tcsh - C shell with file-name completion and command-line editing


tcsh [-bcdefFimnqstvVxX]
[arg ...]

tcsh -l


The tcsh(1) utility is an enhanced but completely compatible version of the Berkeley Software Distribution (BSD) C shell, csh(1). It is a command-language interpreter and can be used both as an interactive login shell and a shell-script command processor. It includes a command-line editor, programmable word completion (covered in "Completion and listing"), spelling correction, a history mechanism (covered in "History substitution"), job control, and a C-like syntax. The NEW FEATURES section describes major enhancements of tcsh(1) over csh(1).

Throughout this topic, features of tcsh(1) not found in most csh(1) implementations (specifically, the 4.4BSD csh(1)) are labeled with plus sign (+), and features that are present in csh(1) but not usually documented are labeled with the letter "u."


If the first argument (argument 0) to the shell is '-', it is a login shell. A login shell can be also specified by invoking the shell with the -l flag as the only argument.

The rest of the flag arguments are interpreted as follows:

Force a "break" from option processing, causing any further shell arguments to be treated as non-option arguments. The remaining arguments will not be interpreted as shell options. You can use this to pass options to a shell script without confusion or possible subterfuge. The shell will not run a set-user ID script without this option.
Read commands from the following argument (which must be present and must be a single argument), stored in the command shell variable for reference, and executed. Any remaining arguments are placed in the argv shell variable.
Load the directory stack from ~/.cshdirs (see "Startup and shutdown") whether or not it is a login shell. (+)
Exit if any invoked command terminates abnormally or yields a non-zero exit status.
Fast start; ignore ~/.tcshrc to start faster.
Interactive shell; prompt for top-level input even if it appears not to be a terminal. Shells are interactive without this option if their inputs and outputs are terminals.
The shell is a login shell. Only applicable if -l is the only flag specified.
Load ~/.tcshrc even if it does not belong to the effective user. Newer versions of su(1) can pass -m to the shell. (+)
Parse commands but do not execute them. This aids in debugging shell scripts.
Accept SIGQUIT (see "Signal handling"), and behave when it is used under a debugger. Job control is disabled. (u)
Take command input from the standard input.
Read and execute a single line of input. A backslash (\) can be used to escape the newline at the end of this line and continue onto another line.
Set the verbose shell variable so that command input is echoed after history substitution.
Set the verbose shell variable even before executing ~/.tcshrc.
Set the echo shell variable so that commands are echoed immediately before execution.
Set the echo shell variable even before executing ~/.tcshrc.

After the processing of flag arguments, if arguments remain but none of the -c, -i, -s, or -t options were given, the first argument is taken as the name of a file of commands, or script, to be executed. The shell opens this file and saves its name for possible resubstitution by "$0." Many systems use either the standard version 6 or version 7 shells whose shell scripts are not compatible with this shell. In these cases, the shell uses such a "standard" shell to execute a script whose first character is not a number sign (#) (and which does not start with a comment).

Remaining arguments are placed in the argv shell variable.


A login shell begins by executing commands from the system files /etc/csh.cshrc and /etc/csh.login. It then executes commands from files in the user's home directory: first ~/.tcshrc (+) or, if ~/.tcshrc is not found, ~/.cshrc, then ~/.history (or the value of the histfile shell variable), then ~/.login, and finally ~/.cshdirs (or the value of the dirsfile shell variable) (+). The shell may read /etc/csh.login before instead of after /etc/csh.cshrc, and ~/.login before instead of after ~/.tcshrc or ~/.cshrc and ~/.history, if so compiled; see the version shell variable. (+)

Non-login shells read only /etc/csh.cshrc and ~/.tcshrc or ~/.cshrc on startup.

Commands like stty(1) and tset(1), which need be run only once per login, usually go in one's ~/.login file. Users who need to use the same set of files with both csh(1) and tcsh(1) can have only a ~/.cshrc that checks for the existence of the tcsh shell variable before using tcsh(1)-specific commands, or can have both a ~/.cshrc and a ~/.tcshrc which sources (see the built-in command) ~/.cshrc. The rest of this manual uses "~/.tcshrc" to mean "~/.tcshrc ~/.tcshrc or, if ~/.tcshrc is not found, ~/.cshrc."

In the normal case, the shell begins reading commands from the terminal, prompting with '> '. Processing of arguments and the use of the shell to process files containing command scripts are described later.) The shell repeatedly reads a line of command input, breaks it into words, places it on the command history list, parses it and executes each command in the line.

You can log out by typing '^D' on an empty line, 'logout' or 'login' or through the shell's autologout mechanism (see the autologout shell variable). When a login shell terminates, it sets the logout shell variable to 'normal' or 'automatic,' as appropriate, then executes commands from the files /etc/csh.logout and ~/.logout. The shell may drop DTR on logout if so compiled; see the version shell variable.

The names of the system login and logout files vary from system to system for compatibility with different csh(1) variants; see FILES.


This topic explains the command-line editor, completion and listing, spelling corrections, and editor commands.

The completion and listing and spelling correction sections describe two sets of functionality that are implemented as editor commands, but which deserve their own treatment. Editor commands lists and describes the editor commands specific to the shell and their default bindings.

The command-line editor (+)

Command-line input can be edited using key sequences much like those used in GNU Emacs or vi(1). The editor is active only when the edit shell variable is set, which it is by default in interactive shells. The bindkey(1) built-in can display and change key bindings. By default, vi-style key bindings are used in the Interix version of the shell. On other systems, Emacs-style bindings may be the default, depending on how the shell was compiled; (unless the shell was compiled otherwise; see the version shell variable. The bindkey built-in can change the key bindings to emacs(1)-style bindings en masse.

The shell always binds the arrow keys (as defined in the TERMCAP environment variable) to the following:


It does this unless doing so would alter another single-character binding. One can set the arrow key escape sequences to the empty string with settc to prevent these bindings. The ANSI/VT100 sequences for arrow keys are always bound.

Other key bindings are, for the most part, what Emacs and vi(1) users would expect and can easily be displayed by bindkey, so there is no need to list them here. Likewise, bindkey can list the editor commands with a short description of each.

Note that editor commands and the shell do not have the same notion of a word as does the shell. The editor delimits words with any non-alphanumeric characters not in the shell variable wordchars, while the shell recognizes only white space and some of the characters with special meanings to it, listed under Lexical structure.

Completion and listing (+)

The shell is often able to complete words when given a unique abbreviation. Type part of a word (for example 'ls /usr/lost') and hit the tab key to run the complete-word editor command. The shell completes the file name '/usr/lost' to '/usr/lost+found/', replacing the incomplete word with the complete word in the input buffer. (Note the terminal '/'; completion adds a '/' to the end of completed directories and a space to the end of other completed words, to speed typing and provide a visual indicator of successful completion. The addsuffix shell variable can be unset to prevent this.) If no match is found (perhaps '/usr/lost+found' does not exist), the terminal bell rings. If the word is already complete (perhaps there is a '/usr/lost' on your system, or perhaps you were thinking too far ahead and typed the whole thing) a '/' or space is added to the end if it is not already there.

Completion works anywhere in the line, not just at the end; completed text pushes the rest of the line to the right. Completion in the middle of a word often results in leftover characters to the right of the cursor, which must be deleted.

Commands and variables can be completed in much the same way. For example, typing 'em[tab]' would complete 'em' to 'emacs' if emacs(1) were the only command on your system beginning with 'em'. Completion can find a command in any directory in path or if given a full path name. Typing 'echo $ar[tab]' completes '$ar' to '$argv' if no other variable begins with 'ar'.

The shell parses the input buffer to determine whether the word you want to complete should be completed as a file name, command or variable. The first word in the buffer and the first word following ';', '|', '|&', '&&' or '||' is considered to be a command. A word beginning with '$' is considered to be a variable. Anything else is a file name. An empty line is 'completed' as a file name.

You can list the possible completions of a word at any time by typing '^D' to run the delete-char-or-list-or-eof editor command. The shell lists the possible completions using the ls-F(1) built-in and reprints the prompt and unfinished command line, for example:

> ls /usr/l[^D]
lbin/	 lib/		local/	lost+found/
> ls /usr/l
If the autolist shell variable is set, the shell lists the remaining choices (if there are any) whenever completion fails:
> set autolist
> nm /usr/lib/libt[tab]
libtermcap.a@ libtermlib.a@
> nm /usr/lib/libterm
If autolist is set to 'ambiguous', choices are listed only when completion fails and adds no new characters to the word being completed.

A file name to be completed can contain variables, your own or others' home directories abbreviated with '~' (see File-name substitution) and directory-stack entries abbreviated with '=' (see Directory-stack substitution). This is illustrated in the following example:

> ls ~k[^D]
kahn	kas	 kellogg
> ls ~ke[tab]
> ls ~kellogg/
> set local = /usr/local
> ls $lo[tab]
> ls $local/[^D]
bin/ etc/ lib/ man/ src/
> ls $local/

Note that variables can also be expanded explicitly with the expand-variables editor command.

delete-char-or-list-or-eof lists only at the end of the line. In the middle of a line, it deletes the character under the cursor, and on an empty line, it logs one out or, if ignoreeof is set, does nothing. 'M-^D', bound to the editor command list-choices, lists completion possibilities anywhere on a line. In addition, list-choices (or any one of the related editor commands that do or do not delete, list and/or log out, listed under delete-char-or-list-or-eof) can be bound to '^D' with the bindkey built-in command.

The complete-word-fwd and complete-word-back editor commands (not bound to any keys by default) can be used to cycle up and down through the list of possible completions, replacing the current word with the next or previous word in the list.

The shell variable fignore can be set to a list of suffixes to be ignored by completion. Consider the following:

> ls
Makefile		condiments.h~   main.o	side.c
README		main.c		meal	side.o
condiments.h	main.c~
> set fignore = (.o \~)
> emacs ma[^D]
main.c   main.c~  main.o
> emacs ma[tab]
> emacs main.c
'main.c~' and 'main.o' are ignored by completion (but not listing), because they end in suffixes in fignore. Note that a '\' was needed in front of '~' to prevent it from being expanded to home as described in the section on file-name substitution. fignore is ignored if only one completion is possible.

If the complete shell variable is set to 'enhance', completion 1) ignores case and 2) considers periods, hyphens and underscores ('.', '-' and '_') to be word separators, and considers hyphens and underscores to be equivalent. For example, if you had the following files:

comp.lang.c	comp.lang.perl   comp.std.c++
comp.lang.c++	comp.std.c
and typed 'mail -f c.l.c[tab]', it would be completed to 'mail -f comp.lang.c', and ^D would list 'comp.lang.c' and 'comp.lang.c++'. 'mail -f c..c++[^D]' would list 'comp.lang.c++' and 'comp.std.c++'. Typing 'rm a—file[^D]' in the following directory
A_silly_file  a-hyphenated-file  another_silly_file
would list all three files because case is ignored and hyphens and underscores are equivalent. Periods, however, are not equivalent to hyphens or underscores.

Completion and listing are affected by several other shell variables: recexact can be set to complete on the shortest possible unique match, even if more typing might result in a longer match:

> ls
fodder   foo	food	 foonly
> set recexact
> rm fo[tab]
just beeps, because 'fo' could expand to 'fod' or 'foo', but if you type another 'o',
> rm foo[tab]
> rm foo
the completion completes on 'foo', even though 'food' and 'foonly' also match. autoexpand can be set to run the expand-history editor command before each completion attempt. You can set autocorrect to correct the spelling of the word to be completed (see Spelling correction) before each completion attempt, and you can set correct to complete commands automatically after you hit 'return'. matchbeep can be set to make completion beep or not beep in a variety of situations, and nobeep can be set to never beep at all. nostat can be set to either a list of directories, patterns that match directories, or both, to prevent the completion mechanism from calling stat(3) for those directories. listmax and listmaxrows can be set to limit the number of items and rows (respectively) that are listed without asking first. recognize_only_executables can be set to make the shell list only executables when listing commands, but it is quite slow.

The complete built-in command can be used to tell the shell how to complete words other than file names, commands, and variables. Completion and listing do not work on glob-patterns (see File-name substitution), but the list-glob and expand-glob editor commands perform equivalent functions for glob-patterns.

Spelling correction (+)

The shell can sometimes correct the spelling of file names, commands, and variable names, in addition to completing and listing them.

The spelling of individual words can be corrected with the spell-word editor command (usually bound to M-s and M-S) and the entire input buffer with spell-line (usually bound to M-$). The correct shell variable can be set to 'cmd' to correct the command name, or 'all' to correct the entire line each time return is typed, and autocorrect can be set to correct the word to be completed before each completion attempt.

When spelling correction is invoked in any of these ways, and the shell thinks that any part of the command line is misspelled, it prompts with the corrected line:

> set correct = cmd
> lz /usr/bin
CORRECT>ls /usr/bin (y|n|e|a)?

You can answer 'y' or space to execute the corrected line, 'e' to leave the uncorrected command in the input buffer, 'a' to abort the command as if '^C' had been hit, and anything else to execute the original line unchanged.

Spelling correction recognizes user-defined completions (see the complete built-in command). If an input word in a position for which a completion is defined resembles a word in the completion list, spelling correction registers a misspelling and suggests the latter word as a correction. However, if the input word does not match any of the possible completions for that position, spelling correction does not register a misspelling.

Like completion, spelling correction works anywhere in the line, pushing the rest of the line to the right, and possibly leaving extra characters to the right of the cursor.

Note that spelling correction is not guaranteed to work the way one intends, and is provided mostly as an experimental feature. Suggestions and improvements are welcome.

Editor commands (+)

'bindkey' lists key bindings and 'bindkey -l' lists and briefly describes editor commands. Only new or especially interesting editor commands are described here. See emacs(1) and vi(1) for descriptions of each editor's key bindings.

The character or characters to which each command is bound by default is given in parentheses. '^character' means a control character. 'M-character' indicates a metacharacter, typed as escape-character on terminals without a metakey. Case counts, but commands that are bound to letters by default are bound to both lowercase and uppercase letters for convenience.

complete-word (tab)
Completes a word as described under "Completion and listing."
complete-word-back (not bound)
Like complete-word-fwd, but steps up from the end of the list.
complete-word-fwd (not bound)
Replaces the current word with the first word in the list of possible completions. May be repeated to step down through the list. At the end of the list, beeps and reverts to the incomplete word.
complete-word-raw (^X-tab)
Like complete-word, but ignores user-defined completions.
copy-prev-word (M-^_)
Copies the previous word in the current line into the input buffer. See also insert-last-word.
dabbrev-expand (M-/)
Expands the current word to the most recent preceding one for which the current is a leading substring, wrapping around the history list (once) if necessary. Repeating dabbrev-expand without any intervening typing changes to the next previous word, and so on, skipping identical matches much like history-search-backward does.
delete-char (not bound)
Deletes the character under the cursor. See also delete-char-or-list-or-eof.
delete-char-or-eof (not bound)
Does delete-char if there is a character under the cursor or end-of-file on an empty line. See also delete-char-or-list-or-eof.
delete-char-or-list (not bound)
Does delete-char if there is a character under the cursor or list-choices at the end of the line. See also delete-char-or-list-or-eof.
delete-char-or-list-or-eof (^D)
Does delete-char if there is a character under the cursor, list-choices at the end of the line, or end-of-file on an empty line. See also those three commands, each of which only does a single action, and delete-char-or-eof, delete-char-or-list and list-or-eof, each of which does a different two out of the three.
down-history (down-arrow, ^N)
Like up-history, but steps down, stopping at the original input line.
end-of-file (not bound)
Signals an end of file, causing the shell to exit unless the ignoreeof shell variable is set to prevent this. See also delete-char-or-list-or-eof.
expand-history (M-space)
Expands history substitutions in the current word. See "History substitution." See also magic-space, toggle-literal-history and the autoexpand shell variable.
expand-glob (^X-*)
Expands the glob-pattern to the left of the cursor. See File-name substitution.
expand-line (not bound)
Like expand-history, but expands history substitutions in each word in the input buffer,
expand-variables (^X-$)
Expands the variable to the left of the cursor. See Variable substitution.
history-search-backward (M-p, M-P)
Searches backwards through the history list for a command beginning with the current contents of the input buffer up to the cursor and copies it into the input buffer. The search string may be a glob-pattern (see File-name substitution) containing '*', '?', '[]' or '{}'. up-history and down-history will proceed from the appropriate point in the history list. Emacs mode only. See also history-search-forward and i-search-back.
history-search-forward (M-n, M-N)
Like history-search-backward, but searches forward.
i-search-back (not bound)
Searches backward like history-search-backward, copies the first match into the input buffer with the cursor positioned at the end of the pattern, and prompts with 'bck: ' and the first match. Additional characters may be typed to extend the search, i-search-back may be typed to continue searching with the same pattern, wrapping around the history list if necessary (i-search-back must be bound to a single character for this to work), or one of the following special characters may be typed:
Appends the rest of the word under the cursor to the search pattern.
delete (or any character bound to backward-delete-char)
Undoes the effect of the last character typed and deletes a character from the search pattern if appropriate.
If the previous search was successful, aborts the entire search. If not, goes back to the last successful search.
Ends the search, leaving the current line in the input buffer.

Any other character not bound to self-insert-command terminates the search, leaving the current line in the input buffer, and is then interpreted as normal input. In particular, a carriage return causes the current line to be executed. Emacs mode only. See also i-search-fwd and history-search-backward.

i-search-fwd (not bound)
Like i-search-back, but searches forward.
insert-last-word (M-_)
Inserts the last word of the previous input line ('!$') into the input buffer. See also copy-prev-word.
list-choices (M-^D)
Lists completion possibilities as described in "Completion and listing." See also delete-char-or-list-or-eof and list-choices-raw.
list-choices-raw (^X-^D)
Like list-choices, but ignores user-defined completions.
list-glob (^X-g, ^X-G)
Lists (through the ls-F built-in) matches to the glob-pattern (see "File-name substitution") to the left of the cursor.
list-or-eof (not bound)
Does list-choices or end-of-file on an empty line. See also delete-char-or-list-or-eof.
magic-space (not bound)
Expands history substitutions in the current line, like expand-history, and appends a space. magic-space is designed to be bound to the spacebar, but is not bound by default.
normalize-command (^X-?)
Searches for the current word in PATH and, if it is found, replaces it with the full path to the executable. Special characters are quoted. Aliases are expanded and quoted, but commands within aliases are not. This command is useful with commands that take commands as arguments, such as 'dbx' and 'sh -x'.
normalize-path (^X-n, ^X-N)
Expands the current word as described under the 'expand' setting of the symlinks shell variable.
overwrite-mode (unbound)
Toggles between input and overwrite modes.
run-fg-editor (M-^Z)
Saves the current input line and looks for a stopped job with a name equal to the last component of the file name part of the EDITOR or VISUAL environment variables, or, if neither is set, 'ed' or 'vi.' If such a job is found, it is restarted as if 'fg %job' had been typed. This is used to toggle back and forth easily between an editor and the shell. Some users bind this command to '^Z' so they can do this even more easily.
run-help (M-h, M-H)
Searches for documentation on the current command, using the same notion of 'current command' as the completion routines, and prints it. There is no way to use a pager; run-help is designed for short help files. Documentation should be in a file named, command.1, command.6, command.8 or command, which should be in one of the directories listed in the HPATH environment variable. If there is more than one help file, only the first is printed.
self-insert-command (text characters)
In insert mode (the default), it inserts the typed character into the input line after the character under the cursor. In overwrite mode, it replaces the character under the cursor with the typed character. The input mode is normally preserved between lines, but the inputmode shell variable can be set to 'insert' or 'overwrite' to put the editor in that mode at the beginning of each line. See also overwrite-mode.
sequence-lead-in (arrow prefix, meta prefix, ^X)
Indicates that the following characters are part of a multi-key sequence. Binding a command to a multi-key sequence really creates two bindings: the first character to sequence-lead-in and the whole sequence to the command. All sequences beginning with a character bound to sequence-lead-in are effectively bound to undefined-key unless bound to another command.
spell-line (M-$)
Attempts to correct the spelling of each word in the input buffer, like spell-word, but ignores words whose first character is one of '!', '.', '\', '^', '-', '*' or '%' to avoid problems with switches, substitutions and the like. See "Spelling correction."
spell-word (M-s, M-S)
Attempts to correct the spelling of the current word as described in the section on spelling correction. Checks each component of a word that appears to be a path name.
toggle-literal-history (M-r, M-R)
Expands or 'unexpands' history substitutions in the input buffer. See also expand-history and the autoexpand shell variable.
undefined-key (any unbound key)
up-history (up-arrow, ^P)
Copies the previous entry in the history list into the input buffer. If histlit is set, uses the literal form of the entry. May be repeated to step up through the history list, stopping at the top.
vi-search-back (?)
Prompts with '?' for a search string (which may be a glob-pattern, as with history-search-backward), searches for it, and copies it into the input buffer. The bell rings if no match is found. Hitting return ends the search and leaves the last match in the input buffer. Hitting escape ends the search and executes the match. vi mode only.
vi-search-fwd (/)
Like vi-search-back, but searches forward.
which-command (M-?)
Does a which (see the description of the built-in command) on the first word of the input buffer.

Lexical structure

The shell splits input lines into words at blanks and tabs. The special characters '&', '|', ';', '<', '>', '(', and ')' and the doubled characters '&&', '||', '<<' and '>>' are always separate words, whether or not they are surrounded by white space.

When the shell's input is not a terminal, the number sign character (#) is taken to begin a comment. Each #, and the rest of the input line on which it appears, is discarded before further parsing.

A special character (including a blank or tab) may be prevented from having its special meaning, and possibly made part of another word, by preceding it with a backslash (\) or enclosing it in single ('"), double ('"') or backward ("') quotes. When not otherwise quoted, a newline preceded by a \ is equivalent to a blank, but inside quotes this sequence results in a newline.

All substitutions except history substitution can be prevented by enclosing the strings (or parts of strings) in which they appear with single quotes or by quoting the crucial character(s) (such as dollar sign ($) or "' for variable substitution or command substitution, respectively) with a backslash (\). History substitutions are quoted in the same way by backslashes, but not by single quotes. Strings quoted with double or backward quotes undergo variable substitution and command substitution, but other substitutions are prevented.

Text inside single or double quotes becomes a single word (or part of one). Metacharacters in these strings, including blanks and tabs, do not form separate words. Only in one special case (see Command substitution) can a double-quoted string yield parts of more than one word; single-quoted strings never do. Backward quotes are special: they signal command substitution, which might result in more than one word.

Quoting complex strings, particularly strings which themselves contain quoting characters, can be confusing. Quotes need not follow conventional rules of punctuation. It may be easier to quote not an entire string, but only those parts of the string which need quoting, using different types of quoting to do so if appropriate.

The backslash_quote shell variable can be set to make backslashes always quote '\', '", and '"'. (+) This might simplify complex quoting tasks, but it can cause syntax errors in csh(1) scripts.


This sections explains various transformations the shell performs on the input in the order in which those transformations occur. It also covers the data structures involved and the commands, and variables that affect them. Substitutions can be prevented by quoting as described in the section on lexical structure.

History substitution

Each command or "event" input from the terminal is saved in the history list. The previous command is always saved, and the history shell variable can be set to a number to save that many commands. The histdup shell variable can be set not to save duplicate events or consecutive duplicate events.

Saved commands are numbered sequentially from 1 and stamped with the time. It is not usually necessary to use event numbers, but the current event number can be made part of the prompt by placing an '!' in the prompt shell variable.

The shell saves history in expanded and literal (unexpanded) forms. If the histlit shell variable is set, commands that display and store history use the literal form.

The history built-in command can print, store in a file, restore and clear the history list at any time, and the savehist and histfile shell variables can be can be set to store the history list automatically on logout and restore it on login.

History substitutions introduce words from the history list into the input stream, making it easy to repeat commands, repeat arguments of a previous command in the current command, or correct spelling mistakes in the previous command with a minimum of typing and a high degree of confidence.

History substitutions begin with the exclamation point (!). They can begin anywhere in the input stream, but they do not nest. The ! may be preceded by a backslash (\) to prevent its special meaning; for convenience, a ! is passed unchanged when it is followed by a blank, tab, newline, = or (.

History substitutions also occur when an input line begins with ^. The characters used to signal history substitution (! and ^) can be changed by setting the histchars shell variable. Any input line that contains a history substitution is printed before it is executed.

A history substitution might have an "event specification", which indicates the event from which words are to be taken; a "word designator", which selects particular words from the chosen event; and/or a "modifier", which manipulates the selected words.

An event specification can be:

A number, referring to a particular event.
An offset, referring to the event n before the current event.
The current event. This should be used carefully in csh(1), where there is no check for recursion. tcsh(1) allows 10 levels of recursion. (+)
The previous event (equivalent to '-1')
The most recent event whose first word begins with the string s
The most recent event that contains the string s. The second '?' can be omitted if it is immediately followed by a newline.

The following is an example of a portion of a history list:

 9  8:30	nroff -man
10  8:31	cp
11  8:36	vi
12  8:37	diff

In the example, the commands are shown with their event numbers and time stamps. The current event, which has not yet been typed, is event 13. '!11' and '!-2' refer to event 11. '!!' refers to the previous event, 12. '!!' can be abbreviated '!' if it is followed by ':' (':' is described below). '!n' refers to event 9, which begins with 'n'. '!?old?' also refers to event 12, which contains 'old'. Without word designators or modifiers, history references simply expand to the entire event, so you might type '!cp' to redo the copy command or '!!|more' if the 'diff' output scrolled off the top of the screen.

History references may be insulated from the surrounding text with braces if necessary. For example, '!vdoc' would look for a command beginning with 'vdoc', and, in this example, not find one, but '!{v}doc' would expand unambiguously to 'vi wumpus.mandoc'. Even in braces, history substitutions do not nest.

(+) While csh(1) expands, for example, '!3d' to event 3 with the letter 'd' appended to it, tcsh(1) expands it to the last event beginning with '3d'. Only completely numeric arguments are treated as event numbers. This makes it possible to recall events beginning with numbers. To expand '!3d' as in csh(1), use '!\3d'.

To select words from an event, follow the event specification by a ':' and a designator for the words you want. The words of an input line are numbered from 0, the first (usually command) word being 0, the second word (first argument) being 1, and so on. The basic word designators are:

The first (command) word
The nth argument
The first argument, equivalent to '1'
The last argument
The word matched by an ?s? search.
A range of words
Equivalent to '0-y'
Equivalent to '^-$', but returns nothing if the event contains only one word
Equivalent to 'x-$'
Equivalent to 'x*', but omitting the last word ('$')

Selected words are inserted into the command line separated by single blanks. For example, the 'diff' command in the previous example might have been typed as 'diff !!:1.old !!:1' (using ':1' to select the first argument from the previous event) or 'diff !-2:2 !-2:1' to select and swap the arguments from the 'cp' command. If the order of the 'diff' did not matter, one could have said 'diff !-2:1-2' or simply 'diff !-2:*'. The 'cp' command might have been written 'cp !#:1.old', using '#' to refer to the current event. '!n:-' would reuse the first two words from the 'nroff' command to say 'nroff -man'.

The ':' separating the event specification from the word designator can be omitted if the argument selector begins with a '^', '$', '*', '%' or '-'. For example, our 'diff' command might have been 'diff !!^.old !!^' or, equivalently, 'diff !!$.old !!$'. However, if '!!' is abbreviated '!', an argument selector beginning with '-' will be interpreted as an event specification.

A history reference can have a word designator, but no event specification. It then references the previous command.

Continuing the 'diff' example, 'diff !^.old !^' might have been used or, to get the arguments in the opposite order, just 'diff !*'.

The word (or words) in a history reference can be edited, or "modified", by following it with one or more modifiers, each preceded by a ':':

Remove a trailing path-name component, leaving the head.
Remove all leading path-name components, leaving the tail.
Remove a file-name extension '.xxx', leaving the root name.
Remove all but the extension.
Change the first lowercase letter to uppercase.
Change the first uppercase letter to lowercase.
Substitute l for r. l is a string like r, not a regular expression as in the ed(1) command. Any character can be used as the delimiter in place of '/'; a '\' can be used to quote the delimiter inside l and r. The character '&' in the r is replaced by l; '\' also quotes '&'. If l is empty (""), the l from a previous substitution or the s from a previous '?s?' event specification is used. The trailing delimiter may be omitted if it is immediately followed by a newline.
Repeat the previous substitution.
Apply the following modifier once to each word.
a (+)
Apply the following modifier as many times as possible to a single word. 'a' and 'g' can be used together to apply a modifier globally. In the current implementation, using the 'a' and 's' modifiers together can produce an infinite loop. For example, ':as/f/ff/' will never terminate. This behavior might change in the future.
Print the new command line, but do not execute it.
Quote the substituted words, preventing further substitutions.
Like q, but break into words at blanks, tabs and newlines.

Modifiers are applied only to the first modifiable word (unless 'g' is used). It is an error for no word to be modifiable.

For example, the 'diff' command might have been written as 'diff !#^:r', using ':r' to remove '.old' from the first argument on the same line ('!#^'). One could say 'echo hello out there', then 'echo !*:u' to capitalize 'hello', 'echo !*:au' to say it out loud, or 'echo !*:agu' to really shout. One might follow 'mail -s "I forgot my password" rot' with '!:s/rot/root' to correct the spelling of 'root' (see the section on spelling correction for a different approach).

There is a special abbreviation for substitutions. '^', when it is the first character on an input line, is equivalent to '!:s^'. Thus '^rot^root' might have been used to make the spelling correction in the previous example. This is the only history substitution that does not explicitly begin with '!'.

(+) In csh(1) as such, only one modifier may be applied to each history or variable expansion. In tcsh(1), more than one may be used; for example:

% mv /usr/man/man1/wumpus.1
% man !$:t:r
man wumpus

In csh(1), the result would be 'wumpus.1:r'. A substitution followed by a colon may need to be insulated from it with braces:

> mv a.out /usr/games/wumpus
> setenv PATH !$:h:$PATH
Bad ! modifier: $.
> setenv PATH !{-2$:h}:$PATH
setenv PATH /usr/games:/bin:/usr/bin:.

The first attempt succeeds in csh(1) but fails in tcsh(1), because tcsh(1) expects another modifier after the second colon rather than '$'.

History can be accessed through the editor as well as through the substitutions just described. The up- and down-history, history-search-backward and -forward, i-search-back and -fwd, vi-search-back and -fwd, copy-prev-word and insert-last-word editor commands search for events in the history list and copy them into the input buffer. The toggle-literal-history editor command switches between the expanded and literal forms of history lines in the input buffer. expand-history and expand-line expand history substitutions in the current word and in the entire input buffer, respectively.

Alias substitution

The shell maintains a list of aliases that can be set, unset, and printed by the alias and unalias commands. After a command line is parsed into simple commands (see the section on commands) the first word of each command, left-to-right, is checked for an alias. If it does, the first word is replaced by the alias. If the alias contains a history reference, it undergoes history substitution as though the original command were the previous input line. If the alias does not contain a history reference, the argument list is left untouched.

Thus if the alias for 'ls' were 'ls -l' the command 'ls /usr' would become 'ls -l /usr', the argument list here would remain undisturbed. If the alias for 'lookup' were 'grep !^ /etc/passwd', 'lookup bill' would become 'grep bill /etc/passwd'. Aliases can be used to introduce parser metasyntax. For example, 'alias print 'pr \!* | lpr" defines a "command" ('print'), which prints its arguments on the line printer.

Alias substitution is repeated until the first word of the command has no alias. If an alias substitution does not change the first word (as in the previous example), it is flagged to prevent a loop. Other loops are detected and cause an error.

Some aliases are referred to by the shell. (See also "Special aliases.")

Variable substitution

The shell maintains a list of variables, each of which has as value a list of zero or more words. The values of shell variables can be displayed and changed with the set and unset commands. The system maintains its own list of "environment" variables. These can be displayed and changed with printenv, setenv and unsetenv.

(+) Variables may be made read-only with 'set -r'. Read-only variables may not be modified or unset; attempting to do so will cause an error. Once a variable is made read-only, it cannot be made writable, so 'set -r' should be used with caution. Environment variables cannot be made read-only.

Some variables are set by the shell or referred to by it. For instance, the argv variable is an image of the shell's argument list, and words of this variable's value are referred to in special ways. Some of the variables referred to by the shell are toggles. Where the shell is concerned, their value does not matter; whether they are set or not, however, is important. For instance, the verbose variable is a toggle that causes command input to be echoed. The -v command-line option sets this variable. "Special shell variables" lists all variables that are referred to by the shell.

Other operations treat variables numerically. The '@' command permits numeric calculations to be performed and the result assigned to a variable. Variable values are always represented as (zero or more) strings, however. For the purposes of numeric operations, the null string is considered to be zero, and the second and subsequent words of multiword values are ignored.

After the input line is aliased and parsed, and before each command is executed, variable substitution is performed keyed by '$' characters. This expansion can be prevented by preceding the '$' with a '\' except within '"'s where it always occurs, and within '"s where it never occurs. Strings quoted by "' are interpreted later (see Command substitution) so '$' substitution does not occur there until later, if at all. A '$' is passed unchanged if followed by a blank, tab, or end-of-line.

Input/output redirections are recognized before variable expansion, and are variable expanded separately. Otherwise, the command name and entire argument list are expanded together. It is thus possible for the first (command) word (to this point) to generate more than one word, the first of which becomes the command name, and the rest of which become arguments.

Unless enclosed in '"' or given the ':q' modifier, the results of variable substitution may eventually be command and file-name substituted. Within '"', a variable whose value consists of multiple words expands to a (portion of a) single word, with the words of the variable's value separated by blanks. When the ':q' modifier is applied to a substitution, the variable will expand to multiple words with each word separated by a blank and quoted to prevent later command or file-name substitution.

The following metasequences are provided for introducing variable values into the shell input. Except as noted, it is an error to reference a variable which is not set.

Substitutes the words of the value of variable name, each separated by a blank. Braces insulate name from following characters which would otherwise be part of it. Shell variables have names consisting of up to 20 letters and digits starting with a letter. The underscore character is considered a letter. If name is not a shell variable, but is set in the environment, that value is returned (but ':' modifiers and the other forms given below are not available in this case).
Substitutes only the selected words from the value of name. The selector is subjected to '$' substitution and may consist of a single number or two numbers separated by a '-'. The first word of a variable's value is numbered '1'. If the first number of a range is omitted, it defaults to '1'. If the last member of a range is omitted, it defaults to '$#name'. The selector '*' selects all words. It is not an error for a range to be empty if the second argument is omitted or in range.
Substitutes the name of the file from which command input is being read. An error occurs if the name is not known.
Equivalent to '$argv[number]'.
Equivalent to '$argv', which is equivalent to '$argv[*]'.

The ':' modifiers described in the section on history substitution, except for ':p', can be applied to the substitutions above. More than one may be used. (+) Braces may be needed to insulate a variable substitution from a literal colon, just as with history substitution; any modifiers must appear within the braces.

The following substitutions can not be modified with ':' modifiers.

Substitutes the string '1' if name is set, '0' if it is not.
Substitutes '1' if the current input file name is known, '0' if it is not. Always '0' in interactive shells.
Substitutes the number of words in name.
Equivalent to '$#argv'. (+)
Substitutes the number of characters in name. (+)
Substitutes the number of characters in $argv[number]. (+)
Equivalent to '$status'. (+)
Substitutes the (decimal) process number of the (parent) shell.
Substitutes the (decimal) process number of the last background process started by this shell.
Substitutes a line from the standard input, with no further interpretation thereafter. You can use it to read from the keyboard in a shell script. (+) While csh(1) always quotes $<, as if it were equivalent to '$<:q', tcsh(1) does not. Furthermore, when tcsh(1) is waiting for a line to be typed, you can type an interrupt to interrupt the sequence into which the line is to be substituted, but csh(1) does not allow this.

The editor command expand-variables, normally bound to '^X-$', can be used to interactively expand individual variables.


The remaining substitutions are applied selectively to the arguments of built-in commands. This means that portions of expressions that are not evaluated are not subjected to these expansions. For commands that are not internal to the shell, the command name is substituted separately from the argument list. This occurs very late, after input-output redirection is performed, and in a child of the main shell.

Command substitution

Command substitution is indicated by a command enclosed in "'. The output from such a command is broken into separate words at blanks, tabs, and newlines; null words are discarded. The output is variable and command substituted and put in place of the original string.

Command substitutions inside double quotes (") retain blanks and tabs; only newlines force new words. The single, final newline does not force a new word in any case. It is thus possible for a command substitution to yield only part of a word, even if the command outputs a complete line.

File-name substitution

If a word contains any of the characters '*', '?', '[' or '{', or begins with the character '~', it is a candidate for file-name substitution, also known as "globbing". This word is then regarded as a pattern ("glob-pattern"), and replaced with an alphabetically sorted list of file names that match the pattern.

In matching file names, a period (.) at the beginning of a file name or immediately following a '/', as well as the character '/', must be matched explicitly. The asterisk character, '*', matches any string of characters, including the null string. The question mark character ,'?', matches any single character. The sequence '[...]' matches any one of the characters enclosed. Within '[...]', a pair of characters separated by '-' matches any character lexically between the two.

(+) Some glob-patterns can be negated: The sequence '[^...]' matches any single character not specified by the characters and/or ranges of characters in the braces.

An entire glob-pattern can also be negated with '^':

> echo *
bang crash crunch ouch
> echo ^cr*
bang ouch

Glob-patterns that do not use '?', '*', or '[]', or those that use '{}' or '~' (below) are not negated correctly.

The metanotation 'a{b,c,d}e' is an abbreviation for 'abe ace ade'. Left-to-right order is preserved:
expands to:
'/usr/source/s1/oldls.c /usr/source/s1/ls.c'

The results of matches are sorted separately at a low level to preserve this order: '../{memo,*box}' might expand to '../memo ../box ../mbox'. (Note that 'memo' was not sorted with the results of matching '*box'.) It is not an error when this construct expands to files that do not exist, but it is possible to get an error from a command to which the expanded list is passed. This construct may be nested. As a special case, the words '{', '}' and '{}' are passed undisturbed.

The character '~' at the beginning of a file name refers to home directories. Standing alone, for example, '~', it expands to the invoker's home directory as reflected in the value of the home shell variable. When followed by a name consisting of letters, digits and '-' characters, the shell searches for a user with that name and substitutes that user's home directory. Thus, '~ken' might expand to '/usr/ken' and '~ken/chmach' to '/usr/ken/chmach'. If the character '~' is followed by a character other than a letter or '/', or it appears somewhere other than at the beginning of a word, it is left undisturbed. A command like 'setenv MANPATH /usr/man:/usr/local/man:~/lib/man' does not, therefore, perform home directory substitution.

It is an error for a glob-pattern containing '*', '?', '[' or '~', with or without '^', not to match any files. However, only one pattern in a list of glob-patterns must match a file (so that, 'rm *.a *.c *.o', for example, would fail only if there were no files in the current directory ending in '.a', '.c', or '.o'), and if the nonomatch shell variable is set, a pattern (or list of patterns) that matches nothing is left unchanged rather than causing an error.

The noglob shell variable can be set to prevent file-name substitution. In addition, you can use the expand-glob editor command, normally bound to '^X-*', to expand individual file-name substitutions interactively.

Directory-stack substitution (+)

The directory stack is a list of directories, numbered from zero, used by the pushd, popd and dirs built-in commands. dirs can print, store in a file, restore and clear the directory stack at any time, and the savedirs and dirsfile shell variables can be set to store the directory stack automatically on logout and restore it on login. The dirstack shell variable can be examined to see the directory stack and set to put arbitrary directories into the directory stack.

The character '=', followed by one or more digits, expands to an entry in the directory stack. The special case '=-' expands to the last directory in the stack, as in the following example:

> dirs -v
0	 /usr/bin
1	 /usr/spool/uucp
2	 /usr/accts/sys
> echo =1
> echo =0/calendar
> echo =-/usr/accts/sys

The noglob and nonomatch shell variables and the expand-glob editor command apply to both directory-stack and file-name substitutions.

Other substitutions (+)

There are several more transformations involving file names, that are not strictly related to the those already mentioned, but which are mentioned here for completeness. Any file name may be expanded to a full path when the symlinks variable is set to 'expand'. Quoting prevents this expansion, and the normalize-path editor command does it on demand. The normalize-command editor command expands commands in PATH into full paths on demand. Finally, cd and pushd interpret '-' as the old working directory (equivalent to the shell variable owd). This is not a substitution at all, but an abbreviation recognized only by those commands. Nonetheless, it can also be prevented by quoting.


The next three sections describe how the shell executes commands and deals with their input and output.

Simple commands, pipelines, and sequences

A simple command is a sequence of words, the first of which specifies the command to be executed. A series of simple commands joined by '|' characters forms a pipeline. The output of each command in a pipeline is connected to the input of the next.

Simple commands and pipelines may be joined into sequences with ';', and are executed sequentially. Commands and pipelines can also be joined into sequences with '||' or '&&', indicating, as in the C language, that the second is to be executed only if the first fails or succeeds respectively.

A simple command, pipeline, or sequence may be placed in parentheses, '()', to form a simple command, which may, in turn, be a component of a pipeline or sequence. A command, pipeline, or sequence can be executed without waiting for it to terminate by following it with an '&'.

Built-in and non-built-in command execution

Built-in commands are executed within the shell. If any component of a pipeline except the last is a built-in command, the pipeline is executed in a subshell.

Parenthesized commands are always executed in a subshell. Thus, the following:

(cd; pwd); pwd
prints the home directory, leaving you where you were (printing this after the home directory), while
cd; pwd
leaves you in the home directory. Parenthesized commands are most often used to prevent cd from affecting the current shell.

When a command to be executed is found not to be a built-in command, the shell attempts to execute the command through execve(3). Each word in the variable path names a directory in which the shell will look for the command. If it is given neither a -c nor a -t option, the shell hashes the names in these directories into an internal table so that it will only try an execve(3) in a directory if there is a possibility that the command resides there. This greatly speeds command location when a large number of directories are present in the search path. If this mechanism has been turned off (through unhash), if the shell was given a -c or -t argument, or in any case for each directory component of path which does not begin with a '/', the shell concatenates the current working directory with the given command name to form a path name of a file which it then attempts to execute.

If the file has execute permissions but is not an executable to the system (that is, it is neither an executable binary nor a script which specifies its interpreter), it is assumed to be a file containing shell commands and a new shell is spawned to read it. The shell special alias may be set to specify an interpreter other than the shell itself.

On systems that do not understand the '#!' script interpreter convention, the shell may be compiled to emulate it; see the version shell variable. If so, the shell checks the first line of the file to interpreter with the given args and feeds the file to it on standard input.


The standard input and standard output of a command may be redirected with the following syntax:

< name
Open file name (which is first variable, command and file-name expanded) as the standard input.
<< word
Read the shell input up to a line which is identical to word. word is not subjected to variable, file-name or command substitution, and each input line is compared to word before any substitutions are done on this input line. Unless a quoting '\', '"', '' or "' appears in word variable and command substitution is performed on the intervening lines, allowing '\' to quote '$', '\' and "'. Commands that are substituted have all blanks, tabs, and newlines preserved, except for the final newline which is dropped. The resultant text is placed in an anonymous temporary file which is given to the command as standard input.
> name
>! name
>& name
>&! name
The file name is used as standard output. If the file does not exist, it is created; if the file exists, it is truncated, its previous contents being lost.

If the shell variable noclobber is set, the file must not exist or be a character special file (such as a terminal or '/dev/null') or an error results. This helps prevent accidental destruction of files. In this case, use the '!' forms to suppress this check.

The forms involving '&' route the diagnostic output into the specified file as well as the standard output. name is expanded in the same way as '<' input file names are.

>> name
>>& name
>>! name
>>&! name
Like '>', but appends output to the end of name. If the shell variable noclobber is set, it is an error for the file not to exist, unless one of the '!' forms is given.

A command receives the environment in which the shell was invoked as modified by the input-output parameters and the presence of the command in a pipeline. Thus, unlike some previous shells, commands run from a file of shell commands have no access to the text of the commands by default; rather they receive the original standard input of the shell. The '<<' mechanism should be used to present inline data. This permits shell command scripts to function as components of pipelines and allows the shell to block read its input. Note that the default standard input for a command run detached is not the empty file /dev/null, but the original standard input of the shell. If this is a terminal, and if the process attempts to read from the terminal, the process will block and the user will be notified (see Jobs).

Diagnostic output may be directed through a pipe with the standard output. Simply use the form '|&' rather than just '|'.

The shell cannot presently redirect diagnostic output without also redirecting standard output, but '(command > output-file )>& error-file' is often an acceptable way to work around this. Either output-file or error-file may be '/dev/tty' to send output to the terminal.


Previous sections described how the shell accepts, parses and executes command lines. This section describes a variety of its useful features.

Control flow

The shell contains a number of commands you can use to regulate the flow of control in command files (shell scripts) and (in limited but useful ways) from terminal input. These commands all operate by forcing the shell to reread or skip in its input and, due to the implementation, restrict the placement of some of the commands.

The foreach, switch, and while statements, as well as the if-then-else form of the if statement, require that the major keywords appear in a single, simple command on an input line.

If the shell's input is not seekable, the shell buffers up input whenever a loop is being read and performs seeks in this internal buffer to accomplish the rereading implied by the loop. (To the extent that this allows, backward gotos will succeed on non-seekable inputs.)


The if, while and exit built-in commands use expressions with a common syntax. The expressions can include any of the operators described in the next three sections. Note that the @ built-in command has its own separate syntax.

Logical, arithmetical, and comparison operators

These operators are similar to those of C and have the same precedence. They include:
||  &&  |  ^  &  ==  !=  =~  !~  <=  >=
<  > <<  >>  +  -  *  /  %  !  ~  (  )

Here the precedence increases to the right, '==' '!=' '=~' and '!~', '<=' '>=' '<' and '>', '<<' and '>>', '+' and '-', '*' '/' and '%' being, in groups, at the same level. The '==' '!=' '=~' and '!~' operators compare their arguments as strings; all others operate on numbers. The operators '=~' and '!~' are like '!=' and '==' except that the right-hand side is a glob-pattern (see File-name substitution) against which the left-hand operand is matched. This reduces the need for use of the switch built-in command in shell scripts when all that is needed is pattern matching.

Strings that begin with '0' are considered octal numbers. Null or missing arguments are considered '0'. The results of all expressions are strings, which represent decimal numbers. It is important to note that no two components of an expression can appear in the same word. Except when they are adjacent to components of expressions that are syntactically significant to the parser ('&' '|' '<' '>' '(' ')'), they should be surrounded by spaces.

Command exit status

Commands can be executed in expressions and their exit status returned by enclosing them in braces ('{}'). Braces should be separated from the words of the command by spaces. Command executions succeed, returning true ('1') if the command exits with status 0. Otherwise, they fail, returning false ('0'). If more detailed status information is required, the command should be executed outside of an expression and the status shell variable examined.

File inquiry operators

Some of these operators perform true/false tests on files and related objects. They are of the form -op file, where op is one of the following:
Read access
Write access
Execute access
Executable in the path or shell built-in; '-X ls' and '-X ls-F' are generally true, but '-X /bin/ls' is not (+)
Zero size
Non-zero size (+)
Plain file
Symbolic link (+) *
Block special file (+)
Character special file (+)
Named pipe (fifo) (+) *
Socket special file (+) *
Set-user-ID bit is set (+)
Set-group-ID bit is set (+)
Sticky bit is set (+)
file (which must be a digit) is an open file descriptor for a terminal device (+)
Applies subsequent operators in a multiple-operator test to a symbolic link rather than to the file to which the link points (+) *

file is command and file-name expanded and tested to determine whether it has the specified relationship to the real user. If file does not exist or is inaccessible or, for the operators indicated by '*', if the specified file type does not exist on the current system, all enquiries return false ('0').

These operators may be combined for conciseness: '-xy file' is equivalent to '-x file && -y file'. (+) For example, '-fx' is true (returns '1') for plain executable files, but not for directories.

L may be used in a multiple-operator test to apply subsequent operators to a symbolic link rather than to the file to which the link points. For example, '-lLo' is true for links owned by the invoking user. Lr, Lw, and Lx are always true for links and false for non-links. L has a different meaning when it is the last operator in a multiple-operator test.

It is possible, but not particularly useful and sometimes misleading to combine operators which expect file to be a file with operators which do not (such as X and t). Following L with a non-file operator can lead to particularly strange results.

Other operators return other information; that is, not just '0' or '1'. (+) They have the same format as before; op may be one of the following:

Last file access time, as the number of seconds since the epoch
Like A, but in timestamp format, such as, 'Fri May 14 16:36:10 1993'
Last file modification time
Like M, but in timestamp format
Last inode modification time
Like C, but in timestamp format
Device number
Inode number
Composite file identifier, in the form device:inode
The name of the file pointed to by a symbolic link
Number of (hard) links
Permissions, in octal, without leading zero
Like P, with leading zero
Equivalent to '-P file & mode'. For example, '-P22 file' returns '22' if file is writable by group and other; it returns '20' if writable by group only; and '0' if writable by neither.
Like Pmode with leading zero
Numeric userid
Username, or the numeric userid if the username is unknown
Numeric groupid
Groupname, or the numeric groupid if the groupname is unknown
Size, in bytes

Only one of these operators may appear in a multiple-operator test, and it must be the last. Note that L has a different meaning at the end of and elsewhere in a multiple-operator test. Because '0' is a valid return value for many of these operators, they do not return '0' when they fail: most return '-1', and F returns ':'.

If the shell is compiled with POSIX defined (see the version shell variable), the result of a file inquiry is based on the permission bits of the file and not on the result of the access(3) system call. For example, if one tests a file with -w whose permissions would ordinarily allow writing, but which is on a file system mounted read-only, the test will succeed in a POSIX shell, but it will fail in a non-POSIX shell.

File inquiry operators can also be evaluated with the filetest built-in command (+).


The shell associates a job with each pipeline. It keeps a table of current jobs, printed by the jobs command, and assigns them small integer numbers. When a job is started asynchronously with '&', the shell prints a line as follows:
[1] 1234

This indicates that the job which was started asynchronously was job number 1 and had one (top-level) process, whose process id was 1234.

If you are running a job and want to do something else, you can hit the suspend key (usually '^Z'), which sends a STOP signal to the current job. The shell will then usually indicate that the job has been 'Suspended' and print another prompt. If the listjobs shell variable is set, all jobs will be listed like the jobs built-in command. If it is set to 'long', the listing will be in long format, like 'jobs -l'. You can then manipulate the state of the suspended job. You can put it in the "background" with the bg command, or run some other commands and eventually bring the job back into the "foreground" with fg. (See also the run-fg-editor editor command.) A '^Z' takes effect immediately. It is like an interrupt in that pending output and unread input are discarded when it is typed. The wait built-in command causes the shell to wait for all background jobs to complete.

The '^]' key sends a delayed suspend signal, which does not generate a STOP signal until a program attempts to read it, to the current job. This can be typed ahead when you have prepared some commands for a job that you want to stop after it has read them. The '^Y' key performs this function in csh(1); in tcsh(1), '^Y' is an editing command. (+)

A job running in the background stops if it tries to read from the terminal. Background jobs are normally allowed to produce output, but this can be disabled by giving the command 'stty tostop'. If you set this tty option, background jobs will stop when they try to produce output like they do when they try to read input.

There are several ways to refer to jobs in the shell. The character '%' introduces a job name. To refer to job number 1, you can name it as '%1'. Just naming a job brings it to the foreground. Thus, '%1' is a synonym for 'fg %1', bringing job 1 back into the foreground. Similarly, '%1 &' resumes job 1 in the background, just like 'bg %1'. A job can also be named by an unambiguous prefix of the string typed in to start it: '%ex' would normally restart a suspended ex(1) job, if there were only one suspended job whose name began with the string 'ex'. It is also possible to use '%?string' to specify a job whose text contains string, if there is only one such job.

The shell maintains a notion of the current and previous jobs. In output pertaining to jobs, the current job is marked with a '+' and the previous job with a '-'. The abbreviations '%+', '%', and (by analogy with the syntax of the history mechanism) '%%' all refer to the current job, and '%-' refers to the previous job.

The job control mechanism requires that the stty(1) option 'new' be set on some systems. It is an artifact from a 'new' implementation of the tty driver that allows the generation of interrupt characters from the keyboard to tell jobs to stop. See stty(1) and the setty built-in command for details on setting options in the new tty driver.

Status reporting

The shell learns immediately when the status of a process changes. It usually informs you whenever a job becomes blocked so that no further progress is possible, but only just before it prints a prompt. This is done so that it does not otherwise disturb your work. If, however, you set the shell variable notify, the shell will notify you immediately of changes of status in background jobs. In addition, the shell command notify marks a single process so that its status changes will be immediately reported. By default, notify marks the current process; simply use 'notify' after starting a background job to mark it.

When you try to leave the shell while jobs are stopped, you will be warned that 'You have stopped jobs.' You can use the jobs command to see what they are. If you do this or immediately try to exit again, the shell will not warn you a second time, and the suspended jobs will be terminated.

Automatic, periodic, and timed events (+)

There are various ways to run commands and take other actions automatically at various times in the "life cycle" of the shell. They are summarized here, and described in detail under the appropriate built-in commands, special shell variables and special aliases.

The sched built-in command puts commands in a scheduled-event list, to be executed by the shell at a given time.

The beepcmd, cwdcmd, periodic and precmd special aliases can be set, respectively, to execute commands when the shell wants to ring the bell, when the working directory changes, every tperiod minutes and before each prompt.

The autologout shell variable can be set to log out or lock the shell after a given number of minutes of inactivity.

The mail shell variable can be set to check for new mail periodically.

The printexitvalue shell variable can be set to print the exit status of commands that exit with a status other than zero.

The rmstar shell variable can be set to ask the user, when 'rm *' is typed, to determine whether that is what was intended.

The time shell variable can be set to execute the time built-in command after the completion of any process that takes more than a given number of CPU seconds.

The watch and who shell variables can be set to report when selected users log in or out, and the log built-in command reports on those users at any time.

Native Language System support (+)

The shell is 8-bit clean (if so compiled; see the version shell variable), and thus supports character sets needing this capability. Native Language System (NLS) support differs, depending on whether or not the shell was compiled to use the system's NLS (again, see version). In either case, 7-bit ASCII is the default for character classification (for example, which characters are printable) and sorting. Changing the LANG or LC_CTYPE environment variables causes a check for possible changes in these respects.

When using the system's NLS, the setlocale(3) function is called to determine appropriate character classification and sorting. This function typically examines the LANG and LC_CTYPE environment variables; refer to the system documentation for further details. When not using the system's NLS, the shell simulates it by assuming that the ISO 8859-1 character set is used whenever either of the LANG and LC_CTYPE variables are set, regardless of their values. Sorting is not affected for the simulated NLS.

In addition, with both real and simulated NLS, all printable characters in the range \200-\377, (that is, those that have M-char bindings) are automatically rebound to the self-insert-command. The corresponding binding for the escape-char sequence, if any, is left alone. These characters are not rebound if the NOREBIND environment variable is set. This may be useful for the simulated NLS or a primitive real NLS, which assumes full ISO 8859-1. Otherwise, all M-char bindings in the range \240-\377 are effectively undone. Explicitly rebinding the relevant keys with bindkey is still possible.

Unknown characters (that is, those that are neither printable nor control characters) are printed in the format \nnn. If the tty is not in 8-bit mode, other 8-bit characters are printed by converting them to ASCII and using standout mode. The shell never changes the 7/8-bit mode of the tty and tracks user-initiated changes of 7/8-bit mode. NLS users (or those who want to use a metakey) might need to explicitly set the tty in 8-bit mode through the appropriate stty(1) command in, for example, the ~/.login file.

Operating system variant support (+)

A number of new built-in commands are provided to support features in particular operating systems. These are described in detail in the built-in commands section.

The VENDOR, OSTYPE, and MACHTYPE environment variables indicate respectively the vendor, operating system and machine type (microprocessor class or machine model) of the system on which the shell thinks it is running. These are particularly useful when you are sharing your home directory between several types of machines. You can, for example, use the following:

set path = (~/bin.$MACHTYPE /usr/ucb /bin /usr/bin .)

in your ~/.login and put executables compiled for each machine in the appropriate directory.

The version shell variable indicates which options were chosen when the shell was compiled.

Note also the newgrp built-in, the afsuser and echo_style shell variables and the system-dependent locations of the shell's input files (see FILES).

Signal handling

Login shells ignore interrupts when reading the file ~/.logout. The shell ignores quit signals unless started with -q. Login shells catch the terminate signal, but non-login shells inherit the terminate behavior from their parents. Other signals have the values which the shell inherited from its parent.

In shell scripts, the shell's handling of interrupt and terminate signals can be controlled with onintr, and its handling of hangups can be controlled with hup and nohup.

The shell exits on a hangup (see also the logout shell variable). By default, the shell's children also do this, but the shell does not send them a hangup when it exits. hup arranges for the shell to send a hangup to a child when it exits, and nohup sets a child to ignore hangups.

Terminal management (+)

The shell uses three different sets of terminal ("tty") modes. It uses 'edit', when editing, 'quote', when quoting literal characters, and 'execute', when executing commands. The shell holds some settings in each mode constant, so commands that leave the tty in a confused state do not interfere with the shell. The shell also matches changes in the speed and padding of the tty. The list of tty modes that are kept constant can be examined and modified with the setty built-in. Note that although the editor uses CBREAK mode (or its equivalent), it takes typed-ahead characters anyway.

The echotc, settc and telltc commands can be used to manipulate and debug terminal capabilities from the command line.

On systems that support SIGWINCH or SIGWINDOW, the shell adapts to window resizing automatically and adjusts the environment variables LINES and COLUMNS if set. If the environment variable TERMCAP contains li# and co# fields, the shell adjusts them to reflect the new window size.


This section describes all of the available built-in commands, special aliases, and special shell variables.

Built-in commands

A synonym for the fg built-in command.
%job &
A synonym for the bg built-in command.
Does nothing, successfully.
Print the values of all shell variables.
@ name = expr
Set the specified name to the value of expr. If expr contains '<', '>', '&' or '', at least that part of expr must be placed within '()'.
@ name[index] = expr
Assign the value of expr to the index'th argument of name. Both name and its index'th component must already exist.

expr may contain the operators '*', '+', and so on, as in C. The space separating the name from the assignment operator is optional. Spaces are mandatory, however, in separating components of expr that would otherwise be single words.

Special postfix '++' and '—' operators increment and decrement name respectively, such as '@ i++'.

Note that the syntax of expr is not related to that which is described in the section on expressions.

alias[name [wordlist]]
Without arguments, prints all aliases. With name, prints the alias for name. With name and wordlist, assigns wordlist as the alias of name. wordlist is command and file-name substituted. name may not be 'alias' or 'unalias'. (See also the unalias built-in command.)
Shows the amount of dynamic memory acquired, categorized according to used and free memory. With an argument, shows the number of free and used blocks in each size category. The categories start at size 8 and double at each step. This command's output can vary across system types, since systems other than the VAX may use a different memory allocator.
bg[%job ...]
Puts the specified jobs (or, without arguments, the current job) into the background, continuing each if it is stopped. job may be a number, a string, '', '%', '+' or '-' as described in the section "Jobs."
bindkey[-l|-d|-e|-v|-u] (+)
bindkey[-a] [-b] [-k] [-r] [] key (+)
bindkey [-a] [-b] [-k] [-c|-s] [] key command (+)
Without options, the first form lists all bound keys and the editor command to which each is bound; the second form lists the editor command to which key is bound; the third form binds the editor command command to key.
Options include:
Lists all editor commands and a short description of each.
Binds all keys to the standard bindings for the default editor.
Binds all keys to the standard GNU Emacs-like bindings.
Binds all keys to the standard vi(1)-like bindings.
Lists or changes key bindings in the alternative key map. This is the key map used in vi(1) command mode.
key is interpreted as a control character written ^character (such as '^A') or C-character (such as 'C-A'), a meta-character written M-character (such as 'M-A'), a function key written F-string (such as 'F-string'), or an extended prefix key written X-character (such as 'X-A').
key is interpreted as a symbolic arrow key name, which may be 'down', 'up', 'left' or 'right'.
Removes key's binding. Be careful: 'bindkey -r' does not bind key to self-insert-command; it unbinds key completely.
command is interpreted as a built-in or external command instead of an editor command.
command is taken as a literal string and treated as terminal input when key is typed. Bound keys in command are themselves reinterpreted; this continues for ten levels of interpretation.
Forces a break from option processing, so the next word is taken as key even if it begins with '-'.
-u (or any invalid option)
Prints a usage message.

key may be a single character or a string. If a command is bound to a string, the first character of the string is bound to sequence-lead-in, and the entire string is bound to the command.

Control characters in key can be literal (they can be typed by preceding them with the editor command quoted-insert, normally bound to '^V') or written caret-character style, such as '^A'. Delete is written '^?' (caret-question mark). key and command can contain backslashed escape sequences (in the style of System V echo(1)) as follows:

Form feed
Carriage return
Horizontal tab
Vertical tab
The ASCII character corresponding to the octal number nnn

\ nullifies the special meaning of the following character, if it has any, notably \ and ^.

Causes execution to resume after the end of the nearest enclosing foreach or while. The remaining commands on the current line are executed. Multilevel breaks are thus possible by writing them all on one line.
Causes a break from a switch, resuming after the endsw.
builtins (+)
Prints the names of all built-in commands.
bye (+)
A synonym for the logout built-in command. Available only if the shell was so compiled; see the version shell variable.
case label:
A label in a switch statement as discussed below.
cd [-p] [-l] [-n|-v] [name]
If a directory name is given, changes the shell's working directory to name. If not, changes to home. If name is '-' it is interpreted as the previous working directory (see Other substitutions). (+) If name is not a subdirectory of the current directory (and does not begin with '/', './' or '../'), each component of the variable cdpath is checked to see if it has a subdirectory name. Finally, if all else fails, but name is a shell variable whose value begins with '/', this is tried to see if it is a directory.

With -p, prints the final directory stack, just like dirs. The -l, -n and -v flags have the same effect on cd as on dirs, and they imply -p. (+)

A synonym for the cd built-in command.
complete [command] [word/pattern/list] [:select]/[[suffix]/] ...]] (+)
Without arguments, lists all completions. With command, lists completions for command. With command, d word, and so on, defines completions.

command may be a full command name or a glob-pattern (see File-name substitution).It can begin with '-' to indicate that completion should be used only when command is ambiguous.

word specifies which word relative to the current word is to be completed, and may be one of the following:

Current-word completion. pattern is a glob-pattern that must match the beginning of the current word on the command line. pattern is ignored when completing the current word.
Like c, but includes pattern when completing the current word.
Next-word completion. pattern is a glob-pattern that must match the beginning of the previous word on the command line.
Like n, but must match the beginning of the word two before the current word.
Position-dependent completion. pattern is a numeric range, with the same syntax used to index shell variables, which must include the current word.

list, the list of possible completions, can be one of the following:

Bindings (editor commands)
Commands (built-in or external commands)
External commands that begin with the supplied path prefix
Directories that begin with the supplied path prefix
Environment variables
File names
File names which begin with the supplied path prefix
Group names
Shell variables
Plain ("text") files
Plain ("text") files that begin with the supplied path prefix
Any variables
User names
Like n, but prints select when list-choices is used.
Words from the variable var
Words from the given list
Words from the output of command

select is an optional glob-pattern. If given, only words from list which match select are considered, and the fignore shell variable is ignored. The last three types of completion may not have a select pattern, and x uses select as an explanatory message when the list-choices editor command is used.

suffix is a single character to be appended to a successful completion. If null, no character is appended. If omitted (in which case the fourth delimiter can also be omitted), a slash is appended to directories and a space to other words.

The next part of this section provides some examples. Some commands take only directories as arguments, so it is not necessary to complete plain files. For example:

> complete cd 'p/1/d/'

completes only the first word following 'cd' ('p/1') with a directory. p-type completion can also be used to narrow down command completion:

> co[^D]
complete compress
> complete -co* 'p/0/(compress)/'
> co[^D]
> compress

This completion completes commands (words in position 0, 'p/0') which begin with 'co' (thus matching 'co*') to 'compress' (the only word in the list). The leading '-' indicates that this completion is to be used only with ambiguous commands.

> complete find 'n/-user/u/'

is an example of n-type completion. Any word following 'find' and immediately following '-user' is completed from the list of users.

> complete cc 'c/-I/d/'

demonstrates c-type completion. Any word following 'cc' and beginning with '-I' is completed as a directory. '-I' is not taken as part of the directory because lowercase c was used.

Different lists are useful with different commands.

> complete alias 'p/1/a/'
> complete man 'p/*/c/'
> complete set 'p/1/s/'
> complete true 'p/1/x:Truth has no options./'

These complete words following 'alias' with aliases, 'man' with commands, and 'set' with shell variables. 'true' has no options, so x does nothing when completion is attempted and prints 'Truth has no options.' when completion choices are listed.

Note that the man(1) example, and several other examples below, could just as well have used 'c/*' or 'n/*' as 'p/*'.

Words can be completed from a variable evaluated at completion time:

> complete ftp 'p/1/$hostnames/'
> set hostnames = (
> ftp [^D]
> ftp [^C]
> set hostnames = (
> ftp [^D]

or from a command run at completion time:

> complete kill 'p/*/'ps | awk \{print\ \$1\}'/'
> kill -9 [^D]
23113 23377 23380 23406 23429 23529 23530 PID

Note that the complete command does not itself quote its arguments, so the braces, space and '$' in '{print $1}' must be quoted explicitly.

One command can have multiple completions. For example:

> complete dbx 'p/2/(core)/' 'p/*/c/'

completes the second argument to 'dbx' with the word 'core' and all other arguments with commands. Note that the positional completion is specified before the next-word completion. Since completions are evaluated from left to right, if the next-word completion were specified first it would always match and the positional completion would never be executed. This is a common mistake when defining a completion.

The select pattern is useful when a command takes only files with particular forms as arguments. For example:

> complete cc 'p/*/f:*.[cao]/'

completes 'cc' arguments only to files ending in '.c', '.a', or '.o'. select can also exclude files, using negation of a glob-pattern as described in the section on file-name substitution. One could use:

> complete rm 'p/*/f:^*.{c,h,cc,C,tex,1,man,l,y}/'

to exclude precious source code from 'rm' completion. You could still type excluded names manually or override the completion mechanism using the complete-word-raw or list-choices-raw editor commands.

The 'C', 'D', 'F' and 'T' lists are like 'c', 'd', 'f' and 't' respectively, but they use the select argument in a different way: to restrict completion to files beginning with a particular path prefix. For example, the Elm mail program uses '=' as an abbreviation for a user's mail directory. One might use:

> complete elm 'c@=@F:$HOME/Mail/@'

to complete 'elm -f =' as if it were 'elm -f ~/Mail/'. Note that '@' is used instead of '/' to avoid confusion with the select argument; '$HOME' is used instead of '~' because home directory substitution only works at the beginning of a word.

suffix adds a nonstandard suffix (not space or '/' for directories) to completed words.

> complete finger 'c/*@/$hostnames/' 'p/1/u/@'

completes arguments to 'finger' from the list of users, appends an '@', and then completes after the '@' from the 'hostnames' variable. Note again the order in which the completions are specified.

The following example is more complex:

> complete find \
'n/-name/f/' 'n/-newer/f/' 'n/-{,n}cpio/f/' \
'n/-exec/c/' 'n/-ok/c/' 'n/-user/u/' \
'n/-group/g/' 'n/-fstype/(nfs 4.2)/' \
'n/-type/(b c d f l p s)/' \
'c/-/(name newer cpio ncpio exec ok user \
group fstype type atime ctime depth inum \
ls mtime nogroup nouser perm print prune \
size xdev)/' \

This completes words following '-name', '-newer', '-cpio' or 'ncpio' (note the pattern which matches both) to files, words following '-exec' or '-ok' to commands, words following 'user' and 'group' to users and groups respectively, and words following '-fstype' or '-type' to members of the given lists. It also completes the switches themselves from the given list (note the use of c-type completion) and completes anything not otherwise completed to a directory.

Programmed completions are ignored if the word being completed is a tilde substitution (beginning with '~') or a variable (beginning with '$'). complete is an experimental feature, and the syntax may change in future versions of the shell. See also the uncomplete built-in command.

Continues execution of the nearest enclosing while or foreach. The rest of the commands on the current line are executed.
Labels the default case in a switch statement. It should come after all case labels.
dirs [-l][-n|-v]
dirs -S|-L [filename] (+)
dirs -c (+)
The first form prints the directory stack. The top of the stack is at the left and the first directory in the stack is the current directory. With -l, '~' or '~name in the output is expanded explicitly to home path name of the home directory for user name. (+) With -n, entries are wrapped before they reach the edge of the screen. (+) With -v, entries are printed one per line, preceded by their stack positions. (+) If more than one of -n or -v is given, -v takes precedence. -p is accepted but does nothing.

With -S, the second form saves the directory stack to filename as a series of cd and pushd commands. With -L, the shell sources filename, which is presumably a directory-stack file saved by the -S option or the savedirs mechanism. In either case, dirsfile is used if filename is not given and ~/.cshdirs is used if dirsfile is unset.

Note that login shells do the equivalent of 'dirs -L' on startup and, if savedirs is set, 'dirs -S' before exiting. Because only ~/.tcshrc is normally sourced before ~/.cshdirs, dirsfile should be set in ~/.tcshrc rather than ~/.login.

The last form clears the directory stack.

echo[-n] word ...
rites each word to the shell's standard output, separated by spaces and terminated with a newline. The echo_style shell variable can be set to emulate (or not) the flags and escape sequences of the BSD and/or System V versions of echo(1); see echo(1).
echotc [-sv] arg ... (+)
Exercises the terminal capabilities (see termcap) in args. For example, 'echotc home' sends the cursor to the home position, 'echotc cm 3 10' sends it to column 3 and row 10, and 'echotc ts 0; echo "This is a test."; echotc fs' prints "This is a test." in the status line.

If arg is 'baud', 'cols', 'lines', 'meta' or 'tabs', prints the value of that capability ("yes" or "no" to indicate that the terminal does or does not have that capability). One might use this to make the output from a shell script less verbose on slow terminals, or limit command output to the number of lines on the screen:

> set history='echotc lines' 
> @ history—

Termcap strings may contain wildcards, which will not echo correctly. Use double quotes when setting a shell variable to a terminal capability string, as in the following example that places the date in the status line:

> set tosl="'echotc ts 0'"

> set frsl="'echotc fs'"
> echo -n "$tosl";date; echo -n "$frsl"

With -s, nonexistent capabilities return the empty string rather than causing an error. With -v, messages are verbose.

See the description of the foreach, if, switch, and while statements.
eval arg ...
Treats the arguments as input to the shell and executes the resulting command(s) in the context of the current shell. This is usually used to execute commands generated as the result of command or variable substitution, since parsing occurs before these substitutions. See tset(1) for a sample use of eval.
exec command
Executes the specified command in place of the current shell.
exit [expr]
The shell exits either with the value of the specified expr (an expression, as described in the section on Expressions) or, without expr, with the value of the status variable.
fg [%job ...]
Brings the specified jobs (or, without arguments, the current job) into the foreground, continuing each if it is stopped. job may be a number, a string, '', '%', '+' or '-' as described under Jobs. See also the run-fg-editor editor command.
filetest -op file ... (+)
Applies op (which is a file inquiry operator as described in the section on file inquiry operators) to each file and returns the results as a space-separated list.
foreach name (wordlist)
Successively sets the variable name to each member of wordlist and executes the sequence of commands between this command and the matching end. (Both foreach and end must appear alone on separate lines.) Use the built-in command continue to continue the loop prematurely; use the built-in command break to terminate it prematurely. When this command is read from the terminal, the loop is read once, prompting with 'foreach? ' (or prompt2) before any statements in the loop are executed. You can rub out any mistake you make typing in a loop at the terminal.
getspath (+)
Prints the system execution path. (TCF only)
getxvers (+)
Prints the experimental version prefix. (TCF only)
glob wordlist
Like echo, but no '\' escapes are recognized and words are delimited by null characters in the output. Useful for programs that use the shell to expand a list of words to matching file names (see “File-name substitution”).
goto word
word is file-name and command-substituted to yield a string of the form 'label'. The shell rewinds its input as much as possible, searches for a line of the form 'label:', possibly preceded by blanks or tabs, and continues execution after that line.
Prints a statistics line indicating how effective the internal hash table has been at locating commands (and avoiding calls to exec). An exec is attempted for each component of the path where the hash function indicates a possible match, and in each component that does not begin with a '/'.

On machines without vfork, prints only the number and size of hash buckets.

history [-hr] [n]
history -S|-L|-M [filename] (+)
history -c (+)
The first form prints the history event list. If n is given, only the n most recent events are printed or saved. With -h, the history list is printed without leading numbers and time stamps in comment form. (This can be used to produce files suitable for loading with 'history -L' or 'source -h'.) With -r, the order of printing is most recent first rather than oldest first.

With -S, the second form saves the history list to filename. If the first word of the savehist shell variable is set to a number, that is the maximum number of lines saved. If the second word of savehist is set to 'merge', the history list is merged with the existing history file instead of replacing it (if there is one) and sorted by timestamp. (+) Merging is intended for an environment like the X Window System with several shells in simultaneous use. Currently, it only succeeds when the shells quit one after another.

With -L, the shell appends filename, which is presumably a history list saved by the -S option or the savehist mechanism, to the history list. -M is like -L, but the contents of filename are merged into the history list and sorted by timestamp. In either case, histfile is used if filename is not given and ~/.history is used if histfile is unset. 'history -L' is exactly like 'source -h' except that it does not require a file name.

Note that login shells do the equivalent of 'history -L' on startup and, if savehist is set, 'history -S' before exiting. Because only ~/.tcshrc is normally sourced before ~/.history, histfile should be set in ~/.tcshrc rather than ~/.login.

If histlit is set, the first and second forms print and save the literal (unexpanded) form of the history list.

The last form clears the history list.

hup [command] (+)
With command, runs command so that it will exit on a hang-up signal; arranges for the shell to send it a hang-up signal when the shell exits. Note that commands can set their own response to hangups, overriding hup. Without an argument (allowed only in a shell script), causes the shell to exit on a hangup for the remainder of the script. (See also Signal handling and the nohup built-in command.)
if (expr) command
If expr (an expression, as described in the section on Expressions) evaluates true, command is executed. Variable substitution on command occurs early, at the same time it does for the rest of the if command. command must be a simple command, not an alias, a pipeline, a command list, or a parenthesized command list. It can have arguments. Input/output redirection occurs even if expr is false and command is thus not executed; this is a bug.
if (expr) then
else if (expr2) then
If the specified expr is true, the commands to the first else are executed. Otherwise, if expr2 is true, the commands to the second else are executed, and so on. Any number of else-if pairs are possible; only one endif is needed. The else part is optional. (The words else and endif must appear at the beginning of input lines. The if must appear alone on its input line or after an else.)
inlib shared-library ... (+)
Adds each shared-library to the current environment. There is no way to remove a shared library. (Domain/OS only.)
jobs [-l]
Lists the active jobs. With -l, lists process IDs in addition to the normal information. On TCF systems, prints the site on which each job is executing.
kill [-signal] %job|pid ...
kill -l
The first form sends the specified signal (or, if none is given, the TERM [terminate] signal) to the specified jobs or processes. job may be a number, a string, '', '%', '+' or '-' as described in the section, Jobs. Signals are either given by number or by name (as given in /usr/include/signal.h, stripped of the prefix 'SIG'). There is no default job; using only 'kill' does not send a signal to the current job. If the signal being sent is TERM (terminate) or HUP (hang up), the job or process is sent a CONT (continue) signal as well. The second form lists the signal names.
limit [-h] [resource [maximum-use]]
Limits the consumption by the current process and each process it creates so that none of the processes can individually exceed maximum-use on the specified resource. If no maximum-use is given, the current limit is printed; if no resource is given, all limitations are given. If the -h flag is given, the hard limits are used instead of the current limits. The hard limits impose a ceiling on the values of the current limits. Only a user with appropriate permissions can raise the hard limits, but any user can lower or raise the current limits within the legal range.

Controllable resources currently include:

maximum-use may be given as a (floating point or integer) number followed by a scale factor. For all limits other than cputime, the default scale is 'k' or 'kilobytes' (1024 bytes); a scale factor of 'm' or 'megabytes' may also be used. For cputime, the default scaling is 'seconds', while 'm' for minutes or 'h' for hours, or a time of the form 'mm:ss' (giving minutes and seconds) may be used.

For both resource names and scale factors, unambiguous prefixes of the names suffice.

log (+)
Prints the watch shell variable and reports on each user indicated in watch who is logged in, regardless of when they last logged in. (See also watchlog.)
Terminates a login shell, replacing it with an instance of /bin/login. This is one way to log off, included for compatibility with sh(1).
Terminates a login shell. Especially useful if ignoreeof is set.
ls-F [-switch ...] [file ...] (+)
Lists files like 'ls -F', but does so much faster. It identifies each type of special file in the listing with a special character:
Block device
Character device
Named pipe (systems with named pipes only)
Socket (systems with sockets only)
Symbolic link (systems with symbolic links only)
Hidden directory (AIX only) or context dependent (HP/UX only)
Network special (HP/UX only)

If the listlinks shell variable is set, symbolic links are identified in more detail (on systems which have them):

Symbolic link to a nondirectory
Symbolic link to a directory
Symbolic link to nowhere

listlinks also slows down ls-F and causes partitions holding files pointed to by symbolic links to be mounted.

If the listflags shell variable is set to 'x', 'a' or 'A', or any combination of these (such as 'xA'), they are used as flags to ls-F, making it act like 'ls -xF', 'ls -Fa', 'ls -FA' or a combination (such as 'ls -FxA'). On computers where 'ls -C' is not the default, ls-F acts like 'ls -CF', unless listflags contains an 'x', in which case it acts like 'ls -xF'. ls-F passes its arguments to ls(1) if it is given any switches, so 'alias ls ls-F' usually behaves correctly. ls-F includes file identification characters when sorting file names; this is a bug.

migrate [-site] pid|%jobid ... (+)
migrate -site(+)
The first form migrates the process or job either to the site specified or the default site determined by the system path. The second form is equivalent to 'migrate -site $$': it migrates the current process to the specified site. Migrating the shell itself can cause unexpected behavior, since the shell does not like to lose its tty. (TCF only)
newgrp [-] group (+)
Equivalent to 'exec newgrp' (see newgrp(1)). Available only if the shell was so compiled; see the version shell variable.
nice [+number] [command]
Sets the scheduling priority for the shell to number, or, without number, to 4. With command, runs command at the appropriate priority. The greater the number, the less cpu the process gets. A user with appropriate privileges can specify negative priority by using 'nice -number ...'. Command is always executed in a subshell, and the restrictions placed on commands in simple if statements apply.
nohup [command]
With command, runs command so that it will ignore hang-up signals. Note that commands can set their own response to hangups, overriding nohup. Without an argument (allowed only in a shell script), causes the shell to ignore hangups for the remainder of the script. (See also Signal handling and the hup built-in command.)
notify [%job ...]
Causes the shell to notify the user asynchronously when the status of any of the specified jobs (or, without %job, the current job) changes, instead of waiting until the next prompt, as it usually does. job may be a number, a string, '', '%', '+' or '-', as described in "Jobs." See also the notify shell variable.
onintr [-|label]
Controls the action of the shell on interrupts. Without arguments, restores the default action of the shell on interrupts, which is to terminate shell scripts or to return to the terminal command input level. With '-', causes all interrupts to be ignored. With label, causes the shell to execute a 'goto label' when an interrupt is received or a child process terminates because it was interrupted.

onintr is ignored if the shell is running detached and in system startup files (see FILES), where interrupts are disabled anyway.

popd [-p] [-l] [-n|-v] [+n]
Without arguments, pops the directory stack and returns to the new top directory. With a number '+n', discards the entry in the stack specified by n.

All forms of popd print the final directory stack, just like dirs. The pushdsilent shell variable can be set to prevent this, and the -p flag can be given to override pushdsilent. The -l, -n and -v flags have the same effect on popd as on dirs. (+)

printenv [name] (+)
Prints the names and values of all environment variables or, with name, the value of the environment variable name.
pushd [-p] [-l] [-n|-v] [name|+n]
Without arguments, exchanges the top two elements of the directory stack. If pushdtohome is set, pushd without arguments does 'pushd ~', like cd. (+) With name, pushes the current working directory onto the directory stack and changes to name. If name is '-', it is interpreted as the previous working directory (see File-name substitution). (+) If dunique is set, pushd removes any instances of name from the stack before pushing it onto the stack. (+) With a number '+n', rotates the element of the directory stack identified by n around to be the top element and changes to it. If dextract is set, however, 'pushd +n' extracts the directory by n, pushes it onto the top of the stack and changes to it. (+)

All forms of pushd print the final directory stack, just like dirs. The pushdsilent shell variable can be set to prevent this, and the -p flag can be given to override pushdsilent. The -l, -n and -v flags have the same effect on pushd as on dirs. (+)

Causes the internal hash table of the contents of the directories in the path variable to be recomputed. This is needed if new commands are added to directories in path while you are logged on. This should only be necessary if you add commands to one of your own directories, or if a systems programmer changes the contents of one of the system directories. Also flushes the cache of home directories built by tilde (~)expansion.
repeat count command
The specified command, which is subject to the same restrictions as the command in the one line if statement above, is executed count times. I/O redirections occur exactly once, even if count is 0.
rootnode //nodename (+)
Changes the rootnode to //nodename, so that '/' will be interpreted as '//nodename'. (Domain/OS only)
sched (+)
sched [+]hh:mm command (+)
The first form prints the scheduled-event list. The sched shell variable can be set to define the format in which the scheduled-event list is printed. The second form adds command to the scheduled-event list.

For example:

> sched 11:00 echo It\'s eleven o\'clock.

causes the shell to echo 'It's eleven o'clock.' at 11 AM. The time may be in 12-hour A.M./P.M. format, as follows:

> sched 5pm set prompt='[%h] It\'s after 5; go home: >'

or may be relative to the current time:

> sched +2:15 /usr/lib/uucp/uucico -r1 -sother

A relative time specification may not use A.M./P.M. format. The third form removes item n from the event list:

> sched
	 1  Wed Apr  4 15:42  /usr/lib/uucp/uucico -r1 -sother
	 2  Wed Apr  4 17:00  set prompt=[%h] It's after 5; go home: >
> sched -2
> sched
	 1  Wed Apr  4 15:42  /usr/lib/uucp/uucico -r1 -sother

A command in the scheduled-event list is executed just before the first prompt is printed after the time when the command is scheduled. It is possible to miss the exact time when the command is to be run, but an overdue command will execute at the next prompt. A command that comes due while the shell is waiting for user input is executed immediately. However, normal operation of a command that is already running will not be interrupted so that a scheduled-event list element may be run.

This mechanism is similar to, but not the same as, the at(1) command on some traditional systems. Its major disadvantage is that it may not run a command at exactly the specified time. Its major advantage is that because sched runs directly from the shell, it has access to shell variables and other structures. This provides you with a mechanism for changing your working environment based on the time of day.

set name ...
set name=word ...
set name=(wordlist) ...
set name[index]=word ...
set -r (+)
set -r name ... (+)
set -r name=word ... (+)
set -r name=(wordlist) ... (+)
The first form of the command prints the value of all shell variables. Variables that contain more than a single word print as a parenthesized word list. The second form sets name to the null string. The third form sets name to the single word.

The fourth form sets name to the list of words in wordlist. In all cases the value is command and file-name expanded. The fifth form sets the index'th component of name to word; this component must already exist. The sixth form lists the names (only) of all shell variables that are read-only. The seventh form makes name read-only, whether or not it has a value. The second form sets name to the null string. The eighth and ninth forms are the same as the third and fourth forms, but make name read-only at the same time.

You can repeat these arguments in a single set(1) command to set multiple variables, make multiple variables read-only, or do both. Note, however, that variable expansion happens for all arguments before any setting occurs. Note also that '=' can be adjacent to both name and word or separated from both by white space, but cannot be adjacent to only one or the other. See also the unset built-in command.

setenv[name [value]]
Without arguments, prints the names and values of all environment variables. Given name, sets the environment variable name to value or, without value, to the null string.
setpath path (+)
Equivalent to setpath(1). Mach only)
setspath LOCAL|site|cpu ... (+)
Sets the system execution path. TCF only)
settc cap value (+)
Tells the shell to behave as though the terminal capability cap (as defined in termcap(5)) has the value value. It does not check for correctness. Concept terminal users may have to use settc xn no to get the lines to wrap correctly at the rightmost column.
setty [-d|-q|-x] [-a] [[+|-]mode (+)
Controls which tty modes the shell does not allow to change (see the section on terminal management). Using -d, -q or -x tells setty to act on the 'edit', 'quote' or 'execute' set of tty modes respectively; without -d, -q or -x, 'execute' is used.

Without other arguments, setty lists the modes in the chosen set that are fixed on ('+mode') or off ('-mode'). The available modes, and thus the display, vary from system to system. With -a, lists all tty modes in the chosen set, whether or not they are fixed. With +mode, -mode, or mode, fixes mode on or off, or removes control from mode in the chosen set. For example, 'setty +echok echoe' fixes 'echok' mode on and allows commands to turn 'echoe' mode on or off, both when the shell is executing commands.

setxvers [string] (+)
Set the experimental version prefix to string, or removes it if string is omitted. (TCF only)
shift [variable]
Without arguments, discards argv[1] and shifts the members of argv to the left. It is an error for argv not to be set or to have less than one word as value. With variable, performs the same function on variable.
source [-h] name [arg ...]
The shell reads and executes commands from name. The commands are not placed on the history list. If arguments (arg) are given, they are placed in argv. (+) You can nestsource commands; if they are nested too deeply, the shell may run out of file descriptors. An error in a source at any level terminates all nested source commands. With -h, commands are placed on the history list instead of being executed, much like 'history -L'.
stop %job|pid ...
Stops the specified jobs or processes that are executing in the background. job may be a number, a string, '', '%', '+' or '-' as described in the "Jobs" section. There is no default job; 'stop' without an argument does not stop the current job.
Causes the shell to stop immediately, much as if it had been sent a stop signal with ^Z. This is most often used to stop shells started by su(1).
switch (string)
case str1:
Each case label is successively matched, against the specified string that is first command and file-name expanded. The file metacharacters '*', '?' and '[...]' can be used in the case labels, which are variable expanded. If none of the labels match before a 'default' label is found, the execution begins after the default label. Each case label and the default label must appear at the beginning of a line. The command breaksw causes execution to continue after the endsw. Otherwise, control may fall through case labels and default labels, as in C. If no label matches, and there is no default, execution continues after the endsw.
telltc (+)
Lists the values of all terminal capabilities (see termcap(5)).
time [command]
Executes command (which must be a simple command, not an alias, a pipeline, a command list or a parenthesized command list) and prints a time summary as described under the time variable. If necessary, an extra shell is created to print the time statistic when the command completes. Without command, prints a time summary for the current shell and its children.
umask [value]
Sets the file creation mask to value, which is given in octal. Common values for the mask are 002, giving all access to the group and read and execute access to others, and 022, giving read and execute access to the group and others. Without value, prints the current file creation mask.
unalias pattern
Removes all aliases whose names match pattern. 'unalias *' thus removes all aliases. It is not an error if no aliases are removed.
uncomplete pattern (+)
Removes all completions whose names match pattern. 'uncomplete *' thus removes all completions. It is not an error if no completions are removed.
Disables the use of the internal hash table to speed location of executed programs.
unlimit [-h] [resource]
Removes the limitation on resource or, if no resource is specified, all resource limitations. With -h, the corresponding hard limits are removed. Only a user with appropriate privileges can do this.
unset pattern
Removes all variables whose names match pattern, unless they are read-only. Thus, 'unset *' removes all variables unless they are read-only; this is not recommended. It is not an error if no variables are removed.
unsetenv pattern
Removes all environment variables whose names match pattern. Thus, 'unsetenv *' removes all environment variables; this is not recommended. It is not an error if no environment variables are removed.
ver[systype [command]] (+)
Without arguments, prints SYSTYPE. With systype, sets SYSTYPE to systype. With systype and command, executes command under systype. systype may be 'bsd4.3' or 'sys5.3'. (Domain/OS only)
The shell waits for all background jobs. If the shell is interactive, an interrupt will disrupt the wait and cause the shell to print the names and job numbers of all outstanding jobs.
watchlog (+)
An alternate name for the log built-in command. Available only if the shell was so compiled; see the version shell variable.
where command (+)
Reports all known instances of command, including aliases, built-ins and executables in path.
which command (+)
Displays the command that will be executed by the shell after substitutions, path searching, and so on. See also the which-command editor command.
while (expr)
Executes the commands between the while and the matching end while expr (an expression, as described in the section on expressions) evaluates non-zero. while and end must appear alone on their input lines. break and continue can be used to terminate or continue the loop prematurely. If the input is a terminal, the user is prompted the first time through the loop (as with foreach).

Special aliases (+)

If set, each of these aliases executes automatically at the indicated time. They are all initially undefined.
Runs when the shell wants to ring the terminal bell.
Runs after every change of working directory. For example, if the user is working on an X window system using xterm(1) and a re-parenting window manager that supports title bars, such as twm(1), and does the following:
> alias cwdcmd  'echo -n "^[]2;${HOST}:$cwd ^G"'

The shell will then change the title of the running xterm(1) to be the name of the host, a colon, and the full current working directory. The following is a more elaborate way to do this:

> alias cwdcmd 'echo -n "^[]2;${HOST}:$cwd^G^[]1;${HOST}^G"'

This will put the hostname and working directory on the title bar, but will place only the hostname in the icon manager menu.

Be forewarned that that putting a cd, pushd or popd in cwdcmd can cause an infinite loop and is therefore highly discouraged.

Runs every tperiod minutes. You can use this to check for common but infrequent changes, such as new mail. For example, if you use the following:
> set tperiod = 30
> alias periodic checknews
the checknews(1) program runs every 30 minutes. If periodic is set, but tperiod is unset or set to 0, periodic behaves like precmd.
Runs just before each prompt is printed. For example, if you use the following:
> alias precmd date

date(1) runs just before the shell prompts for each command. There are no limits on what precmd can be set to do, but discretion should be used.

Specifies the interpreter for executable scripts that do not specify an interpreter. The first word should be a full path name to the desired interpreter (for example, '/bin/csh' or '/usr/local/bin/tcsh').

Special shell variables

The variables described in this section have special meaning to the shell.

The shell sets addsuffix, argv, autologout, command, echo_style, edit, gid, group, home, loginsh, oid, path, prompt, prompt2, prompt3, shell, shlvl, tcsh, term, tty, uid, user and version at startup; they do not change thereafter unless changed by the user. The shell updates cwd, dirstack, owd and status when necessary, and sets logout on logout.

The shell synchronizes afsuser, group, home, path, shlvl, term and user with the environment variables of the same names. Whenever the environment variable changes, the shell changes the corresponding shell variable to match (unless the shell variable is read-only) and vice versa. Although cwd and PWD have identical meanings, they are not synchronized in this manner. The shell also automatically interconverts the different formats of path and PATH.

addsuffix (+)
If set, file name completion adds '/' to the end of directories and a space to the end of normal files when they are matched exactly. Set by default.
afsuser (+)
If set,the autolock feature of autologoutuses its value instead of the local username for kerberos authentication.
ampm (+)
If set, all times are shown in 12-hour A.M/P.M format.
The arguments to the shell. Positional parameters are taken from argv; for example, '$1' is replaced by '$argv[1]'. Set by default, but usually empty in interactive shells.
autocorrect (+)
If set, the spell-word editor command is invoked automatically before each completion attempt.
autoexpand (+
If set, the expand-history editor command is invoked automatically before each completion attempt.
autolist (+)
If set, possibilities are listed after an ambiguous completion. If set to 'ambiguous', possibilities are listed only when no new characters are added by completion.
autologout (+)
The first word is the number of minutes of inactivity before automatic logout. The optional second word is the number of minutes of inactivity before automatic locking. When the shell automatically logs out, it prints 'auto-logout', sets the variable logout to 'automatic' and exits. When the shell automatically locks, you must enter your password to continue working. Five incorrect attempts result in automatic logout. It is set to '60' (automatic logout after 60 minutes, and no locking) by default in login and superuser shells, but not if the shell thinks it is running under a window system (for example, if the the DISPLAY environment variable is set), the tty is a pseudo-tty (pty), or the shell was not so compiled (see the version shell variable). See also the afsuser and logout shell variables.
backslash_quote (+)
If set, backslashes ('\') always quote '\', '", and '"'. This may make complex quoting tasks easier, but it can cause syntax errors in csh(1) scripts.
A list of directories in which cd should search for subdirectories if they are not found in the current directory.
command (+)
If set, the command which was passed to the shell with the -c flag.
complete (+)
If set to 'enhance', completion 1) ignores case, and 2) considers periods, hyphens and underscores ('.', '-' and '_') to be word separators and hyphens and underscores to be equivalent.
correct (+)
If set to 'cmd', commands are automatically corrected for spelling. If set to 'complete', commands are automatically completed. If set to 'all', the entire command line is corrected.
The full path name of the current directory. See also the dirstack and owd shell variables.
dextract (+)
If set, 'pushd +n' extracts the nth directory from the directory stack rather than rotating it to the top.
dirsfile (+)
The default location in which 'dirs -S' and 'dirs -L' look for a history file. If unset, ~/.cshdirs is used. Because only ~/.tcshrc is normally sourced before ~/.cshdirs, dirsfile should be set in ~/.tcshrc rather than ~/.login.
dirstack (+)
An array of all the directories on the directory stack. '$dirstack[1]' is the current working directory, '$dirstack[2]' the first directory on the stack, and so on. Note that the current working directory is '$dirstack[1]' but '=0' in directory-stack substitutions. You can change the stack arbitrarily by setting dirstack, but the first element (the current working directory) is always correct. See also the cwd and owd shell variables.
dunique (+)
If set, pushd removes any instances of name from the stack before pushing it onto the stack.
If set, each command with its arguments is echoed just before it is executed. For non-built-in commands, all expansions occur before echoing. Built-in commands are echoed before command and file name substitution, since these substitutions are then done selectively. Set by the -x command-line option.
echo_style (+)
The style of the echo built-in command. May be set to the following:
Do not echo a newline if the first argument is '-n'.
Recognize backslashed escape sequences in echo strings.
Recognize both the '-n' flag and backslashed escape sequences; the default.
Recognize neither.

Set by default to 'both'. The BSD and System V options are described in the echo(1) reference pages on the appropriate systems.

edit (+)
If set, the command-line editor is used. Set by default in interactive shells.
ellipsis (+)
If set, the '%c'/'%.' and '%C' prompt sequences (see the prompt shell variable) indicate skipped directories with an ellipsis ('...') instead of '/<skipped>'.
fignore (+)
Lists file-name suffixes to be ignored by completion.
In tcsh(1), completion is always used and this variable is ignored. If set in csh(1), file-name completion is used.
gid (+)
The user's real group ID.
group (+)
The user's group name.
A string value determining the characters used in History substitution. The first character of its value is used as the history substitution character, replacing the default character '!'. The second character of its value replaces the character '^' in quick substitutions.
histdup (+)
Controls handling of duplicate entries in the history list. If set to 'all', only unique history events are entered in the history list. If set to 'prev' and the last history event is the same as the current command, the current command is not entered in the history. If set to 'erase' and the same event is found in the history list, that old event gets erased and the current one gets inserted.
histfile (+)
The default location in which 'history -S' and 'history -L' look for a history file. If unset, ~/.history is used. histfile is useful when sharing the same home directory between different machines, or when saving separate histories on different terminals. Because only ~/.tcshrc is normally sourced before ~/.history, histfile should be set in ~/.tcshrc rather than ~/.login.
histlit (+)
If set, built-in and editor commands and the savehist mechanism use the literal (unexpanded) form of lines in the history list. (See also the toggle-literal-history editor command.)
The first word indicates the number of history events to save. The optional second word (+) indicates the format in which history is printed; if not given, '%h\t%T\t%R\n' is used. The format sequences are described below under prompt; note the variable meaning of '%R'. Set to '100' by default.
Initialized to the home directory of the invoker. The file-name expansion of '~' refers to this variable.
If set to the empty string or '0' and the input device is a terminal, the end-of-file command (usually generated by the user by typing '^D' on an empty line) causes the shell to print 'Use "exit" to leave tcsh' instead of exiting. This prevents the shell from accidentally being killed. If set to a number n, the shell ignores n-1 consecutive nth. (+)end-of-files and exits on the If unset, '1' is used; that is, the shell exits on a single '^D'.
inputmode (+)
If set to 'insert' or 'overwrite', puts the editor into that input mode at the beginning of each line.
listflags (+)
If set to 'x', 'a' or 'A', or any combination thereof (such as 'xA'), they are used as flags to ls-F, making it act like 'ls -xF', 'ls -Fa', 'ls -FA' or a combination (such as 'ls -FxA'): 'a' shows all files (even if they start with a '.'); 'A' shows all files but '.' and '..'; and 'x' sorts across instead of down. If the second word of listflags is set, it is used as the path to the ls(1) command.
listjobs (+)
If set, all jobs are listed when a job is suspended. If set to 'long', the listing is in long format.
listlinks (+)
If set, the ls-F built-in command shows the type of file to which each symbolic link points.
listmax (+)
The maximum number of items which the list-choices editor command will list without asking first.
listmaxrows (+)
The maximum number of rows of items that the list-choices editor command will list without asking first.
loginsh (+)
Set by the shell if it is a login shell. Setting or unsetting it within a shell has no effect. (See also shlvl.)
logout (+)
Set by the shell to 'normal' before a normal logout, 'automatic' before an automatic logout, and 'hangup' if the shell was killed by a hangup signal (see Signal handling). See also the autologout shell variable.
The names of the files or directories to check for incoming mail, separated by white space, and optionally preceded by a numeric word. Before each prompt, if 10 minutes have passed since the last check, the shell checks each file and reports: 'You have new mail.' (or if mail contains multiple files,it reports: 'You have new mail in name') if the file size is greater than zero and has a modification time greater than its access time.

If you are in a login shell, no mail file is reported unless it has been modified after the time the shell started up; this prevents redundant notifications. Most login programs will tell you whether or not you have mail when you log in.

If a file specified in mail is a directory, the shell will count each file within that directory as a separate message, and will report 'You have n mails' or 'You have n mails in name', as appropriate. This functionality is provided primarily for systems that store mail in this manner, such as the Andrew Mail System.

If the first word of mail is numeric, it is taken as a different mail checking interval, in seconds.

Under very rare circumstances, the shell may report 'You have mail' instead of 'You have new mail'.

matchbeep (+)
If set to 'never', completion never beeps.
If set to 'nomatch', it beeps only when there is no match.
If set to 'ambiguous, it beeps when there are multiple matches.
If set to 'notunique', it beeps when there is one exact and other longer matches.
If unset, 'ambiguous' is used.
nobeep (+)
If set, beeping is completely disabled. See also visiblebell.
If set, restrictions are placed on output redirection to ensure that files are not accidentally destroyed and that '>>' redirections refer to existing files (as described in the input/output section).
If set, file-name substitution and directory-stack substitution are inhibited. This is most useful in shell scripts that do not deal with file names, or after a list of file names has been obtained and further expansions are not desirable.
nokanji (+)
If set and the shell supports Kanji (see the version shell variable), it is disabled so that the metakey can be used.
If set, a file-name substitution or directory-stack substitution that does not match any existing files is left untouched rather than causing an error. It is still an error for the substitution to be malformed; for example, 'echo [' still gives an error.
nostat (+)
A list of directories (or glob-patterns that match directories; see the section on file-name substitution) for which stat(2)should not be called during a completion operation. This is usually used to exclude directories for which stat(2)takes too much time, for example, /afs.
If set, the shell announces job completions asynchronously. The default is to present job completions just before printing a prompt.
oid (+)
The user's real organization ID. (Domain/OS only)
owd (+)
The old working directory, equivalent to the '-' used by cd and pushd. See also the cwd and dirstack shell variables.
A list of directories in which to look for executable commands. A null word specifies the current directory. If there is no path variable, only full path names will execute. path is set by the shell at startup from the PATH environment variable or, if PATH does not exist, to a system-dependent default something like '(/usr/local/bin /usr/bsd /bin /usr/bin .)'. The shell may put '.' first or last in path, or omit it entirely, depending on how it was compiled; see the version shell variable. A shell that is given neither the -c nor the -t option hashes the contents of the directories in path after reading ~/.tcshrc and each time path is reset. If you add a new command to a directory in path while the shell is active, you may need to do a rehash for the shell to find it.
printexitvalue (+)
If set and an interactive program exits with a non-zero status, the shell prints 'Exit status'.
The string that is printed before reading each command from the terminal. prompt may include any of the following formatting sequences (+), which are replaced by the given information:
The current working directory.
The current working directory, but with your home directory represented by '~' and other users' home directories represented by '~user' (as described in file-name substitution). '~user' substitution happens only if the shell has already used '~user' in a path name in the current session.
%c[[0]n], %.[[0]n]
The trailing component of the current working directory, or n trailing components if a digit n is given. If n begins with '0', the number of skipped components precede the trailing component(s) in the format:

If the ellipsis shell variable is set, skipped components are represented by an ellipsis so the whole becomes '...trailing'. '~' substitution is done as in '%~' above, but the '~' component is ignored when counting trailing components.

Like %c, but without '~' substitution.
%h,%!, !
The current history event number.
The full hostname.
The hostname up to the first '.'.
Start (stop) standout mode.
%B (%b)
Start (stop) boldfacing mode.
%U (%u)
Start (stop) underline mode.
%t, %a
The time of day in 12-hour A.M./P.M. format.
Like %t, but in 24-hour format (but see the ampm shell variable).
The 'precise' time of day in 12-hour A.M./P.M. format, with seconds.
Like %p, but in 24-hour format (but see the ampm shell variable).
c is parsed as in bindkey.
c is parsed as in bindkey.
A single '%'.
The user name.
The weekday in 'Day' format.
The day in 'dd' format.
The month in 'Mon' format.
The month in 'mm' format.
The year in 'yy' format.
The year in 'yyyy' format.
The tty of the shell.
Clears from the end of the prompt to end of the display or the end of the line.
'>' (or the first character of the promptchars shell variable) for normal users; '#' (or the second character of promptchars) for the superuser.
Includes string as a literal escape sequence. It should be used only to change terminal attributes and should not move the cursor location. This cannot be the last sequence in prompt.
The return code of the command executed just before the prompt.
In prompt2, the status of the parser. In prompt3, the corrected string. In history, the history string.

%B, %S, %U and %{string%} are available only in eight-bit-clean shells; see the version shell variable.

The bold, standout and underline sequences are often used to distinguish a superuser shell. For example:

> set prompt = "%m [%h] %B[%@]%b [%/] you rang? "
tut [37] [2:54pm] [/usr/accts/sys] you rang? _

Set by default to '%# ' in interactive shells.

prompt2 (+)
The string that prompts the user at the beginning of while(1) and foreach(1) loops and after lines ending in ‘\’. The same format sequences can be used as those that are used in prompt; note the variable meaning of '%R'. Set by default to '%R? ' in interactive shells.
prompt3 (+)
The string with which to prompt when confirming automatic spelling correction. The same format sequences can be used as those used in prompt; note the variable meaning of '%R'. Set by default to 'CORRECT>%R (y|n|e)? ' in interactive shells.
promptchars (+)
If set (to a two-character string), the '%#' formatting sequence in the prompt shell variable is replaced with the first character for normal users and the second character for the superuser.
pushdtohome (+)
If set, pushd without arguments does 'pushd ~', like cd.
pushdsilent (+)
If set, pushd and popd do not print the directory stack.
recexact (+)
If set, completion completes on an exact match even if a longer match is possible.
recognize_only_executables (+)
If set, command listing displays only files in the path that are executable. Slow.
rmstar (+)
If set, the user is prompted before 'rm *' is executed.
savedirs (+)
If set, the shell does 'dirs -S' before exiting.
If set, the shell does 'history -S' before exiting. If the first word is set to a number, that is the maximum number of lines saved. (The number must be less than or equal to history.) If the second word is set to 'merge', the history list is merged with the existing history file instead of replacing it (if there is one) and sorted by time stamp; the most recent events are retained. (+)
sched (+)
The format in which the sched built-in command prints scheduled events; if not given, '%h\t%T\t%R\n' is used. The format sequences are described above under prompt; note the variable meaning of '%R'.
The file in which the shell resides. This is used in forking shells to interpret files that have execute bits set, but which are not executable by the system. (See the description of Built-in and non-built-in command execution.) Initialized to the (system-dependent) home of the shell.
shlvl (+)
The number of nested shells. Reset to 1 in login shells. See also loginsh.
The status returned by the last command. If it terminated abnormally, 0200 is added to the status. Built-in commands that fail return exit status '1', all other built-in commands return status '0'.
symlinks (+)
Can be set to several different values to control symbolic link ('symlink') resolution.

The following section presents some examples. It begins with some sample directories:

> cd /tmp
> mkdir from from/src to
> ln -s from/src to/dist

The following behavior occurs with symlinks unset:

> cd /tmp/to/dist; echo $cwd
> cd ..; echo $cwd

The following behavior occurs with symlinks set to 'chase':

> cd /tmp/to/dst; echo $cwd
> cd ..; echo $cwd

The following behavior occurs with symlinks set to 'ignore':

> cd /tmp/to/dist; echo $cwd
> cd ..; echo $cwd

The following behavior occurs with symlinks set to 'expand':

> cd /tmp/to/dist; echo $cwd
> cd ..; echo $cwd
> cd /tmp/to/dist; echo $cwd
> cd ".."; echo $cwd
> /bin/echo ..
> /bin/echo ".."

Note that 'expand' expansion works just like 'ignore' for built-in commands like cd(1), is prevented by quoting, and occurs before file names are passed to non-built-in commands.

tcsh (+)
The version number of the shell in the format 'R.VV.PP', where 'R' is the major release number, 'VV' the current version and 'PP' the patch level.
The terminal type. Usually set in ~/.login as described in startup and shutdown.
If set to a number, the time built-in executes automatically after each command that exceeds that number of CPU seconds. If there is a second word, it is used as a format string for the output of the time built-in. (u) The following sequences may be used in the format string:
The time, in cpu seconds, the process spent in user mode.
The time, in cpu seconds, the process spent in kernel mode.
The elapsed (wall clock) time, in seconds.
The CPU percentage computed as (%U + %S) / %E.
Number of times the process was swapped.
The average amount in (shared) text space used, in kilobytes.
The average amount in (unshared) data/stack space used, in kilobytes.
The total space used (%X + %D), in kilobytes.
The maximum memory the process had in use at any time, in kilobytes.
The number of major page faults (page needed to be brought from disk).
The number of minor page faults.
The number of input operations.
The number of output operations.
The number of socket messages received.
The number of socket messages sent.
The number of signals received.
The number of voluntary context switches (waits).
The number of involuntary context switches.

Only the first four sequences are supported on systems without Berkeley Software Design (BSD) resource limit functions. The default time format is '%Uu %Ss %E %P %X+%Dk %I+%Oio %Fpf+%Ww' for systems that support resource usage reporting, and '%Uu %Ss %E %P' for systems that do not.

Note that the CPU percentage can be higher than 100% on multiprocessors.

tperiod (+)
The period, in minutes, between executions of the periodic special alias.
tty (+)
The name of the tty, or empty if not attached to one.
uid (+)
The user's real user ID.
The user's login name.
If set, causes the words of each command to be printed, after history substitution (if any). Set by the -v command-line option.
version (+)
The version ID stamp. It contains the version number of the shell (see tcsh), origin, release date, vendor, operating system and machine (see VENDOR, OSTYPE and MACHTYPE), and a comma-separated list of options that were set at compile time. Options that are set by default in the distribution are noted.
The shell is eight-bit clean; default
The shell is not eight-bit clean
The system's Native Language System (NLS) is used; default for systems with NLS
Login shells execute /etc/csh.login before instead of after /etc/csh.cshrc, and they execute ~/.login before instead of after ~/.tcshrc and ~/.history.
'.' is put last in path for security; default
'.' is omitted from path for security
vi-style editing is the default rather than emacs
Login shells drop Data Terminal Ready (DTR) when exiting
bye is a synonym for logout, and log is a synonym for watchlog
autologout is enabled; default
Kanji is used, and the International Organization for Standardization (ISO) character set is ignored, unless the nokanji shell variable is set
The system's malloc(3) is used
The '#!<program> <args>' convention is emulated when executing shell scripts
The newgrp built-in is available
The shell attempts to set the REMOTEHOST environment variable
The shell verifies your password with the kerberos server if local authentication fails. The afsuser shell variable or the AFSUSER environment variable override your local username if set.

An administrator can enter additional strings to indicate differences in the local version.

visiblebell (+)
If set, a screen flash is used rather than the audible bell. See also nobeep.
watch (+)
A list of user/terminal pairs that are watched for logins and logouts. If the user is 'any,' all terminals are watched for the given user. If the terminal is ‘any,’ all users are watched for the given terminal. Setting watch to '(any any)' watches all users and terminals. For example:
set watch = (george ttyd1 any console $user any)

reports activity of the user 'george' on ttyd1, any user on the console, and oneself (or a trespasser) on any terminal.

Logins and logouts are checked every 10 minutes by default, but the first word of watch can be set to specify the interval, in minutes, at which the check should occur. For example:

set watch = (1 any any)

reports any login/logout once every minute. The log built-in command triggers a watch report at any time. All current logins are reported (as with the log built-in) when watch is first set.

The who shell variable controls the format of watch reports.

who (+)
The format string for watch messages. The following sequences are replaced by the given information:
The name of the user who logged in/out.
The observed action (such as, 'logged on', 'logged off' or 'replaced olduser on').
The terminal (tty) on which the user logged in or out.
The full hostname of the remote host, or 'local' if the login or logout was from the local host.
The hostname of the remote host up to the first '.'. The full name is printed if it is an IP address or an X Window System display.

%M and %m are available only on systems that store the remote hostname in /etc/utmp. If unset, either '%n has %a %l from %m.' is used, or, on systems that do not store the remote hostname, '%n has %a %l.' is used.

wordchars (+)
A list of non-alphanumeric characters to be considered part of a word by editor commands such as forward-word, backward-word, and so on. If unset, '*?_-.[]~=' is used.


The tcsh(1) utility uses of the following environment variables:

Equivalent to the afsuser shell variable.
The number of columns in the terminal. See Terminal management.

Used by X Window System (see X(5)). If set, the shell does not set autologout.
The path name to a default editor. See also the VISUAL environment variable and the run-fg-editor editor command.
Equivalent to the group shell variable.
Equivalent to the home shell variable.
HOST (+)
Initialized to the name of the machine on which the shell is running, as determined by the gethostname(3) system call.
Initialized to the type of machine on which the shell is running, as determined at compile time. This variable is obsolete and will be removed in a future version.
A colon-separated list of directories in which the run-help editor command looks for command documentation.
Gives the preferred character environment. See Native Language System support.
If set, only ctype character handling is changed. See Native Language System support.
The number of lines in the terminal. See Terminal management.
The machine type (microprocessor class or machine model), as determined at compile time.
If set, printable characters are not rebound to self-insert-command. See Native Language System support.
The operating system, as determined at compile time.
A colon-separated list of directories in which to look for executables. Equivalent to the path shell variable, but in a different format.
PWD (+)
Equivalent to the cwd shell variable, but not synchronized to it; updated only after an actual directory change.
The host from which the user has logged in remotely, if this is the case and the shell is able to determine it. Set only if the shell was so compiled; see the version shell variable.
Equivalent to the shlvl shell variable.
The current system type. (Domain/OS only)
Equivalent to the term shell variable.
The terminal capability string. See Terminal management.
Equivalent to the user shell variable.
The vendor, as determined at compile time.
The path name to a default full-screen editor. See also the EDITOR environment variable and the run-fg-editor editor command.


The tcsh(1) utility uses the following files:

Read first by every shell. Interix systems use /etc/cshrc. ConvexOS, Stellix and Intel use /etc/cshrc. NeXT systems use /etc/cshrc.std. A/UX, AMIX, Cray and IRIX have no equivalent in csh(1), but read this file in tcsh(1) anyway. Solaris 2.x does not have it either, but tcsh(1) reads /etc/.cshrc. (+)
Read by login shells after /etc/csh.cshrc. Interix systems read /etc/csh.login. ConvexOS, Stellix and Intel use /etc/login, NeXT systems use /etc/login.std, Solaris 2.x uses /etc/.login and A/UX, AMIX, Cray and IRIX use /etc/cshrc.
~/.tcshrc (+)
Read by every shell after /etc/csh.cshrc or its equivalent.
Read by every shell, if ~/.tcshrc does not exist, after /etc/csh.cshrc or its equivalent. This document uses ~/.tcshrc ~/.tcshrc to mean ~/.tcshrc ~/.tcshrc or, if ~/.tcshrc is not found, ~/.cshrc.
Read by login shells after ~/.tcshrc if savehist is set, but see also histfile.
Read by login shells after ~/.tcshrc or ~/.history. The shell may be compiled to read ~/.login before instead of after ~/.tcshrc and ~/.history; see the version shell variable.
~/.cshdirs (+)
Read by login shells after ~/.login if savedirs is set, but see also dirsfile.
Read by login shells at logout. Interix systems read /etc/csh.logout. ConvexOS, Stellix and Intel use /etc/logout. NeXT systems use /etc/logout.std. A/UX, AMIX, Cray and IRIX have no equivalent in csh(1), but read this file in tcsh(1). Solaris 2.x does not have it either, but tcsh(1) reads /etc/.cshrc. (+)
Read by login shells at logout after /etc/csh.logout or its equivalent.
Used to interpret shell scripts not starting with a '#'.
Temporary file for <<.
Source of home directories for '~name' substitutions.

The order in which startup files are read may differ if the shell was so compiled. See the section on startup and shutdown and the version shell variable.


This document describes tcsh(1) as a single entity, but experienced csh(1) users might want to note the new features of tcsh(1).

New features include the following:


When a suspended command is restarted, the shell prints the directory it started in if this is different from the current directory. This can be misleading or even wrong, as the job may have changed directories internally.

Shell built-in functions are not stoppable/restartable. Command sequences of the form 'a ; b ; c' are also not handled gracefully when stopping is attempted. If you suspend 'b', the shell will immediately execute 'c'. This is especially noticeable if this expansion results from an alias. It is sufficient to place the sequence of commands in parentheses to force it to a subshell; that is: '( a ; b ; c )'.

Control over tty output after processes are started is primitive. In a virtual terminal interface, much more interesting things could be done with output control.

Alias substitution is most often used to clumsily simulate shell procedures; shell procedures should be provided rather than aliases.

Commands within loops are not placed in the history list. Control structures should be parsed rather than being recognized as built-in commands. This would allow control commands to be placed anywhere, to be combined with '|', and to be used with '&' and ';' metasyntax.

foreach does not ignore "here" documents when looking for its end.

It should be possible to use the ':' modifiers on the output of command substitutions.

The screen update for lines longer than the screen width is very poor if the terminal cannot move the cursor up (that is, terminal type 'dumb').

HPATH and NOREBIND do not need to be environment variables.

Glob-patterns that do not use '?', '*' or '[]' or which use '{}' or '~' are negated incorrectly.

The single-command form of if does output redirection even if the expression is false and the command is not executed.

ls-F includes file-identification characters when sorting file names.

Report bugs to, preferably with fixes. If you want to help maintain and test tcsh, send mail to with the text 'subscribe tcsh <your name>' on a line by itself in the body. You can also 'subscribe tcsh-bugs <your name>' to get all bug reports, or 'subscribe tcsh-diffs <your name>' to get the development list plus diffs for each patchlevel.


In 1964, DEC produced the PDP-6. The PDP-10 was a later implementation. It was renamed the DECsystem-10 in 1970 or so when DEC brought out the second model, the KI10.

TENEX was created at Bolt, Beranek & Newman in Cambridge, Massachusetts in 1972 as an experiment in demand-paged virtual memory operating systems. They built a new pager for the DEC PDP-10 and created the operating system to go with it. It was extremely successful in academia.

In 1975, DEC brought out a new model of the PDP-10, the KL10; they intended to have only a version of TENEX, which they had licensed from BBN, for the new box. They called their version TOPS-20 (their capitalization is trademarked). A lot of TOPS-10 users ('The OPerating System for PDP-10') objected; thus DEC found themselves supporting two incompatible systems on the same hardware—but then there were six on the PDP-11.

TENEX and TOPS-20 to version 3, had command completion through a user-code-level subroutine library called ULTCMD. With version 3, DEC moved all that capability and more into the monitor (or 'kernel'), accessed by the COMND% JSYS ('Jump to SYStem' instruction, the supervisor call mechanism).

The creator of tcsh(1) was impressed by this feature and several others of TENEX and TOPS-20, and created a version of csh(1) which mimicked them.


Words can be no longer than 1024 characters.

The system limits argument lists to 10240 characters.

The number of arguments to a command that involves file-name expansion is limited to 1/6th the number of characters allowed in an argument list.

Command substitutions can substitute no more characters than are allowed in an argument list.

To detect looping, the shell restricts the number of alias substitutions on a single line to 20.


By default, Interix does not execute files with the set-user-ID (setuid) or set-group-ID (setgid) mode bit set for security reasons. If an attempt is made to execute such a file, the ENOSETUID error is returned. For more information and and instructions for enabling execution of files with these mode bits set, see The superuser account and appropriate privileges in Windows Services for UNIX Help.





















Introduction to the C Shell


This manual documents tcsh 6.06.00 (Cornell) 1995-04-29.


William Joy
Original author of csh(1)
J.E. Kulp, IIASA, Laxenburg, Austria
Job control and directory-stack features
Ken Greer, HP Labs, 1981
File-name completion
Mike Ellis, Fairchild, 1983
Command-name recognition/completion
Paul Placeway, Ohio State CIS Dept., 1983-1993
Command-line editor, prompt routines, new glob syntax and numerous fixes and speedups
Karl Kleinpaste, CCI 1983-4
Special aliases, directory stack extraction information, login/logout watch, scheduled events, and the idea of the new prompt format
Rayan Zachariassen, University of Toronto, 1984
ls-F and which built-ins and numerous bug fixes, modifications and speedups
Chris Kingsley, Caltech
Fast storage allocator routines
Chris Grevstad, TRW, 1987
Incorporated 4.3BSD csh(1) into tcsh(1)
Christos S. Zoulas, Cornell U. EE Dept., 1987-94
Ports to HPUX, SVR2 and SVR3, a SysV version of getwd.c, SHORT_STRINGS support and a new version of sh.glob.c
James J Dempsey, BBN, and Paul Placeway, OSU, 1988
A/UX port
Daniel Long, NNSC, 1988
Patrick Wolfe, Kuck and Associates, Inc., 1988
vi mode cleanup
David C Lawrence, Rensselaer Polytechnic Institute, 1989
autolist and ambiguous completion listing
Alec Wolman, DEC, 1989
Newlines in the prompt
Matt Landau, BBN, 1989
Ray Moody, Purdue Physics, 1989
Magic spacebar history expansion
Mordechai ????, Intel, 1989
printprompt() fixes and additions
Kazuhiro Honda, Dept. of Computer Science, Keio University, 1989
Automatic spelling correction and prompt3
Per Hedeland, Ellemtel, Sweden, 1990-
Various bugfixes, improvements and manual updates
Hans J. Albertsson (Sun Sweden)
ampm, settc and telltc
Michael Bloom
Interrupt handling fixes
Michael Fine, Digital Equipment Corp
Extended key support
Eric Schnoebelen, Convex, 1990
Convex support, lots of csh(1) bug fixes, save and restore of directory stack
Ron Flax, Apple, 1990
A/UX 2.0 (re)port
Dan Oscarsson, LTH Sweden, 1990
NLS support and simulated NLS support for non NLS sites, fixes
Johan Widen, SICS Sweden, 1990
shlvl, Mach support, correct-line, 8-bit printing
Matt Day, Sanyo Icon, 1990
POSIX termio support, SysV limit fixes
Jaap Vermeulen, Sequent, 1990-91
Vi mode fixes, expand-line, window change fixes, Symmetry port
Martin Boyer, Institut de recherche d'Hydro-Quebec, 1991
autolist beeping options, modified the history search to search for the whole string from the beginning of the line to the cursor.
Scott Krotz, Motorola, 1991
Minix port
David Dawes, Sydney U. Australia, Physics Dept., 1991
SVR4 job control fixes
Jose Sousa, Interactive Systems Corp., 1991
Extended vi(1) fixes and vi(1) delete command
Marc Horowitz, MIT, 1991
ANSIfication fixes, new exec hashing code, imake fixes, where
Bruce Sterling Woodcock,, 1991-1995
ETA and Pyramid port, Makefile and lint fixes, ignoreeof=n addition, and various other portability changes and bug fixes
Jeff Fink, 1992
complete-word-fwd and complete-word-back
Harry C. Pulley, 1992
Coherent port
Andy Phillips, Mullard Space Science Lab U.K., 1992
Beto Appleton, IBM Corp., 1992
Walking process group fixes, csh(1) bug fixes, POSIX file tests, POSIX SIGHUP
Scott Bolte, Cray Computer Corp., 1992
CSOS port
Kaveh R. Ghazi, Rutgers University, 1992
Tek, m88k, Titan and Masscomp ports and fixes
Mark Linderman, Cornell University, 1992
OS/2 port
Mika Liljeberg, liljeber@kruuna.Helsinki.FI, 1992
Linux port
Tim P. Starrin, NASA Langley Research Center Operations, 1993
Read-only variables
Dave Schweisguth, Yale University, 1993-4
New manpage and tcsh.man2html
Larry Schwimmer, Stanford University, 1993
AFS and HESIOD patches
Luke Mewburn, RMIT University, 1994
Enhanced directory printing in prompt


Bryan Dunlap, Clayton Elwell, Karl Kleinpaste, Bob Manson, Steve Romig, Diana Smetters, Bob Sutterfield, Mark Verber, Elizabeth Zwicky and all the other people at Ohio State for suggestions and encouragement

All the people on the net, for putting up with, reporting bugs in, and suggesting new additions to each and every version

Richard M. Alderson III, for writing the 'T in tcsh' section