info gawk

9.2 User-Defined Functions

Complicated awk programs can often be simplified by defining your own functions. User-defined functions can be called just like built-in ones (see section Function Calls), but it is up to you to define them, i.e., to tell awk what they should do.

9.2.1 Function Definition Syntax		How to write definitions and what they mean.
9.2.2 Function Definition Examples		An example function definition and what it does.
9.2.3 Calling User-Defined Functions		Things to watch out for.
9.2.4 The `return` Statement		Specifying the value a function returns.
9.2.5 Functions and Their Effects on Variable Typing		How variable types can change at runtime.