1. The bash shell is a free version of the Bourne shell, the first Unix shell, and includes many additional features.

2. In addition to the style in which the program was written, Bourne reused portions of ALGOL 68's "if ~ then ~ elif ~ then ~ else ~ fi", "case ~ in ~ esac" and "for/while ~ do ~ od" (using done instead of od) clauses in the common Unix Bourne shell syntax.