Bash

Bash, a contraction of Bourne Again SHell, is GNU's command-line interpreter for Unix, included by default with Mac OS X through macOS Mojave (10.14).

Description
Bash is a POSIX-compliant shell with full Bourne shell syntax, and some commands built in. The Bourne Again Shell supports -style command-line editing, job control, functions, and on-line help. Written by at the, version 1.14.1 includes a yacc parser, the interpreter, and documentation.

Bash on Mac OS X
Bash has been the default command-line shell for Mac OS X since its NeXTSTEP origins. In 2019, Apple replaced bash with zsh in new installations of macOS Catalina (10.15). Upgrades to Catalina will retain the user's existing installation of bash with a notification in case the user would like to switch to zsh.