http://www.perlmonks.org?node_id=330902

Q&A > subroutines > How can I write and call subroutines in separate files? - Answer contributed by gridlock

What you can do is write your subroutines in seperate perl (.pl) files. Whenever you need to call them, all you need to do is include them with your code (use the require statement). Each file should end with a true expression, traditionally 1;.