Well, you may be in luck. There's that old expression, "Only perl can parse Perl." And it happens that there's a B:: module that might help you out.

B::Xref

Here's how you use it:

perl -MO=Xref source1.pl >source1.xref
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By doing that, you'll now have a file, "source1.xref", containing a list of all of the symols used in your source code.

From there, you could do that with any number of programs, and quickly write a little script that compares the symbols found in each crossref file, to alert you to symbols that don't appear in all files.

Even if you don't bother with writing a comparison/alert script, the B::Xref module is probably a good solution since it organizes the symbols by package and subroutine for quick visual comparison.