C Shell Command Line

Computer History Notes - Herong's Tutorial Notes

∟1978 - The C Shell Developed by Bill Joy

∟C Shell Command Line

This section provides a quick introduction of C shell command line.

The C shell is really a command line interface that takes a command line entered by the user on the standard input, execute the command, and returns command result on the standard output.

A command line consists of a list of strings or words. The first word is called the command name. Other words of the command line are called command arguments.

A number of interesting features are supported on the C shell command line. Those features are applied in the following order before the command line gets executed:

History Substitution - Brings in parts of previously executed commands.
Alias Substitution - Replaces user defined aliases with their definitions.
I/O Redirection - Changes input and/or output from terminal console to other commands or files.
Variable Substitution - Replaces shell variables with their values.
Command Substitution - Replaces commands with their outputs.
Filename Substitution - Replaces filename wildcard characters with real file names.

After a command line is passed through above substitutions, it will be executed in different ways based on the command name, the first word of the command line:

If the command name refers to a C shell built in command, the C shell will execute this command.
If the command name refers to a file name with a path name, the C shell will execute the program represented by the path name
If the command name refers to a file name without any path name, the C shell will search the file name in the directories defined in the "path" variable.
If the above process fails, the C shell will return an error.

Examples of C shell command lines:

%set java home=/usr/local/lib/jdk1.1.1

%/bin/echo $java home
/usr/local/lib/jdk1.1.1

%/echo $java home
/usr/local/lib/jdk1.1.1

%who
herong     tty1     Jul 21 21:36
tom        tty2     Jul 21 18:15

%dothis
dothis: Command not found.