csh

TCSH(1) TCSH(1)

NAME

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


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

DESCRIPTION

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), pro-
grammable word completion (see Completion and listing), spelling cor-
rection (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
labeled with "(u)".


Argument list processing
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 argument.


The rest of the flag arguments are interpreted as follows:


-b Forces a ""break"" from option processing, causing any further
shell arguments to be treated as non-option arguments. The remain-
ing arguments will not be interpreted as shell options. This may
be used to pass options to a shell script without confusion or pos-
sible subterfuge. The shell will not run a set-user ID script
without this option.


-c 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 argu-
ments are placed in the argv shell variable.


-d The shell loads the directory stack from ~/.cshdirs as described
under Startup and shutdown, whether or not it is a login shell. (+)


-Dname[=value]
Sets the environment variable name to value. (Domain/OS only) (+)


-e The shell exits if any invoked command terminates abnormally or
yields a non-zero exit status.


-f The shell ignores ~/.tcshrc, and thus starts faster.


-F The shell uses fork(2) instead of vfork(2) to spawn processes.
(Convex/OS only) (+)


-i 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 are terminals.


-l The shell is a login shell. Applicable only if -l is the only flag
specified.


-m The shell loads ~/.tcshrc even if it does not belong to the effec-
tive user. Newer versions of su(1) can pass -m to the shell. (+)


-n The shell parses commands but does not execute them. This aids in
debugging shell scripts.


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


-s Command input is taken from the standard input.


-t The shell reads and executes a single line of input. A "" may be
used to escape the newline at the end of this line and continue
onto another line.


-v Sets the verbose shell variable, so that command input is echoed
after history substitution.


-x Sets the echo shell variable, so that commands are echoed immedi-
ately before execution.


-V Sets the verbose shell variable even before executing ~/.tcshrc.


-X Is to -x as -V is to -v.


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 ver-
sion 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 comment.


Remaining arguments are placed in the argv shell variable.


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


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


For examples of startup files, please consult tcshrc.source-
forge.net.


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, ~/.cshrc".


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


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 vari-
able). When a login shell terminates it sets the logout shell variable
to "normal" or "automatic" as appropriate, then executes commands from
the files /etc/csh.logout and ~/.logout. The shell may drop DTR on
logout if so compiled; see the version shell variable.


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


Editing
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 their default bindings.


The command-line editor (+)
Command-line input can be edited using key sequences much like those
used in GNU Emacs or vi(1). The editor is active only when the edit
shell variable is set, which it is by default in interactive shells.
The bindkey builtin can display and change key bindings. Emacs-style
key bindings are used by default (unless the shell was compiled other-
wise; see the version shell variable), but bindkey can change the key
bindings to vi-style bindings en masse.


The shell always binds the arrow keys (as defined in the TERMCAP envi-
ronment variable) to


down down-history
up up-history
left backward-char
right forward-char


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


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


Note that editor commands 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 recog-
nizes only whitespace and some of the characters with special meanings
to it, listed under Lexical structure.


Completion and listing (+)
The shell is often able to complete words when given a unique abbrevia-
tion. 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 vari-
able 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 there.


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 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 path or if given a full pathname.
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 filename, command or vari-
able. The first word in the buffer and the first word following ";",
"|", "|&", "&&" or "||" is considered to be a command. A word begin-
ning with "$" is considered to be a variable. Anything else is a file-
name. An empty line is "completed" as a filename.


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 and unfinished command line, for example:


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


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


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


If autolist is set to "ambiguous", choices are listed only when comple-
tion fails and adds no new characters to the word being completed.


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 sub-
stitution). For example,


> 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/


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


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 pos-
sibilities 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 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.


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


> ls
Makefile condiments.h~ main.o side.c
README main.c meal side.o
condiments.h main.c~
> set fignore = (.o ~)
> emacs ma[^D]
main.c main.c~ main.o
> emacs ma[tab]
> emacs main.c


"main.c~" and "main.o" are ignored by completion (but not listing),
because they end in suffixes in fignore. Note that a "" was needed in
front of "~" to prevent it from being expanded to home as described
under Filename substitution. fignore is ignored if only one completion
is possible.


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


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


and typed "mail -f c.l.c[tab]", it would be completed to "mail -f
comp.lang.c", and ^D would list "comp.lang.c" and "comp.lang.c++".
"mail -f c..c++[^D]" would list "comp.lang.c++" and "comp.std.c++".
Typing "rm a--file[^D]" in the following directory


A_silly_file a-hyphenated-file another_silly_file


would list all three files, because case is ignored and hyphens and
underscores are equivalent. Periods, however, are not equivalent to
hyphens or underscores.


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


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


just beeps, because "fo" could expand to "fod" or "foo", but if we type
another "o",


> rm foo[tab]
> rm foo


the completion completes on "foo", even though "food" and "foonly" also
match. autoexpand can be set to run the expand-history editor command
before each completion attempt, autocorrect can be set to spelling-cor-
rect the word to be completed (see Spelling correction) before each
completion attempt and correct can be set to complete commands automat-
ically after one hits "return". matchbeep can be set to make comple-
tion 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 quite slow.


Finally, the complete builtin command can be used to tell the shell how
to complete words other than filenames, commands and variables. Com-
pletion and listing do not work on glob-patterns (see Filename substi-
tution), but the list-glob and expand-glob editor commands perform
equivalent functions for glob-patterns.


Spelling correction (+)
The shell can sometimes correct the spelling of filenames, commands and
variable names as well as completing and listing them.


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 completed before each completion attempt.


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


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


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
unchanged.


Spelling correction recognizes user-defined completions (see the com-
plete 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 pos-
sible completions for that position, spelling correction does not reg-
ister a misspelling.


Like completion, spelling correction works anywhere in the line, push-
ing the rest of the line to the right and possibly leaving extra char-
acters to the right of the cursor.


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


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


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


complete-word (tab)
Completes a word as described under Completion and listing.


complete-word-back (not bound)
Like complete-word-fwd, but steps up from the end of the list.


complete-word-fwd (not bound)
Replaces the current word with the first word in the list of
possible completions. May be repeated to step down through the
list. At the end of the list, beeps and reverts to the incom-
plete word.


complete-word-raw (^X-tab)
Like complete-word, but ignores user-defined completions.


copy-prev-word (M-^_)
Copies the previous word in the current line into the input
buffer. See also insert-last-word.


dabbrev-expand (M-/)
Expands the current word to the most recent preceding one for
which the current is a leading substring, wrapping around the
history list (once) if necessary. Repeating dabbrev-expand
without any intervening typing changes to the next previous
word etc., skipping identical matches much like history-search-
backward does.


delete-char (bound to "Del" if using the standard /etc/csh.cshrc)
Deletes the character under the cursor. See also delete-char-
or-list-or-eof.


delete-char-or-eof (not bound)
Does delete-char if there is a character under the cursor or
end-of-file on an empty line. See also delete-char-or-list-or-
eof.


delete-char-or-list (not bound)
Does delete-char if there is a character under the cursor or
list-choices at the end of the line. See also delete-char-or-
list-or-eof.


delete-char-or-list-or-eof (^D)
Does delete-char if there is a character under the cursor,
list-choices at the end of the line or end-of-file on an empty
line. See also those three commands, each of which 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 of the
three.


down-history (down-arrow, ^N)
Like up-history, but steps down, stopping at the original input
line.


end-of-file (not bound)
Signals an end of file, causing the shell to exit unless the
ignoreeof shell variable (q.v.) is set to prevent this. See
also delete-char-or-list-or-eof.


expand-history (M-space)
Expands history substitutions in the current word. See History
substitution. See also magic-space, toggle-literal-history and
the autoexpand shell variable.


expand-glob (^X-*)
Expands the glob-pattern to the left of the cursor. See File-
name substitution.


expand-line (not bound)
Like expand-history, but expands history substitutions in each
word in the input buffer,


expand-variables (^X-$)
Expands the variable to the left of the cursor. See Variable
substitution.


history-search-backward (M-p, M-P)
Searches backwards through the history list for a command
beginning with the current contents of the input buffer up to
the cursor and copies it into the input buffer. The search
string may be a glob-pattern (see Filename substitution) con-
taining "*", "?", "[]" or "{}". up-history and down-history
will proceed from the appropriate point in the history list.
Emacs mode only. See also history-search-forward and i-search-
back.


history-search-forward (M-n, M-N)
Like history-search-backward, but searches forward.


i-search-back (not bound)
Searches backward like history-search-backward, copies the
first match into the input buffer with the cursor positioned at
the end of the pattern, and prompts with "bck: " and the first
match. Additional characters may be typed to extend the
search, i-search-back may be typed to continue searching with
the same pattern, wrapping around the history list if neces-
sary, (i-search-back must be bound to a single character for
this to work) or one of the following special characters may 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 typed 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 suc-
cessful 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 (not bound)
Like i-search-back, but searches forward.


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


list-choices (M-^D)
Lists completion possibilities as described under Completion
and listing. See also delete-char-or-list-or-eof and list-
choices-raw.


list-choices-raw (^X-^D)
Like list-choices, but ignores user-defined completions.


list-glob (^X-g, ^X-G)
Lists (via the ls-F builtin) matches to the glob-pattern (see
Filename 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 inserts a space. magic-space is designed to be
bound to the space bar, but is not bound by default.


normalize-command (^X-?)
Searches for the current word in PATH and, if it is found,
replaces it with the full path to the executable. Special
characters are quoted. Aliases are expanded and quoted but
commands within aliases are not. This command is useful with
commands that take commands as arguments, e.g., "dbx" and "sh
-x".


normalize-path (^X-n, ^X-N)
Expands the current word as described under the "expand" set-
ting 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. If the special alias helpcom-
mand is defined, it is run with the command name as a sole
argument. Else, documentation should be in a file named com-
mand.help, command.1, command.6, command.8 or command, which
should be in one of the directories listed in the HPATH envi-
ronment 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 over-
write 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 charac-
ter 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 pathname.


toggle-literal-history (M-r, M-R)
Expands or "unexpands" history substitutions in the input
buffer. See also expand-history and the autoexpand shell vari-
able.


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


vi-search-back (?)
Prompts with "?" for a search string (which may be a glob-pat-
tern, as with history-search-backward), searches for it and
copies it into the input buffer. The bell rings if no match is
found. Hitting return ends the search and leaves the last
match in the input buffer. Hitting escape ends the search and
executes the match. vi mode only.


vi-search-fwd (/)
Like vi-search-back, but searches forward.


which-command (M-?)
Does a which (see the description of the builtin command) on
the first word of the input buffer.


yank-pop (M-y)
When executed immediately after a yank or another yank-pop,
replaces the yanked string with the next previous string from
the killring. This also has the effect of rotating the kill-
ring, such that this string will be considered the most
recently killed by a later yank command. Repeating yank-pop
will cycle through the killring any number of times.


Lexical structure
The shell splits input lines into words at blanks and tabs. The spe-
cial characters "&", "|", ";", "<", ">", "(", and ")" and the doubled
characters "&&", "||", "<<" and ">>" are always separate words, whether
or not they are surrounded by whitespace.


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 parsing.


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


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 charac-
ter(s) (e.g., "$" or """ for Variable substitution or Command substitu-
tion 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 prevented.


Text inside single or double quotes becomes a single word (or part of
one). Metacharacters in these strings, including blanks and tabs, do
not form separate words. Only in one special case (see Command substi-
tution 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 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 may be easier to quote not an
entire string, but only those parts of the string which need quoting,
using different types of quoting to do so if appropriate.


The backslash_quote shell variable (q.v.) can be set to make back-
slashes always quote "", """, and """. (+) This may make complex
quoting tasks easier, but it can cause syntax errors in csh(1) scripts.


Substitutions
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 Lexical structure.


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


Saved commands are numbered sequentially from 1 and stamped with the
time. It is not usually necessary to use event numbers, but the cur-
rent event number can be made part of the prompt by placing an "!" 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 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
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 confi-
dence.


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 substitution is printed before it is executed.


A history substitution may have an ""event specification"", which indi-
cates the event from which words are to be taken, a ""word designa-
tor"", which selects particular words from the chosen event, and/or a
""modifier"", which manipulates the selected words.


An event specification can be


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


For example, consider this bit of someone"s history list:


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


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 screen.


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


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


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
are:


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


Selected words are inserted into the command line separated by single
blanks. For example, the "diff" command in the previous example might
have been typed as "diff !!:1.old !!:1" (using ":1" to select the first
argument from the previous event) or "diff !-2:2 !-2:1" to select and
swap the arguments from the "cp" command. If 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 hurkle.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 abbre-
viated "!", an argument selector beginning with "-" will be interpreted
as an event specification.


A history reference may have a word designator but no event specifica-
tion. 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 !*".


The word or words in a history reference can be edited, or ""modi-
fied"", by following it with one or more modifiers, each preceded by a
":":


h Remove a trailing pathname component, leaving the head.
t Remove all leading pathname components, leaving the tail.
r Remove a filename extension ".xxx", leaving the root name.
e Remove all but the extension.
u Uppercase the first lowercase letter.
l Lowercase the first uppercase letter.
s/l/r/ 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 substitu-
tion or the s from a previous "?s?" event specification is
used. The trailing delimiter may be omitted if it is imme-
diately followed by a newline.
& Repeat the previous substitution.
g Apply the following modifier once to each word.
a (+) Apply the following modifier as many times as possible to a
single word. "a" and "g" can be used together to apply a
modifier globally. In the current implementation, using
the "a" and "s" modifiers together can lead to an infinite
loop. For example, ":as/f/ff/" will never terminate. This
behavior might change in the future.
p Print the new command line but do not execute it.
q Quote the substituted words, preventing further substitu-
tions.
x Like q, but break into words at blanks, tabs and newlines.


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


For example, the "diff" command might have been written as "diff wum-
pus.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 pre-
vious example. This is the only history substitution which does not
explicitly begin with "!".


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


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


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


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


The first attempt would succeed in csh but fails in tcsh, because tcsh
expects another modifier after the second colon rather than "$".


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 respectively.


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 Commands) the first word of each com-
mand, 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 orig-
inal command were the previous input line. If the alias does not con-
tain a history reference, the argument list is left untouched.


Thus if the alias for "ls" were "ls -l" the command "ls /usr" would
become "ls -l /usr", the argument list here 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 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 Special aliases.


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


(+) 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 read-only.


Some variables are set by the shell or referred to by it. For
instance, the argv variable is an image of the shell"s argument list,
and words of this variable"s value are referred to in special ways.
Some of the variables referred to by the shell are toggles; 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 "@" command permits
numeric calculations to be performed and the result assigned to a vari-
able. 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 multi-
word values are ignored.


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


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


Unless enclosed in """ or given the ":q" modifier the results of vari-
able 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 substitu-
tion the variable will expand to multiple words with each word sepa-
rated by a blank and quoted to prevent later command or filename sub-
stitution.


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


$name
${name} Substitutes the words of the value of variable name, each sepa-
rated by a blank. Braces insulate name from following charac-
ters 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 are not available in this case).
$name[selector]
${name[selector]}
Substitutes only the selected words from the value of name.
The selector is subjected to "$" substitution and may consist
of a single number or two numbers separated by a "-". The
first word of a variable"s value is numbered "1". If the first
number of a range is omitted it defaults to "1". If the last
member of a range is omitted it defaults to "$#name". The
selector "*" selects all words. It is not an error for a range
to be empty if the second argument is omitted or in range.
$0 Substitutes the name of the file from which command input is
being read. An error occurs if the name is not known.
$number
${number}
Equivalent to "$argv[number]".
$* Equivalent to "$argv", which is equivalent to "$argv[*]".


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 mod-
ifiers must appear within the braces.


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


$?name
${?name}
Substitutes the string "1" if name is set, "0" if it is not.
$?0 Substitutes "1" if the current input filename is known, "0" if
it is not. Always "0" in interactive shells.
$#name
${#name}
Substitutes the number of words in name.
$# Equivalent to "$#argv". (+)
$%name
${%name}
Substitutes the number of characters in name. (+)
$%number
${%number}
Substitutes the number of characters in $argv[number]. (+)
$? Equivalent to "$status". (+)
$$ Substitutes the (decimal) process number of the (parent) shell.
$! Substitutes the (decimal) process number of the last background
process started by this shell. (+)
$_ Substitutes 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 this.


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


Command, filename and directory stack substitution
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 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 vari-
able and command substituted and put in place of the original string.


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


Filename substitution
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 which match the pattern.


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 charac-
ters, 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/or ranges of
characters in the braces.


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


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


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


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
words "{", "}" and "{}" are passed undisturbed.


The character "~" at the beginning of a filename refers to home direc-
tories. 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 home direc-
tory 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, e.g., "rm *.a *.c
*.o" would fail only if there were no files in the current directory