The simplest function of the shell is to launch other programs. You type
the name of the program you want to run, followed by the arguments you
want, and the shell asks the system to run the program for you.

Of course, graphical windowing systems also fill this need. Technically,
Windows 95 provides a graphical shell, and the X Window system is another
kind of graphical shell. But ``shell'' is commonly used to mean
``command-line shell.''

Needless to say, the hackers who work on shells aren't satisfied with
simply launching commands. Your shell has a bewildering number of
convenient and powerful features if you would like to take advantage of
them.

There are countless different shells available; most are based on either
the Bourne shell or the C shell, two of the oldest shells. The original
Bourne shell's program name is sh, while csh is the C shell. Bourne shell
variants include the Bourne Again Shell from the GNU project (bash, the
Debian default), the Korn shell (ksh), and the Z shell (zsh). There is
also ash, a traditional implementation of the Bourne shell. The most
common C shell variant is tcsh (the t pays tribute to the TENEX and
TOPS-20 operating systems, which inspired some of tcsh's improvements over
csh).

bash is probably the best choice for new users. It is the default and has
all the features you're likely to need. But all the shells have loyal
followings; if you want to experiment, install some different shell
packages and change your shell with the chsh command. Just type chsh,
supply a password when asked, and choose a shell. When you next log in,
you'll be using the new shell.