In essence, all shells do the same thing;
they just differ in the way they do it, the
options and settings they recognize, and the special features they
offer. The following list describes the Mac OS X shells, all of which
are included with the
/bin directory, and are
available to all users on the system.
tcsh is an evolved version of csh , a shell whose syntax is based loosely on the C programming language. It’s quite popular for interactive use, and is the default shell for new users on Mac OS X.
Mac OS X includes a /bin/csh command, but it’s really just an alias to /bin/tcsh.
The Bourne Again Shell (a pun on the Bourne Shell, the very first Unix shell program) is, like tcsh, a conceptual child of the earlier csh shell, but it is more commonly used, and is probably the most popular shell in use across Unix systems today. Many Mac OS X newcomers will recognize it as the default shell on most Linux distributions.
bash is aliased to /bin/sh, so that shell scripts run in Darwin will actually run through bash.
Among the popular shell programs in the whole Unix sphere, zsh is the newest. It attempts to meld the better features of bash and tcsh into a single shell, as well as add a lot more—one of its more well-known unique features is programmable tab completion.
The following table displays features that are common to Mac OS X’s shells.