UNIX if it isn't already present.

Bash, a.k.a. the Bourne Again shell, originally written by Brian Fox of the Free Software Foundation, is the default shell for Linux users. Bash is an attempt to create a "best of all shells" that not only provides backward compatibility with the original UNIX Bourne shell, but also the most useful features of both the C shell and Korn shell. Another advantage is that Bash, as an open software product, is freely available and can be found in all Linux distributions, and it can be downloaded and installed on just about any version of UNIX if it isn't already present.