csh - a shell (command interpreter) with C-like syntax
csh [-bcefimnstvVxX] [argument ...]
csh [-l]
csh is a command language interpreter incorporating a history mechanism
(see History substitutions), job control facilities (see
Jobs), interactive
file name and user name completion (see File name
completion), and a
C-like syntax. It is used both as an interactive login
shell and a shell
script command processor.
Argument list processing [Toc] [Back]
If the first argument (argument 0) to the shell is a dash
(`-'), then
this is a login shell. A login shell also can be specified
by invoking
the shell with the -l flag as the only argument.
The rest of the flag arguments are interpreted as follows:
-b This flag 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 (single) following argument which must
be present. Any remaining arguments are placed in
argv.
-e The shell exits if any invoked command terminates abnormally or
yields a non-zero exit status.
-f The shell will start faster, because it will neither
search for
nor execute commands from the file .cshrc in the invoker's home
directory.
-i The shell is interactive and prompts for its top-level input, even
if it appears not to 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 Read .cshrc, regardless of its owner and group. This
option is
dangerous and should only be used by su(1).
-n Commands are parsed, but not executed. This aids in
syntactic
checking of shell scripts. When used interactively,
the shell can
be terminated by pressing control-D (end-of-file
character), since
exit will not work.
-s Command input is taken from the standard input.
-t A single line of input is read and executed. A backslash (`')
may be used to escape the newline at the end of this
line and continue
onto another line.
-v Causes the verbose variable to be set, with the effect that command
input is echoed after history substitution.
-x Causes the echo variable to be set, so that commands
are echoed
immediately before execution.
-V Causes the verbose variable to be set even before
.cshrc is executed.
-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 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 will
execute such a
``standard'' shell if the first character of a script is not
a hash mark
(`#'); i.e., if the script does not start with a comment.
Remaining arguments
initialize the variable argv.
An instance of csh begins by executing commands from the
file
/etc/csh.cshrc and, if this is a login shell,
/etc/csh.login. It then
executes commands from .cshrc in the home directory of the
invoker, and,
if this is a login shell, the file .login in the same location. It is
typical for users on CRTs to put the command stty crt in
their .login
file, and to also invoke tset(1) there.
In the normal case, the shell will begin reading commands
from the terminal,
prompting with `% .' Processing of arguments and the
use of the
shell to process files containing command scripts will be
described later.
The shell repeatedly performs the following actions: a line
of command
input is read and broken into ``words''. This sequence of
words is
placed on the command history list and parsed. Finally each
command in
the current line is executed.
When a login shell terminates it executes commands from the
files .logout
in the user's home directory and /etc/csh.logout.
Lexical structure [Toc] [Back]
The shell splits input lines into words at blanks and tabs
with the following
exceptions. The characters `&', `|', `;', `<', `>',
`(', and `)'
form separate words. If doubled in `&&', `||', `<<', or
`>>', these
pairs form single words. These parser metacharacters may be
made part of
other words, or have their special meaning prevented, by
preceding them
with a backslash (`'). A newline preceded by a `' is equivalent to a
blank.
Strings enclosed in matched pairs of quotations, `'', ``',
or `"', form
parts of a word; metacharacters in these strings, including
blanks and
tabs, do not form separate words. These quotations have semantics to be
described later. Within pairs of `'' or `"' characters, a
newline preceded
by a `' gives a true newline character.
When the shell's input is not a terminal, the character `#'
introduces a
comment that continues to the end of the input line. This
special meaning
is prevented when preceded by `' and in quotations using
``', `'',
and `"'.
Commands [Toc] [Back]
A simple command is a sequence of words, the first of which
specifies the
command to be executed. A simple command or a sequence of
simple commands
separated by `|' characters forms a pipeline. The
output of each
command in a pipeline is connected to the input of the next.
Sequences
of pipelines may be separated by `;', and are then executed
sequentially.
A sequence of pipelines may be executed without immediately
waiting for
it to terminate by following it with a `&'.
Any of the above may be placed in `(' `)' to form a simple
command (that
may be a component of a pipeline, for example). It is also
possible to
separate pipelines with `||' or `&&' showing, as in the C
language, that
the second is to be executed only if the first fails or succeeds, respectively.
(See Expressions.)
Jobs [Toc] [Back]
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 that looks like:
[1] 1234
showing 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 ^Z
(control-Z), which sends a SIGSTOP signal to the current
job. The shell
will then normally show that the job has been ``Stopped'',
and print another
prompt. You can then manipulate the state of this
job, putting it
in the background with the bg command, or run some other
commands and
eventually bring the job back into the foreground with the
fg command. A
^Z takes effect immediately and is like an interrupt in that
pending output
and unread input are discarded when it is typed. There
is another
special key ^Y that does not generate a SIGSTOP signal until
a program
attempts to read(2) it. This request can usefully be typed
ahead when
you have prepared some commands for a job that you wish to
stop after it
has read them.
A job being run in the background will stop 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 number 1 back into the
foreground.
Similarly, saying %1 & resumes job number 1 in the background. Jobs can
also be named by prefixes of the string typed in to start
them, if these
prefixes are unambiguous; thus %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, which
specifies 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
about jobs, the current job is marked with a `+' and the
previous job
with a `-'. The abbreviation `%+' refers to the current job
and `%-'
refers to the previous job. For close analogy with the syntax of the
history mechanism (described below), `%%' is also a synonym
for the current
job.
The job control mechanism requires that the stty(1) option
new be set.
It is an artifact from a new implementation of the tty driver that allows
generation of interrupt characters from the keyboard to tell
jobs to
stop. See stty(1) for details on setting options in the new
tty driver.
Status reporting [Toc] [Back]
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 that 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 try to exit again immediately,
the shell will
not warn you a second time, and the suspended jobs will be
terminated.
File name completion [Toc] [Back]
When the file name completion feature is enabled by setting
the shell
variable filec (see set), csh will interactively complete
file names and
user names from unique prefixes when they are input from the
terminal
followed by the escape character (the escape key, or control-[). For example,
if the current directory looks like
DSC.OLD bin cmd lib xmpl.c
DSC.NEW chaosnet cmtest mail xmpl.o
bench class dev mbox xmpl.out
and the input is
% vi ch<escape>
csh will complete the prefix ``ch'' to the only matching
file name
``chaosnet'', changing the input line to
% vi chaosnet
However, given
% vi D<escape>
csh will only expand the input to
% vi DSC.
and will sound the terminal bell to indicate that the expansion is incomplete,
since there are two file names matching the prefix
`D'.
If a partial file name is followed by the end-of-file character (usually
control-D), then, instead of completing the name, csh will
list all file
names matching the prefix. For example, the input
% vi D<control-D>
causes all files beginning with `D' to be listed:
DSC.NEW DSC.OLD
while the input line remains unchanged.
The same system of escape and end-of-file can also be used
to expand partial
user names, if the word to be completed (or listed) begins with the
tilde character (`~'). For example, typing
cd ~ro<escape>
may produce the expansion
cd ~root
The use of the terminal bell to signal errors or multiple
matches can be
inhibited by setting the variable nobeep.
Normally, all files in the particular directory are candidates for name
completion. Files with certain suffixes can be excluded
from consideration
by setting the variable fignore to the list of suffixes
to be ignored.
Thus, if fignore is set by the command
% set fignore = (.o .out)
then typing
% vi x<escape>
would result in the completion to
% vi xmpl.c
ignoring the files "xmpl.o" and "xmpl.out". However, if the
only completion
possible requires not ignoring these suffixes, then
they are not ignored.
In addition, fignore does not affect the listing of
file names by
control-D. All files are listed regardless of their suffixes.
Substitutions [Toc] [Back]
We now describe the various transformations the shell performs on the input
in the order in which they occur.
History substitutions [Toc] [Back]
History substitutions place words from previous command input as portions
of new commands, 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 `!' and may
begin anywhere
in the input stream (with the proviso that they do not
nest). This `!'
may be preceded by a `' to prevent its special meaning; for
convenience,
a `!' character 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.)
Any input line that contains history substitution is
echoed on the
terminal before it is executed as it would have been typed
without history
substitution.
Commands input from the terminal that consist of one or more
words are
saved on the history list. The history substitutions reintroduce sequences
of words from these saved commands into the input
stream. The
size of the history list is controlled by the history variable; the previous
command is always retained, regardless of the value of
the history
variable. Commands are numbered sequentially from 1.
For definiteness, consider the following output from the
history command:
9 write michael
10 ex write.c
11 cat oldwrite.c
12 diff *write.c
The commands are shown with their event numbers. It is not
usually necessary
to use event numbers, but the current event number
can be made
part of the prompt by placing a `!' in the prompt string.
With the current event 13 we can refer to previous events by
event number
`!11', relatively as in `!-2' (referring to the same event),
by a prefix
of a command word as in `!d' for event 12 or `!wri' for
event 9, or by a
string contained in a word in the command as in `!?mic?' also referring
to event 9. These forms, without further change, simply
reintroduce the
words of the specified events, each separated by a single
blank. As a
special case, `!!' refers to the previous command; thus `!!'
alone is a
redo.
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 first (command) word
n n'th argument
^ first argument; i.e., `1'
$ last argument
% word matched by (immediately preceding) ?s?
search
x-y range of words
-y abbreviates `0-y'
* abbreviates `^-$', or nothing if only 1 word
in event
x* abbreviates `x-$'
x- like `x*' but omitting word `$'
The `:' separating the event specification from the word
designator can
be omitted if the argument selector begins with a `^', `$',
`*', `-', or
`%'. After the optional word designator, a sequence of modifiers can be
placed, each preceded by a `:'. The following modifiers are
defined:
h Remove a trailing pathname component, leaving
the head.
r Remove a trailing `.xxx' component, leaving
the root name.
e Remove all but the extension `.xxx' part.
s/l/r/ Substitute l for r.
t Remove all leading pathname components, leaving the tail.
& Repeat the previous substitution.
g Apply the change once on each word, prefixing
the above;
e.g., `g&'.
a Apply the change as many times as possible on
a single
word, prefixing the above. It can be used together with
`g' to apply a substitution globally.
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.
Unless preceded by a `g' the change is applied only to the
first modifiable
word. With substitutions, it is an error for no word
to be applicable.
The left-hand side of substitutions are not regular expressions in the
sense of the editors, but instead strings. Any character
may be used as
the delimiter in place of `/'; a `' quotes the delimiter into the l and
r strings. The character `&' in the right-hand side is replaced by the
text from the left. A `' also quotes `&'. A NULL l (`//')
uses the
previous string either from an l or from a contextual scan
string s in
`!?s newline follows immediately as may the trailing `?'
in a contextual scan.
A history reference may be given without an event specification; e.g.,
`!$'. Here, the reference is to the previous command unless
a previous
history reference occurred on the same line in which case
this form repeats
the previous reference. Thus ``!?foo?^ !$'' gives the
first and
last arguments from the command matching ``?foo?''.
A special abbreviation of a history reference occurs when
the first nonblank
character of an input line is a `^'. This is equivalent to
``!:s^'' providing a convenient shorthand for substitutions
on the text
of the previous line. Thus ^lb^lib fixes the spelling of
``lib'' in the
previous command. Finally, a history substitution may be
surrounded with
`{' and `}' if necessary to insulate it from the characters
that follow.
Thus, after ls -ld ~paul we might do !{l}a to do ls -ld
~paula, while !la
would look for a command starting with ``la''.
Quotations with ' and "
The quotation of strings by `'' and `"' can be used to prevent all or
some of the remaining substitutions. Strings enclosed in
`'' are prevented
from any further interpretation. Strings enclosed in
`"' may be
expanded as described below.
In both cases the resulting text becomes (all or part of) a
single word;
only in one special case (see Command Substitution below)
does a `"'
quoted string yield parts of more than one word; `'' quoted
strings never
do.
Alias substitution [Toc] [Back]
The shell maintains a list of aliases that can be established, displayed
and modified by the alias and unalias commands. After a
command line is
scanned, it is parsed into distinct commands and the first
word of each
command, left-to-right, is checked to see if it has an
alias. If it
does, then the text that is the alias for that command is
reread with the
history mechanism available as though that command were the
previous input
line. The resulting words replace the command and argument list. If
no reference is made to the history list, then the argument
list is left
unchanged.
Thus if the alias for ``ls'' is ``ls -l'', the command ls
/usr would map
to ls -l /usr, the argument list here being undisturbed.
Similarly, if
the alias for ``lookup'' was ``grep !^ /etc/passwd'' then
lookup bill
would map to grep bill /etc/passwd.
If an alias is found, the word transformation of the input
text is performed
and the aliasing process begins again on the reformed
input line.
Looping is prevented if the first word of the new text is
the same as the
old by flagging it to prevent further aliasing. Other loops
are detected
and cause an error.
Note that the mechanism allows aliases to introduce parser
metasyntax.
Thus, we can alias print 'pr* | lpr' to make a command that
pr's its
arguments to the line printer.
Variable substitution [Toc] [Back]
The shell maintains a set of variables, each of which has as
value a list
of zero or more words. Some of these 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.
The values of variables may be displayed and changed by using the set and
unset commands. Of the variables referred to by the shell a
number 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 that
causes command input to be echoed. The setting of this
variable results
from the -v command-line option.
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 additional words of
multiword values
are ignored.
After the input line is aliased and parsed, and before each
command is
executed, variable substitution is performed, keyed by `$'
characters.
This expansion can be prevented by preceding the `$' with a
`' except
within double quotes (`"'), where it always occurs, and
within single
quotes (`''), where it never occurs. Strings quoted by
backticks (` `)
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 that is not set.
$name
${name}
Are replaced by the words of the value of
variable name,
each separated by a blank. Braces insulate
name from following
characters that 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 here).
$name[selector]
${name[selector]}
May be used to select only some of the words
from the value
of name. The selector is subjected to `$'
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 number 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.
$#name
${#name}
Gives the number of words in the variable.
This is useful
for later use in a ``$argv[selector]''.
$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[*]''.
The modifiers `:e', `:h', `:t', `:r', `:q', and `:x' may be
applied to
the substitutions above as may `:gh', `:gt', and `:gr'. If
braces `{'
`}' appear in the command form then the modifiers must appear within the
braces. The current implementation allows only one `:' modifier on each
`$' expansion.
The following substitutions may 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.
$$ Substitute the (decimal) process number of the
(parent)
shell. Do NOT use this mechanism for generating temporary
file names; see mktemp(1) instead.
$! Substitute the (decimal) process number of the
last background
process started by this shell.
$< Substitutes a line from the standard input,
with no further
interpretation. It can be used to read from
the keyboard
in a shell script.
Command and filename substitution [Toc] [Back]
The remaining substitutions, command and filename substitution, are applied
selectively to the arguments of built-in commands. By
selectively,
we mean that portions of expressions which are not evaluated
are not subjected
to these expansions. For commands that 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 [Toc] [Back]
Command substitution is shown by a command enclosed in ``'.
The output
from such a command is normally broken into separate words
at blanks,
tabs, and newlines, with null words being discarded; this
text then replaces
the original string. Within double quotes (`"'), only newlines
force new words; blanks and tabs are preserved.
In any case, the single final newline does not force a new
word. Note
that it is thus possible for a command substitution to yield
only part of
a word, even if the command outputs a complete line.
Filename substitution [Toc] [Back]
If a word contains any of the characters `*', `?', `[', or
`{', or begins
with the character `~', then that word is a candidate for
filename substitution,
also known as ``globbing''. This word is then
regarded as a
pattern, and replaced with an alphabetically sorted list of
file names
that match the pattern. In a list of words specifying filename substitution
it is an error for no pattern to match an existing file
name, but it
is not required for each pattern to match. Only the
metacharacters `*',
`?', and `[' imply pattern matching, the characters `~' and
`{' being
more akin to abbreviations.
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 (inclusive).
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 variable home. 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 does not appear at the beginning of a
word, it is left undisturbed.
The metanotation ``a{b,c,d}e'' is a shorthand for ``abe ace
ade''. Left
to right order is preserved, with results of matches being
sorted separately
at a low level to preserve this order. This construct may be
nested. Thus, ``~source/s1/{oldls,ls}.c'' expands to
``/usr/source/s1/oldls.c /usr/source/s1/ls.c'' without
chance of error if
the home directory for ``source'' is ``/usr/source''. Similarly
``../{memo,*box}'' might expand to ``../memo ../box
../mbox''. (Note
that ``memo'' was not sorted with the results of the match
to ``*box''.)
As a special case `{', `}', and `{}' are passed undisturbed.
Input/output
The standard input and the 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 that is
identical to
word. word is not subjected to variable, command, or filename
substitution, and each input line is compared to word
before any substitutions are done on the input
line. Unless
a quoting `', `"', `'' or ``' appears in
word, variable
and command substitution is performed on
the intervening
lines, allowing `' to quote `$', `' and
``'. Commands
that 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 that is given to the command as
its standard
input.
> name
>! name
>& name
>&! name
The file name is used as the standard output.
If the file
does not exist then it is created; if the file
exists, it
is truncated; its previous contents are lost.
If the 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. Here, the `!'
forms can be
used to suppress this check.
The forms involving `&' route the standard error 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
Uses file name as the standard output; like
`>' but places
output at the end of the file. If the variable noclobber
is set, then it is an error for the file not
to exist unless
one of the `!' forms is given. Otherwise
similar to
`>'.
A command receives the environment in which the shell was
invoked as modified
by the input-output parameters and the presence of the
command in a
pipeline. Thus, unlike some previous shells, commands run
from a file of
shell commands have no access to the text of the commands by
default; instead
they receive the original standard input of the shell.
The `<<'
mechanism should be used to present inline data. This permits shell command
scripts to function as components of pipelines and allows the shell
to block read its input. Note that the default standard input for a command
run detached is not modified to be the empty file
/dev/null; instead
the standard input remains as 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
above).
The standard error output may be directed through a pipe
with the standard
output. Simply use the form `|&' instead of just `|'.
Expressions [Toc] [Back]
Several of the built-in commands (to be described later)
take expressions,
in which the operators are similar to those of C,
with the same
precedence, but with the opposite grouping: right to left.
These expressions
appear in the @, exit, if, and while commands. The
following operators
are available:
|| && | ^ & == != =~ !~ <= >= < > << >> +
- * / %
! ~ ( )
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
pattern (containing, e.g., *'s, ?'s, and instances of
``[...]'') against
which the left-hand operand is matched. This reduces the
need for use of
the switch statement in shell scripts when all that is really needed is
pattern matching.
Strings that begin with `0' are considered octal numbers.
Null or missing
arguments are considered `0'. The results of all expressions are
strings, which represent decimal numbers. It is important
to note that
no two components of an expression can appear in the same
word; except
when adjacent to components of expressions that are syntactically significant
to the parser (`&', `|', `<', `>', `(', and `)'), they
should be
surrounded by spaces.
Also available in expressions as primitive operands are command executions
enclosed in `{' and `}' and file enquiries of the form
-l name
where l is one of:
r read access
w write access
x execute access
e existence
o ownership
z zero size
f plain file
d directory
The specified name is command and filename expanded and then
tested to
see if it has the specified relationship to the real user.
If the file
does not exist or is inaccessible then all enquiries return
false, i.e.,
`0'. 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 an expression and the variable
status examined.
Control flow [Toc] [Back]
The shell contains several commands that 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, because of 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 goto's will succeed on non-seekable inputs.)
Built-in commands [Toc] [Back]
Built-in commands are executed within the shell. If a
built-in command
occurs as any component of a pipeline except the last then
it is executed
in a sub-shell.
alias
alias name
alias name wordlist
The first form prints all aliases. The second
form prints
the alias for name. The final form assigns
the specified
wordlist as the alias of name; wordlist is
command and
filename substituted. name is not allowed to
be ``alias''
or ``unalias''.
alloc Shows the amount of dynamic memory acquired,
broken down
into used and free memory. With an argument
shows the number
of free and used blocks in each size category. The
categories start at size 8 and double at each
step. This
command's output may vary across system types,
since systems
other than the VAX may use a different
memory allocator.
bg
bg %job ...
Puts the current or specified jobs into the
background,
continuing them if they were stopped.
break Causes execution to resume after the end of
the nearest enclosing
foreach or while. The remaining commands on the
current line are executed. Multi-level breaks
are thus
possible by writing them all on one line.
breaksw
Causes a break from a switch, resuming after
the endsw.
case label:
A label in a switch statement as discussed below.
cd
cd name
chdir
chdir name
Change the shell's working directory to directory name. If
no argument is given then change to the home
directory of
the user. If name is not found as a subdirectory of the
current directory (and does not begin with
`/', `./' or
`../'), then each component of the variable
cdpath is
checked to see if it has a subdirectory name.
Finally, if
all else fails but name is a shell variable
whose value begins
with `/', then this is tried to see if it
is a directory.
continue
Continue execution of the nearest enclosing
while or
foreach. The rest of the commands on the current line are
executed.
default:
Labels the default case in a switch statement.
The default
should come after all case labels.
dirs Prints the directory stack; the top of the
stack is at the
left, the first directory in the stack being
the current
directory.
echo wordlist
echo -n wordlist
The specified words are written to the shell's
standard
output, separated by spaces, and terminated
with a newline
unless the -n option is specified.
else
end
endif
endsw See the description of the foreach, if,
switch, and while
statements below.
eval arg ...
(As in sh(1).) The arguments are read as input
to the shell
and the resulting command(s) executed in the
context of the
current shell. This is usually used to execute commands
generated as the result of command or variable
substitution,
since parsing occurs before these substitutions. See
tset(1) for an example of using eval.
exec command
The specified command is executed in place of
the current
shell.
exit
exit (expr)
The shell exits either with the value of the
status variable
(first form) or with the value of the
specified expr
(second form).
fg
fg %job ...
Brings the current or specified jobs into the
foreground,
continuing them if they were stopped.
foreach name (wordlist)
...
end The variable name is successively set to each
member of
wordlist and the sequence of commands between
this command
and the matching end are executed. (Both
foreach and end
must appear alone on separate lines.) The
built-in command
continue may be used to continue the loop prematurely and
the built-in command break to terminate it
prematurely.
When this command is read from the terminal,
the loop is
read once prompting with `?' before any statements in the
loop are executed. If you make a mistake typing in a loop
at the terminal you can rub it out.
glob wordlist
Like echo but no `' escapes are recognized and
words are
delimited by NUL characters in the output.
Useful for programs
that wish to use the shell to filename
expand a list
of words.
goto word
The specified word is filename and command expanded to
yield a string of the form `label'. The shell
rewinds its
input as much as possible and searches for a
line of the
form ``label:'', possibly preceded by blanks
or tabs. Execution
continues after the specified line.
hashstat
Print a statistics line showing how effective
the internal
hash table has been at locating commands (and
avoiding
exec's). An exec is attempted for each component of the
path where the hash function indicates a possible hit, and
in each component that does not begin with a
`/'.
history
history n
history -r n
history -h n
Displays the history event list; if n is given, only the n
most recent events are printed. The -r option
reverses the
order of printout to be most recent first instead of oldest
first. The -h option causes the history list
to be printed
without leading numbers. This format produces
files suitable
for sourcing using the -h option to
source.
if (expr) command
If the specified expression evaluates to true,
then the
single command with arguments is executed.
Variable substitution
on command happens early, at the
same time it
does for the rest of the if command. command
must be a
simple command, not a pipeline, a command
list, or a parenthesized
command list. Input/output redirection occurs
even if expr is false, i.e., when command is
not executed
(this is a bug).
if (expr) then
...
else if (expr2) then
...
else
...
endif If the specified expr is true then the commands up to the
first else are executed; otherwise if expr2 is
true then
the commands up to the second else are executed, etc. Any
number of else-if pairs are possible; only one
endif is
needed. The else part is likewise optional.
(The words
else and endif must appear at the beginning of
input lines;
the if must appear alone on its input line or
after an
else.)
jobs
jobs -l
Lists the active jobs; the -l option lists
process IDs in
addition to the normal information.
kill %job
kill [-s signal_name] pid
kill -sig pid ...
kill -l [exit_status]
Sends either the SIGTERM (terminate) signal or
the specified
signal to the specified jobs or processes. Signals
are either given by number or by names (as
given in
<signal.h>, stripped of the prefix ``SIG'').
The signal
names are listed by ``kill -l''; if an
exit_status is specified,
only the corresponding signal name will
be written.
There is no default; just saying ``kill'' does
not send a
signal to the current job. If the signal being sent is
SIGTERM (terminate) or SIGHUP (hangup), then
the job or
process will be sent a SIGCONT (continue) signal as well.
limit
limit resource
limit resource maximum-use
limit -h
limit -h resource
limit -h resource maximum-use
Limits the consumption by the current process
and each process
it creates to not individually exceed
maximum-use on
the specified resource. If no maximum-use is
given, then
the current limit is printed; if no resource
is given, then
all limitations are given. If the -h flag is
given, the
hard limits are used instead of the current
limits. The
hard limits impose a ceiling on the values of
the current
limits. Only the superuser may raise the hard
limits, but
a user may lower or raise the current limits
within the legal
range.
Resources controllable currently include:
cputime the maximum number of CPU-seconds to be used
by each process.
filesize the largest single file (in
bytes) that can
be created.
datasize the maximum growth of the data+stack region
via sbrk(2) beyond the end of
the program
text.
stacksize the maximum size of the automatically-extended
stack region.
coredumpsize the size of the largest core
dump (in bytes)
that will be created.
memoryuse the maximum size (in bytes) to
which a process's
resident set size (RSS)
may grow.
memorylocked The maximum size (in bytes)
which a process
may lock into memory using the
mlock(2) function.
maxproc The maximum number of simultaneous processes
for this user ID.
openfiles The maximum number of simultaneous open files
for this user ID.
vmemoryuse the maximum size (in bytes) to
which a process's
total size may grow.
The maximum-use may be given as a (floating
point or integer)
number followed by a scale factor. For
all limits
other than cputime the default scale is `k' or
``kilobytes'' (1024 bytes); a scale factor of
`m' or
``megabytes'' may also be used. For cputime
the default
scale is ``seconds''; a scale factor of `m'
for minutes or
`h' for hours, or a time of the form ``mm:ss''
giving minutes
and seconds also may be used.
For both resource names and scale factors, unambiguous prefixes
of the names suffice.
login Terminate a login shell, replacing it with an
instance of
/usr/bin/login. This is one way to log off,
included for
compatibility with sh(1).
logout Terminate a login shell. Especially useful if
ignoreeof is
set.
nice
nice +number
nice command
nice +number command
The first form sets the scheduling priority
for this shell
to 4. The second form sets the priority to
the given
number. The final two forms run command at
priority 4 and
number respectively. The greater the number,
the less CPU
the process will get. The superuser may specify negative
priority by using ``nice -number ...''.
command is always
executed in a sub-shell, and the restrictions
placed on
commands in simple if statements apply.
nohup
nohup command
The first form can be used in shell scripts to
cause
hangups to be ignored for the remainder of the
script. The
second form causes the specified command to be
run with
hangups ignored. All processes detached with
`&' are effectively
nohup'ed.
notify
notify %job ...
Causes the shell to notify the user asynchronously when the
status of the current or specified jobs
change; normally
notification is presented before a prompt.
This is automatic
if the shell variable notify is set.
onintr
onintr -
onintr label
Control the action of the shell on interrupts.
The first
form restores the default action of the shell
on interrupts,
which is to terminate shell scripts or
to return to
the terminal command input level. The second
form onintr -
causes all interrupts to be ignored. The final form causes
the shell to execute a goto label when an interrupt is received
or a child process terminates because
it was interrupted.
In any case, if the shell is running detached
and interrupts
are being ignored, all forms of onintr
have no meaning
and interrupts continue to be ignored by
the shell and
all invoked commands. Finally, onintr statements are ignored
in the system startup files where interrupts are disabled
(/etc/csh.cshrc, /etc/csh.login).
popd
popd +n
Pops the directory stack, returning to the new
top directory.
With an argument ``+n'' discards the n'th
entry in the
stack. The members of the directory stack are
numbered
from the top starting at 0.
pushd
pushd name
pushd +n
With no arguments, pushd exchanges the top two
elements of
the directory stack. Given a name argument,
pushd changes
to the new directory (ala cd) and pushes the
old current
working directory (as in cwd) onto the directory stack.
With a numeric argument, pushd rotates the
n'th argument of
the directory stack around to be the top element and
changes to it. The members of the directory
stack are numbered
from the top starting at 0.
rehash Causes the internal hash table of the contents
of the directories
in the path variable to be recomputed. This is
needed if new commands are added to directories in the path
while you are logged in. This should only be
necessary if
you add commands to one of your own directories, or if a
systems programmer changes the contents of a
system directory.
repeat count command
The specified command, which is subject to the
same restrictions
as the command in the one line if
statement
above, is executed count times. I/O redirections occur exactly
once, even if count is 0.
set
set name
set name=word
set name[index]=word
set name=(wordlist)
The first form of the command shows the value
of all shell
variables. Variables that have other than a
single word as
their value print as a parenthesized word
list. The second
form sets name to the null string. The third
form sets
name to the single word. The fourth form sets
the index'th
component of name to word; this component must
already exist.
The final form sets name to the list of
words in
wordlist. The value is always command and
filename expanded.
These arguments may be repeated to set multiple values in a
single set command. Note however, that variable expansion
happens for all arguments before any setting
occurs.
setenv
setenv name
setenv name value
The first form lists all current environment
variables. It
is equivalent to printenv(1). The last form
sets the value
of environment variable name to be value, a
single string.
The second form sets name to an empty string.
The most
commonly used environment variables USER,
TERM, and PATH
are automatically imported to and exported
from the csh
variables user, term, and path; there is no
need to use
setenv for these.
shift
shift variable
The members of argv are shifted to the left,
discarding
argv[1]. It is an error for argv not to be
set or to have
less than one word as value. The second form
performs the
same function on the specified variable.
source name
source -h name
The shell reads commands from name. source
commands may be
nested; if they are nested too deeply t
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