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In UNIX, the shell is a program which prompts the user and directs the operating system to do what the user wants. When you login to your account, you see the prompt displayed, ``vega1%''. This means that the shell is waiting for you to type a command. The shell is actually just a regular program like any other, yet it is a user interface which allows you to execute other programs.
Your user account is initialized with the tcsh, an enhanced version of csh (the c-shell). Most literature describes csh and should be compatible with tcsh. Among the additional features of tcsh are filename completion (with the TAB key) and previous command repetition (with the UP and DOWN arrow keys). You can change this shell with the chsh command to one of many available shells.
The shell is a very powerful tool that can be customized. Using just
tcsh, new commands can
be created, old ones altered, input and output files dynamically
redefined, and even entire programs written without ever using
a compiler. Chapter contains a number of useful hints
to get more out of the shell. Consult the man page (see Getting Help)
or the manual on csh, which is part of CS1000supp,
purchasable at DoIT, for more information on
the many features of the c-shell.