1:csh

tcsh [-bcdefFimnqstvVxX] [-Dname[=value]] [arg ...]

tcsh is an enhanced but completely compatible version of the Berkeley UNIX C shell, csh(1). It is a command language interpreter usable both as an interactive login shell and a shell script command processor. It includes a command-line editor (see The command-line editor), programmable word completion (see Completion and listing), spelling correction (see Spelling correction), a history mechanism (see History substitution), job control (see Jobs) and a C-like syntax. The NEW FEATURES section describes major enhancements of tcsh over csh(1). Throughout this manual, features of tcsh not found in most csh(1) implementations (specifically, the 4.4BSD csh) are labeled with `(+)', and features which are present in csh(1) but not usually documented are

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

The rest of the flag arguments are interpreted as

Forces 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. This may be used to pass options to a shell script without confusion or possible subterfuge. The shell will not run a set-user ID script without this

Commands are read 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

The shell loads the directory stack from ~/.cshdirs as described under Startup and shutdown, whether or

Sets the environment variable name to value.

The shell exits if any invoked command terminates abnormally

The shell ignores ~/.tcshrc, and thus starts

The shell uses fork(2) instead of vfork(2) to

The shell is interactive and prompts for its top-level input, even if it appears to not be a terminal. Shells are interactive without this option if their inputs and outputs

The shell is a login shell. Applicable only if -l is

The shell loads ~/.tcshrc even if it does not belong to the effective user. Newer versions of su(1) can

The shell parses commands but does not execute them. This

The shell accepts SIGQUIT (see Signal handling) and behaves when it is used under a debugger. Job control is

The shell reads and executes a single line of input. A `' may be used to escape the newline at the end of this line

Sets the verbose shell variable, so that command

Sets the echo shell variable, so that commands are

Sets the verbose shell variable even before executing

After 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'. Because many systems use either the standard version 6 or version 7 shells whose shell scripts are not compatible with this shell, the shell uses such a `standard' shell to execute a script whose first character is not a `#', i.e., that does not start with a

Remaining arguments are placed in the argv shell

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

Non-login shells read only /etc/csh.cshrc and

For examples of startup files, please consult

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 can have only a ~/.cshrc which checks for the existence of the tcsh shell variable (q.v.) before using tcsh-specific commands, or can have both a ~/.cshrc and a ~/.tcshrc which sources (see the builtin command) ~/.cshrc. The rest of this manual uses `~/.tcshrc' to mean `~/.tcshrc or, if ~/.tcshrc is not found,

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

One can log out by typing `^D' on an empty line, `logout' or `login' or via 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

The names of the system login and logout files vary from system to system for compatibility with different

We first describe The command-line editor. 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. Finally, Editor commands lists and describes the editor commands specific to the shell and

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 builtin can display and change key bindings. Emacs-style key bindings are used by default (unless the shell was compiled otherwise; see the version shell variable), but bindkey can change the key bindings to

The shell always binds the arrow keys (as defined in the

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

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

Note that editor commands 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 whitespace and some of the characters with special meanings to it,

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 filename `/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' doesn't 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 isn't already

Completion works anywhere in the line, not at just 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 that need to be

Commands and variables can be completed in much the same way. For example, typing `em[tab]' would complete `em' to `emacs' if emacs 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 pathname. Typing `echo $ar[tab]' would complete `$ar' to `$argv' if no other

The shell parses the input buffer to determine whether the word you want to complete should be completed as a filename, 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 filename. An empty line is `completed' as a

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 builtin (q.v.) and reprints the prompt

> ls /usr/l[^D]
lbin/ lib/ local/ lost+found/

If the autolist shell variable is set, the shell lists the remaining choices (if any) whenever completion

> set autolist
> nm /usr/lib/libt[tab]
libtermcap.a@ libtermlib.a@

If autolist is set to `ambiguous', choices are listed only when completion fails and adds no new characters to the

A filename to be completed can contain variables, your own or others' home directories abbreviated with `~' (see Filename substitution) and directory stack entries abbreviated with `=' (see Directory stack

> ls ~k[^D]
kahn kas kellogg
> ls ~ke[tab]

> set local = /usr/local
> ls $lo[tab]
> ls $local/[^D]
bin/ etc/ lib/ man/ src/

Note that variables can also be expanded explicitly with the

delete-char-or-list-or-eof lists at only 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, and list-choices (or any one of the related editor commands that do or don't delete, list and/or log out, listed under delete-char-or-list-or-eof) can be bound to `^D' with the bindkey builtin command if so

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

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

> 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]

`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 under Filename substitution. fignore is ignored if only one

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 hyphens and underscores to be equivalent. If you had the

comp.lang.c comp.lang.perl 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]'

A_silly_file a-hyphenated-file

would list all three files, because case is ignored and hyphens and underscores are equivalent. Periods, however,

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

> ls
fodder foo food foonly
> set recexact

just beeps, because `fo' could expand to `fod' or `foo', but

> rm foo[tab]

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, autocorrect can be set to spelling-correct the word to be completed (see Spelling correction) before each completion attempt and correct can be set to complete commands automatically after one hits `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 a list of directories and/or patterns that match directories to prevent the completion mechanism from stat(2)ing 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

Finally, the complete builtin command can be used to tell the shell how to complete words other than filenames, commands and variables. Completion and listing do not work on glob-patterns (see Filename substitution), but the list-glob and expand-glob editor commands

The shell can sometimes correct the spelling of filenames, commands and variable names as well as completing and

Individual words can be spelling-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

When spelling correction is invoked in any of these ways and the shell thinks that any part of the command line is

> set correct = cmd
> lz /usr/bin

One 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

Spelling correction recognizes user-defined completions (see the complete builtin 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

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

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

`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

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

Completes a word as described under Completion and

Like complete-word-fwd, but steps up from the end of

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

Like complete-word, but ignores user-defined

Copies the previous word in the current line into the input

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 etc., skipping identical matches

delete-char (bound to `Del' if using the standard

Deletes the character under the cursor. See also

Does delete-char if there is a character under the cursor or end-of-file on an empty line. See also

Does delete-char if there is a character under the cursor or list-choices at the end of the line. See

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 does only a single action, and delete-char-or-eof, delete-char-or-list and list-or-eof, each of which does a different two out

Like up-history, but steps down, stopping at the

Signals an end of file, causing the shell to exit unless the ignoreeof shell variable (q.v.) is set to prevent this. See also

Expands history substitutions in the current word. See History substitution. See also magic-space, toggle-literal-history and the autoexpand

Expands the glob-pattern to the left of the cursor. See

Like expand-history, but expands history

Expands the variable to the left of the cursor. See

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 Filename 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

Like history-search-backward, but searches

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

Appends the rest of the word under the cursor to the search

delete (or any character bound to

Undoes the effect of the last character typed and deletes a character from the search pattern if

If the previous search was successful, aborts the entire search. If not, goes back to the last successful

Ends the search, leaving the current line in the input

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

Like i-search-back, but searches

Inserts the last word of the previous input line (`!$') into the input buffer. See also

Lists completion possibilities as described under Completion and listing. See also delete-char-or-list-or-eof and

Like list-choices, but ignores user-defined

Lists (via the ls-F builtin) matches to the glob-pattern (see Filename substitution) to the left

Does list-choices or end-of-file on an empty line. See also

Expands history substitutions in the current line, like expand-history, and appends a space. magic-space is designed to be bound to the space bar,

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, e.g., `dbx' and

Expands the current word as described under the `expand'

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 between an editor and the shell easily. Some people bind this command

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. If the special alias helpcommand is defined, it is run with the command name as a sole argument. Else, documentation should be in a file named command.help, 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

In insert mode (the default), inserts the typed character into the input line after the character under the cursor. In overwrite mode, 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

sequence-lead-in (arrow prefix, meta prefix,

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

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 `%', or which contain `', `*' or `?', to avoid problems with switches, substitutions and the like. See Spelling

Attempts to correct the spelling of the current word as described under Spelling correction. Checks each component of a word which appears to be a

Expands or `unexpands' history substitutions in the input buffer. See also expand-history and the

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

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.

Like vi-search-back, but searches

Does a which (see the description of the builtin

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

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

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

Furthermore, all Substitutions (see below) 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) (e.g., `$' or ``' for Variable substitution or Command substitution respectively) with `'. (Alias substitution is no exception: quoting in any way any character of a word for which an alias has been defined prevents substitution of the alias. The usual way of quoting an alias is to precede it with a backslash.) History substitution is prevented by backslashes but not by single quotes. Strings quoted with double or backward quotes undergo Variable substitution and Command substitution, but other substitutions are

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 below) 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 (q.v.), which may

Quoting complex strings, particularly strings which themselves contain quoting characters, can be confusing. Remember that quotes need not be used as they are in human writing! 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

The backslash_quote shell variable (q.v.) can be set to make backslashes always quote `', `, and `"'. (+) This may make complex quoting tasks easier, but it can cause

We now describe the various transformations the shell performs on the input in the order in which they occur. We note in passing the data structures involved and the commands and variables which affect them. Remember that substitutions can be prevented by quoting as described under

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 to not save duplicate events or

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

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

The history builtin 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

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 fix spelling mistakes in the previous command with little typing and a high degree of

History substitutions begin with the character `!'. They may begin anywhere in the input stream, but they do not nest. The `!' may be preceded by a `' 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 `^'. This special abbreviation will be described later. The characters used to signal history substitution (`!' and `^') can be changed by setting the histchars shell variable. Any input line which contains a history

A history substitution may 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

An offset, referring to the event n before the

The current event. This should be used carefully in csh(1), where there is no check for recursion.

The most recent event whose first word begins with the

The most recent event which contains the string s. The second `?' can be omitted if it is immediately followed

For example, consider this bit of someone's history

9 8:30 nroff -man wumpus.man
10 8:31 cp wumpus.man wumpus.man.old
11 8:36 vi wumpus.man

The commands are shown with their event numbers and time stamps. The current event, which we haven't typed in yet, 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 we might type `!cp' to redo the copy command or `!!|more' if the `diff' output scrolled off the top of the

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

(+) While csh(1) expands, for example, `!3d' to event 3 with the letter `d' appended to it, tcsh 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

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

Equivalent to `^-$', but returns nothing if the event

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 we didn't care about the order of the `diff' we might have said `diff !-2:1-2' or simply `diff !-2:*'. The `cp' command might have been written `cp wumpus.man !#:1.old', using `#' to refer to the current event. `!n:- hurkle.man' 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

A history reference may have a word designator but no event specification. It then references the previous command. Continuing our `diff' example, we could have said simply `diff !^.old !^' or, to get the arguments in the opposite

The word or words in a history reference can be edited, or ``modified, by following it with one or more modifiers,

Remove a trailing pathname component, leaving the

Remove all leading pathname components, leaving the

Remove a filename extension `.xxx', leaving the root

Substitute l for r. l is simply a string like r, not a regular expression as in the eponymous ed(1) command. Any character may 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

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 lead to an infinite loop. For example, `:as/f/ff/' will never terminate. This behavior

Print the new command line but do not execute

Quote the substituted words, preventing further

Like q, but break into words at blanks, tabs and

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

For example, the `diff' command might have been written as `diff wumpus.man.old !#^:r', using `:r' to remove `.old' from the first argument on the same line (`!#^'). We 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. We might follow `mail -s "I forgot my password" rot' with `!:s/rot/root' to correct the spelling of `root' (but see Spelling correction for a

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

(+) In csh as such, only one modifier may be applied to each history or variable expansion. In tcsh, more

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

In csh, the result would be `wumpus.1:r'. A substitution followed by a colon may need to be insulated

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

The first attempt would succeed in csh but fails in tcsh, because tcsh expects another modifier

Finally, 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

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

Thus if the alias for `ls' were `ls -l' the command `ls /usr' would become `ls -l /usr', the argument list here being undisturbed. If the alias for `lookup' were `grep !^ /etc/passwd' then `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 pr(1)s its arguments to

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

Some aliases are referred to by the shell; see Special

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

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

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; the shell does not care what their value is, only whether they are set or not. For instance, the verbose variable is a toggle which causes command input to be echoed. The -v command line option sets this variable. Special shell variables lists all variables which are referred to by

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

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 below) so `$' substitution does not occur there until later, if at all. A `$' is passed unchanged if followed by a blank, tab, or

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

Unless enclosed in `"' or given the `:q' modifier the results of variable substitution may eventually be command and filename 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

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

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, then that value is returned (but `:' modifiers and the other forms given below

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

Substitutes the name of the file from which command input is being read. An error occurs if the name is not

Equivalent to `$argv', which is equivalent to

The `:' modifiers described under 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 (q.v.); any modifiers must appear within the

The following substitutions can not be modified with `:'

Substitutes the string `1' if name is set, `0' if it

Substitutes `1' if the current input filename is known, `0'

Substitutes the number of characters in name.

Substitutes the number of characters in

Substitutes the (decimal) process number of the (parent)

Substitutes the (decimal) process number of the last

Substitutes the command line of the last command executed.

Substitutes a line from the standard input, with no further interpretation thereafter. It can be used to read from the keyboard in a shell script. (+) While csh always quotes $<, as if it were equivalent to `$<:q', tcsh does not. Furthermore, when tcsh is waiting for a line to be typed the user may type an interrupt to interrupt the sequence into which the line is to be substituted, but csh does not allow

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

Command, filename and directory stack

The remaining substitutions are applied selectively to the arguments of builtin commands. This means that portions of expressions which are not evaluated are not subjected to these expansions. For commands which 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

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, and null words are discarded. The output is variable and command substituted

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

If a word contains any of the characters `*', `?', `[' or `{' or begins with the character `~' it is a candidate for filename 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

In matching filenames, the character `.' at the beginning of a filename or immediately following a `/', as well as the character `/' must be matched explicitly. The character `*' matches any string of characters, including the null string. The character `?' matches any single character. The sequence `[...]' matches any one of the characters enclosed. Within `[...]', a pair of characters separated by `-' matches any

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

An entire glob-pattern can also be negated with

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

Glob-patterns which do not use `?', `*', or `[]' or which use `{}' or `~' (below) are not negated

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

The character `~' at the beginning of a filename refers to home directories. Standing alone, i.e., `~', 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 their 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 appears elsewhere 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, do

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, e.g., `rm *.a *.c *.o' 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) which matches nothing is left unchanged rather than causing an

The noglob shell variable can be set to prevent filename substitution, and the expand-glob editor command, normally bound to `^X-*', can be used to interactively expand individual filename

The directory stack is a list of directories, numbered from zero, used by the pushd, popd and dirs builtin commands (q.v.). 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

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. For

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

The noglob and nonomatch shell variables and the expand-glob editor command apply to directory

There are several more transformations involving filenames, not strictly related to the above but mentioned here for completeness. Any filename may be expanded to a full path when the symlinks variable (q.v.) 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 by only those commands. Nonetheless, it too can be prevented by

The next three sections describe how the shell executes

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

Simple commands and pipelines may be joined into sequences with `;', and will be 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