How can I open a pipe both to and from a command?

The IPC::Open2 module (part of the standard perl distribution) is an easy-to-use approach that internally uses pipe(), fork(), and exec() to do the job. Make sure you read the deadlock warnings in its documentation, though (see IPC::Open2). See perlipc/"Bidirectional Communication with Another Process" and perlipc/"Bidirectional Communication with Yourself"

You may also use the IPC::Open3 module (part of the standard perl distribution), but be warned that it has a different order of arguments from IPC::Open2 (see IPC::Open3).