A simple command (designated cmd below) consists of a command name, possibly followed by one or more arguments. This basic form may be modified or combined with other commands to form more complex command sequences:

cmd             Run cmd
cmd &           Run cmd in the background
cmd > file      Write cmd output to file (overwrites file)
cmd >> file     Write cmd output to file (appends to file)
cmd < file      Take cmd input from file
cmd1 ; cmd2     Run cmd1, then cmd2
cmd1 | cmd2     Write cmdl output to input of cmd2
(cmd1 ; cmd2)   Run cmdl cmd cmd2 in subshell
cmd1 'cmd2'     Use cmd2 to produce arguments for cmd1

The shell reads one or more files from your home directory when it starts up, and possibly one file when it terminates. The files are described in the following table. No error occurs if any given file does not exist.

At startup, a login shell reads, in order, ˜/.cshrc, ˜/.history, ˜/.login, and (for tcsh only) ˜/.cshdirs. A non-login shell reads only ˜/.cshrc at startup.

At termination, a login shell reads ˜/.logout and writes ˜/.history and (for tcsh only) ˜/.cshdirs if the appropriate variables are set. (˜/.history is saved if savehist is set. In tcsh, ˜/.cshdirs is saved if savedirs is set.) A non-login shell simply exits.

To execute commands in ˜/.cshrc that will only apply to interactive shells, place them inside the following construct:

if ($?prompt) then
    commands
endif

To execute commands only for tcsh, place them inside this construct:

if ($?tcsh) then
    commands
endif

There are two types of variables: shell variables and environment variables. Shell variables are available only to the shell in which they are defined. Environment variables are available to the current shell and also to other processes (including subshells) that are started from the shell. By convention, shell variables are lowercase and environment variables are uppercase.

Some useful shell variables are listed in the table below.

Many environment variables (such as HOME, PATH, SHELL, TERM, and USER) are used like the corresponding shell variables with lowercase names. Other useful environment variables are listed in the table below.

Several characters have special meaning to the shell.

The shell’s history mechanism allows you to recall previous events (commands) and then repeat them. To enable command history, set the history shell variable in ˜/.cshrc to the number of events that you want the shell to remember. To preserve your history across logins, set the savehist shell variable.

The history command displays your current history:

history          Display entire history list
history n        Display last n events from history list

% mroe file1 file2 file3
mroe: Command not found.
% ^ro^or
more file1 file2 file3

To move around the file system, you specify a directory name as the argument to a directory-changing command. The directories shown below have special names.

The cd command changes to a given directory, which becomes your current directory:

cd                 Move to your home directory
cd dir1            Move down one level to dir1
cd dir1/dir2       Move down two levels, through dir1 to dir2
cd ..              Move up one level to parent directory
cd ../..           Move up two levels to parent of parent
cd ../dir3         Move up a level, then back down to dir3
cd /               Move to root directory (top of file system)
cd ˜dubois         Move to home directory of dubois account
cd -               Move to last location (tcsh only)

The shell maintains a directory stack. Stack entries are numbered, starting from 0. pushd and popd change directory (like cd ), but they also add and remove entries from the stack as shown below:

pushd dir        Add dir to stack and change to it
pushd            Exchange top two stack entries
pushd +n         Rotate stack so entry n is on top
popd             Drop top entry and return to previous entry
popd +n          Drop entry n entry from stack (tcsh, some versions of csh)

The dirs command displays or clears the directory stack:

dirs             Display stack
dirs -l          Display stack using long names (no ˜name abbreviations)
dirs -n          Display stack, wrapping output (tcsh only)
dirs -v          Display stack, including entry numbers, one line per entry (tcsh only)
dirs -c          Clear stack (tcsh only)

In tcsh, the –l, –n, and –v flags can also be used with cd, pushd, and popd, and have the same meaning as for dirs.

In tcsh, typing =n at the beginning of a command argument is equivalent to typing the value of stack entry n. =- refers to the final entry. Filename completion may be used with arguments that begin with =n/ or =-/.

Aliases allow short names to be given to commands or command sequences. Invoking the alias name is equivalent to invoking the corresponding commands. To create or display alias definitions, or to remove aliases, use the following commands:

alias name definition     Define alias name
alias name                Display definition for alias name
alias                     Display all alias definitions
unalias name              Remove alias name
unalias *                 Remove all aliases

If a definition contains special characters, it should be quoted.

When you invoke an alias, any arguments are added to the end of the command to which the alias expands. To place arguments at a specific location within the command, use one of the following sequences in the alias definition.

To use filename completion, type a prefix of a filename and hit the completion key. If the prefix is unique, the shell types the rest of the filename for you. Otherwise, it types as much as is common to all matches, and then beeps. In tcsh, the completion key is TAB and filename completion is always active. In csh, the completion key is ESC; in addition, you must set the filec variable in ˜/.cshrc to turn on filename completion.

To list completion matches for a prefix (e.g., when the prefix is ambiguous), type CTRL-D.

Words beginning with ˜ are completed as home directory references. In tcsh, words beginning with $ are completed as variable names and words beginning with =n are completed as though they began with the directory named by directory stack n.

Setting the fignore shell variable to a list of filename suffixes causes names ending in those suffixes to be ignored for completion.

tcsh allows programmed completions to be specified using the complete command, as shown below:

complete command word/pattern/list/suffix

command is the command to which the completion applies. The argument following the command is a completion rule that specifies how to complete a word or words from the command. Although the delimiter between parts of a completion rule is often a dash, it can be any character.

There may be more than one completion rule. Each rule has the parts listed below.

The word specifier determines how pattern is interpreted. If word is p, pattern indicates the word position or positions to which the rule applies. Otherwise, pattern is a filename pattern and the rule applies to any word whose leftmost part is matched by the pattern.

n         Word n
m-n       Words m through n
m*        Words m through last word
*         All words

The word lists from which completions can be chosen are listed below.

Job control allows you to suspend or terminate jobs, or move jobs between the foreground and background. Job control commands are shown below. When used, %j indicates the job of interest.

The job specifier %j has the following forms.

The fg and bg commands have the shorthand forms listed below.

If the notify shell variable is set, the shell notifies you immediately when background jobs finish. Otherwise, notification occurs when the next prompt is printed.

Use stty to specify whether or not background jobs can write to your terminal, as shown below:

stty tostop       Force background jobs to stop when ready to write to terminal
stty -tostop      Allow background jobs to write to terminal

tcsh lets you interactively browse up and down through your history list, selecting and editing commands before executing them.

Use CTRL-P and CTRL-N (or up arrow and down arrow) to move up and down through your history list. Each recalled command is displayed on the current command line. To execute the command, hit RETURN. To cancel it, hit CTRL-C.

To edit commands, tcsh provides a command line editor that uses emacs-like or vi-like key bindings. Select the appropriate set using bindkey -e or bindkey -v. Some of the most useful editing commands are shown in the rest of this section. (Use bindkey with no arguments to see all your key bindings.)

bindkey -e            Select emacs bindings
bindkey -v            Select vi bindings
bindkey -d            Restore default bindings
bindkey -u            Display bindkey usage message
bindkey -l            List editing commands and their meanings
bindkey               List all key bindings
bindkey key           List binding for key
bindkey key cmd       Bind key to editing command cmd
bindkey -c key cmd    Bind key to UNIX command cmd
bindkey -s key str    Bind key to string str
bindkey -r key        Remove binding for key