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Basic C Shell

This is a very brief guide to how to use cshell to speed up your use of Unix commands. Googling ``C Shell Tutorial'' can lead you to more detailed information.

Change Your Shell To tcsh

Open a terminal, if you can not use left/right arrow to edit your commands, you are NOT using tcsh. To formally check it, type command

echo $shell
If you see

you are using tcsh. Otherwise, enter command:

passwd -r nis -e

when prompted. The new setting will be effective after around 10 minutes. For the purpose of this tutorial, use command

to start an instance of tcsh.


  1. Check you shell and set it to tcsh if necessary.
  2. If necessary, use tcsh command to enter tcsh. Note that you can use exit command to exit this shell.

A Tour of C Shell Features


All the features of cshell can be set in .cshrc. This is a plain text file located under you home directory. It will be loaded and executed whenever you open a shell window. After you edit this file (with any text editor of your choice), use source ~/.cshrc command to activate the change.


  1. Open .cshrc with emacs. (Or vi if you prefer). Try to understand each line of it.

Change $path

$path contains a list of directories to be searched when running programs or shell scripts. For example, the command Splus is in /usr/local/bin. If /usr/local/bin is not in your $path, you will have to enter the full path name /usr/local/bin/Splus to start Splus, rather than simply Splus. Usually, we set $path in ~/.cshrc, which will be executed whenever a new shell is started. The syntax of setting $path is:

set path = ( $path /home/helpdesk/bin ~/bin .)
To check the content of your current $path, use command

echo $path
Note that '~' means your home directory, '.' means current directory. The above set path command add /home/helpdesk/bin ~/bin and . to your $path.


  1. check you $path.
  2. Add /home/helpdesk/bin to your $path by editing .cshrc file.
  3. source .cshrc to activate the change.
  4. check your $path again.

Command Line Editing

Tcsh records up to $history your previous commands. You can set $history in your .cshrc file as follows

set history=50
Then, history command will list all your previous commands and

will execute command 27. !! is used to repeat your alst command.

You can also use the arrow keys to navigate the command history and edit the command line. It is also very important to know how to use the middle button of your mouse. Try to select your previous command with the left button and paste it with your middle button.

Command Line Completion

The <TAB> key is very useful in tcsh. Whenever you press <tab>, tcsh will try to complete your command, file or directory name. That is to say, you can enter

instead of xterm if xterm is the only command in your searching path that begin with xt. This is especially useful if you have very long file/directory names.


  1. enter the following commands, try to use your mouse, arrrow and tab keys to simplify the task.

    1. cat .cshrc have a look at .cshrc file. Try to use tab key.
    2. more .cshrc try to use mousr copy and paste, (You might not be able to use this function if you are using windows++xwin32+ssh.) or up/down arrow keys.

Standard Input/Output, Pipe

You need to understand some basics about standard input/output of Unix commands. Briefly, Unix programs usually read from their standard input, like the keyboard, output to their standard output, like the terminal. We can redirect their standard input/output in the following ways:

  1. Redirect standard output to a file: 
    cat a.c b.c > sum.c
  2. Add the standard output to another file
    cat c.c >> sum.c
  3. Redirect standard input from a file:
    cat < a.c
  4. Use the output of the first program as the input of another program: (pipe)
    cat a.c | more


Alias, as its name implies, maps a (shorter) name to another (long) name. It can be used to give shortcuts to existing commands, create new commands or even 'overwrite' existing commands. For example, command

alias ll 'ls -l'
maps ll to ls -l so that ls -l will be called whenever ll is entered as a command. It is perfectly all right to use command

alias ls 'ls -l'
to alias ls to ls -l. The result of this alias is to add a default option -l to the ls command. This trick is most frequently used on the dangerous rm command,

alias rm 'rm -i'
since the default rm command removes files without warning.

Alias can also handle parameters. Here I only demonstrate the simplest case where you use \!* as the parameters. For example:

alias mcd 'mkdir -p \!*; cd \!*'
When you call

mcd stat
it will be expanded to

mkdir stat; cd stat


Can you mak the following aliases? You can use unalias command to disable an alias.

  1. findjob: list all running jobs and then find jobs that match a string (use ps -ef, pipe and grep) .
  2. ssh7: ssh to
  3. emacs: Add an & at the end of emacs command automatically.
  4. rxvt: set default foreground, background to rxvt command. (Use -fg green -bg black options.)

Other Useful Features


set cdpath = (~ ~/public_html ~/stat )
and you can use cd stat410 to change your current directory to ~/stat/stat410 even when you are not under ~/stat.


set prompt= %n@%m:%~ %
will set your prompt to username@machine name: current directory %.

Control Structure

You do need to understand more about variables, expressions before you can use control structure or write a shell script. Here are two very simple examples about how they can be used:

  1. Configure for different platforms:
    if ( $OS = 'Linux' ) then 
    source .rc.Linux 
    source .rc.Unix 
  2. Using loops to process multiple files:
foreach file in (*) 
move $file $file.bak 
Starting from the above basics, you can learn:

to simplify every routine of your Unix life.

$Date: 2003/07/17 02:49:21 $

$Revision: 1.1 $

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Basic C Shell

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Statistics Helpdesk 2003-08-11