Bash command line man page and help. Bash is a sh-compatible command language processor that executes commands read from standard input or a file. Bash also contains the useful properties of Korn and C shell (ksh and csh). The purpose of Bash is to properly implement the Shell and Utilities portion of the IEEE POSIX specification (IEEE 1003.1 standard). By default, Bash can be configured to be POSIX-compliant.