Duplex is a set of shell scripts (bash) that emulate duplex printing (on both sides of the paper) for sheet-fed printers that do not support duplex printing in hardware. It can operate as a pipe so that applications can use it as a duplex printing driver. Its unique feature is its ability to print many duplex print jobs in one batch, printing the odd sides of all jobs and then the even sides in just two passes. It has a limited graphical interface.