Programming Perl, 4th Edition

Chapter 7. Subroutines

Like many languages, Perl provides for user-defined subroutines.^[115] These subroutines may be defined anywhere in the main program, loaded in from other files via the do, require, or use keywords, or generated at runtime using eval. You can even load them at runtime with the mechanism described in the section Autoloading in Chapter 10. You can call a subroutine indirectly, using a variable containing either its name or a reference to the routine, or through an object, letting the object determine which subroutine should really be called. You can generate anonymous subroutines, accessible only through references, and if you want, use these to clone new, nearly identical functions via closures (which are covered in the section by that name in Chapter 8).

^[115] We’ll also call them functions, but functions are the same thing as subroutines in Perl. Sometimes we’ll even call them methods, which are defined the same way, but called differently.