
Joost       downtime n. The period during which a system
            is error-free and immune from user input.
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