Variables (Linux in a Nutshell, 4th Edition)

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.

Variable	Description
${var}	The value of variable var.
${var[i]}	Select word or words in position i of var. i can be a single number, a range m-n, a range -n (missing m implies 1), a range m- (missing n implies all remaining words), or * (select all words). i also can be a variable that expands to one of these values.
${#var}	The number of words in var.
${#argv}	The number of arguments.
$0	Name of the program.
${argv[n]}	Individual arguments on command line (positional parameters); 1 ≤ n ≤ 9.
${n}	Same as ${argv[n]}.
*${argv[]}**	All arguments on command line.
$*	Same as *{$argv[]}**.
$argv[$#argv]	The last argument.
${?var}	Return 1 if var is set, 0 if not.
$$	Process number of current shell; useful as part of a filename for creating temporary files with unique names.
${?name}	Return 1 if name is set, 0 if not.
$?0	Return 1 if input filename is known, 0 if not.

8.4.1.1. Examples

Sort the third through last arguments and save the output in a file whose name is unique to this process:

sort $argv[3-] > tmp.$$

Process .tcshrc commands only if the shell is interactive (i.e., the prompt variable must be set):

if ($?prompt) then
   set commands,
   alias commands,
   etc.
endif

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. Prevents further substitution. Useful when the variable contains filename metacharacters that should not be expanded.
:x: Quote a pattern, expanding it into a wordlist.

8.4.2.1. Examples using pathname modifiers

The following table shows the effect of pathname modifiers if the aa variable is set as follows:

set aa=(/progs/num.c /book/chap.ps)

Variable portion	Specification	Output result
Normal variable	echo $aa	/progs/num.c /book/chap.ps
Second root	echo $aa[2]:r	/book/chap
Second header	echo $aa[2]:h	/book
Second tail	echo $aa[2]:t	chap.ps
Second extension	echo $aa[2]:e	ps
Root	echo $aa:r	/progs/num /book/chap.ps
Global root	echo $aa:gr	/progs/num /book/chap
Header	echo $aa:h	/progs /book/chap.ps
Global header	echo $aa:gh	/progs /book
Tail	echo $aa:t	num.c /book/chap.ps
Global tail	echo $aa:gt	num.c chap.ps
Extension	echo $aa:e	c /book/chap.ps
Global extension	echo $aa:ge	c ps

8.4.2.2. Examples using quoting modifiers

Unless quoted, the shell expands variables to represent files in the current directory:

% set a="[a-z]*" A="[A-Z]*"
% echo "$a" "$A"
[a-z]* [A-Z]*

% echo $a $A
at cc m4 Book Doc

% echo $a:x $A
[a-z]* Book Doc

% set d=($a:q $A:q)
% echo $d
at cc m4 Book Doc

% echo $d:q
[a-z]* [A-Z]*

% echo $d[1] +++ $d[2]
at cc m4 +++ Book Doc

% echo $d[1]:q
[a-z]*

8.4.3. Predefined Shell Variables

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

set var=value

or by simply turning the variable on:

set var

In the following table, variables that accept values are shown with the equals sign followed by the type of value they accept; the value is then described. (Note, however, that variables such as argv, cwd, and status are never explicitly assigned.) For variables that are turned on or off, the table describes what they do when set. tcsh automatically sets (and, in some cases, updates) the variables addsuffix, argv, autologout, command, cwd, dirstack, echo-style, edit, gid, home, loginsh, logout, oid, owd, path, prompt, prompt2, prompt3, shell, shlvl, status, tcsh, term, tty, uid, user, and version.

Variable	Description
addsuffix	Append / to directories and a space to files during tab completion to indicate a precise match.
afsuser	Set value to be used instead of the local username for Kerberos authentication with the autologout locking feature.
ampm	Display all times in 12-hour format.
argv=(args)	List of arguments passed to current command; default is ( ).
autocorrect	Check spelling before attempting to complete commands.
autoexpand	Expand history (such as ! references) during command completion.
autolist[=ambiguous]	Print possible completions when correct one is ambiguous. If ambiguous is specified, print possible completions only when completion adds no new characters.
autologout=logout-minutes [locking-minutes]	Log out after logout-minutes of idle time. Lock the terminal after locking-minutes of idle time, requiring a password before continuing. Not used if the DISPLAY environment variable is set.
backslash_quote	Always allow backslashes to quote \, ', and ".
catalog	Use tcsh.${catalog} as the filename of the message catalog. The default is tcsh.
cdpath=dirs	List of alternate directories to search when locating arguments for cd, popd, or pushd.
color	Turn on color for ls-F, ls, or both. Setting to nothing is equivalent to setting for both.
colorcat	Enable color escape sequence for Native Language System (NLS) support and display NLS messages in color.
command	If set, hold the command passed to the shell with the -c option.
complete=enhance	When enhance, ignore case in completion, treat ., -, and _ as word separators, and consider _ and - to be the same.
continue=cmdlist	If set to a list of commands, continue those commands instead of starting new ones.
continue_args=cmdlist	Like continue, but execute the following: echo `pwd` $argv > ~/.`cmd_pause; %cmd`
correct={cmd\|complete\|all}	When cmd, spellcheck commands. When complete, complete commands. When all, spellcheck whole command line.
cwd=dir	Full pathname of current directory.
dextract	When set, the pushd command extracts the desired directory and puts it at the top of the stack instead of rotating the stack.
dirsfile=file	History file consulted by dirs -S and dirs -L. Default is ~/.cshdirs.
dirstack	Directory stack, in array format. dirstack[0] is always equivalent to cwd. The other elements can be artificially changed.
dspmbyte=code	Enable use of multibyte code; for use with Kanji. See the tcsh manpage for details.
dunique	Make sure that each directory exists only once in the stack.
echo	Redisplay each command line before execution; same as csh -x command.
echo_style={bsd\|sysv\|both\|none}	Don't echo a newline with -n option (bsd), parse escaped characters (sysv), do both, or do neither.
edit	Enable command-line editor. Set by default for interactive shells.
ellipsis	For use with prompt variable. Use ... to represent skipped directories.
fignore=suffs	List of filename suffixes to ignore during filename completion.
gid	User's group ID.
group	User's group name.
histchars=ab	A two-character string that sets the characters to use in history substitution and quick substitution (default is !^).
histdup={all\|prev\|erase}	Maintain a record only of unique history events (all), do not enter a new event when it is the same as the previous one (prev), or remove an old event that is the same as the new one (erase).
histfile=file	History file consulted by history -S and history -L. Default is ~/.history.
histlit	Do not expand history lines when recalling them.
history=n format	The first word indicates the number of commands to save in the history list. The second indicates the format with which to display that list (see Section 8.4.4 for possible formats).
home=dir	Home directory of user, initialized from HOME. The ~ character is shorthand for this value.
ignoreeof	Ignore an end-of-file (EOF) from terminals; prevents accidental logout.
implicitcd	If directory name is entered as a command, cd to that directory. Can be set to verbose to echo the cd to standard output.
inputmode={insert\|overwrite}	Control editor's mode.
killdup={all\|prev\|erase}	Enter only unique strings in the kill ring (all), do not enter new string when it is the same as the current killed string (prev), or erase from the kill ring an old string that is the same as the current string (erase).
killring=num	Set the number of killed strings to keep in memory to num. The default is 30. If unset or set to a number less than 2, keep only the most recent killed string.
listflags=flags	One or more of the x, a, or A options for the ls-F built-in command. Second word can be set to path for ls command.
listjobs[=long]	When a job is suspended, list all jobs (in long format, if specified).
listlinks	In ls -F command, include type of file to which links point.
listmax=`num`	Do not allow list-choices to print more than num choices before prompting.
listmaxrows=`num`	Do not allow list-choices to print more than num rows of choices before prompting.
loginsh	Set if shell is a login shell.
logout	Indicates status of an imminent logout (normal, automatic, or hangup).
mail=(n files)	One or more files checked for new mail every 5 minutes or (if `n` is supplied) every `n` seconds.
matchbeep={never\|nomatch\|ambiguous\|notunique}	Specifies circumstances under which completion should beep: never, if no match exists, if multiple matches exist, or if multiple matches exist and one is exact. If unset, ambiguous is used.
nobeep	Disable beeping.
noclobber	Don't redirect output to an existing file; prevents accidental destruction of files.
noding	Don't print "DING!" in prompt time specifiers when the hour changes.
noglob	Turn off filename expansion; useful in shell scripts.
nokanji	Disable Kanji (if supported).
nonomatch	Treat filename metacharacters as literal characters if no match exists (e.g., vi ch`` creates new file ch`` instead of printing "No match").
nostat=directory-list	Do not stat directory-list during completion.
notify	Declare job completions when they occur.
owd	Old working directory.
path=(dirs)	List of pathnames in which to search for commands to execute. Initialized from PATH; the default is . /usr/ucb /usr/bin.
printexitvalue	Print all nonzero exit values.
prompt='str'	String that prompts for interactive input; default is %. See Section 8.4.4 later in this chapter for formatting information.
prompt2='str'	String that prompts for interactive input in foreach and while loops and continued lines (those with escaped newlines). See Section 8.4.4 for formatting information.
prompt3='str'	String that prompts for interactive input in automatic spelling correction. See Section 8.4.4 for formatting information.
promptchars=cc	Use the two characters specified as cc with the %# prompt sequence to indicate normal users and the superuser, respectively.
pushdsilent	Do not print directory stack when pushd and popd are invoked.
pushdtohome	Change to home directory when pushd is invoked without arguments.
recexact	Consider completion to be concluded on first exact match.
recognize_only_executables	When command completion is invoked, print only executable files.
rmstar	Prompt before executing the command rm *.
rprompt=string	The string to print on the right side of the screen while the prompt is displayed on the left. Specify as for prompt.
savedirs	Execute dirs -S before exiting.
savehist=max [merge]	Execute history -S before exiting. Save no more than max lines of history. If specified, merge those lines with previous history saves, and sort by time.
sched=string	Format for sched's printing of events. See Section 8.4.4 for formatting information.
shell=file	Pathname of the shell program.
shlvl	Number of nested shells.
status=`n`	Exit status of last command. Built-in commands return 0 (success) or 1 (failure).
symlinks={chase\|ignore\|expand}	Specify manner in which to deal with symbolic links. Expand them to real directory name in cwd (chase), treat them as real directories (ignore), or expand arguments that resemble pathnames (expand).
tcsh	Version of tcsh.
term	Terminal type.
time='n %c'	If command execution takes more than n CPU seconds, report user time, system time, elapsed time, and CPU percentage. Supply optional `%``c` flags to show other data.
tperiod	Number of minutes between executions of periodic alias.
tty	Name of tty, if applicable.
uid	User ID.
user	Username.
verbose	Display a command after history substitution; same as tcsh -v.
version	Shell's version and additional information, including options set at compile time.
visiblebell	Flash screen instead of beeping.
watch=([n] user terminal...)	Watch for user logging in at terminal, where terminal can be a tty name or any. Check every n minutes, or 10 by default.
who=string	Specify information to be printed by watch.
wordchars=chars	List of all nonalphanumeric characters that may be part of a word. Default is *?_-.[ ]~=.

8.4.4. Formatting for the Prompt Variable

tcsh provides a list of substitutions that can be used in formatting the prompt. 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
%$var: The value of the shell or environment variable var
%{string%}: Include string as a literal escape sequence to change terminal attributes (but should not move the cursor location); cannot be the last sequence in the prompt
\c, ^c: Parse c as in the bindkey built-in command
%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
%j: The number of jobs
%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 use full pathnames instead of ~ notation
%D: Day of month (e.g., 09, 10)
%L: Clear from the end of the prompt to the end of the display or the line.
%M: Fully qualified hostname
%P: Current time, with seconds (24-hour format)
%R: In prompt2, the parser status; in prompt3, the corrected string; and in history, the history string
%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)

8.4.6. Environment Variables

tcsh maintains a set of environment variables, which are distinct from shell variables and aren't really part of the shell. Shell variables are meaningful only within the current shell, but environment variables are exported automatically, making them available globally. For example, 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 tcsh shell variables. When either one changes, the value is copied to the other.

AFSUSER: Alternative to local user for Kerberos authentication with autologout locking; same as afsuser.
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:

COLUMNS: Number of columns on terminal.
DISPLAY: Identifies user's display for the X Window System. If set, the shell doesn't set autologout.
EDITOR: Pathname to default editor. See also VISUAL.
HOST: Name of machine.
HOSTTYPE: Type of machine. Obsolete; will be removed eventually.
HPATH: Colon-separated list of directories to search for documentation.
LANG: Preferred language. Used for native language support.
LC_CTYPE: The locale, as it affects character handling. Used for native language support.
LINES: Number of lines on the screen.
LOGNAME: Another name for the USER variable.
LS_COLORS: Colors for use with the ls command. See the tcsh manpage for detailed information.
MACHTYPE: Type of machine.
MAIL: The file that holds mail. Used by mail programs. This is not the same as the shell variable mail, which only checks for new mail.
NOREBIND: Printable characters not rebound. Used for native language support.
OSTYPE: Operating system.
PWD: The current directory; the value is copied from cwd.
REMOTEHOST: Machine name of remote host.
SHELL: Undefined by default; once initialized to shell, the two are identical.
TERMCAP: The file that holds the cursor-positioning codes for your terminal type. Default is /etc/termcap.
VENDOR: System vendor.
VISUAL: Pathname to default full-screen editor. See also EDITOR.