A Perl program that you call via backticks to process its output is just like any other program. It has to print the output. Using return does not work. Your child Perl program does not work alone, so it won't work when called via backticks or system either.

If you want to structure your programs and keep common parts in a single file, look at do or require to load Perl code from files and call the common code as a subroutine.