Just do

print "$_\n" for keys %INC;
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when you want to know which modules are require()'d or use()'d.

So, this

#!/usr/bin/perl
$file = shift or die "Use: $0 perlprogram\n";
do $file;
print "$_\n" for keys %INC;
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Will print out all loaded files AFTER the normal program ends. Not bullet proof, but should work fine for normal cases.