The Bourne again shell (bash) is a console shell developed by the GNU project that was released in 1989. Originally written by Brian Fox, it has become the de facto standard and is used by default in almost all Linux operating systems, OS X, Novell NetWare, Android, as well as on Windows. The bash was inspired by the sh shell, which was extremely popular around the time bash was created.

The bash shell was written as an open source replacement to the Bourne shell that was the default command-line interpreter for Unix. The bash supports many features, including the autocompletion of commands and filename wildcards.