The C Shell

start up of C shell


After the csh program starts, it is programmed to execute two files in the user's home directory: the .cshrc file and then the .login file. These files allow users to initialize their own environments.

The .cshrc file
the .cshrc file contains C shell variable settings and is executed every a csh subshell is started. aliases and history are normally set here.
 
 
Sample .cshrc
set noclobber
set ignoreeof
set history=25
set savehist=5
set prompt=x7f\! stardust >"
set filec fignore=(.0)
set cdpath=(/home/joy/bin /usr/bin)
alias m more
alias status '(date; du -s)'
alias cd 'cd\!*; set prompt=x7f<$cwd>"'		 avoid remove file using redirection
avoid log out with Ctrl-d
the last 25 command in history cmd
history saved after log out

exclude files in filename completion
a list of path elements
a shorthand notation for cmd
 

 

The .login file
The .login file is executed one time when user first log on. It normally contains environment variables and terminal settings. It is the file where window applications are usually started. Since environment variables are inherited by processes spawned from this shell and only need to be set once, and terminal settings do not have to be reset for every process, those settings belong in the .login file.
 
 
Sample .login
setenv TERM sun
setenv OPENWIN /usr/local/ow3
set path=(4usr/bin /usr/local)
echo " welcome aboard "
if("'tty'"=="/dev/console") then
 echo "use openwindows?" 
 sleep 5
  $OPENWIN/bin/openwin
endif
/usr/games/fortuen		 set environment variable TERM
variable for window application
search path
 
 
 
 
 
 
 

The rehash command
The shell builds an internal hash table consisting of the contents of the directories listed in the search path. If dot is in the search path, the files in the dot directory, the current working directory, are not put on the hash table. For efficiency, the shell uses the hash table to find commands that are typed at the command line, rather than searching the path each time. If a new command is added to one of the directories already listed in the search path, the internal hash table must be recomputed. This is done by typeing
%rehash
The hash table is also automatically recomputed when you change your path at the prompt or start another shell.

The hashstat command
The hashstat command displays performance statistics to show the effectiveness of its search for commands from the hash table.

The source command
The source command is a shell build-in command, that is, part of the shell's internal code. It is used to execute a command or set of commands from a file.
%source .login

The Shell prompts
The C Shell has two prompts: the primary prompt (%) and the secondary prompt (?).
% set prompt = "$LOGNAME>"
The secondary prompt appears when you are writing online scripts at the prompt. Whenever shell programming constructs are entered, followed by a new line, the secondary prompt appears and continues to appear until the construct is properly terminated.
 
Secondary prompt example
% foreach pal (joe tom ann)
? mail $pal < memo
? end
%

Command Grouping
A command line can consist of multiple commands. Each command is separated by a semicolon and the command line is terminated with a new line.
% ls; pwd; cal 1995
% (ls; pwd; cal 1997) > outputfile

Conditional execution of commands
With conditional execution, two command strings are separated ty && or ||

% grep '^tom' /etc/passwd && mail tom <letter
If first command is successful, the second command after the && is executed

% grep '^tom' /etc/passwd || echo "tom is not a user here"
If first command fails(has a non zero exit status), the second command after || is executed

Command in background
%man xview | lp&

Reexecuting commands
If you type !!, the last command is reexecuted. If you type ! followed by a number, the number is associated with the command from the history list and the command is executed. If you type ! followed by a letter, the last command that started with that letter is executed. The caret (^) is also used as a shortcut method for editing the previous command.
 
Reexecuting commands example
%date
%!!
%!3
%!d
%dare
%^r^t		 run date command
rerun data command
 

type erro
replace r with t in last cmd, run date 

Filename Completion: The filec variable
When running interactively, the C Shell provides a shortcut method for typing a filename or user name. The build-in filec variable, when set, is used for what is called filename completion. If you type the first few significant characters of a file in the current working directory and press the ESC key, the shell fills in the rest of the filename, provided that there are not a number of other files beginning with the same characters.