Perl functions are available to you at any place in your script and they do not need any declaration to use, being installed within your system with Perl packages. You can do a search at CPAN and find an almost exhaustive presentation of all the built-in Perl functions, grouped by categories or alphabetically. If you want to write your own function, you can use a user-defined subroutine and than call it anywhere within your Perl code.
It’s beyond the scope of this section to clear all the aspects related to functions in a programming language. In general, a function has a name and represents a block of code which we can call anywhere we need in a program source. We use the functions in order not to repeat indefinitely the same block of code using the copy and paste techniques.
In this section you'll find a lot of examples regarding these built-in functions. The functions are presented grouped by categories, in a how to topic format.