Bash is a shell, or command language interpreter, for the GNU operating system.
Bash is an sh-compatible shell that incorporates useful features from the Korn 
shell (ksh) and C shell (csh). It is intended to conform to the IEEE POSIX 
P1003.2/ISO 9945.2 Shell and Tools standard. It offers functional improvements 
over sh for both programming and interactive use. In addition, most sh scripts 
can be run by Bash without modification.