Unix provides the facility to work in different command environments,
or shells. Two common examples of these are the C and
Bourne shells, although many other different shells exist. The major
reasons for choosing between shells are related to the running of command
files and their associated command languages; there is very little difference
to the basic commands.
The C shell is the main shell discussed as a working environment, with added details of the tcsh (which is an enhanced version of the C shell). The shell script language used is the original Bourne shell language; available on all Unix systems.