Network programming is all about interprocess communication (IPC). One process exchanges data with another. Depending on the application, the two processes may be running on the same machine, may be running on two machines on the same segment of a local area network, or may be halfway across the world from each other. The two processes may be related to each other—for example, one may have been launched under the control of the other—or they may have been written decades apart by different authors for different operating systems.

The simplest form of IPC that Perl offers is the pipe. A pipe is a filehandle that connects the current script to the standard input or standard output of another process. Pipes are fully implemented on UNIX, VMS, and Microsoft Windows ports of Perl, and implemented on the Macintosh only in the MPW environment.