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; these include command line editing, unlimited size
command history, job control, shell functions and aliases, indexed
arrays of unlimited size, and integer arithmetic in any base from two
to sixty-four. In addition, most sh scripts can be run by Bash without
modification.