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.TI CSHELL/GENERAL
The C Shell Command Interpreter


The Unix shell is a program that accepts commands from a user
and calls up programs to perform them.
As it is also the only way of calling up programs,
the shell effectively surrounds the Unix kernel, which is a special
program having exclusive access to the computer hardware (memory,
processor, disks, etc.) which other programs need to run.

Most Unix systems in the world offer users the choice of logging in to
one of two shells:  (1) the standard shell from Bell Labs,
also called the Bourne shell after its author; or (2) the C shell
from UC Berkeley, reputed to have a syntax like the C language.
The C shell is more convenient for interactive use than the Bourne shell,
although it is less efficient for certain applications.

The C shell provides a variety of very useful services,
but not always in a particularly obvious way.
This is partly the fault of the shell and partly the fault
of the documentation.
The ultimate reference consists of the tersely worded
manual pages for "csh" (type "man csh" to see them).
As most people find this difficult to read, a document called "An
Introduction to the C Shell" is also available.
Here is a brief list of the C shell's features.

History Substitution:
allows previous commands to be redone, possibly with changes

Job Control:
allows programs to be switched from the foreground to the background,
putting programs on hold while intermediate results are checked

Command Aliases:
provides for renaming commands, abbreviating long commands, or
turning off selected commands

C Shell Programming:
has many useful high-level control structures and variable handling
capabilities which make conventional programming less attractive

Filename Substitutions:
provides for abbreviating groups of files and selecting filenames
based on patterns

Input/Output Redirection:
has input/output constructs for diverting input from any file or program
and output to any file or program

Start Up Processing at Login:
provides for commands to be executed automatically on logging in
and customization of personal accounts

The help topics on the C shell below do not cover the entire
story and some of them will be revised in the near future.
You might do well to read them in the order of the list,
though this is not required.

general          The C Shell Command Interpreter
internals        Internal Operation of the C Shell
flowcontrol      Control Statements:  Branching and Looping
expressions      Expressions:  Arithmetic, Logic Operations, and Decisions
history          Reusing Previous Commands and Command Parts
aliases          Renaming and Abbreviating Commands

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