File: gawk.info,  Node: Extension Intro,  Next: Plugin License,  Up: Dynamic Extensions

17.1 Introduction
=================

An "extension" (sometimes called a "plug-in") is a piece of external
compiled code that 'gawk' can load at runtime to provide additional
functionality, over and above the built-in capabilities described in the
rest of this Info file.

   Extensions are useful because they allow you (of course) to extend
'gawk''s functionality.  For example, they can provide access to system
calls (such as 'chdir()' to change directory) and to other C library
routines that could be of use.  As with most software, "the sky is the
limit"; if you can imagine something that you might want to do and can
write in C or C++, you can write an extension to do it!

   Extensions are written in C or C++, using the "application
programming interface" (API) defined for this purpose by the 'gawk'
developers.  The rest of this major node explains the facilities that
the API provides and how to use them, and presents a small example
extension.  In addition, it documents the sample extensions included in
the 'gawk' distribution and describes the 'gawkextlib' project.  *Note
Extension Design::, for a discussion of the extension mechanism goals
and design.