Bash is a Unix command shell written for the GNU project. Its name is an acronym for "Bourne-Again SHell": a pun on the Bourne shell sh, which was the original Unix shell. The Bash command syntax is largely backward-compatible with sh, and includes ideas drawn from ksh and csh, such as the command history, the directory stack, the $RANDOM variable, and the POSIX form of command substitution, '$('.
The original Bourne shell was written by Stephen Bourne. Bash was primarily written by Brian Fox and Chet Ramey.
Bash is the default shell on most GNU/Linux systems, and it can be run on most Unix-like operating systems. It has also been ported to Microsoft Windows by the Cygwin project.
Bash is distributed under the GNU General Public License. It is available for download from many sites on the Internet, including the GNU project FTP site. The latest released version is 2.05β.
The complex bash script bashforth shows several bash programming techniques, by implementing a version of the extensible programming language Forth