csh(1) UNIX System V(User Environment Utilities) csh(1)
NAME
csh - shell command interpreter with a C-like syntax
SYNOPSIS
csh [ -bcefinstvVxX ] [ argument . . . ]
DESCRIPTION
csh, the C shell, is a command interpreter with a syntax reminiscent of
the C language. It provides a number of convenient features for
interactive use that are not available with the standard (Bourne) shell,
including filename completion, command aliasing, history substitution,
job control, and a number of built-in commands. As with the standard
shell, the C shell provides variable, command and filename substitution.
Initialization and Termination
When first started, the C shell normally performs commands from the
.cshrc file in your home directory, provided that it is readable and you
either own it or your real group ID matches its group ID. If the shell is
invoked with a name that starts with `-', as when started by login(1),
the shell runs as a login shell. In this case, after executing commands
from the .cshrc file, the shell executes commands from the .login file in
your home directory; the same permission checks as those for .cshrc are
applied to this file. Typically, the .login file contains commands to
specify the terminal type and environment.
As a login shell terminates, it performs commands from the .logout file
in your home directory; the same permission checks as those for .cshrc
are applied to this file.
Interactive Operation
After startup processing is complete, an interactive C shell begins
reading commands from the terminal, prompting with hostname% (or
hostname# for the privileged user). The shell then repeatedly performs
the following actions: a line of command input is read and broken into
words. This sequence of words is placed on the history list and then
parsed, as described under USAGE, below. Finally, the shell executes
each command in the current line.
Noninteractive Operation
When running noninteractively, the shell does not prompt for input from
the terminal. A noninteractive C shell can execute a command supplied as
an argument on its command line, or interpret commands from a script.
The following options are available:
-b Force a break from option processing. Subsequent command-line
arguments are not interpreted as C shell options. This allows the
passing of options to a script without confusion. The shell does
not run a set-user-ID script unless this option is present.
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-c Read commands from the first filename argument (which must be
present). Remaining arguments are placed in argv, the argument-
list variable.
-e Exit if a command terminates abnormally or yields a nonzero exit
status.
-f Fast start. Read neither the .cshrc file, nor the .login file (if a
login shell) upon startup.
-i Forced interactive. Prompt for command-line input, even if the
standard input does not appear to be a terminal (character-special
device).
-n Parse (interpret), but do not execute commands. This option can be
used to check C shell scripts for syntax errors.
-s Take commands from the standard input.
-t Read and execute a single command line. A `\' (backslash) can be
used to escape each newline for continuation of the command line
onto subsequent input lines.
-v Verbose. Set the verbose predefined variable; command input is
echoed after history substitution (but before other substitutions)
and before execution.
-V Set verbose before reading .cshrc.
-x Echo. Set the echo variable; echo commands after all substitutions
and just before execution.
-X Set echo before reading .cshrc.
Except with the options -c, -i, -s or -t, the first nonoption argument is
taken to be the name of a command or script. It is passed as argument
zero, and subsequent arguments are added to the argument list for that
command or script.
USAGE
Filename Completion
When enabled by setting the variable filec, an interactive C shell can
complete a partially typed filename or user name. When an unambiguous
partial filename is followed by an ESC character on the terminal input
line, the shell fills in the remaining characters of a matching filename
from the working directory.
If a partial filename is followed by the EOF character (usually typed as
CTRL-d), the shell lists all filenames that match. It then prompts once
again, supplying the incomplete command line typed in so far.
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When the last (partial) word begins with a tilde (~), the shell attempts
completion with a user name, rather than a file in the working directory.
The terminal bell signals errors or multiple matches; this can be
inhibited by setting the variable nobeep. You can exclude files with
certain suffixes by listing those suffixes in the variable fignore. If,
however, the only possible completion includes a suffix in the list, it
is not ignored. fignore does not affect the listing of filenames by the
EOF character.
Lexical Structure
The shell splits input lines into words at space and tab characters,
except as noted below. The characters &, |, ;, <, >, (, and ) form
separate words; if paired, the pairs form single words. These shell
metacharacters can be made part of other words, and their special meaning
can be suppressed by preceding them with a `\' (backslash). A newline
preceded by a \ is equivalent to a space character.
In addition, a string enclosed in matched pairs of single-quotes ('),
double-quotes ("), or backquotes (`), forms a partial word;
metacharacters in such a string, including any space or tab characters,
do not form separate words. Within pairs of backquote (`) or double-
quote (") characters, a newline preceded by a `\' (backslash) gives a
true newline character. Additional functions of each type of quote are
described, below, under Variable Substitution, Command Substitution, and
Filename Substitution.
When the shell's input is not a terminal, the character # introduces a
comment that continues to the end of the input line. Its special meaning
is suppressed when preceded by a \ or enclosed in matching quotes.
Command Line Parsing
A simple command is composed of a sequence of words. The first word
(that is not part of an I/O redirection) specifies the command to be
executed. A simple command, or a set of simple commands separated by |
or |& characters, forms a pipeline. With |, the standard output of the
preceding command is redirected to the standard input of the command that
follows. With |&, both the standard error and the standard output are
redirected through the pipeline.
Pipelines can be separated by semicolons (;), in which case they are
executed sequentially. Pipelines that are separated by && or || form
conditional sequences in which the execution of pipelines on the right
depends upon the success or failure, respectively, of the pipeline on the
left.
A pipeline or sequence can be enclosed within parentheses `( )' to form a
simple command that can be a component in a pipeline or sequence.
A sequence of pipelines can be executed asynchronously, or in the
background by appending an `&'; rather than waiting for the sequence to
finish before issuing a prompt, the shell displays the job number (see
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Job Control, below) and associated process IDs, and prompts immediately.
History Substitution
History substitution allows you to use words from previous command lines
in the command line you are typing. This simplifies spelling corrections
and the repetition of complicated commands or arguments. Command lines
are saved in the history list, the size of which is controlled by the
history variable. The most recent command is retained in any case. A
history substitution begins with a ! (although you can change this with
the histchars variable) and may occur anywhere on the command line;
history substitutions do not nest. The ! can be escaped with \ to
suppress its special meaning.
Input lines containing history substitutions are echoed on the terminal
after being expanded, but before any other substitutions take place or
the command gets executed.
Event Designators
An event designator is a reference to a command-line entry in the history
list.
! Start a history substitution, except when followed by a space
character, tab, newline, = or (.
!! Refer to the previous command. By itself, this substitution
repeats the previous command.
!n Refer to command-line n .
!-n Refer to the current command-line minus n.
!str Refer to the most recent command starting with str.
!?str[?]
Refer to the most recent command containing str.
!{...}
Insulate a history reference from adjacent characters (if
necessary).
Word Designators
A `:' (colon) separates the event specification from the word
designator. It can be omitted if the word designator begins with a ^, $,
*, - or %. If the word is to be selected from the previous command, the
second ! character can be omitted from the event specification. For
instance, !!:1 and !:1 both refer to the first word of the previous
command, while !!$ and !$ both refer to the last word in the previous
command. Word designators include:
# The entire command line typed so far.
0 The first input word (command).
n The n'th argument.
^ The first argument, that is, 1.
$ The last argument.
% The word matched by (the most recent) ?s search.
x-y A range of words; -y abbreviates 0-y.
* All the arguments, or a null value if there is just one word
in the event.
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x* Abbreviates x-$.
x- Like x* but omitting word $.
Modifiers
After the optional word designator, you can add a sequence of one or more
of the following modifiers, each preceded by a :.
h Remove a trailing pathname component, leaving the head.
r Remove a trailing suffix of the form `.xxx', leaving the
basename.
e Remove all but the suffix.
s/l/r[/]
Substitute r for l.
t Remove all leading pathname components, leaving the tail.
& Repeat the previous substitution.
g Apply the change to the first occurrence of a match in each
word, by prefixing the above (for example, g&).
p Print the new command but do not execute it.
q Quote the substituted words, escaping further substitutions.
x Like q, but break into words at each space character, tab or
newline.
Unless preceded by a g, the modification is applied only to the first
string that matches l; an error results if no string matches.
The left-hand side of substitutions are not regular expressions, but
character strings. Any character can be used as the delimiter in place
of /. A backslash quotes the delimiter character. The character &, in
the right hand side, is replaced by the text from the left-hand-side. The
& can be quoted with a backslash. A null l uses the previous string
either from a l or from a contextual scan string s from !?s. You can
omit the rightmost delimiter if a newline immediately follows r; the
rightmost ? in a context scan can similarly be omitted.
Without an event specification, a history reference refers either to the
previous command, or to a previous history reference on the command line
(if any).
Quick Substitution
^l^r[^]
This is equivalent to the history substitution: !:s^l^r[^].
Aliases
The C shell maintains a list of aliases that you can create, display, and
modify using the alias and unalias commands. The shell checks the first
word in each command to see if it matches the name of an existing alias.
If it does, the command is reprocessed with the alias definition
replacing its name; the history substitution mechanism is made available
as though that command were the previous input line. This allows history
substitutions, escaped with a backslash in the definition, to be replaced
with actual command-line arguments when the alias is used. If no history
substitution is called for, the arguments remain unchanged.
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Aliases can be nested. That is, an alias definition can contain the name
of another alias. Nested aliases are expanded before any history
substitutions is applied. This is useful in pipelines such as
alias lm 'ls -l \!* | more'
which when called, pipes the output of ls(1V) through more(1).
Except for the first word, the name of the alias may not appear in its
definition, nor in any alias referred to by its definition. Such loops
are detected, and cause an error message.
I/O Redirection
The following metacharacters indicate that the subsequent word is the
name of a file to which the command's standard input, standard output, or
standard error is redirected; this word is variable, command, and
filename expanded separately from the rest of the command.
< Redirect the standard input.
<<word Read the standard input, up to a line that is identical
with word, and place the resulting lines in a temporary
file. Unless word is escaped or quoted, variable and
command substitutions are performed on these lines. Then,
invoke the pipeline with the temporary file as its
standard input. word is not subjected to variable,
filename, or command substitution, and each line is
compared to it before any substitutions are performed by
the shell.
> >! >& >&!
Redirect the standard output to a file. If the file does
not exist, it is created. If it does exist, it is
overwritten; its previous contents are lost.
When set, the variable noclobber prevents destruction of
existing files. It also prevents redirection to terminals
and /dev/null, unless one of the ! forms is used. The &
forms redirect both standard output and the the standard
error (diagnostic output) to the file.
>> >>& >>! >>&!
Append the standard output. Like >, but places output at
the end of the file rather than overwriting it. If
noclobber is set, it is an error for the file not to
exist, unless one of the ! forms is used. The & forms
append both the standard error and standard output to the
file.
Variable Substitution
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The C shell maintains a set of variables, each of which is composed of a
name and a value. A variable name consists of up to 20 letters and
digits, and starts with a letter (the underscore is considered a letter).
A variable's value is a space-separated list of zero or more words.
To refer to a variable's value, precede its name with a `$'. Certain
references (described below) can be used to select specific words from
the value, or to display other information about the variable. Braces
can be used to insulate the reference from other characters in an input-
line word.
Variable substitution takes place after the input line is analyzed,
aliases are resolved, and I/O redirections are applied. Exceptions to
this are variable references in I/O redirections (substituted at the time
the redirection is made), and backquoted strings (see Command
Substitution).
Variable substitution can be suppressed by preceding the $ with a \,
except within double-quotes where it always occurs. Variable substitution
is suppressed inside of single-quotes. A $ is escaped if followed by a
space character, tab or newline.
Variables can be created, displayed, or destroyed using the set and unset
commands. Some variables are maintained or used by the shell. For
instance, the argv variable contains an image of the shell's argument
list. Of the variables used by the shell, a number are toggles; the
shell does not care what their value is, only whether they are set or
not.
Numerical values can be operated on as numbers (as with the @ built-in).
With numeric operations, an empty value is considered to be zero; the
second and subsequent words of multiword values are ignored. For
instance, when the verbose variable is set to any value (including an
empty value), command input is echoed on the terminal.
Command and filename substitution is subsequently applied to the words
that result from the variable substitution, except when suppressed by
double-quotes, when noglob is set (suppressing filename substitution), or
when the reference is quoted with the :q modifier. Within double-quotes,
a reference is expanded to form (a portion of) a quoted string; multiword
values are expanded to a string with embedded space characters. When the
:q modifier is applied to the reference, it is expanded to a list of
space-separated words, each of which is quoted to prevent subsequent
command or filename substitutions.
Except as noted below, it is an error to refer to a variable that is not
set.
$var
${var} These are replaced by words from the value of var, each
separated by a space character. If var is an environment
variable, its value is returned (but `:' modifiers and
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the other forms given below are not available).
$var[index]
${var[index]} These select only the indicated words from the value of
var. Variable substitution is applied to index, which may
consist of (or result in) a either single number, two
numbers separated by a `-', or an asterisk. Words are
indexed starting from 1; a `*' selects all words. If the
first number of a range is omitted (as with $argv[-2]), it
defaults to 1. If the last number of a range is omitted
(as with $argv[1-]), it defaults to $#var (the word
count). It is not an error for a range to be empty if the
second argument is omitted (or within range).
$#name
${#name} These give the number of words in the variable.
$0 This substitutes the name of the file from which command
input is being read. An error occurs if the name is not
known.
$n
${n} Equivalent to $argv[n].
$* Equivalent to $argv[*].
The modifiers :e, :h, :q, :r, :t and :x can be applied (see History
Substitution), as can :gh, :gt and :gr. If {} (braces) are used, then
the modifiers must appear within the braces. The current implementation
allows only one such modifier per expansion.
The following references may not be modified with : modifiers.
$?var
${?var}
Substitutes the string 1 if var is set or 0 if it is not set.
$?0 Substitutes 1 if the current input filename is known, or 0 if it is
not.
$$ Substitute the process number of the (parent) shell.
$< Substitutes a line from the standard input, with no further
interpretation thereafter. It can be used to read from the
keyboard in a C shell script.
Command and Filename Substitutions
Command and filename substitutions are applied selectively to the
arguments of built-in commands. Portions of expressions that are not
evaluated are not expanded. For non-built-in commands, filename
expansion of the command
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name is done separately from that of the argument list; expansion occurs
in a subshell, after I/O redirection is performed.
Command Substitution
A command enclosed by backquotes (`...`) is performed by a subshell. Its
standard output is broken into separate words at each space character,
tab and newline; null words are discarded. This text replaces the
backquoted string on the current command line. Within double-quotes, only
newline characters force new words; space and tab characters are
preserved. However, a final newline is ignored. It is therefore
possible for a command substitution to yield a partial word.
Filename Substitution
Unquoted words containing any of the characters *, ?, [ or {, or that
begin with ~, are expanded (also known as globbing) to an alphabetically
sorted list of filenames, as follows:
* Match any (zero or more) characters.
? Match any single character.
[ ... ] Match any single character in the enclosed list(s) or
range(s). A list is a string of characters. A range is
two characters separated by a minus-sign (-), and
includes all the characters in between in the ASCII
collating sequence [see ascii(7)].
{ str, str, ... } Expand to each string (or filename-matching pattern)
in the comma-separated list. Unlike the pattern-
matching expressions above, the expansion of this
construct is not sorted. For instance, {b,a} expands
to `b' `a', (not `a' `b'). As special cases, the
characters { and }, along with the string {}, are
passed undisturbed.
~[ user ] Your home directory, as indicated by the value of the
variable home, or that of user, as indicated by the
password entry for user.
Only the patterns *, ? and [...] imply pattern matching; an error
results if no filename matches a pattern that contains them. The `.'
(dot character), when it is the first character in a filename or pathname
component, must be matched explicitly. The / (slash) must also be
matched explicitly.
Expressions and Operators
A number of C shell built-in commands accept expressions, in which the
operators are similar to those of C and have the same precedence. These
expressions typically appear in the @, exit, if, set and while commands,
and are often used to regulate the flow of control for executing
commands. Components of an expression are separated by white space.
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Null or missing values are considered 0. The result of all expressions
are strings, which may represent decimal numbers.
The following C shell operators are grouped in order of precedence:
(...) grouping
~ one's complement
! logical negation
* / % multiplication, division, remainder (These
are right associative, which can lead to
unexpected results. Group combinations
explicitly with parentheses.)
+ - addition, subtraction (also right
associative)
<< >> bitwise shift left, bitwise shift right
< > <= >= less than, greater than, less than or equal
to, greater than or equal to
== != =~ !~ equal to, not equal to, filename-substitution
pattern match (described below), filename-
substitution pattern mismatch
& bitwise AND
^ bitwise XOR (exclusive or)
| bitwise inclusive OR
&& logical AND
|| logical OR
The operators: ==, !=, =~, and !~ compare their arguments as strings;
other operators use numbers. The operators =~ and !~ each check whether
or not a string to the left matches a filename substitution pattern on
the right. This reduces the need for switch statements when pattern-
matching between strings is all that is required.
Also available are file inquiries:
-r filename Return true, or 1 if the user has read access.
Otherwise it returns false, or 0.
-w filename True if the user has write access.
-x filename True if the user has execute permission (or search
permission on a directory).
-e filename True if file exists.
-o filename True if the user owns file.
-z filename True if file is of zero length (empty).
-f filename True if file is a plain file.
-d filename True if file is a directory.
If file does not exist or is inaccessible, then all inquiries return
false.
An inquiry as to the success of a command is also available:
{ command } If command runs successfully, the expression evaluates
to true, 1. Otherwise it evaluates to false 0. (Note
that, conversely, command itself typically returns 0
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when it runs successfully, or some other value if it
encounters a problem. If you want to get at the
status directly, use the value of the status variable
rather than this expression).
Control Flow
The shell contains a number of commands to regulate the flow of control
in scripts, and within limits, from the terminal. These commands operate
by forcing the shell either to reread input (to loop), or to skip input
under certain conditions (to branch).
Each occurrence of a foreach, switch, while, if...then and else built-in
must appear as the first word on its own input line.
If the shell's input is not seekable and a loop is being read, that input
is buffered. The shell performs seeks within the internal buffer to
accomplish the rereading implied by the loop. (To the extent that this
allows, backward goto commands will succeed on nonseekable inputs.)
Command Execution
If the command is a C shell built-in, the shell executes it directly.
Otherwise, the shell searches for a file by that name with execute
access. If the command-name contains a /, the shell takes it as a
pathname, and searches for it. If the command-name does not contain a /,
the shell attempts to resolve it to a pathname, searching each directory
in the path variable for the command. To speed the search, the shell
uses its hash table (see the rehash built-in) to eliminate directories
that have no applicable files. This hashing can be disabled with the -c
or -t, options, or the unhash built-in.
As a special case, if there is no / in the name of the script and there
is an alias for the word shell, the expansion of the shell alias is
prepended (without modification), to the command line. The system
attempts to execute the first word of this special (late-occurring)
alias, which should be a full pathname. Remaining words of the alias's
definition, along with the text of the input line, are treated as
arguments.
When a pathname is found that has proper execute permissions, the shell
forks a new process and passes it, along with its arguments to the kernel
(using the execve(2) system call). The kernel then attempts to overlay
the new process with the desired program. If the file is an executable
binary (in a.out(4) format) the kernel succeeds, and begins executing the
new process. If the file is a text file, and the first line begins with
#!, the next word is taken to be the pathname of a shell (or command) to
interpret that script. Subsequent words on the first line are taken as
options for that shell. The kernel invokes (overlays) the indicated
shell, using the name of the script as an argument.
If neither of the above conditions holds, the kernel cannot overlay the
file (the execve(2) call fails); the C shell then attempts to execute the
file by spawning a new shell, as follows:
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⊕ If the first character of the file is a #, a C shell is invoked.
⊕ Otherwise, a standard (Bourne) shell is invoked.
Signal Handling
The shell normally ignores QUIT signals. Background jobs are immune to
signals generated from the keyboard, including hangups (HUP). Other
signals have the values that the C shell inherited from its environment.
The shell's handling of interrupt and terminate signals within scripts
can be controlled by the onintr
built-in. Login shells catch the TERM signal; otherwise this signal is
passed on to child processes. In no case are interrupts allowed when a
login shell is reading the .logout file.
Job Control
The shell associates a numbered job with each command sequence, to keep
track of those commands that are running in the background or have been
stopped with TSTP signals (typically CTRL-z). When a command, or command
sequence (semicolon separated list), is started in the background using
the & metacharacter, the shell displays a line with the job number in
brackets, and a list of associated process numbers:
[1] 1234
To see the current list of jobs, use the jobs built-in command. The job
most recently stopped (or put into the background if none are stopped) is
referred to as the current job, and is indicated with a `+'. The
previous job is indicated with a `-'; when the current job is terminated
or moved to the foreground, this job takes its place (becomes the new
current job).
To manipulate jobs, refer to the bg, fg, kill, stop and % built-ins.
A reference to a job begins with a `%'. By itself, the percent-sign
refers to the current job.
% %+ %% The current job.
%- The previous job.
%j Refer to job j as in: `kill -9 %j'. j can be a job
number, or a string that uniquely specifies the command-
line by which it was started; `fg %vi' might bring a
stopped vi job to the foreground, for instance.
%?string Specify the job for which the command-line uniquely
contains string.
A job running in the background stops when it attempts to read from the
terminal. Background jobs can normally produce output, but this can be
suppressed using the `stty tostop' command.
Status Reporting
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While running interactively, the shell tracks the status of each job and
reports whenever a finishes or becomes blocked. It normally displays a
message to this effect as it issues a prompt, so as to avoid disturbing
the appearance of your input. When set, the notify variable indicates
that the shell is to report status changes immediately. By default, the
notify command marks the current process; after starting a background
job, type notify to mark it.
Built-In Commands
Built-in commands are executed within the C shell. If a built-in command
occurs as any component of a pipeline except the last, it is executed in
a subshell.
: Null command. This command is interpreted, but performs no
action.
alias [ name [ def ] ]
Assign def to the alias name. def is a list of words that may
contain escaped history-substitution metasyntax. name is not
allowed to be alias or unalias. If def is omitted, the alias
name is displayed along with its current definition. If both
name and def are omitted, all aliases are displayed.
bg [%job] . . .
Run the current or specified jobs in the background.
break Resume execution after the end of the nearest enclosing foreach
or while loop. The remaining commands on the current line are
executed. This allows multilevel breaks to be written as a
list of break commands, all on one line.
breaksw Break from a switch, resuming after the endsw.
case label:
A label in a switch statement.
cd [ dir ]
chdir [ dir ]
Change the shell's working directory to directory dir. If no
argument is given, change to the home directory of the user.
If dir is a relative pathname not found in the current
directory, check for it in those directories listed in the
cdpath variable. If dir is the name of a shell variable whose
value starts with a /, change to the directory named by that
value.
continue Continue execution of the nearest enclosing while or foreach.
default: Labels the default case in a switch statement. The default
should come after all case labels. Any remaining commands on
the command line are first executed.
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dirs [ -l ]
Print the directory stack, most recent to the left; the first
directory shown is the current directory. With the -l
argument, produce an unabbreviated printout; use of the ~
notation is suppressed.
echo [ -n ] list
The words in list are written to the shell's standard output,
separated by space characters. The output is terminated with a
newline unless the -n option is used.
eval argument ...
Reads the arguments as input to the shell, and executes the
resulting command(s). 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 how to use eval.
exec command
Execute command in place of the current shell, which
terminates.
exit [ (expr) ]
The shell exits, either with the value of the STATUS variable,
or with the value of the specified by the expression expr.
fg % [ job ]
Bring the current or specified job into the foreground.
foreach var (wordlist)
...
end The variable var is successively set to each member of
wordlist. The sequence of commands between this command and
the matching end is executed for each new value of var. (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 up once prompting with ? before any statements in
the loop are executed.
glob wordlist
Perform filename expansion on wordlist. Like echo, but no \
escapes are recognized. Words are delimited by NULL characters
in the output.
goto label
The specified label is filename and command expanded to yield a
label. The shell rewinds its input as much as possible and
searches for a line of the form label: possibly preceded by
space or tab characters. Execution continues after the
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indicated line. It is an error to jump to a label that occurs
between a while or for built-in, and its corresponding end.
hashstat Print a statistics line indicating how effective the internal
hash table has been at locating commands (and avoiding execs).
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 [ -hr ] [ n ]
Display the history list; if n is given, display only the n
most recent events.
-r Reverse the order of printout to be most recent first
rather than oldest first.
-h Display the history list without leading numbers. This
is used to produce files suitable for sourcing using the
-h option to source.
if (expr) command
If the specified expression evaluates to true, 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.
Note: I/O redirection occurs even if expr is false, when
command is not executed (this is a bug).
if (expr) then
...
else if (expr2) then
...
else
...
endif If expr"" is true, commands up to the first else are executed.
Otherwise, if expr2 is true, the commands between the else if
and the second else are executed. Otherwise, commands between
the else and the endif are executed. Any number of else if
pairs are allowed, but only one else. Only one endif is
needed, but it is required. The words else and endif must be
the first nonwhite characters on a line. The if must appear
alone on its input line or after an else.)
jobs[ -l ]
List the active jobs under job control.
-l List process IDs, in addition to the normal information.
kill [ -sig ] [ pid ] [ %job ] ...
kill -l Send the TERM (terminate) signal, by default, or the signal
specified, to the specified process ID, the job indicated, or
the current job. Signals are either given by number or by
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name. There is no default. Typing kill does not send a signal
to the current job. If the signal being sent is TERM
(terminate) or HUP (hangup), then the job or process is sent a
CONT (continue) signal as well.
-l List the signal names that can be sent.
limit [ -h ] [ resource [ max-use ] ]
Limit the consumption by the current process or any process it
spawns, each not to exceed max-use on the specified resource.
If max-use is omitted, print the current limit; if resource is
omitted, display all limits.
-h Use hard limits instead of the current limits. Hard
limits impose a ceiling on the values of the current
limits. Only the privileged user may raise the hard
limits.
resource is one of:
cputime Maximum CPU seconds per process.
filesize Largest single file allowed.
datasize Maximum data size (including stack)
for the process.
stacksize Maximum stack size for the process.
coredumpsize Maximum size of a core dump (file).
max-use is a number, with an optional scaling factor, as
follows:
nh Hours (for cputime).
nk n kilobytes. This is the default for all but
cputime.
nm n megabytes or minutes (for cputime).
mm:ss Minutes and seconds (for cputime).
login [ username |-p ]
Terminate a login shell and invoke login(1). The .logout file
is not processed. If username is omitted, login prompts for
the name of a user.
-p Preserve the current environment (variables).
logout Terminate a login shell.
nice [ +n |-n ] [ command ]
Increment the process priority value for the shell or for
command by n. The higher the priority value, the lower the
priority of a process, and the slower it runs. When given,
command is always run in a subshell, and the restrictions
placed on commands in simple if commands apply. If command is
omitted, nice increments the value for the current shell. If
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no increment is specified, nice sets the process priority value
to 4. The range of process priority values is from -20 to 20.
Values of n outside this range set the value to the lower, or
to the higher boundary, respectively.
+n Increment the process priority value by n.
-n Decrement by n. This argument can be used only by
the privileged user.
nohup [ command ]
Run command with HUPs ignored. With no arguments, ignore HUPs
throughout the remainder of a script. When given, command is
always run in a subshell, and the restrictions placed on
commands in simple if commands apply. All processes detached
with & are effectively nohup'd.
notify [ %job ] ...
Notify the user asynchronously when the status of the current,
or of specified jobs, changes.
onintr [ - |label ]
Control the action of the shell on interrupts. With no
arguments, onintr restores the default action of the shell on
interrupts. (The shell terminates shell scripts and returns to
the terminal command input level). With the - argument, the
shell ignores all interrupts. With a label argument, the shell
executes a goto label when an interrupt is received or a child
process terminates because it was interrupted.
popd [+n] Pop the directory stack, and cd to the new top directory. The
elements of the directory stack are numbered from 0 starting at
the top.
+n Discard the n'th entry in the stack.
pushd [+n |dir]
Push a directory onto the directory stack. With no arguments,
exchange the top two elements.
+n Rotate the n'th entry to the top of the stack and cd to
it.
dir Push the current working directory onto the stack and
change to dir.
rehash Recompute the internal hash table of the contents of
directories listed in the path variable to account for new
commands added.
repeat count command
Repeat command count times. command is subject to the same
restrictions as with the one-line if statement.
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set [var [ = value ] ]
set var[n] = word
With no arguments, set displays the values of all shell
variables. Multiword values are displayed as a parenthesized
list. With the var argument alone, set assigns an empty (null)
value to the variable var. With arguments of the form var =
value set assigns value to var, where value is one of:
word A single word (or quoted string).
(wordlist) A space-separated list of words enclosed
in parentheses.
Values are command and filename expanded before being assigned.
The form set var[n] = word replaces the n'th word in a
multiword value with word.
setenv [ VAR [ word ] ]
With no arguments, setenv displays all environment variables.
With the VAR argument sets the environment variable VAR to have
an empty (null) value. (By convention, environment variables
are normally given upper-case names.) With both VAR and word
arguments setenv sets the environment variable NAME to the
value word, which must be either a single word or a quoted
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. In addition, the shell sets the PWD
environment variable from the csh variable cwd whenever the
latter changes.
shift [ variable ]
The components of argv, or variable, if supplied, are shifted
to the left, discarding the first component. It is an error
for the variable not to be set, or to have a null value.
source [ -h ] name
Reads commands from name. source commands may be nested, but
if they are nested too deeply the shell may run out of file
descriptors. An error in a sourced file at any level
terminates all nested source commands.
-h Place commands from the the file name on the history
list without executing them.
stop [ %job ] ...
Stop the current or specified background job.
suspend Stop the shell in its tracks, much as if it had been sent a
stop signal with ^Z. This is most often used to stop shells
started by su.
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switch (string)
case label:
...
breaksw
...
default:
...
breaksw
endsw Each label is successively matched, against the specified
string, which is first command and filename expanded. The file
metacharacters *, ? and [...] may be used in the case labels,
which are variable expanded. If none of the labels match
before a default label is found, execution begins after the
default label. Each case statement and the default statement
must appear at the beginning of a line. The command breaksw
continues execution after the endsw. Otherwise control falls
through subsequent case and default statements as with C. If
no label matches and there is no default, execution continues
after the endsw.
time [ command ]
With no argument, print a summary of time used by this C shell
and its children. With an optional command, execute command
and print a summary of the time it uses.
umask [ value ]
Display the file creation mask. With value set the file
creation mask. value is given in octal, and is XORed with the
permissions of 666 for files and 777 for directories to arrive
at the permissions for new files. Common values include 002,
giving complete access to the group, and read (and directory
search) access to others, or 022, giving read (and directory
search) but not write permission to the group and others.
unalias pattern
Discard aliases that match (filename substitution) pattern.
All aliases are removed by unalias *.
unhash Disable the internal hash table.
unlimit [ -h ] [ resource ]
Remove a limitation on resource. If no resource is specified,
then all resource limitations are removed. See the description
of the limit command for the list of resource names.
-h Remove corresponding hard limits. Only the privileged
user may do this.
unset pattern
Remove variables whose names match (filename substitution)
pattern. All variables are removed by `unset *'; this has
noticeably distasteful side-effects.
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unsetenv variable
Remove variable from the environment. Pattern matching, as
with unset is not performed.
wait Wait for background jobs to finish (or for an interrupt) before
prompting.
while (expr)
...
end While expr is true (evaluates to non-zero), repeat commands
between the while and the matching end statement. break and
continue may be used to terminate or continue the loop
prematurely. The while and end must appear alone on their
input lines. If the shell's input is a terminal, it prompts
for commands with a question-mark until the end command is
entered and then performs the commands in the loop.
% [ job ] [ & ]
Bring the current or indicated job to the foreground. With the
ampersand, continue running job in the background.
@ [ var =expr ]
@ [ var [n] =expr ]
With no arguments, display the values for all shell variables.
With arguments, the variable var, or the n'th word in the value
of var , to the value that expr evaluates to. (If [n] is
supplied, both var and its n'th component must already exist.)
If the expression contains the characters >, <, & or |, then at
least this part of expr must be placed within parentheses.
The operators *=, +=, etc., are available as in C. The space
separating the name from the assignment operator is optional.
Spaces are, however, mandatory in separating components of expr
that would otherwise be single words.
Special postfix operators, ++ and -- increment or decrement
name, respectively.
Environment Variables and Predefined Shell Variables
Unlike the standard shell, the C shell maintains a distinction between
environment variables, which are automatically exported to processes it
invokes, and shell variables, which are not. Both types of variables are
treated similarly under variable substitution. The shell sets the
variables argv, cwd, home, path, prompt, shell, and status upon
initialization. The shell copies the environment variable USER into the
shell variable user, TERM into term, and HOME into home, and copies each
back into the respective environment variable whenever the shell
variables are reset. PATH and path are similarly handled. You need only
set path once in the .cshrc or .login file. The environment variable PWD
is set from cwd whenever the latter changes. The following shell
variables have predefined meanings:
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argv Argument list. Contains the list of command line arguments
supplied to the current invocation of the shell. This variable
determines the value of the positional parameters $1, $2, and so
on.
cdpath Contains a list of directories to be searched by the cd, chdir,
and popd commands, if the directory argument each accepts is not
a subdirectory of the current directory.
cwd The full pathname of the current directory.
echo Echo commands (after substitutions), just before execution.
fignore A list of filename suffixes to ignore when attempting filename
completion. Typically the single word `.o'.
filec Enable filename completion, in which case the CTRL-d character
CTRL-d) and the ESC character have special significance when
typed in at the end of a terminal input line:
EOT Print a list of all filenames that start with the preceding
string.
ESC Replace the preceding string with the longest unambiguous
extension.
hardpaths
If set, pathnames in the directory stack are resolved to contain
no symbolic-link components.
histchars
A two-character string. The first character replaces ! as the
history-substitution character. The second replaces the carat
(^) for quick substitutions.
history The number of lines saved in the history list. A very large
number may use up all of the C shell's memory. If not set, the C
shell saves only the most recent command.
home The user's home directory. The filename expansion of ~ refers to
the value of this variable.
ignoreeof
If set, the shell ignores EOF from terminals. This protects
against accidentally killing a C shell by typing a CTRL-d.
mail A list of files where the C shell checks for mail. If the first
word of the value is a number, it specifies a mail checking
interval in seconds (default 5 minutes).
nobeep Suppress the bell during command completion when asking the C
shell to extend an ambiguous filename.
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noclobber
Restrict output redirection so that existing files are not
destroyed by accident. > redirections can only be made to new
files. >> redirections can only be made to existing files.
noglob Inhibit filename substitution. This is most useful in shell
scripts once filenames (if any) are obtained and no further
expansion is desired.
nonomatch
Returns the filename substitution pattern, rather than an error,
if the pattern is not matched. Malformed patterns still result
in errors.
notify If set, the shell notifies you immediately as jobs are completed,
rather than waiting until just before issuing a prompt.
path The list of directories in which to search for commands. path is
initialized from the environment variable PATH, which the C shell
updates whenever path changes. A null word specifies the current
directory. The default is typically: (. /usr/ucb /usr/bin). If
path becomes unset only full pathnames will execute. An
interactive C shell will normally hash the contents of the
directories listed after reading .cshrc, and whenever path is
reset. If new commands are added, use the rehash command to
update the table.
prompt The string an interactive C shell prompts with. Noninteractive
shells leave the prompt variable unset. Aliases and other
commands in the .cshrc file that are only useful interactively,
can be placed after the following test: `if ($?prompt == 0)
exit', to reduce startup time for noninteractive shells. A ! in
the prompt string is replaced by the current event number. The
default prompt is hostname% for mere mortals, or hostname# for
the privileged user.
savehist
The number of lines from the history list that are saved in
~/.history when the user logs out. Large values for savehist
slow down the C shell during startup.
shell The file in which the C shell resides. This is used in forking
shells to interpret files that have execute bits set, but that
are not executable by the system.
status The status returned by the most recent command. If that command
terminated abnormally, 0200 is added to the status. Built-in
commands that fail return exit status 1, all other built-in
commands set status to 0.
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time Control automatic timing of commands. Can be supplied with one
or two values. The first is the reporting threshold in CPU
seconds. The second is a string of tags and text indicating which
resources to report on. A tag is a percent sign (%) followed by
a single upper-case letter (unrecognized tags print as text):
%D Average amount of unshared data space used in
Kilobytes.
%E Elapsed (wallclock) time for the command.
%F Page faults.
%I Number of block input operations.
%K Average amount of unshared stack space used in
Kilobytes.
%M Maximum real memory used during execution of the
process.
%O Number of block output operations.
%P Total CPU time - U (user) plus S (system) - as a
percentage of E (elapsed) time.
%S Number of seconds of CPU time consumed by the kernel on
behalf of the user's process.
%U Number of seconds of CPU time devoted to the user's
process.
%W Number of swaps.
%X Average amount of shared memory used in Kilobytes.
The default summary display outputs from the %U, %S, %E, %P, %X,
%D, %I, %O, %F and %W tags, in that order.
verbose Display each command after history substitution takes place.
FILES
~/.cshrc Read at beginning of execution by each shell.
~/.login Read by login shells after .cshrc at login.
~/.logout Read by login shells at logout.
~/.history
Saved history for use at next login.
/usr/bin/sh
Standard shell, for shell scripts not starting with a `#'.
/tmp/sh* Temporary file for `<<'.
/etc/passwd
Source of home directories for `~name'.
SEE ALSO
login(1), sh(1)
access(2), exec(2), fork(2), pipe(2) in the Programmer's Reference Manual
a.out(4), environ(4), termio(4), ascii(5) in the System Administrator's
Reference Manual
DIAGNOSTICS
You have stopped jobs.
You attempted to exit the C shell with stopped jobs under job
control. An immediate second attempt to exit will succeed,
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terminating the stopped jobs.
NOTES
Words can be no longer than 1024 characters. The system limits argument
lists to 1,048,576 characters. However, the maximum number of arguments
to a command for which filename expansion applies is 1706. Command
substitutions may expand to no more characters than are allowed in the
argument list. To detect looping, the shell restricts the number of
alias substitutions on a single line to 20.
When a command is restarted from a stop, the shell prints the directory
it started in if this is different from the current directory; this can
be misleading (that is, wrong) as the job may have changed directories
internally.
Shell built-in functions are not stoppable/restartable. Command
sequences of the form a ; b ; c are also not handled gracefully when
stopping is attempted. If you suspend b, the shell never executes c.
This is especially noticeable if the expansion results from an alias. It
can be avoided by placing the sequence in parentheses to force it into a
subshell.
Control over terminal output after processes are started is primitive;
use the Sun Window system if you need better output control.
Multiline shell procedures should be provided, as they are with the
standard (Bourne) shell.
Commands within loops, prompted for by ?, are not placed in the history
list.
Control structures should be parsed rather than being recognized as
built-in commands. This would allow control commands to be placed
anywhere, to be combined with |, and to be used with & and ; metasyntax.
It should be possible to use the : modifiers on the output of command
substitutions. There are two problems with : modifier usage on variable
substitutions: not all of the modifiers are available, and only one
modifier per substitution is allowed.
The g (global) flag in history substitutions applies only to the first
match in each word, rather than all matches in all words. The the
standard text editors consistently do the latter when given the g flag in
a substitution command.
Quoting conventions are confusing. Overriding the escape character to
force variable substitutions within double quotes is counterintuitive and
inconsistent with the Bourne shell.
Symbolic links can fool the shell. Setting the hardpaths variable
alleviates this.
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`set path' should remove duplicate pathnames from the pathname list.
These often occur because a shell script or a .cshrc file does something
like `set path=(/usr/local /usr/hosts $path)' to ensure that the named
directories are in the pathname list.
The only way to direct the standard output and standard error separately
is by invoking a subshell, as follows:
example% (command > outfile) >& errorfile
Although robust enough for general use, adventures into the esoteric
periphery of the C shell may reveal unexpected quirks.
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