Why don't you just make filefinder into a module? That way, you can choose what (if anything) to import into the main namespace.

Another alternative might be to load filefinder into its own package, and use fully scoped names (you can alias the ones you want in the main package:

package FileFinder;
require "filefinder" || die "couldn't open filefinder: $!";
package main;
FileFinder::someSubroutine();
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