tcsh — Invoke a C shell

Description

The tcsh shell is an enhanced but completely compatible version of the Berkeley UNIX C shell, tcsh. 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, programmable word completion, spelling correction, a history mechanism, job control, and a C-like syntax.

You can invoke the shell by typing an explicit tcsh command. A login shell can also be specified by invoking the shell with the –l option as the only argument.

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, 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 reads /etc/csh.login after /etc/csh.cshrc.

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

Commands like stty, which need be run only once per login, typically go in the user's ~/.login file.

In the normal case, the shell begins reading commands from the terminal, prompting with >. The shell repeatedly reads a line of command input, breaks it into words, places it on the command history list, and then parses and executes each command in the line. See Command execution.

Options

If the first argument (argument 0) to the tcsh shell is - (hyphen), then it is a login shell. You can also specify the login shell by invoking the tcsh shell with the –l as the only argument.

After processing of option arguments, if arguments remain but none of the –c, –i, –s, or –t 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. Since many systems use shells whose shell scripts are not compatible with this shell, the tcsh shell uses such a standard shell to execute a script whose character is not a #, that is, which does not start with a comment.

Remaining arguments are placed in the argv shell variable.

tcsh shell editing

In this topic, we first describe the Command-Line Editor. We then discuss Completion and Listing and Spelling Correction which describe two sets of functionality that are implemented as editor commands but which deserve their own treatment. Finally, the Editor Commands topic lists and describes the editor commands specific to the tcsh shell and their default bindings.

Command-line editor

Command-line input can be edited using key sequences much like those used in GNU Emacs or vi. The editor is active only when the edit shell variable is set, which it is by default in interactive shells. The bindkey built-in command can display and change key bindings. Emacs-style key bindings are used by default, but bindkey can change the key bindings to vi-style bindings.

Completion and listing

The tcsh shell is often able to complete words when given a unique abbreviation. Type part of a word (for example ls /usr/lost) and press 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 / (forward slash); 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 (for example, /usr/lost+found doesn't exist), the terminal bell rings. If the word is already complete (for example, there is a /usr/lost on your system, or you were thinking too far ahead and typed the whole thing), a / or space is added to the end if it isn't 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 need to 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 were the only command on your system beginning with 'em'. Completion can find a command in any directory in the path or if given a full path name. Typing echo $ar[tab] would complete '$ar' to '$argv' if no other variable began 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.

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

> 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 if multiple matches are possible, and if the completion adds no new characters to the name to be matched.

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

or

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

delete-char-or-list-or-eof only lists 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, and list-choices (or any one of the related editor commands which do or don't delete, list and log out, listed under delete-char-or-list-or-eof) can be bound to ^D with the bindkey built-in command if so desired.

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.

    > 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 

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.

comp.lang.c comp.lang.perl comp.std.c++
comp.lang.c++ comp.std.c

A_silly_file a-hyphenated-file another_silly_file

> ls
fodder foo food foonly
> set recexact
> rm fo[tab]

> rm foo[tab]
> rm foo 

>set listflags=x>
ls-F /u/pluto
Dir1/exe1*
>set nostat=(/u/pluto/)
>ls-F /u/pluto
Dir1exe1
>

Finally, 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 tcsh shell can sometimes correct the spelling of file names, commands and variable names as well as completing and listing them.

Individual words can be corrected for spelling with the spell-word editor command (typically bound to M-s and M-S where M = Meta Key or escape (ESC) key) and the entire input buffer with spell-line (typically 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.

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

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.

Spelling correction is not guaranteed to work the way one intends, and is provided mostly as an experimental feature.

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 and vi 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 and M-character a meta character, typed as escape-character on terminals without a meta key. Case counts, but commands which are bound to letters by default are bound to both lower- and uppercase letters for convenience.

complete-word

Completes a word as described in Completion and listing.

complete-word-back

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

complete-word-fwd

Replaces the current word with the first word in the list of possible completions. can be repeated to step down through the list. At the end of the list, beeps and reverts to the incomplete word.

complete-word-raw

Like complete-word, but ignores user-defined completions.

copy-prev-word

Copies the previous word in the current line into the input buffer. See also insert-last-word.

dabbrev-expand

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 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 file. 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 delete-char-or-eof, delete-char-or-list and list-or-eof.

down-history

Like up-history, but steps down, stopping at the original input line.

end-of-file

Signals an end of file, causing the tcsh 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 substition. 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. For example:

>ls test*[^X-*]

would expand to

>ls test1.c test2.c

if those were the only two files in your directory that begin with 'test'. 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 can 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 can be typed to extend the search. i-search-back can 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 can be typed:

^W

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 and deletes a character from the search pattern if appropriate.

^G

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

escape

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

Like i-search-back, but searches forward.

insert-last-word (M-_)

Inserts the last word of the previous line (!$) into the input buffer. See also copy-prev-word.

list-choices (M-D)

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

list-choices-raw (^X-^D)

Like list-choices, but ignores user-defined completions.

list-glob (^X-g, ^X-G)

Lists (via the ls-F) 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 which take commands as arguments, for example, 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 between an editor and the shell easily. Some people 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.help, command.1, command.6, command.8 or command, which should be in one of the directories listed in the HPATH enviroment variable. If there is more than one help file only the first is printed.

self-insert-command (text characters)

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 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 '%', or which contain '\', '*' 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 under Spelling correction. Checks each component of a word which 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)

Beeps.

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. Can be repeated to step up through the history list, stopping at the top.

vi-search-back (?)

Prompts with ? for a search string (which can 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 (built-in command) on the first word of the input buffer. which displays the command that is executed by the shell after substitutions and path searching. The displayed command has passed access checks by the security product based on the effective ids of the user.

Command syntax

The tcsh 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 tcsh 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 parsing.

A special character (including a blank or tab) can 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 (' ` ') quotation marks. When not otherwise quoted a newline preceded by a \ is equivalent to a blank, but inside quotes this sequence results in a newline.

Furthermore, all substitutions (see Substitutions) except history substitution can be prevented by enclosing the strings (or parts of strings) in which they appear with single quotation marks or by quoting the crucial characters (for example, '$' 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 quotation marks. Strings quoted with double or backward quotation marks undergo Variable substitution and Command substitution, but other substitutions are prevented.

Text inside single or double quotation marks 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. Remember that quotes need not be used as they are in human writing. It might 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 make complex quoting tasks easier, but it can cause syntax errors in csh (or tcsh) scripts.

Substitutions

This topic describes the various transformations the tcsh shell performs on input in the order in which they occur. The topic will cover data structures involved and the commands and variables which affect them. Remember that substitutions can be prevented by quoting as described in Command syntax.

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 to not save duplicate events or consecutive duplicate events.

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

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

History substitutions begin with the character !. They can begin anywhere in the input stream, but they do not nest. The ! can 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 ^. The characters used to signal history substitution (! and ^ (caret)) can be changed by setting the histchars shell variable. Any input line which contains a history substitution is printed before it is executed.

A history substitution can 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 a modifier, which manipulates the selected words.

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

History references can 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 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 expand !3d as in csh say !\3d.

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 - (hyphen) 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 our diff example, we could have said simply diff !^.old !^or, to get the arguments in the opposite order, just diff !*.

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 different approach).

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 with !.

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

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

Alias substitution

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 Command execution) 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 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 /usrwould 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 prints its arguments to 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 tcsh built-in commands.

Variable substitution

The tcsh shell maintains a list of variables, each of which has as value a list of zero or more words. The values of tcsh 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 can be made read-only with set -r. Read-only variables cannot 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 read-only.

Some variables are set by the tcsh 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 tcsh 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 the shell.

Other operations treat variables numerically. The @ (at) 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 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 double quotation marks (") where it always occurs, and within single quotation marks ( ' ) where it never occurs. Strings quoted by backward quotation marks or accents (`) 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 double quotation marks (") or given the :q modifier the results of variable substitution can 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 remaining substitutions are applied selectively to the arguments of tcsh built-in 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 tcsh 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, and null words are discarded. The output is variable and command substituted and put in place of the original string.

Command substitutions inside double quotation marks ( " ) 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 which match the pattern.

In matching file names, the character . (period) at the beginning of a file name or immediately following a / (forward slash), 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 character lexically between the two.

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

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

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, such as, like the following example, where ../{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 can 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 - (hyphen) 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 home directory substitution as one might hope. 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, for example, 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 instead of causing an error.

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

Directory stack substitution

The directory stack is a list of directories, numbered from zero, used by the pushd, popd and dirs built-in commands for tcsh. 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.

    > 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 =-
    /usr/accts/sys

Other substitutions

There are several more transformations involving file names, not strictly related to the Directory stack substitution, but mentioned here for completeness. Any file name can 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 - (hyphen) as the old working directory (equivalent to the tcsh shell variable owd). This is not a substitution at all, but an abbreviation recognized only by those commands. Nonetheless, it too can be prevented by quoting.

Command execution

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

Built-in and non-built-in command execution

Built-in commands for tcsh 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.

(cd; pwd); pwd

cd; pwd

When a command to be executed is found not to be a built-in command the tcsh shell attempts to execute the command via execve. Each word in the variable path names a directory in which the tcsh 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 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 (via 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), then it is assumed to be a file containing shell commands and a new shell is spawned to read it. The shell special alias can be set to specify an interpreter other than the shell itself.

Input or output

The standard input and standard output of a command can be redirected with the following syntax listed in Table 1.

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; instead 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. 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, then the process will block and the user is notified (see Jobs).

Diagnostic output can be directed through a pipe with the standard output. Simply use the form |& instead of just |.

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

Features

Having described how the shell accepts, parses and executes command lines, we now turn to a variety of its useful features.

Control flow

The tcsh shell contains a number of commands which can be used to regulate the flow of control in command files (shell scripts) and (in limited by useful ways) from terminal output. 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.)

Expressions

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 topics. Note that the @ built-in command has its own separate syntax.

Logical, arithmetical, and comparison operators

|| && | ^ & == !=  =~  !~  <=  >=
< > << >>  + - * / % ! ~ (  )

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 adjacent to components of expressions which 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 ({}). The braces must be separated from the words of the command by spaces. Command executions succeed, returning true, that is, 1, if the command exits with status 0, otherwise they fail, returning false (0). If more detailed status information is required, then the command should be executed outside of an expression and the status shell variable examined.

File inquiry operators

These operators can 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 can be used in a multiple-operator test to apply subsequent operators to a symbolic link instead of 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 ture 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 useful, and sometimes misleading, to combine operators which expect file to be a file with operators which do not (for example, X and t). Following L with a non-file operator can lead to particularly strange results.

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

File inquiry operators for use with file tagging and the filetest built-in command

–B file

• True if the file is tagged as binary
• False if the file is not tagged or tagged as text
• Returns codeset if the file is tagged as mixed text and binary, that is, txtflag = OFF and codeset stored in file tag

–T file

• False if the file is not tagged or if it is tagged as txtflag = OFF
• Returns codeset if the file is tagged as text

if ( -T file == IBM-1047 )  #True if tagged as IBM-1047 text
if ( -B file )              #True if tagged as binary

Jobs

[1] 1234

If you are running a job and want to do something else you can press the suspend key (typically ^Z), which sends a STOP signal to the current job. The shell will then normally indicate that the job has been 'Suspended' and print another prompt. If the listjobs shell variable is set, all jobs is listed like the jobs built-in command; if it is set to 'long' the listing is 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 and 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; in tcsh , ^Y is an editing command.

A job being run in the background stops if it tries to read from the terminal. Background jobs are typically allowed to produce output, but this can be disabled by giving the command stty tostop. If you set the stty option, then 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. If you want to refer to job number 1, you can name it as %1. Just naming a job brings it to the foreground; thus %' is a synonym for fg %1, bringing job 1 back into the foreground. Similarly, saying %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 job, if there were only one suspended job whose name began with the string 'ex'. It is also possible to say %? 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 + (plus) and the previous job with a - (hyphen). 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 option new be set on some systems. It is an artifact from a new implementation of the tty driver which allows generation of interrupt characters from the keyboard to tell jobs to stop. See stty and the setty tcsh built-in command for details on setting options in the new tty driver.

Status reporting

The tcsh shell learns immediately whenever a process changes state. It normally 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. There is also a shell command notify which marks a single process so that its status changes are immediately reported. By default notify marks the current process; simply say 'notify' after starting a background job to mark it.

When you try to leave the shell while jobs are stopped, you are 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 are 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.

• 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 t-period minutes and before each prompt.
• The autologout shell variable can be set to log out of 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 which exit with a status other than zero.
• The rmstar shell variable can be set to ask the user, when rm * is typed, if that is really what was meant.
• 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.

National language system report

When using the system's multicultural support, the setlocale 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.

Unknown characters (those that are neither printable nor control characters) are printed in the format \nnn.

The version shell variable indicates what options were chosen when the shell was compiled. Note also the newgrp built-in and echo_style shell variable and the locations of the shell's input files (see tcsh files).

Restriction: The tcsh shell currently does not support three locales. They are IBM-1388 (Chinese), IBM-933 (Korean) and IBM-937 (Traditional Chinese).

Handling signals

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 do too, 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.

Managing terminals

The shell uses three different sets of terminal (tty) modes: edit, used when editing, quote, used when quoting literal characters, and execute, used when executing commands. The shell holds some settings in each mode constant, so commands which 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. 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.

The tcsh shell adapts to window resizing automatically and adjusts the environment variables LINES and COLUMNS if set.

tcsh built-in commands

The following table lists the tcsh built-in commands, which are not /bin/sh built-ins.

Other tcsh built-in commands are also found in the z/OS shell. In some cases, they might differ in function; see the specific command description for a discussion of the tcsh version of the command.

tcsh shell and environment variables

The variables described in this topic have special meaning to the tcsh shell. The tcsh shell sets addsuffix, argv, autologout, command, echo_style, edit, gid, group, home, loginsh, 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 tcsh shell updates cwd, dirstack, owd, and status when necessary, and sets logout on logout.

The shell synchronizes 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 automatically interconverts the different formats of path and PATH.

set dirsfile = ~/.cshdirs

 > echo $echo_style
 bsd
 > echo "\n"
 \n
 > echo -n "test"
 test>
 > set echo_style=sysv
 > echo $echo_style
 sysv
 > echo "\n"

 > echo -n "test"
 -n test
 > set echo_style=both
 > echo $echo_style
 both
 > echo -n "test"
 test> echo "\n"

 >set echo_style=none
 > echo $echo_style
 none
 > echo -n "test"
 -n test
 > echo "\n"
 \n
 >

set histfile = ~/.history 

set savehist = ( 15 merge )

set watch = (george ttyd 1 any console $user any)

set watch = (1 any any)

tcsh shell variables not described in the Table 2 are described as follows:

prompt

The string which is printed before reading each command from the terminal. prompt can include any of the following formatting sequences, which are replaced by the given information:

%/

The current working directory.

%~

The current working directory, but with one's home directory represented by ~ and other users' home directories represented by ~user as per 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 components in the format /trailing. If the ellipsis shell variable is set, skipped components are represented by an ellipsis so the whole becomes …trailing. ~ substitution is done as in %~~ , but the ~ component is ignored when counting trailing components.

%C

Like %c, but without ^ substitution.

%h, %!, !

The current history event number.

%M

The full hostname.

%m

The hostname up to the first '.' (period).

%S (%s)

Start (stop) standout mode.

%B (%b)

Start (stop) boldfacing mode.

%U (%u)

Start (stop) underline mode.

%t, %@

The time of day in 12–hour AM/PM format.

%T

Like %t, but in 24–hour format (but see the ampm shell variable).

%p

The precise time of day in 12–hour AM/PM format, with seconds.

%P

Like %p, but in 24–hour format (but see the ampm shell variable).

\c

c is parsed as in bindkey.

^c

c is parsed as in bindkey.

%%

A single %.

%n

The user name.

%d

The weekday in 'Day' format.

%D

The day in 'dd' format.

%w

The month in 'Mon' format.

%W

The month in 'mm' format.

%y

The year in 'yy' format.

%Y

The year in 'yyyy' format.

%l

The tcsh shell's tty.

%L

Clears from the end of the prompt to end of the display or the end of the line.

%$

Expands the shell or environment variable name immediately after the $.

%#

> (or the first character of the promptchars shell variable) for normal users, # (or the second character of promptchars) for the superuser.

%{string%}

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.

%R

In prompt2, the status of the parser. In prompt3, the corrected string. In history, the history string.

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] [2:54] [/usr/accts/sys] you rang? _

Set by default to %# in interactive shells.

symlinks

Can be set to several different values to control symbolic link ('symlink') resolution:

• If set to chase, whenever the current directory changes to a directory containing a symbolic link, it is expanded to the real name of the directory to which the link points. This does not work for the user's home directory.
• If set to ignore, the shell tries to construct a current directory relative to the current directory before the link was crossed. This means that cding through a symbolic link and then cd..'ing returns one to the original directory. This only affects built-in commands and file name completion.
• If set to expand, the shell tries to fix symbolic links by actually expanding arguments which look like path names. This affects any command, not just built-ins. Unfortunately, this does not work for hard-to-recognize file names, such as those embedded in command options. Expansion can be prevented by quoting. While this setting is typically the most convenient, it is sometimes misleading and sometimes confusing when it fails to recognize an argument which should be expanded. A compromise is to use ignore and use the editor command normalize-path (bound by default to ^X-n) when necessary.

Some examples are in order. First, let's set up some play directories:

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

Here's the behavior with symlinks unset,

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

here's the behavior with symlinks set to chase,

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

here's the behavior with symlinks set to ignore,

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

and here's the behavior with symlinks set to expand.

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

expand expansion:

1. works just like ignore for built-ins like cd,
2. is prevented by quoting, and
3. happens before file names are passed to non-built-in commands.

time

If set to a number, then the time built-in command executes automatically after each command which takes more than that many CPU seconds. If there is a second word, it is used as a format string for the output of the time built-in. The following sequences can be used in the format string:

%U

The time the process spent in user mode in cpu seconds.

%S

The time the process spent in kernel mode in cpu seconds.

%E

The elapsed (wall clock) time in seconds.

%P

The CPU percentage computed as (%U + %S) / %E.

%W

The number of times the process was swapped.

%X

The average amount in (shared) text space used in Kbytes.

%D

The average amount in (unshared) data/stack space used in Kbytes.

%K

The total space used (%X + %D) in Kbytes.

%M

The maximum memory the process had in use at any time in Kbytes.

%F

The number of major page faults (page needed to be brought from disk).

%R

The number of minor page faults.

%I

The number of input operations.

%O

The number of output operations.

%r

The number of socket messages received.

%s

The number of socket messages sent.

%k

The number of signals received.

%w

The number of voluntary context switches (waits).

%c

The number of involuntary context switches.

Only the first four sequences are supported on systems without 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.

The following table contains a list of tcsh environment variables.

Using tcsh shell variables to control automatic conversion

(set _TAG_REDIR_OUT=TXT; command >file)

You can also use these shell variables for commands in a pipeline. For example, they can be used to tag the standard output of each command that is writing to a pipeline or to tag the standard input of each command that is reading from a pipeline.

tcsh files

/etc/csh.cshrc

Read first by every shell.

/etc/csh.login

Read by login shells after /etc/csh.cshrc.

~/.tcshrc

Read by every shell after /etc/csh.cshrc or its equivalent.

~/.history

Read by login shells after ~/.tcshrc if savehist is set. See also histfile.

~/.login

The shell reads ~/.login after ~/.tcshrc and ~/.history. See the version shell variable.

~/.cshdirs

Read by login shells after ~/.login if savedirs is set. See also dirsfile.

~/.logout

Read by login shells at logout.

/bin/sh

Used to interpret shell scripts not starting with a #.

/tmp/sh*

Temporary file for < <.

tcsh shell: problems and limitations

When a suspended command is restarted, the tcsh shell prints the directory it started in if this is different from the current directory. This can be misleading (that is, wrong) as the job might 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 tcsh shell will then immediately execute 'c'. This is especially noticeable if this expansion results from an alias. It suffices to place the sequence of commands in ()'s to force it to a subshell, for example, ( 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 instead of aliases.

Commands within loops are not placed in the history list. Control structures should be parsed instead of 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 ; (semicolon) metasyntax.

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

It should be possible to use the : (colon) 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 (terminal type 'dumb').

It is not necessary for HPATH and NOREBIND to be environment variables.

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

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 and does not handle control characters in file names well. It cannot be interrupted.

The visiblebell shell variable is currently not implemented.

In file name and programmed completion, the 'C' completion rule word list type does not correctly select completion from the given directory.

There are three locales (code pages) which the tcsh shell will not correctly support: IBM-1388 (Chinese), IBM-933 (Korean) and IBM-937 (Traditional Chinese).

If you want to help maintain and test tcsh, send mail to listserv@mx.gw.com with the text 'subscribe tcsh '.

Related information

: (colon), @ (at), alias, bg, break, cd, continue, echo, eval, exec, exit, fg, history, jobs, kill, newgrp, nice, nohup, printenv, set, shift, stop, suspend, time, umask, unalias, unset, wait