See the current Perl documentation for pipe.

Here is our local, out-dated (pre-5.6) version:

pipe - open a pair of connected filehandles


Opens a pair of connected pipes like the corresponding system call. Note that if you set up a loop of piped processes, deadlock can occur unless you are very careful. In addition, note that Perl's pipes use stdio buffering, so you may need to set $| to flush your WRITEHANDLE after each command, depending on the application.

See Open2, Open3, and Bidirectional Communication for examples of such things.