Bourne Again SHell

bash (the "Bourne Again SHell") is the GNU implementation of a Unix shell which is intended to be compatible with the original UNIX Bourne Shell (/bin/sh) by Stephen R. Bourne. bash was primarily written and is maintained by Brian Fox and Chet Ramey. The name follows a Free Software Foundation tradition for whimsical and pun-referential names.

In functionality bash goes well beyond the original Bourne shells and closely matches the extensions of David Korn's "Korn Shell" (ksh), though bash and ksh use different syntax to create a coprocess or an associative array. bash also adds a number of interactive features drawn from Bill Joy's C Shell (including the many "bang expansion operators" for things like !! (expand to entire previous command), !-2 (expand to penultimate command), !$ (expand to last argument of previous command) etc).