The Bourne Again Shell

The Bourne Again shell (named in punning tribute to Steve Bourne's shell) was created for use in the GNU project.[2] The GNU project was started by Richard Stallman of the Free Software Foundation (FSF) for the purpose of creating a UNIX-compatible operating system and replacing all of the commercial UNIX utilities with freely distributable ones. GNU embodies not only new software utilities, but a new distribution concept: the copyleft. Copylefted software may be freely distributed so long as no restrictions are placed on further distribution (for example, the source code must be made freely available).

bash, intended to be the standard shell for the GNU system, was officially "born" on Sunday, January 10, 1988. Brian Fox wrote the original versions of bash and readline and continued to improve the shell up until 1993. Early in 1989 he was joined by Chet Ramey, who was responsible for numerous bug fixes and the inclusion of many useful features. Chet Ramey is now the official maintainer of bash and continues to make further enhancements.

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In keeping with the GNU principles, all versions of bash since 0.99 have been freely available from the FSF. bash has found its way onto every major version of UNIX and is rapidly becoming the most popular Bourne shell derivative. It is the standard shell included with Linux, a widely used free UNIX operating system, and Apple's Mac OS X.

In 1995 Chet Ramey began working on a major new release, 2.0, which was released to the public for the first time on December 23, 1996. bash 2.0 added a range of new features to the old release (the one before being 1.14.7) and brought the shell into better compliance with various standards. bash 3.0 improves on the previous version and rounds out the feature list and standards compliance.

This book describes bash 3.0. It is applicable to all previous releases of bash. Any features of the current release that are different in, or missing from, previous releases will be noted in the text.