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 Web page.
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 chapter 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.
See Extension API Design, for a discussion of the extension mechanism
goals and design.