Your problem is much more easily and cleanly solved by the above answers, so use those. This is just an academic comment ;-).

<don't do this>

Perl can actually use the C preprocessor if you invoke the interpreter with the -P flag. Then your #includes and other such C pragmas will work. However, as is typical for Perl, the kludgely preprocessor directives have been superceded by more Perlish (i.e., easier, safer, more huggable) constructs. #define constants should use the const module; #includes should be replaced by real modules with use or require. Since these aren't preprocessor directives, #ifdefs are unnecessary.

</don't do this>