tcsh is an enhanced but completely compatible version of the Berkeley
UNIX C shell, csh(1).
It is a command language interpreter usable both as an interactive login
shell and a shell script command processor.
It includes a command-line editor (see The command-line editor),
programmable word completion (see Completion and listing),
spelling correction (see Spelling correction),
a history mechanism (see History substitution),
job control (see Jobs)
and a C-like syntax.
The NEW FEATURES section describes major enhancements of tcsh
over csh(1).
Throughout this manual, features of
tcsh not found in most csh(1) implementations
(specifically, the 4.4BSD csh)
are labeled with `(+)', and features which are present in csh(1)
but not usually documented are labeled with `(u)'.
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 remaining
arguments will not be interpreted as shell options. This may be used to pass
options to a shell script without confusion or possible subterfuge. The shell
will not run a set-user ID script without this 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 arguments 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. (+)
-D\fIname\fR[=\fIvalue\fR]
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. Only applicable if -l is the only
flag specified.
-m
The shell loads ~/.tcshrc even if it does not belong to the effective
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
immediately before execution.
-V
Sets the verbose shell variable even before executing ~/.tcshrc.
-X
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'. Since many systems use either the standard
version 6 or version 7 shells whose shell scripts are not compatible
with this shell, the shell uses such a `standard' shell to execute a script
whose first character is not a `#', i.e. which does not start with a
comment.
Remaining arguments are placed in the argv shell variable.
A login shell begins by executing commands from the system files
/etc/csh.cshrc and /etc/csh.login.
It then executes commands from files in the user's home directory:
first ~/.tcshrc (+)
or, if ~/.tcshrc is not found, ~/.cshrc,
then ~/.history (or the value of the histfile shell variable),
then ~/.login,
and finally ~/.cshdirs (or the value of the dirsfile shell variable) (+).
The shell may read /etc/csh.login before instead of after
/etc/csh.cshrc, and ~/.login before instead of after
~/.tcshrc or ~/.cshrc and ~/.history, if so compiled;
see the version shell variable. (+)
Non-login shells read only /etc/csh.cshrc and ~/.tcshrc
or ~/.cshrc on startup.
Commands like stty(1) and tset(1),
which need be run only once per login, usually go in one's ~/.login file.
Users who need to use the same set of files with both csh(1) and
tcsh 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 terminal,
prompting with `> '. (Processing of arguments and the use of the shell to
process files containing command scripts are described later.)
The shell repeatedly reads a line of command input, breaks it into words,
places it on the command history list, parses it and executes each command
in the line.
One can log out by typing `^D' on an empty line, `logout' or `login' or
via the shell's autologout mechanism (see the autologout shell variable).
When a login shell terminates it sets the logout shell variable to
`normal' or `automatic' as appropriate, then
executes commands from the files
/etc/csh.logout and ~/.logout. The shell may drop DTR on logout
if so compiled; see the version shell variable.
The names of the system login and logout files vary from system to system for
compatibility with different csh(1) variants; see FILES.
We first describe The command-line editor.
The Completion and listing and Spelling correction sections
describe two sets of functionality which 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.
Command-line input can be edited using key sequences much like those used in
GNU Emacs or vi(1).
The editor is active only when the edit shell variable is set, which
it is by default in interactive shells.
The bindkey builtin can display and change key bindings.
Emacs-style key bindings are used by default
(unless the shell was compiled otherwise; see the version shell variable),
but bindkey can change the key bindings to vi-style bindings en masse.
The shell always binds the arrow keys (as defined in the TERMCAP
environment variable) to
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 recognizes only whitespace
and some of the characters with special meanings to it, listed under
Lexical structure.
The shell is often able to complete words when given a unique abbreviation.
Type part of a word (for example `ls /usr/lost') and hit the tab key to
run the complete-word editor command.
The shell completes the filename `/usr/lost' to `/usr/lost+found/',
replacing the incomplete word with the complete word in the input buffer.
(Note the terminal `/'; completion adds a `/' to the
end of completed directories and a space to the end of other completed words,
to speed typing and provide a visual indicator of successful completion.
The addsuffix shell variable can be unset to prevent this.)
If no match is found (perhaps `/usr/lost+found' doesn't exist),
the terminal bell rings.
If the word is already complete (perhaps there is a `/usr/lost' on your
system, or perhaps you were thinking too far ahead and typed the whole thing)
a `/' or space is added to the end if it isn't already 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 path or if
given a full pathname.
Typing `echo $ar[tab]' would complete `$ar' to `$argv'
if no other variable began with `ar'.
The shell parses the input buffer to determine whether the word you want to
complete should be completed as a filename, command or variable.
The first word in the buffer and the first word following
`;', `|', `|&', `&&' or `||' is considered to be a command.
A word beginning with `$' is considered to be a variable.
Anything else is a filename. An empty line is `completed' as a 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
completion 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 substitution). 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 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/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',
the completion completes on `foo', even though `food' and `foonly'
also match.
autoexpand can be set to run the expand-history editor command
before each completion attempt, autocorrect can be set to
spelling-correct the word to be completed (see Spelling correction)
before each completion attempt and correct can be set to complete
commands automatically after one hits `return'.
matchbeep can be set to make completion beep or not beep in a variety
of situations, and nobeep can be set to never beep at all.
nostat can be set to a list of directories and/or patterns which
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.
Completion and listing do not work on glob-patterns (see Filename substitution),
but the list-glob and expand-glob editor commands perform
equivalent functions for glob-patterns.
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
complete builtin command). If an input word in a position for
which a completion is defined resembles a word in the completion list,
spelling correction registers a misspelling and suggests the latter
word as a correction. However, if the input word does not match any of
the possible completions for that position, spelling correction 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.
Beware: spelling correction is not guaranteed to work the way one intends,
and is provided mostly as an experimental feature.
Suggestions and improvements are welcome.
`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 which are bound
to letters by default are bound to both lower- and uppercase letters for
convenience.
complete-word \fR(tab)
Completes a word as described under Completion and listing.
complete-word-back \fR(not bound)
Like complete-word-fwd, but steps up from the end of the list.
complete-word-fwd \fR(not bound)
Replaces the current word with the first word in the list of possible
completions. May be repeated to step down through the list.
At the end of the list, beeps and reverts to the incomplete word.
complete-word-raw \fR(^X-tab)
Like complete-word, but ignores user-defined completions.
copy-prev-word \fR(M-^_)
Copies the previous word in the current line into the input buffer.
See also insert-last-word.
dabbrev-expand \fR(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 \fR(not bound)
Deletes the character under the cursor.
See also delete-char-or-list-or-eof.
delete-char-or-eof \fR(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 \fR(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 \fR(^D)
Does delete-char if there is a character under the cursor,
list-choices at the end of the line
or end-of-file on an empty line.
See also those three commands, each of which only does a single action, and
delete-char-or-eof, delete-char-or-list and list-or-eof,
each of which does a different two out of the three.
down-history \fR(down-arrow, ^N)
Like up-history, but steps down, stopping at the original input line.
end-of-file \fR(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 \fR(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 \fR(^X-*)
Expands the glob-pattern to the left of the cursor.
See Filename substitution.
expand-line \fR(not bound)
Like expand-history, but
expands history substitutions in each word in the input buffer,
expand-variables \fR(^X-$)
Expands the variable to the left of the cursor.
See Variable substitution.
history-search-backward \fR(M-p, M-P)
Searches backwards through the history list for a command beginning with
the current contents of the input buffer up to the cursor and copies it
into the input buffer.
The search string may be a glob-pattern (see Filename substitution)
containing `*', `?', `[]' or `{}'.
up-history and down-history will proceed from the
appropriate point in the history list.
Emacs mode only.
See also history-search-forward and i-search-back.
history-search-forward \fR(M-n, M-N)
Like history-search-backward, but searches forward.
i-search-back \fR(not bound)
Searches backward like history-search-backward, copies the first match
into the input buffer with the cursor positioned at the end of the pattern,
and prompts with `bck: ' and the first match. Additional characters may be
typed to extend the search, i-search-back may be typed to continue
searching with the same pattern, wrapping around the history list if
necessary, (i-search-back must be bound to a
single character for this to work) or one of the following special characters
may be typed:
Any other character not bound to self-insert-command terminates the
search, leaving the current line in the input buffer, and
is then interpreted as normal input. In particular, a carriage return
causes the current line to be executed.
Emacs mode only.
See also i-search-fwd and history-search-backward.
i-search-fwd \fR(not bound)
Like i-search-back, but searches forward.
insert-last-word \fR(M-_)
Inserts the last word of the previous input line (`!$') into the input buffer.
See also copy-prev-word.
list-choices \fR(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 \fR(^X-^D)
Like list-choices, but ignores user-defined completions.
list-glob \fR(^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 \fR(not bound)
Does list-choices
or end-of-file on an empty line.
See also delete-char-or-list-or-eof.
magic-space \fR(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 \fR(^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, e.g. `dbx' and `sh -x'.
normalize-path \fR(^X-n, ^X-N)
Expands the current word as described under the `expand' setting
of the symlinks shell variable.
overwrite-mode \fR(unbound)
Toggles between input and overwrite modes.
run-fg-editor \fR(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 \fR(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 helpcommand is defined, it is run with the
command name as a sole argument. Else,
documentation should be in a file named command.help, command.1,
command.6, command.8 or command, which should be in one
of the directories listed in the HPATH environment variable.
If there is more than one help file only the first is printed.
self-insert-command \fR(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 \fR(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 \fR(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 \fR(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 \fR(M-r, M-R)
Expands or `unexpands' history substitutions in the input buffer.
See also expand-history and the autoexpand shell variable.
undefined-key \fR(any unbound key)
up-history \fR(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 \fR(?)
Prompts with `?' for a search string (which may be a glob-pattern, as with
history-search-backward), searches for it and copies it into the
input buffer. The bell rings if no match is found.
Hitting return ends the search and leaves the last match in the input
buffer.
Hitting escape ends the search and executes the match.
vi mode only.
vi-search-fwd \fR(/)
Like vi-search-back, but searches forward.
which-command \fR(M-?)
Does a which (see the description of the builtin command) on the
first word of the input buffer.
The shell splits input lines into words at blanks and tabs. The special
characters `&', `|', `;', `<', `>', `(', and `)' and the doubled characters
`&&', `||', `<<' and `>>' are always separate words, whether or not they are
surrounded by 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 character(s)
(e.g. `$' or ``' for Variable substitution or Command substitution respectively)
with `\\'. (Alias substitution is no exception: quoting in any way any
character of a word for which an alias has been defined prevents
substitution of the alias. The usual way of quoting an alias is to precede it
with a backslash.) History substitution is prevented by
backslashes but not by single quotes. Strings quoted with double or backward
quotes undergo Variable substitution and Command substitution, but other
substitutions are prevented.
Text inside single or double quotes becomes a single word (or part of one).
Metacharacters in these strings, including blanks and tabs, do not form
separate words. Only in one special case (see Command substitution
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 backslashes
always quote `\\', `'', and `"'. (+) This may make complex quoting tasks
easier, but it can cause syntax errors in csh(1) scripts.
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.
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 usually necessary to use event numbers, but the current event number
can be made part of the prompt by placing an `!' in the prompt shell variable.
The shell 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 confidence.
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 indicates
the event from which words are to be taken, a ``word designator'',
which selects particular words from the chosen event, and/or a ``modifier'',
which manipulates the selected words.
An event specification can be
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
n
^
The first argument, equivalent to `1'
$
%
The word matched by an ?s? search
x-y
-y
*
Equivalent to `^-$', but returns nothing if the event contains only 1 word
x*
x-
Equivalent to `x*', but omitting the last word (`$')
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 !!$'. However, if `!!' is abbreviated `!',
an argument selector beginning with `-' will be interpreted as an event
specification.
A history reference may have a word designator but no event specification.
It then references the previous command.
\" Not true, but we thought it was for a long time ...
, unless a previous history reference
occurred on the same line in which case this form repeats the previous
reference. Thus `!?foo?^ !$' gives the first and last arguments from the
command matching `?foo?'.
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 ``modified'',
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 substitution or the
s from a previous `?s?' event specification is used.
The trailing delimiter may be omitted if it is immediately followed by a newline.
&
Repeat the previous substitution.
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 substitutions.
x
Like q, but break into words at blanks, tabs and newlines.
Modifiers are applied only to the first modifiable word (unless `g' is used).
It is an error for no word to be modifiable.
For example, the `diff' command might have been written as `diff 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 `!'.
(+) 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.
The shell maintains a list of aliases which can be set, unset and printed by
the alias and unalias commands. After a command line is parsed
into simple commands (see Commands) the first word of each command,
left-to-right, is checked to see if it has an alias. If so, the first word is
replaced by the alias. If the alias contains a history reference, it undergoes
History substitution (q.v.) as though the original command were the
previous input line. If the alias does not contain a history reference, the
argument list is left 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 \e!* | 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.
The shell maintains a list of variables, each of which has as value a list of
zero or more words.
The values of shell variables can be displayed and changed with the
set and unset commands.
The system maintains its own list of ``environment'' variables.
These can be displayed and changed with printenv, setenv and
unsetenv.
(+) Variables may be made read-only with `set -r' (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 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 `\e' except within `"'s
where it always occurs, and within `''s where it never occurs.
Strings quoted by ``' are interpreted later (see Command substitution
below) so `$' substitution does not occur there until later,
if at all. A `$' is passed unchanged if followed by a blank, tab, or
end-of-line.
Input/output redirections are recognized before variable expansion, and are
variable expanded separately. Otherwise, the command name and entire argument
list are expanded together. It is thus possible for the first (command) word
(to this point) to generate more than one word, the first of which becomes the
command name, and the rest of which become arguments.
Unless enclosed in `"' or given the `:q' modifier the results of variable
substitution may eventually be command and filename substituted. Within `"', a
variable whose value consists of multiple words expands to a (portion of a)
single word, with the words of the variable's value separated by blanks. When
the `:q' modifier is applied to a substitution the variable will expand to
multiple words with each word separated by a blank and quoted to prevent later
command or filename substitution.
The following metasequences are provided for introducing variable values into
the shell input. Except as noted, it is an error to reference a variable which
is not set.
$name
${name}
Substitutes the words of the value of variable name, each separated
by a blank. Braces insulate name from following characters which would
otherwise be part of it. Shell variables have names consisting of up to 20
letters and digits starting with a letter. The underscore character is
considered a letter. If name is not a shell variable, but is set in the
environment, then that value is returned (but `:' modifiers and the other forms
given below 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 modifiers 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. (+)
$_
Substitures 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.
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 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
quotes (`"') retain blanks and tabs; only newlines force new words. The single
final newline does not force a new word in any case. It is thus possible for a
command substitution to yield only part of a word, even if the command outputs
a complete line.
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 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/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 directories.
Standing alone, i.e. `~', it expands to the invoker's home directory as
reflected in the value of the home shell variable. When followed by a
name consisting of letters, digits and `-' characters the shell searches for a
user with that name and substitutes their home directory; thus `~ken' might
expand to `/usr/ken' and `~ken/chmach' to `/usr/ken/chmach'. If the character
`~' is followed by a character other than a letter or `/' or appears elsewhere
than at the beginning of a word, it is left undisturbed.
A command like `setenv MANPATH /usr/man:/usr/local/man:~/lib/man' does not,
therefore, do 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, e.g., `rm *.a *.c *.o' would fail
only if there were no files in the current directory ending in `.a', `.c', or
`.o'), and if the nonomatch shell variable is set a pattern (or list
of patterns) which matches nothing is left unchanged rather than causing
an error.
The noglob shell variable can be set to prevent filename substitution,
and the expand-glob editor command, normally bound to `^X-*', can be
used to interactively expand individual filename substitutions.
The directory stack is a list of directories, numbered from zero, used by the
pushd, popd and dirs builtin commands (q.v.).
dirs can print, store in a file, restore and clear the directory stack
at any time, and the savedirs and dirsfile shell variables can be set to
store the directory stack automatically on logout and restore it on login.
The dirstack shell variable can be examined to see the directory stack and
set to put arbitrary directories into the directory stack.
The character `=' followed by one or more digits expands to an entry in
the directory stack. The special case `=-' expands to the last directory in
the stack. For example,
> 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
The noglob and nonomatch shell variables and the expand-glob
editor command apply to directory stack as well as filename substitutions.
There are several more transformations involving filenames, not strictly
related to the above but mentioned here for completeness.
Any filename may be expanded to a full path when the
symlinks variable (q.v.) is set to `expand'.
Quoting prevents this expansion, and
the normalize-path editor command does it on demand.
The normalize-command editor command expands commands in PATH into
full paths on demand.
Finally, cd and pushd interpret `-' as the old working directory
(equivalent to the shell variable owd).
This is not a substitution at all, but an abbreviation recognized only by
those commands. Nonetheless, it too can be prevented by quoting.
The next three sections describe how the shell executes commands and
deals with their input and output.
A simple command is a sequence of words, the first of which specifies the
command to be executed. A series of simple commands joined by `|' characters
forms a pipeline. The output of each command in a pipeline is connected to the
input of the next.
Simple commands and pipelines may be joined into sequences with `;', and will
be executed sequentially. Commands and pipelines can also be joined into
sequences with `||' or `&&', indicating, as in the C language, that the second
is to be executed only if the first fails or succeeds respectively.
A simple command, pipeline or sequence may be placed in parentheses, `()',
to form a simple command, which may in turn be a component of a pipeline or
sequence. A command, pipeline or sequence can be executed
without waiting for it to terminate by following it with an `&'.
Builtin commands are executed within the shell. If any component of a
pipeline except the last is a builtin command, the pipeline is executed
in a subshell.
Parenthesized commands are always executed in a subshell.
thus prints the home directory, leaving you where you were
(printing this after the home directory), while
leaves you in the home directory. Parenthesized commands are most often
used to prevent cd from affecting the current shell.
When a command to be executed is found not to be a builtin command the shell
attempts to execute the command via execve(2). Each word in the variable
path names a directory in which the shell will look for the
command. If it is given neither a -c nor a -t option, the shell
hashes the names in these directories into an internal table so that it will
only try an execve(2) 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
(i.e. 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 may be set
to specify an interpreter other than the shell itself.
On systems which do not understand the `#!' script interpreter convention
the shell may be compiled to emulate it; see the version shell
variable. If so, the shell checks the first line of the file to
see if it is of the form `#!interpreter arg ...'. If it is,
the shell starts interpreter with the given args and feeds the
file to it on standard input.
The standard input and standard output of a command may be redirected with the
following syntax:
< name
Open file name (which is first variable, command and filename
expanded) as the standard input.
<< word
Read the shell input up to a line which is identical to word. word
is not subjected to variable, filename or command substitution, and each input
line is compared to word before any substitutions are done on this input
line. Unless a quoting `\e', `"', `' or ``' appears in word variable and
command substitution is performed on the intervening lines, allowing `\e' to
quote `$', `\e' and ``'. Commands which are substituted have all blanks, tabs,
and newlines preserved, except for the final newline which is dropped. The
resultant text is placed in an anonymous temporary file which is given to the
command as standard input.
> name
>! name
>& name
>&! name
The file name is used as standard output. If the file does not exist
then it is created; if the file exists, its is truncated, its previous contents
being lost.
If the shell variable noclobber is set, then the file must not exist or be a
character special file (e.g. a terminal or `/dev/null') or an error results.
This helps prevent accidental destruction of files. In this case the `!' forms
can be used to suppress this check.
The forms involving `&' route the diagnostic output into the specified file as
well as the standard output. name is expanded in the same way as `<'
input filenames are.
>> name
>>& name
>>! name
>>&! name
Like `>', but appends output to the end of name.
If the shell variable noclobber is set, then it is an error for
the file not to exist, unless one of the `!' forms is given.
A command receives the environment in which the shell was invoked as modified
by the input-output parameters and the presence of the command in a pipeline.
Thus, unlike some previous shells, commands run from a file of shell commands
have no access to the text of the commands by default; rather they receive the
original standard input of the shell. The `<<' mechanism should be used to
present inline data. This permits shell command scripts to function as
components of pipelines and allows the shell to block read its input. Note
that the default standard input for a command run detached is not
the empty file /dev/null, but the original standard input of the shell.
If this is a terminal and if the process attempts to read from the terminal,
then the process will block and the user will be notified (see Jobs).
Diagnostic output may be directed through a pipe with the standard output.
Simply use the form `|&' rather than just `|'.
The shell cannot presently redirect diagnostic output without also redirecting
standard output, but `(command > output-file) >& error-file'
is often an acceptable workaround. Either output-file or
error-file may be `/dev/tty' to send output to the terminal.
Having described how the shell accepts, parses and executes
command lines, we now turn to a variety of its useful features.
The shell contains a number of commands which can be used to regulate the
flow of control in command files (shell scripts) and (in limited but
useful ways) from terminal input. These commands all operate by forcing the
shell to reread or skip in its input and, due to the implementation,
restrict the placement of some of the commands.
The foreach, switch, and while statements, as well as the
if-then-else form of the if statement, require that the major
keywords appear in a single simple command on an input line as shown below.
If the shell's input is not seekable, the shell buffers up input whenever
a loop is being read and performs seeks in this internal buffer to
accomplish the rereading implied by the loop. (To the extent that this
allows, backward gotos will succeed on non-seekable inputs.)
The if, while and exit builtin commands
use expressions with a common syntax. The expressions can include any
of the operators described in the next three sections. Note that the @
builtin command (q.v.) has its own separate syntax.
These operators are similar to those of C and have the same precedence.
They include
|| && | ^ & == != =~ !~ <= >=
< > << >> + - * / % ! ~ ( )
Here the precedence increases to the right, `==' `!=' `=~' and `!~', `<='
`>=' `<' and `>', `<<' and `>>', `+' and `-', `*' `/' and `%' being, in
groups, at the same level. The `==' `!=' `=~' and `!~' operators compare
their arguments as strings; all others operate on numbers. The operators
`=~' and `!~' are like `!=' and `==' except that the right hand side is a
glob-pattern (see Filename substitution) against which the left hand
operand is matched. This reduces the need for use of the switch
builtin command in shell scripts when all that is really needed is
pattern matching.
Strings which 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.
Commands can be executed in expressions and their exit status
returned by enclosing them in braces (`{}'). Remember that the braces should
be separated from the words of the command by spaces. Command executions
succeed, returning true, i.e. `1', if the command exits with status 0,
otherwise they fail, returning false, i.e. `0'. If more detailed status
information is required then the command should be executed outside of an
expression and the status shell variable examined.
Some of these operators perform true/false tests on files and related
objects. They are of the form -op file, where op is one of
r
w
x
X
Executable in the path or shell builtin, e.g. `-X ls' and `-X ls-F' are
generally true, but `-X /bin/ls' is not (+)
e
o
z
s
f
d
l
b
c
Character special file (+)
p
S
Socket special file (+) *
u
Set-user-ID bit is set (+)
g
Set-group-ID bit is set (+)
k
t
file (which must be a digit) is an open file descriptor
for a terminal device (+)
R
Has been migrated (convex only) (+)
L
Applies subsequent operators in a multiple-operator test to a symbolic link
rather than to the file to which the link points (+) *
file is command and filename expanded and then tested to
see if it has the specified relationship to the real user. If file
does not exist or is inaccessible or, for the operators indicated by `*',
if the specified file type does not exist on the current system,
then all enquiries return false, i.e. `0'.
These operators may be combined for conciseness: `-xy file' is
equivalent to `-x file && -y file'. (+) For example, `-fx' is true
(returns `1') for plain executable files, but not for directories.
L may be used in a multiple-operator test to apply subsequent operators
to a symbolic link rather than to the file to which the link points.
For example, `-lLo' is true for links owned by the invoking user.
Lr, Lw and Lx are always true for links and false for
non-links. L has a different meaning when it is the last operator
in a multiple-operator test; see below.
It is possible but not useful, and sometimes misleading, to combine operators
which expect file to be a file with operators which do not,
(e.g. X and t). Following L with a non-file operator
can lead to particularly strange results.
Other operators return other information, i.e. not just `0' or `1'. (+)
They have the same format as before; op may be one of
A
Last file access time, as the number of seconds since the epoch
A:
Like A, but in timestamp format, e.g. `Fri May 14 16:36:10 1993'
M
Last file modification time
M:
Like M, but in timestamp format
C
Last inode modification time
C:
Like C, but in timestamp format
D
I
F
Composite file identifier, in the form device:inode
L
The name of the file pointed to by a symbolic link
N
P
Permissions, in octal, without leading zero
P:
Like P, with leading zero
P\fImode
Equivalent to `-P file & mode', e.g. `-P22 file' returns
`22' if file is writable by group and other, `20' if by group only,
and `0' if by neither
P\fImode\fB:
Like Pmode:, with leading zero
U
U:
Username, or the numeric userid if the username is unknown
G
G:
Groupname, or the numeric groupid if the groupname is unknown
Z
Only one of these operators may appear in a multiple-operator test, and it
must be the last. Note that L has a different meaning at the end of and
elsewhere in a multiple-operator test. Because `0' is a valid return value
for many of these operators, they do not return `0' when they fail: most
return `-1', and F returns `:'.
If the shell is compiled with POSIX defined (see the version shell
variable), the result of a file inquiry is based on the permission bits of
the file and not on the result of the access(2) system call.
For example, if one tests a file with -w whose permissions would
ordinarily allow writing but which is on a file system mounted read-only,
the test will succeed in a POSIX shell but fail in a non-POSIX shell.
File inquiry operators can also be evaluated with the filetest builtin
command (q.v.) (+).
The shell associates a job with each pipeline. It keeps a table of
current jobs, printed by the jobs command, and assigns them small integer
numbers. When a job is started asynchronously with `&', the shell prints a
line which looks like
indicating that the job which was started asynchronously was job number 1 and
had one (top-level) process, whose process id was 1234.
If you are running a job and wish to do something else you may hit the suspend
key (usually `^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 will be listed
like the jobs builtin command; if it is set to `long' the listing will
be in long format, like `jobs -l'.
You can then manipulate the state of the suspended job.
You can put it in the
``background'' with the bg command or run some other commands and
eventually bring the job back into the ``foreground'' with fg.
(See also the run-fg-editor editor command.)
A `^Z' takes effect immediately and is like an interrupt
in that pending output and unread input are discarded when it is typed.
The wait builtin 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(2) it, to the current job.
This can usefully be typed ahead when you have prepared some commands for a
job which you wish to stop after it has read them.
The `^Y' key performs this function in csh(1); 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 normally allowed to produce output, but this can
be disabled by giving the command `stty tostop'. If you set this tty 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 wish to refer to job number 1, you can name it
as `%1'. Just naming a job brings it to the foreground; thus `%1' is a synonym
for `fg %1', bringing job 1 back into the foreground. Similarly, 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(1) 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 `+' and the previous job
with a `-'. The abbreviations `%+', `%', and (by analogy with the syntax of
the history mechanism) `%%' all refer to the current job, and `%-' refers
to the previous job.
The job control mechanism requires that the stty(1) option `new' be set
on some systems. It is an artifact from a `new' implementation of the tty
driver which allows generation of interrupt characters from the keyboard to
tell jobs to stop. See stty(1) and the setty builtin command for
details on setting options in the new tty driver.
The 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 will be 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 will be
warned that `You have stopped jobs.' You may use the jobs command to see
what they are. If you do this or immediately try to exit again, the shell will
not warn you a second time, and the suspended jobs will be terminated.
There are various ways to run commands and take other actions automatically
at various times in the ``life cycle'' of the shell. They are summarized here,
and described in detail under the appropriate Builtin commands,
Special shell variables and Special aliases.
The sched builtin command puts commands in a scheduled-event list,
to be executed by the shell at a given time.
The beepcmd, cwdcmd, periodic, precmd, and postcmd
Special aliases can be set, respectively, to execute commands when the shell wants
to ring the bell, when the working directory changes, every tperiod
minutes, before each prompt, and before each command gets executed.
The autologout shell variable can be set to log out or lock the shell
after a given number of minutes of inactivity.
The mail shell variable can be set to check for new mail periodically.
The printexitvalue shell variable can be set to print the exit status
of commands 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 builtin
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 builtin command reports
on those users at any time.
The shell is eight bit clean
(if so compiled; see the version shell variable)
and thus supports character sets needing this capability.
NLS support differs depending on whether or not
the shell was compiled to use the system's NLS (again, see version).
In either case, 7-bit ASCII is the default for character classification
(e.g. which characters are printable) and sorting,
and changing the LANG or LC_CTYPE environment variables
causes a check for possible changes in these respects.
When using the system's NLS, the setlocale(3) function is called
to determine appropriate character classification and sorting.
This function typically examines the LANG and LC_CTYPE
environment variables; refer to the system documentation for further details.
When not using the system's NLS, the shell simulates it by assuming that the
ISO 8859-1 character set is used
whenever either of the LANG and LC_CTYPE variables are set, regardless of
their values. Sorting is not affected for the simulated NLS.
In addition, with both real and simulated NLS, all printable
characters in the range \e200-\e377, i.e. those that have
M-char bindings, are automatically rebound to self-insert-command.
The corresponding binding for the escape-char sequence, if any, is
left alone.
These characters are not rebound if the NOREBIND environment variable
is set. This may be useful for the simulated NLS or a primitive real NLS
which assumes full ISO 8859-1. Otherwise, all M-char bindings in the
range \e240-\e377 are effectively undone.
Explicitly rebinding the relevant keys with bindkey
is of course still possible.
Unknown characters (i.e. those that are neither printable nor control
characters) are printed in the format \ennn.
If the tty is not in 8 bit mode, other 8 bit characters are printed by
converting them to ASCII and using standout mode. The shell
never changes the 7/8 bit mode of the tty and tracks user-initiated
changes of 7/8 bit mode. NLS users (or, for that matter, those who want to
use a meta key) may need to explicitly set
the tty in 8 bit mode through the appropriate stty(1)
command in, e.g., the ~/.login file.
A number of new builtin commands are provided to support features in
particular operating systems. All are described in detail in the
Builtin commands section.
On systems that support TCF (aix-ibm370, aix-ps2),
getspath and setspath get and set the system execution path,
getxvers and setxvers get and set the experimental version prefix
and migrate migrates processes between sites. The jobs builtin
prints the site on which each job is executing.
Under Domain/OS, inlib adds shared libraries to the current environment,
rootnode changes the rootnode and ver changes the systype.
Under Mach, setpath is equivalent to Mach's setpath(1).
Under Masscomp/RTU and Harris CX/UX, universe sets the universe.
Under Harris CX/UX, ucb or att runs a command under the specified
universe.
Under Convex/OS, warp prints or sets the universe.
The VENDOR, OSTYPE and MACHTYPE environment variables
indicate respectively the vendor, operating system and machine type
(microprocessor class or machine model) of the
system on which the shell thinks it is running.
These are particularly useful when sharing one's home directory between several
types of machines; one can, for example,
set path = (~/bin.$MACHTYPE /usr/ucb /bin /usr/bin .)
in one's ~/.login and put executables compiled for each machine in the
appropriate directory.
The version shell
variable indicates what options were chosen when the shell was compiled.
Note also the newgrp builtin, the afsuser and
echo_style shell variables and the system-dependent locations of
the shell's input files (see FILES).
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.
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 builtin.
Note that although the editor uses CBREAK mode (or its equivalent),
it takes typed-ahead characters anyway.
The echotc, settc and telltc commands can be used to
manipulate and debug terminal capabilities from the command line.
On systems that support SIGWINCH or SIGWINDOW, the shell
adapts to window resizing automatically and adjusts the environment
variables LINES and COLUMNS if set. If the environment
variable TERMCAP contains li# and co# fields, the shell adjusts
them to reflect the new window size.
