csh(1) General Commands Manual csh(1)
Name
csh - C shell Command Interpreter
Syntax
csh [-cefinstvVxX] [arg...]
Description
The command is a command language interpreter that consists of a history mechanism, job control facilities, and a C-like syntax. While
this command has a set of built-in functions that it performs directly, the command line interpreter also reads and translates commands
that invokes other programs. Additionally, you can create shell scripts which the command can interpret. Shell scripts are files which
contain executable instructions.
The percent sign (%) represents the system prompt. It indicates that you can begin entering commands to the system. Each command line
that you type is read and broken into words. This sequence of words is placed on a command history list and then parsed. When the entire
command line has executed, the percent sign reappears and you can enter another command. See the History Substitution and Jobs sections
for more information.
To use the command's full job control facilities, you must invoke the tty driver described in This driver allows generation of interrupt
characters from the keyboard which stop execution of a job. For details on setting options in the tty driver, see
Note that your environment setup is controlled by commands in the home directory of your .cshrc file. The command executes these commands
when you enter the system. Additionally, if this is a login shell, the Shell also executes the commands in your .login file. These files
usually contain your options for the tty driver and (terminal settings). When a login shell session ends, commands are executed from the
.logout file in your home directory.
Lexical Structure
The shell splits input lines into words at blanks and tabs with the following exceptions:
o ampersand (&)
o bar ( | )
o semicolon ( ; )
o Left (<) and right (>) angle brackets
o Left (() and right ()) parenthesis
The previous metacharacters form separate words. If doubled as follows, these metacharacters form single words:
o Doubled ampersand (&&)
o Double bars (||)
o Double left (<<) and right (>>) brackets
o Backslash ()
o Single (` `) and double (" ") quotation marks.
Metacharacters can be a part of other words. Additionally, if you do not want a metacharacter to be interpreted as such by the system, you
can precede it with a backslash e (e). A new line that is preceded by a is equivalent to a blank.
Strings enclosed in single quotes (` `) or strings enclosed in double quotes (" ") form parts of a word. Metacharacters in these strings,
including blanks and tabs, do not form separate words. This is described in more detail later. Within single quotes or double quotes, a
new line preceded by a backslash () gives a true new line character.
When the shell's input is not a terminal, the pound sign (#) introduces a comment which continues to the end of the input line. It is pre-
vented this special meaning when preceded by a backslash () and single or double quotation marks.
Commands
A command is a word or sequence of words that directs the system to perform a certain function. You can separate commands with a bar ( | )
which forms a pipeline. The output that results from each command in the pipeline is connected to the input of the next. For example, in
the following pipeline, a file is copied and the output is piped to standard output (the screen):
% cp /example/dir/test . | more
You can form and execute several pipelines by separating each pipeline with a semicolon (;). You can also force a command to complete exe-
cution in the background by typing an ampersand (&) at the end of the command line.
You can form a simple command (which may be a component of a pipeline and so on) by placing any of the above in parenthesis (()). As in
the C language, you can also separate pipelines with a double bar (||) or double ampersands (&&). The double bar tells the command inter-
preter to execute the second command only if the first command fails. The double ampersands tells the command interpreter to execute the
second command if the first command is successful.
Jobs
The Shell associates each command or pipeline with a job index. By typing jobs at the system prompt, a table of the current jobs is
printed on your screen. Each job listed has a small integer number associated with it. For example, if you force a job into the back-
ground using an ampersand (&), the shell displays the job number and process id of that job as follows:
[1] 1234
In the previous example, the job number is 1 indicating that this is a background job and the process id is 1234.
If you are running a job in the foreground, you can suspend execution of that job by typing a CTRL/Z. The Shell then indicates that the
job has been stopped and the system prompt reappears. If you type jobs at the prompt, the display indicates that a job has been stopped.
You can either enter another command at the prompt or you can manipulate the state of the job you suspended as follows:
o Place the job in background by using the bg command.
o Continue to execute the job by placing it in the foreground using the fg command.
A CTRL/Z takes effect immediately and is like an interrupt. For example, pending output and unread output are discarded when the CTRL/Z is
issued. You can also type a CTRL/Y which does not generate a stop signal until a program attempts to perform a operation.
If a job that is being run in the background attempts to read from the terminal, it will stop. Background jobs can produce output. You
can prevent background jobs from producing output by issuing the following command:
stty tostop
There are several ways to refer to jobs in the shell. For example, to bring job number 1 into the foreground, type %1 or fg %1. Simi-
larly, %1 & returns job 1 to the background. If a job does not have an ambiguous prefix, you can restart a job by it's prefix. For exam-
ple, %ex would restart a suspended job, if it is the only suspended job. You use also use %?string which specifies a job whose command
line contains string. Again, string cannot be an ambiguous name.
The Shell tracks the current and previous jobs. For example, in output displays of jobs, the current job is marked with a plus sign (+)
and the previous job is marked with a minus sign (-). Hence, you can type %+ for the current job and %- for the previous job. You can
also specify %% which specifies the current job.
Status Reporting
The Shell performs status reporting when the process state changes. For example, if a job becomes blocked and further processing is not
possible, the Shell informs you just before it prints a prompt. If, however, you set the Shell variable notify, the Shell provides you
with immediate status of background jobs. As opposed to notifying you of all changes in background jobs, the Shell command notify can mark
a single process so that only its status change is reported. To mark a single file, type notify after starting a background job. By
default, only the current process is marked.
If you try to exit from the Shell while jobs are stopped, the following warning appears:
You have stopped jobs.
You can use the jobs command to view the stopped jobs. If you immediately try to exit again, the Shell does not provide a second warning
and suspended jobs are terminated.
Substitutions
The various transformations the shell performs on the input is now described in the order in which they occur.
History Substitutions
History substitutions allow you to use words from previously typed commands as portions of new commands. This enables you to repeat com-
mands, arguments, or fix spelling mistakes from the previous command.
An exclamation point (!) marks the beginning of a history substitution. It can appear anywhere in the input stream (including the begin-
ning) as long as it is not nested. An input line that contains history substitution is echoed to the screen before it is executed.
The exclamation point (!) may be preceded by a backslash () if you want to escape its special meaning. If an exclamation point is fol-
lowed by a blank, tab, new line, equal sign (=), or left parenthesis ((), it is passed unchanged.
Any command line that is typed at the terminal is saved on the history list. You can increase or decrease the size of your history list
using the history variable; the previous command is always retained regardless of its value. Commands are numbered sequentially from 1. To
display the history on your terminal, type history at the prompt as follows:
% history
This command lists the commands that were previously typed. For example:
1 write michael
2 ex write.c
3 cat oldwrite.c
4 diff*write.c
The commands are shown with their event numbers. Although it is not usually necessary to use event numbers, you can reinvoke any command
by combining the exclamation point (!) with any event number. For example, if you are referencing the previous history list, !4 reinvokes
the command line diff*write.c. You can also reinvoke a command without the event number as long as it is not ambiguous. For example, !c
invokes event 3 or !wri invokes event 1. The line !?mic? also refers to event 1. If you type !!, the last command entered in reinvoked.
To select words from an event, follow the event specification with a colon (:) and a designator for the desired words. The words of a
input line are numbered from 0, the first (usually command) word being 0, the second word (first argument) being 1, and so forth. The
basic word designators are:
0 first (command) word
n n'th argument
! first argument, that is `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 `$'
The colon (:) separating the event specification from the word designator can be omitted if the argument selector begins with a `!', `$',
`*' `-' or `%'. After the optional word designator can be placed a sequence of modifiers, each preceded by a colon (:). 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 globally, prefixing the above, for example, `g&'.
p Print the new command but do not execute it.
q Quote the substituted words, preventing further substitutions.
x Like q, but break into words at blanks, tabs and new lines.
Unless preceded by a `g' the modification 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 rather 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 `' quotes `&' also. A null l uses the previous string either from a l or from a contextual scan
string s in `!?s?'. The trailing delimiter in the substitution may be omitted if a new line follows immediately as may the trailing `?' in
a contextual scan.
A special abbreviation of a history reference occurs when the first non-blank character of an input line is a circumflex (^). 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 lb in the previous command. Finally, a history substitution may be surrounded with `{' and `}' if necessary to insulate it
from the characters which follow. Thus, after `ls -ld ~paul' we might do `!{l}a' to do `ls -ld ~paula', while `!la' would look for a com-
mand starting `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 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
The shell maintains a list of aliases that can be established, displayed, and modified by the alias and unalias commands.
After the shell scans a command line, it parses the line into distinct commands. Then, the shell checks the first word of each command, in
left-to-right order, to determine if the command line contains an alias. When the shell finds an alias, it substitutes the definition of
the alias for the alias in the command line. The shell reads the definition of the alias using the history mechanism and treats the defini-
tion as if it was the previous input line. If the alias definition makes no reference to the history list, the shell leaves the command's
argument unchanged.
For example, the following command creates an alias called ``ls:''
% alias ls 'ls -l'
After you issue this alias command, you receive information about files such as their mode, number of links, owner, and so on when you use
the ls alias. For example, the following shows the output from the ls alias created in the preceeding example:
% ls usrsmithtext_file
-rw-r--r-- 1 smith 21 Mar 12 11:53 text_file
You can also create aliases that allow you to supply arguments on the command line and arguments in the alias definition, as shown in the
following example:
% alias lookup 'grep !^ /etc/passwd'
You must specify ``'' before the ! to prevent the substitution from occurring in the alias command. The following shows the output from
the lookup alias:
% lookup smith
smith:2vruqPosbG/bE:1321:10::usrsmith:bincsh
The lookup alias finds and displays user Smith's entry in the file.
You can specify an alias within an alias definition. After the shell finds an alias and substitutes its definition, it searches again for
aliases. The shell flags definitions that begin with the same word as the alias to prevent infinite loops. Other loops are detected and
cause an error.
You can use parser metasyntax in an alias command. For example, the following is a valid command that creates the print alias:
% alias print 'pr !* | lpr'
The print alias pipes output from the command to the command.
Variable Substitution
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 num-
ber are toggles; the shell does not care what their value is, only whether they are set or not. For instance, the verbose variable is a
toggle which causes command input to be echoed. The 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 subsequent words of multiword values are ignored.
After the input line is aliased and parsed, and before each command is executed, variable substitution is performed keyed by `$' charac-
ters. This expansion can be prevented by preceding the `$' with a `' except within `"'s where it always occurs, and within `''s where it
never occurs. Strings quoted by ``' are interpreted later (see Command substitution below) so `$' substitution does not occur there until
later, if at all. A `$' is passed unchanged if followed by a blank, tab, or end-of-line.
Input/output redirections are recognized before variable expansion, and are variable expanded separately. 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 file name substituted.
Within `"' a variable whose value consists of multiple words expands to a (portion of) a single word, with the words of the variables value
separated by blanks. When the `:q' modifier is applied to a substitution the variable will expand to multiple words with each word sepa-
rated by a blank and quoted to prevent later command or file name substitution.
The following metasequences are provided for introducing variable values into the shell input. Except as noted, it is an error to refer-
ence a variable which 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
which would otherwise be part of it. Shell variables have names consisting of up to 20 letters and digits starting with a letter.
The underscore character is considered a letter.
If name is not a shell variable, but is set in the environment, then that value is returned (but : modifiers and the other forms given
below are not available in this case).
$name[selector]
${name[selector]}
May be used to select only some of the words from the value of name. The selector is subjected to `$' substitution and may consist of
a single number or two numbers separated by a `-'. The first word of a variables value is numbered `1'. If the first number of a
range is omitted it defaults to `1'. If the last member of a range is omitted it defaults to `$#name'. The selector `*' selects all
words. It is not an error for a range to be empty if the second argument is omitted or in range.
$#name
${#name}
Gives the number of words in the variable. This is useful for later use in a `[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 `: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 colon (:) modifier
on each `$' expansion." The following substitutions may not be modified with colon (:) modifiers.
$?name
${?name}
Substitutes the string `1' if name is set, `0' if it is not.
$?0
Substitutes `1' if the current input file name is known, `0' if it is not.
$$
Substitute the (decimal) 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
shell script.
Command And File Name Substitution
The remaining substitutions, command and file name substitution, are applied selectively to the arguments of built-in commands. This means
that portions of expressions which are not evaluated are not subjected to these expansions. For commands which are not internal to the
shell, the command name is substituted separately from the argument list. This occurs very late, after input-output redirection is per-
formed, and in a child of the main shell.
Command Substitution
Command substitution is indicated by a command enclosed in ``'. The output from such a command is normally broken into separate words at
blanks, tabs and new lines, with null words being discarded, this text then replacing the original string. Within `"'s, only new lines
force new words; blanks and tabs are preserved.
In any case, the single final new line 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.
File Name Substitution
If a word contains any of the characters `*', `?', `[' or `{' or begins with the character `~', then that word is a candidate for file name
substitution, also known as `globbing'. This word is then regarded as a pattern, and replaced with an alphabetically sorted list of file
names which match the pattern. In a list of words specifying file name 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 charac-
ters `~' and `{' being more akin to abbreviations.
In matching file names, the character `.' at the beginning of a file name 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 sin-
gle character. The sequence `[...]' matches any one of the characters enclosed. Within `[...]', a pair of characters separated by `-'
matches any character lexically between the two.
The character `~' at the beginning of a file name is used to refer to home directories. Standing alone, that is `~', it expands to the
invokers 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 appears not 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 sep-
arately 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' whether or not these files exist without any 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 matching `*box'.) As a special case `{', `}' and `{}' are passed undisturbed.
Input/output
The standard input and standard output of a command may be redirected with the following syntax:
< name
Open file name (which is first variable, command and file name expanded) as the standard input.
<< word
Read the shell input up to a line which is identical to word. Word is not subjected to variable, file name or command substitution,
and each input line is compared to word before any substitutions are done on this input line. Unless a quoting `', `"', `'' or ``'
appears in word variable and command substitution is performed on the intervening lines, allowing `' to quote `$', `' and ``'. Com-
mands which are substituted have all blanks, tabs, and new lines preserved, except for the final new line which is dropped. The
resultant text is placed in an anonymous temporary file which is given to the command as standard input.
> name
>! name
>& name
>&! name
The file name is used as standard output. If the file does not exist then it is created; if the file exists, it is truncated, its
previous contents being lost.
If the variable noclobber is set, then the file must not exist or be a character special file (for example, a terminal or `/dev/null')
or an error results. This helps prevent accidental destruction of files. In this case the `!' forms can be used and suppress this
check.
The forms involving `&' route the diagnostic output into the specified file as well as the standard output. Name is expanded in the
same way as `<' input file names are.
>> name
>>& name
>>! name
>>&! name
Uses file name as 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 com-
mand in a pipeline. Thus, unlike some previous shells, commands run from a file of shell commands have no access to the text of the com-
mands by default; rather they receive the original standard input of the shell. The `<<' mechanism should be used to present inline data.
This permits shell command scripts to function as components of pipelines and allows the shell to block read its input. Note that the
default standard input for a command run detached is not modified to be the empty file `/dev/null'; rather 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.)
Diagnostic output may be directed through a pipe with the standard output. Simply use the form `|&' rather than just `|'.
Expressions
A number of the built-in commands (to be described subsequently) take expressions, in which the operators are similar to those of C, with
the same precedence. 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 num-
bers. The operators `=~' and `!~' are like `!=' and `==' except that the right hand side is a pattern (containing, for example, `*'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 which begin with `0' are considered octal numbers. Null or missing arguments are considered `0'. The result of all expressions
are strings, which represent decimal numbers. It is important to note that no two components of an expression can appear in the same word;
except when adjacent to components of expressions which are syntactically significant to the parser (`&' `|' `<' `>' `(' `)') they should
be surrounded by spaces.
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 file name 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, that is `0'. Command executions succeed, returning true, that is
`1', if the command exits with status 0, otherwise they fail, returning false, that is `0'. If more detailed status information is
required then the command should be executed outside of an expression and the variable status examined.
Control Flow
The shell contains a number of commands which can be used to regulate the flow of control in command files (shell scripts) and (in limited
but useful ways) from terminal input. These commands all operate by forcing the shell to reread or skip in its input and, due to the
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
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 subshell.
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 file name substituted. Name is not allowed to be alias or unalias.
alloc
Shows the amount of dynamic core in use, broken down into used and free core, and address of the last location in the heap. With an
argument shows each used and free block on the internal dynamic memory chain indicating its address, size, and whether it is used or
free. This is a debugging command and may not work in production versions of the shell; it requires a modified version of the system
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 new line 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 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 up once prompting with `?' before any statements in the loop are exe-
cuted. 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 null characters in the output. Useful for programs which wish
to use the shell to file name expand a list of words.
goto word
The specified word is file name 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 indicating 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 which 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 print-
out to be most recent first rather than oldest first. The -h option causes the history list to be printed 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 true, then the single command with arguments is executed. Variable substitution on command hap-
pens 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, 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 to the first else are executed; else if expr2 is true then the commands 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; given the -l options lists process id's in addition to the normal information.
kill %job
kill -sig %job ...
kill pid
kill -sig pid ...
kill -l
Sends either the TERM (terminate) signal or the specified signal to the specified jobs or processes. Signals are either given by num-
ber or by names (as given in /usr/include/signal.h, stripped of the prefix ``SIG''). The signal names are listed by ``kill -l''.
There is no default, saying just `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 will be sent a CONT (continue) signal as well.
limit
limit resource
limit 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.
The following resources can be controlled:
o cputime (maximum number of cpu-seconds to be used by each process)
o filesize (largest single file which can be created)
o datasize (the maximum growth of the data+stack region by beyond the end of the program text)
o stacksize (the maximum size of the automatically-extended stack region)
o coredumpsize (the size of the largest core dump that can be created).
o memoryuse (the maximum amount of main memory a process is allowed to occupy)
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
scaling is `seconds', while `m' for minutes or `h' for hours, or a time of the form `mm:ss' giving minutes and seconds 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 /bin/login. This is one way to log off, included for compatibility with
logout
Terminate a login shell. Especially useful if ignoreeof is set.
nice
nice +number
nice command
nice +number command
The first form sets the nice for this shell to 4. The second form sets the nice to the given number. The final two forms run command
at priority 4 and number respectively. The super-user may specify negative niceness by using `nice -number ...'. Command is always
executed in a sub-shell, and the restrictions place 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 changes; 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 ter-
minate 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.
popd
popd +n
Pops the directory stack, returning to the new top directory. With a argument `+n' discards the nth entry in the stack. The elements
of the directory stack are numbered from 0 starting at the top.
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 (using and pushes the old current working directory (as in csw) onto the directory stack. With a numeric argument, rotates
the nth argument of the directory stack around to be the top element and changes to it. The members of the directory stack are num-
bered 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 com-
mands 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 one of the system directories.
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 which have other than a single word as 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. In all cases the value is command and file name 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 name value
Sets the value of environment variable name to be value, a single string. The most commonly used environment variable USER, TERM, and
PATH are automatically imported to and exported from the 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 the shell may run out of file
descriptors. An error in a source at any level terminates all nested source commands. Normally input during source commands is not
placed on the history list; the -h option causes the commands to be placed in the history list without being executed.
stop
stop %job ...
Stops the current or specified job which is executing in the background.
suspend
Causes the shell to stop 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
switch (string)
case str1:
...
breaksw
...
default:
...
breaksw
endsw
Each case label is successively matched, against the specified string which is first command and file name 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, then the execution begins after the default label. Each case label and the default label must appear at the
beginning of a line. The command breaksw causes execution to continue after the endsw. Otherwise control may fall through case
labels and default labels as in C. If no label matches and there is no default, execution continues after the endsw.
time
time command
With no argument, a summary of time used by this shell and its children is printed. If arguments are given the specified simple com-
mand is timed and a time summary as described under the time variable is printed. If necessary, an extra shell is created to print
the time statistic when the command completes.
umask
umask value
The file creation mask is displayed (first form) or set to the specified value (second form). The mask is given in octal. Common
values for the mask are 002 giving all access to the group and read and execute access to others or 022 giving all access except no
write access for users in the group or others.
unalias pattern
All aliases whose names match the specified pattern are discarded. Thus all aliases are removed by `unalias *'. It is not an error
for nothing to be unaliased.
unhash
Use of the internal hash table to speed location of executed programs is disabled.
unlimit resource
unlimit
Removes the limitation on resource. If no resource is specified, then all resource limitations are removed.
unset pattern
All variables whose names match the specified pattern are removed. Thus all variables are removed by `unset *'; this has noticeably
distasteful side-effects. It is not an error for nothing to be unset.
unsetenv pattern
Removes all variables whose name match the specified pattern from the environment. See also the setenv command above and
wait
All background jobs are waited for. It the shell is interactive, then an interrupt can disrupt the wait, at which time the shell
prints names and job numbers of all jobs known to be outstanding.
while (expr)
...
end
While the specified expression evaluates non-zero, the commands between the while and the matching end are evaluated. Break and con-
tinue may be used to terminate or continue the loop prematurely. (The while and end must appear alone on their input lines.) Prompt-
ing occurs here the first time through the loop as for the foreach statement if the input is a terminal.
%job
Brings the specified job into the foreground.
%job &
Continues the specified job in the background.
@
@ name = expr
@ name[index] = expr
The first form prints the values of all the shell variables. The second form sets the specified name to the value of expr. If the
expression contains `<', `>', `&' or `|' then at least this part of the expression must be placed within `(' `)'. The third form
assigns the value of expr to the index'th argument of name. Both name and its index'th component must already exist.
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 which would otherwise be single words.
Special postfix `++' and `--' operators increment and decrement name respectively, that is `@ i++'.
Pre-defined And Environment Variables
The following variables have special meaning to the shell. Of these, argv, cwd, home, path, prompt, shell and status are always set by the
shell. Except for cwd and status this setting occurs only at initialization; these variables will not then be modified unless this is done
explicitly by the user.
This shell copies the environment variable USER into the variable user, TERM into term, and HOME into home, and copies these back into the
environment whenever the normal shell variables are reset. The environment variable PATH is likewise handled. It is not necessary to
worry about its setting other than in the file as inferior processes will import the definition of path from the environment, and re-export
it if you then change it.
argv Set to the arguments to the shell, it is from this variable that positional parameters are substituted, that is `$1' is
replaced by `$argv[1]', and so forth.
cdpath Gives a list of alternate directories searched to find subdirectories in chdir commands.
cwd The full pathname of the current directory.
echo Set when the -x command line option is given. Causes each command and its arguments to be echoed just before it is exe-
cuted. For non-built-in commands all expansions occur before echoing. Built-in commands are echoed before command and file
name substitution, since these substitutions are then done selectively.
histchars Can be given a string value to change the characters used in history substitution. The first character of its value is used
as the history substitution character, replacing the default character !. The second character of its value replaces the
character ! in quick substitutions.
history Can be given a numeric value to control the size of the history list. Any command which has been referenced in this many
events will not be discarded. Too large values of history may run the shell out of memory. The last executed command is
always saved on the history list.
home The home directory of the invoker, initialized from the environment. The file name expansion of `~' refers to this vari-
able.
ignoreeof If set the shell ignores end-of-file from input devices which are terminals. This prevents shells from accidentally being
killed by control-D's.
mail The files where the shell checks for mail. This is done after each command completion which will result in a prompt, if a
specified interval has elapsed. The shell says `You have new mail.' if the file exists with an access time not greater
than its modify time.
If the first word of the value of mail is numeric it specifies a different mail checking interval, in seconds, than the
default, which is 10 minutes.
If multiple mail files are specified, then the shell says `New mail in name' when there is mail in the file name.
noclobber As described in the section on Input/output, restrictions are placed on output redirection to insure that files are not
accidentally destroyed, and that `>>' redirections refer to existing files.
noglob If set, file name expansion is inhibited. This is most useful in shell scripts which are not dealing with file names, or
after a list of file names has been obtained and further expansions are not desirable.
nonomatch If set, it is not an error for a file name expansion to not match any existing files; rather the primitive pattern is
returned. It is still an error for the primitive pattern to be malformed, that is `echo [' still gives an error.
notify If set, the shell notifies asynchronously of job completions. The default is to rather present job completions just before
printing a prompt.
path Each word of the path variable specifies a directory in which commands are to be sought for execution. A null word speci-
fies the current directory. If there is no path variable then only full path names will execute. The usual search path is
`.', `/bin' and `/usr/bin', but this may vary from system to system. For the super-user the default search path is `/etc',
`/bin' and `/usr/bin'. A shell which is given neither the -c nor the -t option will normally hash the contents of the
directories in the path variable after reading and each time the path variable is reset. If new commands are added to these
directories while the shell is active, it may be necessary to give the rehash or the commands may not be found.
prompt The string which is printed before each command is read from an interactive terminal input. If a `!' appears in the string
it will be replaced by the current event number unless a preceding `' is given. Default is `% ', or `# ' for the super-
user.
savehist is given a numeric value to control the number of entries of the history list that are saved in ~/.history when the user
logs out. Any command which has been referenced in this many events will be saved. During start up the shell sources
~/.history into the history list enabling history to be saved across logins. Too large values of savehist will slow down
the shell during start up.
shell The file in which the shell resides. This is used in forking shells to interpret files which have execute bits set, but
which are not executable by the system. (See the description of Non-built-in Command Execution below.) Initialized to the
(system-dependent) home of the shell.
status The status returned by the last command. If it terminated abnormally, then 0200 is added to the status. Built-in commands
which fail return exit status `1', all other built-in commands set status `0'.
time Controls automatic timing of commands. If set, then any command which takes more than this many cpu seconds will cause a
line giving user, system, and real times and a utilization percentage which is the ratio of user plus system times to real
time to be printed when it terminates. The time command can be used to cause a command to be timed no matter how much CPU
time it takes. Thus
% time cp /etc/rc /usr/bill/rc
0.0u 0.1s 0:01 8% 2+1k 3+2io 1pf+0w
% time wc /etc/rc /usr/bill/rc
52 178 1347 /etc/rc
52 178 1347 /usr/bill/rc
104 356 2694 total
0.1u 0.1s 0:00 13% 3+3k 5+3io 7pf+0w
%
The preceding example indicates that the cp command used a negligible amount of user time (u) and about 1/10th of a second
system time (s); the elapsed time was 1 second (0:01), there was an average memory usage of 2k bytes of program space and 1k
bytes of data space over the cpu time involved (2+1k); the program did three disk reads and two disk writes (3+2io), and
took one page fault and was not swapped (1pf+0w). The word count command on the other hand used 0.1 seconds of user time
and 0.1 seconds of system time in less than a second of elapsed time. The percentage `13%' indicates that over the period
when it was active the command `wc' used an average of 13 percent of the available CPU cycles of the machine.
verbose Set by the -v command line option, causes the words of each command to be printed after history substitution.
Non-built-in Command Execution
When a command to be executed is found to not be a built-in command the shell attempts to execute the command via Each word in the variable
path names a directory from which the shell will attempt to execute the command. If it is given neither a -c nor a -t option, the shell
will hash the names in these directories into an internal table so that it will only try an exec in a directory if there is a possibility
that the command resides there. This greatly speeds command location when a large number of directories are present in the search path.
If this mechanism has been turned off (via unhash), or if the shell was given a -c or -t argument, and in any case for each directory com-
ponent of path which does not begin with a `/', the shell concatenates with the given command name to form a path name of a file which it
then attempts to execute.
Parenthesized commands are always executed in a subshell. Thus `(cd ; pwd) ; pwd' prints the home directory; leaving you where you were
(printing this after the home directory), while `cd ; pwd' leaves you in the home directory. Parenthesized commands are most often used to
prevent chdir from affecting the current shell.
If the file has execute permissions but is not an executable binary to the system, then it is assumed to be a file containing shell com-
mands and a new shell is spawned to read it.
If there is an alias for shell then the words of the alias will be prepended to the argument list to form the shell command. The first
word of the alias should be the full path name of the shell (for example, `$shell'). Note that this is a special, late occurring, case of
alias substitution, and only allows words to be prepended to the argument list without modification.
Argument List Processing
If argument 0 to the shell is `-' then this is a login shell. The flag arguments are interpreted as follows:
-c The first argument word is taken to be a command string. All remaining argument words 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 invokers home
directory.
-i The shell is interactive and prompts for its top-level input, even if stdin appears not to be a terminal. Shells are interactive
without this option if their inputs and outputs are terminals.
-n Commands are parsed, but not executed. This aids in syntactic checking of shell scripts.
-s Command input is taken from the standard input.
-t A single line of input is read and executed. A `' may be used to escape the new line 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 Causes the echo variable to be set before `.cshrc' is executed.
After processing of flag arguments if arguments remain but none of the -c, -i, -s, or -t options was 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 `#', that is if the script does not start with a comment.
Remaining arguments initialize the variable argv.
Signal Handling
The shell normally ignores quit signals. Jobs running detached (either by `&' or the bg or %... & commands) are immune to signals gener-
ated from the keyboard, including hangups. Other signals have the values which the shell inherited from its parent. The shells handling
of interrupts and terminate signals in shell scripts can be controlled by onintr. Login shells catch the terminate signal; otherwise this
signal is passed on to children from the state in the shell's parent. In no case are interrupts allowed when a login shell is reading the
file `.logout'.
Command And Filename Recognition
The command recognizes and completes user name aliases, commands (including built-in commands), and filenames. To use this feature, do the
following:
1. Type enough characters at the prompt to make your input to the system unique.
2. Press the ESC key.
If your input is unique, the Shell completes the input line. If the input is not unique, the terminal signals you with a beep. If you
receive a beep, type CTRL/D for a list of options. You can then type the additional characters that will make your text unique. After you
have provided more input, press the ESC key again.
Command Line Editing
The command allows you to visually edit command lines using either a or environment. The interface is modal and supports a subset of com-
mands. The interface is modeless and supports a subset of commands. See the Editing Interface section for a list of the available and
commands.
To set the editing environment, define the Shell environment variable CSHEDIT as or If the environment variable CSHEDIT is not defined, the
command searches for your EDITOR environment variable. When your EDITOR environment variable is set to or the command defaults to the com-
mand interface. If your EDITOR environment is not set to any of the previously mentioned editors, the default is the command interface.
Note that if neither the CSHEDIT or EDITOR environment variables are defined, the command defaults to the command interface.
The new history modifier (:v) allows you to pull commands from the history list to make them available for editing in visual edit mode.
The symbol :v tells the Shell that you want to enter visual edit mode. For example, the following command line invokes edit mode for the
previously typed command line:
!cp:v
When you press the ESC key as the first character on a command line, it is equivalent to typing the following:
!!:v
Thus, the previous example invokes edit mode for the last command you entered.
Another useful editing feature is scrolling through the history list. After you have entered edit mode by typing either !command:v or the
ESC key, you can use the up-arrow and down-arrow keys to scroll through the history list and you may edit any command line in that history
list.
When you are in edit mode, all control characters are displayed as a space character. Additional control characters cannot be inserted.
Existing control characters are preserved.
Editing Interface
The available commands follow:
h Move left one character (r).
l Move right one character (r).
0 Move to the start of the line.
$ Move to the end of the line.
w move forward one word (r).
b Move back one word (r).
e Move to end of word (r).
fx Move forward onto character (r).
Fx Move back onto character (r).
tx Move forward up to character (r).
Tx Move back up to character (r).
% Move to matching bracket ({[]}).
i Insert text before cursor.
I Insert text at beginning of line.
a Append text after cursor.
A Append text at end of line.
c Change text (o).
C Change to end of line (eol) (c$).
<esc> End insertion.
x Delete char under cursor (r).
X Delete character before cursor (r).
r Replace a character (r).
~ Change case of current character (r).
d Delete text (o).
D Delete to eol (d$).
u Undo last change.
U Undo all changes.
. Repeat last text change command (r).
p Put text from previous delete after cursor (r).
P Put text from previous delete before cursor (r).
^L,^R Redraw command line.
/word Search back through the history list for a command containing the specified word. If the specified word is not delineated
by white space in the history list, the search fails. Typing ESCAPE or CTRL/C aborts this command.
n Repeat last history search.
<RETURN> End edit and execute command.
^C Quit; no command executed.
(r) A repeat count is accepted.
(o) Works within a cursor motion object.
The available commands follow:
^@ Set mark (keyword null).
^A Move to beginning of line.
^B, Move backward a character.
^C Exit command line edit; do not execute a command.
^D Delete next character (to kill buffer).
^E Move to end of line.
^F, Move forward a character.
^G Cancel partial command.
^H,DEL Delete previous character (to kill buffer).
^K Kill (delete) to end of line (to kill buffer).
^L Redraw line display.
^R Search reverse for a single character.
^S Search forward for a single character.
^T Transpose two characters before cursor.
^Un Specify a repeat count before command (default of n is 4).
^W Delete between cursor and mark (to kill buffer).
^Y Yank from kill buffer.
CR,NL End edit and execute command.
ESC-^C End edit and execute command.
ESC-B Move backward a word.
ESC-D Delete next word.
ESC-F Move forward a word.
ESC-H Delete previous word.
ESC-DEL Delete previous word.
ESC-n Repeat count before command.
^X^C End edit and execute command.
^Xu Undo last change.
^XU Undo all changes.
^X~ Change case of next character.
^X^Sword Search back through the history list for a command containing a specified word. If the specified word is not delineated by
white space in the history list, the search fails. Typing ESCAPE or CTRL/C aborts this command.
^X^S Repeat last history search command. You must be in search mode to issue this command. Note that ^G cancels the previous
search word so that you can enter a new word.
Restrictions
Words can be no longer than 1024 characters.
The system limits argument lists to 10240 characters.
The number of arguments to a command which involves file name expansion is limited to 1/6'th the number of characters allowed in an argu-
ment list.
Command substitutions may substitute no more characters than are allowed in an 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 will then immediately execute `c'. This is especially noticeable if this expansion
results from an alias. It suffices to place the sequence of commands in ()'s to force it to a subshell, that is `( a ; b ; c )'.
Commands within loops, prompted for by `?', are not placed in the history list. Control structure should be parsed rather than being rec-
ognized 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 colon (:) modifiers on the output of command substitutions. All and more than one colon (:) modifier
should be allowed on `$' substitutions.
Symbolic links fool the shell. In particular, dirs and `cd ..' don't work properly once you've crossed through a symbolic link.
Files
~/.cshrc Read at beginning of execution by each shell.
~/.login Read by login shell, after `.cshrc' at login.
~/.logout Read by login shell, at logout.
/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
sh(1), time(1), access(2), execve(2), fork(2), killpg(2), pipe(2), sigvec(2), setrlimit(2), umask(2), wait(2), tty(4), a.out(5), envi-
ron(7), time(7)
"An Introduction to the C shell", Supplementary Documents, Volume 1: General User
csh(1)