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 lan-
guage 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 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)'.
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 spec-
ified 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 inter-
preted as shell options. This may be used to pass
options to a shell script without confusion or possi-
ble 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. (+)
-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. 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 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'.
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.
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 vari-
able), 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 vari-
able. (+)
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 exis-
tence 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 argu-
ments and the use of the shell to process files containing
command scripts are described later.) The shell repeat-
edly reads a line of command input, breaks it into words,
places it on the command history list, parses it and exe-
cutes 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 termi-
nates 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.
Editing
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 com-
mands 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 com-
piled 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
down down-history
up up-history
left backward-char
right forward-char
unless doing so would alter another single-character bind-
ing. 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 descrip-
tion 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.
Completion and listing (+)
The shell is often able to complete words when given a
unique abbreviation. Type part of a word (for example `ls
/usr/lost') and hit the tab key to run the complete-word
editor command. The shell completes the filename
`/usr/lost' to `/usr/lost+found/', replacing the incom-
plete 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 ter-
minal 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 `$argv' if no
other variable began with `ar'.
The shell parses the input buffer to determine whether the
word you want to complete should be completed as a file-
name, command or variable. The first word in the buffer
and the first word following `;', `|', `|&', `&&' or `||'
is considered to be a command. A word beginning with `$'
is considered to be a variable. Anything else is a file-
name. An empty line is `completed' as a 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 abbre-
viated 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 possibili-
ties 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 com-
mands (not bound to any keys by default) can be used to
cycle up and down through the list of possible comple-
tions, replacing the current word with the next or previ-
ous word in the list.
The shell variable fignore can be set to a list of suf-
fixes 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 substi-
tution. fignore is ignored if only one completion is pos-
sible.
If the complete shell variable is set to `enhance',
completion 1) ignores case and 2) considers periods,
hyphens and underscores (`.', `-' and `_') to be word sep-
arators 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-correct the
word to be completed (see Spelling correction) before each
completion attempt and correct can be set to complete com-
mands automatically after one hits `return'. matchbeep
can be set to make completion beep or not beep in a vari-
ety 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, com-
mands and variables. Completion and listing do not work
on glob-patterns (see Filename substitution), but the
list-glob and expand-glob editor commands perform equiva-
lent 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 any-
thing 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 correc-
tion. However, if the input word does not match any of the
possible completions for that position, spelling correc-
tion does not register a misspelling.
Like completion, spelling correction works anywhere in the
line, pushing the rest of the line to the right and possi-
bly 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.
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 which are bound to letters by
default are bound to both lower- and uppercase letters for
convenience.
complete-word (tab)
Completes a word as described under Completion and
listing.
complete-word-back (not bound)
Like complete-word-fwd, but steps up from the end
of the list.
complete-word-fwd (not bound)
Replaces the current word with the first word in
the list of possible completions. May be repeated
to step down through the list. At the end of the
list, beeps and reverts to the incomplete word.
complete-word-raw (^X-tab)
Like complete-word, but ignores user-defined com-
pletions.
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 pre-
ceding one for which the current is a leading sub-
string, wrapping around the history list (once) if
necessary. Repeating dabbrev-expand without any
intervening typing changes to the next previous
word etc., skipping identical matches much like
history-search-backward does.
delete-char (not bound)
Deletes the character under the cursor. See also
delete-char-or-list-or-eof.
delete-char-or-eof (not bound)
Does delete-char if there is a character under the
cursor or end-of-file on an empty line. See also
delete-char-or-list-or-eof.
delete-char-or-list (not bound)
Does delete-char if there is a character under the
cursor or list-choices at the end of the line.
See also delete-char-or-list-or-eof.
delete-char-or-list-or-eof (^D)
Does delete-char if there is a character under the
cursor, list-choices at the end of the line or
end-of-file on an empty line. See also those
three commands, each of which only does a single
action, and delete-char-or-eof, delete-char-or-
list and list-or-eof, each of which does a differ-
ent 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 cur-
sor. See Filename substitution.
expand-line (not bound)
Like expand-history, but expands history substitu-
tions 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) contain-
ing `*', `?', `[]' or `{}'. up-history and down-
history will proceed from the appropriate point in
the history list. Emacs mode only. See also his-
tory-search-forward and i-search-back.
history-search-forward (M-n, M-N)
Like history-search-backward, but searches for-
ward.
i-search-back (not bound)
Searches backward like history-search-backward,
copies the first match into the input buffer with
the cursor positioned at the end of the pattern,
and prompts with `bck: ' and the first match.
Additional characters may be typed to extend the
search, i-search-back may be typed to continue
searching with the same pattern, wrapping around
the history list if necessary, (i-search-back must
be bound to a single character for this to work)
or one of the following special characters may be
typed:
^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 charac-
ter 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 successful
search.
escape Ends the search, leaving the current
line in the input buffer.
Any other character not bound to self-insert-com-
mand 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 com-
pletions.
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 appends a space. magic-
space is designed to be bound to the spacebar, but
is not bound by default.
normalize-command (^X-?)
Searches for the current word in PATH and, if it
is found, replaces it with the full path to the
executable. Special characters are quoted. Aliases
are expanded and quoted but commands within
aliases are not. This command is useful with com-
mands which 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' setting of the symlinks shell variable.
overwrite-mode (unbound)
Toggles between input and overwrite modes.
run-fg-editor (M-^Z)
Saves the current input line and looks for a
stopped job with a name equal to the last compo-
nent of the file name part of the EDITOR or VISUAL
environment variables, or, if neither is set, `ed'
or `vi'. If such a job is found, it is restarted
as if `fg %job' had been typed. This is used to
toggle back and forth between an editor and the
shell easily. Some people bind this command to
`^Z' so they can do this even more easily.
run-help (M-h, M-H)
Searches for documentation on the current command,
using the same notion of `current command' as the
completion routines, and prints it. There is no
way to use a pager; run-help is designed for short
help files. Documentation should be in a file
named command.help, command.1, command.6, com-
mand.8 or command, which should be in one of the
directories listed in the HPATH enviroment vari-
able. If there is more than one help file only
the first is printed.
self-insert-command (text characters)
In insert mode (the default), inserts the typed
character into the input line after the character
under the cursor. In overwrite mode, replaces the
character under the cursor with the typed charac-
ter. The input mode is normally preserved between
lines, but the inputmode shell variable can be set
to `insert' or `overwrite' to put the editor in
that mode at the beginning of each line. See also
overwrite-mode.
sequence-lead-in (arrow prefix, meta prefix, ^X)
Indicates that the following characters are part
of a multi-key sequence. Binding a command to a
multi-key sequence really creates two bindings:
the first character to sequence-lead-in and the
whole sequence to the command. All sequences
beginning with a character bound to sequence-lead-
in are effectively bound to undefined-key unless
bound to another command.
spell-line (M-$)
Attempts to correct the spelling of each word in
the input buffer, like spell-word, but ignores
words whose first character is one of `-', `!',
`^' or `%', or which contain `\', `*' or `?', to
avoid problems with switches, substitutions and
the like. See Spelling correction.
spell-word (M-s, M-S)
Attempts to correct the spelling of the current
word as described under Spelling correction.
Checks each component of a word which appears to
be a 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 variable.
undefined-key (any unbound key)
Beeps.
up-history (up-arrow, ^P)
Copies the previous entry in the history list into
the input buffer. If histlit is set, uses the
literal form of the entry. May be repeated to
step up through the history list, stopping at the
top.
vi-search-back (?)
Prompts with `?' for a search string (which may be
a glob-pattern, as with history-search-backward),
searches for it and copies it into the input
buffer. The bell rings if no match is found. Hit-
ting 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.
Lexical structure
The shell splits input lines into words at blanks and
tabs. The special characters `&', `|', `;', `<', `>',
`(', and `)' and the doubled characters `&&', `||', `<<'
and `>>' are always separate words, whether or not they
are surrounded by 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 pre-
vented 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 respec-
tively) 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 back-
slashes but not by single quotes. Strings quoted with
double or backward quotes undergo Variable substitution
and Command substitution, but other substitutions are pre-
vented.
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 them-
selves 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.
Substitutions
We now describe the various transformations the shell per-
forms on the input in the order in which they occur. We
note in passing the data structures involved and the com-
mands and variables which affect them. Remember that sub-
stitutions 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 num-
ber 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 com-
mands, repeat arguments of a previous command in the cur-
rent 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 set-
ting 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 specifica-
tion'', 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 care-
fully 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 unam-
biguously 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 `^-$', but returns nothing if
the event contains only 1 word
x* Equivalent to `x-$'
x- Equivalent to `x*', but omitting the last word
(`$')
Selected words are inserted into the command line sepa-
rated by single blanks. For example, the `diff' command
in the previous example might have been typed as `diff
!!:1.old !!:1' (using `:1' to select the first argument
from the previous event) or `diff !-2:2 !-2:1' to select
and swap the arguments from the `cp' command. If we didn't
care about the order of the `diff' we might have said
`diff !-2:1-2' or simply `diff !-2:*'. The `cp' command
might have been written `cp wumpus.man !#:1.old', using
`#' to refer to the current event. `!n:- hurkle.man'
would reuse the first two words from the `nroff' command
to say `nroff -man hurkle.man'.
The `:' separating the event specification from the word
designator can be omitted if the argument selector begins
with a `^', `$', `*', `%' or `-'. For example, our `diff'
command might have been `diff !!^.old !!^' or, equiva-
lently, `diff !!$.old !!$'. However, if `!!' is abbrevi-
ated `!', 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 com-
mand. 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, leav-
ing 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 epony-
mous 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 fur-
ther 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 equiv-
alent 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.
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 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 refer-
ence, 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 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; attempt-
ing 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 per-
formed keyed by `$' characters. This expansion can be
prevented by preceding the `$' with a `\' except within
`"'s where it always occurs, and within `''s where it
never occurs. Strings quoted by ``' are interpreted later
(see Command substitution below) so `$' substitution does
not occur there until later, if at all. A `$' is passed
unchanged if followed by a blank, tab, or end-of-line.
Input/output redirections are recognized before variable
expansion, and are variable expanded separately. Other-
wise, 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 other-
wise be part of it. Shell variables have names
consisting of up to 20 letters and digits starting
with a letter. The underscore character is con-
sidered a letter. If name is not a shell vari-
able, 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]
${name[selector]}
Substitutes only the selected words from the value
of name. The selector is subjected to `$' substi-
tution 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 com-
mand 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 interac-
tive 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[num-
ber]. (+)
$? Equivalent to `$status'. (+)
$$ Substitutes the (decimal) process number of the
(parent) shell.
$! Substitutes the (decimal) process number of the
last background process started by this shell.
$< Substitutes a line from the standard input, with
no further interpretation thereafter. 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 sepa-
rate words at blanks, tabs and newlines, and null words
are discarded. The output is variable and command substi-
tuted and put in place of the original string.
Command substitutions inside double quotes (`"') retain
blanks and tabs; only newlines force new words. The sin-
gle 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 com-
plete 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 charac-
ter `*' matches any string of characters, including the
null string. The character `?' matches any single charac-
ter. The sequence `[...]' matches any one of the charac-
ters enclosed. Within `[...]', a pair of characters sepa-
rated 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 pre-
serve 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 consist-
ing 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. How-
ever, 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 end-
ing 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 indi-
vidual filename substitutions.
Directory stack substitution (+)
The directory stack is a list of directories, numbered
from zero, used by the pushd, popd and dirs builtin com-
mands (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 directo-
ries 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.
Other substitutions (+)
There are several more transformations involving file-
names, 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 nor-
malize-path editor command does it on demand. The normal-
ize-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. Nonethe-
less, it too can be prevented by quoting.
Commands
The next three sections describe how the shell executes
commands and deals with their input and output.
Simple commands, pipelines and sequences
A simple command is a sequence of words, the first of
which specifies the command to be executed. A series of
simple commands joined by `|' characters forms a pipeline.
The output of each command in a pipeline is connected to
the input of the next.
Simple commands and pipelines may be joined into sequences
with `;', and 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 respec-
tively.
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 and non-builtin command execution
Builtin commands are executed within the shell. If any
component of a pipeline except the last is a builtin com-
mand, the pipeline is executed in a subshell.
Parenthesized commands are always executed in a subshell.
(cd; pwd); pwd
thus prints the home directory, leaving you where you were
(printing this after the home directory), while
cd; pwd
leaves you in the home directory. Parenthesized commands
are most often used to prevent cd from affecting the cur-
rent 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 direc-
tory 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 mech-
anism has been turned off (via unhash), if the shell was
given a -c or -t argument or in any case for each direc-
tory 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 exe-
cutable 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 inter-
preter 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 inter-
preter with the given args and feeds the file to it on
standard input.
Input/output
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 identi-
cal 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
`\', `"', `' or ``' appears in word variable and
command substitution is performed on the interven-
ing lines, allowing `\' to quote `$', `\' 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 con-
tents 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 destruc-
tion of files. In this case the `!' forms can be
used to suppress this check.
The forms involving `&' route the diagnostic out-
put into the specified file as well as the stan-
dard 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 com-
mands 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 pre-
sent 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.
Features
Having described how the shell accepts, parses and exe-
cutes command lines, we now turn to a variety of its use-
ful features.
Control flow
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 implementa-
tion, 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.)
Expressions
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.
Logical, arithmetical and comparison operators
These operators are similar to those of C and have the
same precedence. They include
|| && | ^ & == != =~ !~ <= >=
< > << >> + - * / % ! ~ ( )
Here the precedence increases to the right, `==' `!=' `=~'
and `!~', `<=' `>=' `<' and `>', `<<' and `>>', `+' and
`-', `*' `/' and `%' being, in groups, at the same level.
The `==' `!=' `=~' and `!~' operators compare their argu-
ments 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 sub-
stitution) against which the left hand operand is matched.
This reduces the need for use of the switch builtin com-
mand 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 syntacti-
cally significant to the parser (`&' `|' `<' `>' `(' `)')
they should be surrounded by spaces.
Command exit status
Commands can be executed in expressions and their exit
status returned by enclosing them in braces (`{}'). Remem-
ber that the braces should be separated from the words of
the command by spaces. Command executions succeed, return-
ing 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.
File inquiry operators
Some of these operators perform true/false tests on files
and related objects. They are of the form -op file, where
op is one of
r Read access
w Write access
x Execute access
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 Existence
o Ownership
z Zero size
s Non-zero size (+)
f Plain file
d Directory
l Symbolic link (+) *
b Block special file (+)
c Character special file (+)
p Named pipe (fifo) (+) *
S Socket special file (+) *
u Set-user-ID bit is set (+)
g Set-group-ID bit is set (+)
k Sticky bit is set (+)
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-opera-
tor 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 exam-
ple, `-fx' is true (returns `1') for plain executable
files, but not for directories.
L may be used in a multiple-operator test to apply subse-
quent 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 multi-
ple-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 sec-
onds 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 Device number
I Inode number
F Composite file identifier, in the form
device:inode
L The name of the file pointed to by a symbolic
link
N Number of (hard) links
P Permissions, in octal, without leading zero
P: Like P, with leading zero
Pmode 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
Pmode: Like Pmode:, with leading zero
U Numeric userid
U: Username, or the numeric userid if the user-
name is unknown
G Numeric groupid
G: Groupname, or the numeric groupid if the
groupname is unknown
Z Size, in bytes
Only one of these operators may appear in a multiple-oper-
ator test, and it must be the last. Note that L has a dif-
ferent 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 ver-
sion 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.) (+).
Jobs
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
[1] 1234
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 pend-
ing 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 unam-
bigous 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 gener-
ation 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.
Status reporting
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 termi-
nated.
Automatic, periodic and timed events (+)
There are various ways to run commands and take other
actions automatically at various times in the ``life
cycle'' of the shell. They are summarized here, and
described in detail under the appropriate Builtin com-
mands, 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 and precmd Special aliases
can be set, respectively, to execute commands when the
shell wants to ring the bell, when the working directory
changes, every tperiod minutes and before each prompt.
The autologout shell variable can be set to log out or
lock the shell after a given number of minutes of inactiv-
ity.
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.
Native Language System support (+)
The shell is eight bit clean (if so compiled; see the ver-
sion 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 char-
acters are printable) and sorting, and changing the LANG
or LC_CTYPE environment variables causes a check for pos-
sible 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 print-
able characters in the range \200-\377, 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 primi-
tive real NLS which assumes full ISO 8859-1. Otherwise,
all M-char bindings in the range \240-\377 are effectively
undone. Explicitly rebinding the relevant keys with bind-
key is of course still possible.
Unknown characters (i.e. those that are neither printable
nor control characters) are printed in the format \nnn.
If the tty is not in 8 bit mode, other 8 bit characters
are printed by converting them to ASCII and using standout
mode. The shell never changes the 7/8 bit mode of the tty
and tracks user-initiated changes of 7/8 bit mode. NLS
users (or, 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.
OS variant support (+)
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 cur-
rent 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).
Signal handling
Login shells ignore interrupts when reading the file
~/.logout. The shell ignores quit signals unless started
with -q. Login shells catch the terminate signal, but
non-login shells inherit the terminate behavior from their
parents. Other signals have the values which the shell
inherited from its parent.
In shell scripts, the shell's handling of interrupt and
terminate signals can be controlled with onintr, and its
handling of hangups can be controlled with hup and nohup.
The shell exits on a hangup (see also the logout shell
variable). By default, the shell's children 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.
Terminal management (+)
The shell uses three different sets of terminal (``tty'')
modes: `edit', used when editing, `quote', used when quot-
ing literal characters, and `execute', used when executing
commands. The shell holds some settings in each mode con-
stant, 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 t