8.4.1. Variable Substitution

In the following substitutions, braces ({}) are optional, except when needed to separate a variable name from following characters that would otherwise be considered part of the name:

8.4.2. Variable Modifiers

Except for $?var, $$, and $?0, the variable substitutions in the preceding section may be followed by one of these modifiers (when braces are used, the modifier goes inside them):

:r

Return the variable's root (the portion before the last dot).

:e

Return the variable's extension.

:h

Return the variable's header (the directory portion).

:t

Return the variable's tail (the portion after the last slash).

:gr

Return all roots.

:ge

Return all extensions.

:gh

Return all headers.

:gt

Return all tails.

:q

Quote a wordlist variable, keeping the items separate. Useful when the variable contains filename metacharacters that should not be expanded.

:x

Quote a pattern, expanding it into a wordlist.

8.4.3. Predefined Shell Variables

Variables can be set in one of two ways, by assigning a value:

set var=value

set var

8.4.4. Formatting for the Prompt Variable

tcsh provides a list of substitutions that can be used in formatting the prompt. (csh allows only plain-string prompts and the ! history substitution shown in the following list.) The list of available substitutions includes:

%%

Literal %

%/

The present working directory

%~

The present working directory, in ~ notation

%#

# for the superuser, > for others

%?

Previous command's exit status

%b

End boldfacing

%c[[0]n], %.[[0]n]

The last n (default 1) components of the present working directory; if 0 is specified, replace removed components with /<skipped>

%d

Day of the week (e.g., Mon, Tue)

%h, %!, !

Number of current history event

%l

Current tty

%m

First component of hostname

%n

Username

%p

Current time, with seconds (12-hour mode)

%s

End standout mode (reverse video)

%t, %@

Current time (12-hour format)

%u

End underlining

%w

Month (e.g., Jan, Feb)

%y

Year (e.g., 99, 00)

%B

Begin boldfacing

%C

Similar to %c, but uses full pathnames instead of ~ notation

%D

Day of month (e.g., 09, 10)

%M

Fully qualified hostname

%P

Current time, with seconds (24-hour format)

%S

Begin standout mode (reverse video)

%T

Current time (24-hour format)

%U

Begin underlining

%W

Month (e.g., 09, 10)

%Y

Year (e.g., 1999, 2000)

8.4.5. Sample .cshrc File

# PREDEFINED VARIABLES

set path=(~ ~/bin /usr/ucb /bin /usr/bin . )
set mail=(/usr/mail/tom)

if ($?prompt) then             # settings for interactive use
  set echo
  set noclobber ignoreeof

  set cdpath=(/usr/lib /usr/spool/uucp)
# Now I can type cd macros
# instead of cd /usr/lib/macros

  set history=100
  set prompt='tom \!% '         # includes history number
  set time=3

# MY VARIABLES

  set man1="/usr/man/man1"     # lets me do   cd $man1, ls $man1
  set a="[a-z]*"               # lets me do   vi $a
  set A="[A-Z]*"               # or           grep string $A

# ALIASES

  alias c "clear; dirs"        # use quotes to protect ; or |
  alias h "history|more"
  alias j jobs -l
  alias ls ls -sFC             # redefine ls command
  alias del 'mv \!* ~/tmp_dir' # a safe alternative to rm
endif

8.4.6. Environment Variables

The C shell maintains a set of environment variables, which are distinct from shell variables and aren't really part of the C shell. Shell variables are meaningful only within the current shell, but environment variables are exported automatically, making them available globally. For example, C-shell variables are accessible only to a particular script in which they're defined, whereas environment variables can be used by any shell scripts, mail utilities, or editors you might invoke.

Environment variables are assigned as follows:

setenv VAR value

By convention, environment variable names are all uppercase. You can create your own environment variables, or you can use the predefined environment variables that follow.

The following environment variables have corresponding C-shell variables. When either one changes, the value is copied to the other (italics means the variable is specific to tcsh):

GROUP

User's group name; same as group.

HOME

Home directory; same as home.

PATH

Search path for commands; same as path.

SHLVL

Number of nested shell levels; same as shlvl.

TERM

Terminal type; same as term.

USER

User's login name; same as user.

Other environment variables, which do not have corresponding shell variables, include the following (italics means the variable is specific to tcsh):