Alternation (string expansion)

Bash

Screenshot of a Bash session
Original author(s)	Brian Fox
Initial release	June 8, 1989; 27 years ago (1989-06-08)
Stable release	4.4.5 / November 16, 2016; 6 months ago (2016-11-16)
Repository	git.savannah.gnu.org/cgit/bash.git
Written in	C
Operating system	Unix-like, macOS (system includes an older GNU GPL v2 version); current version available through third parties Windows (newer GNU GPL v3+ version)
Platform	GNU
Available in	Multilingual (gettext)
Type	Unix shell, command language
License	GNU GPL v3+
Website	www.gnu.org/software/bash/

Bash is a Unix shell and command language written by Brian Fox for the GNU Project as a free software replacement for the Bourne shell. First released in 1989, it has been distributed widely as the default login shell for Linux distributions and Apple's macOS (formerly OS X). A version is also available for Windows 10.

Bash is a command processor that typically runs in a text window, where the user types commands that cause actions. Bash can also read and execute commands from a file, called a script. Like all Unix shells, it supports filename globbing (wildcard matching), piping, here documents, command substitution, variables, and control structures for condition-testing and iteration. The keywords, syntax and other basic features of the language are all copied from sh. Other features, e.g., history, are copied from csh and ksh. Bash is a POSIX-compliant shell, but with a number of extensions.