csh(1)
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csh Command
a shell (command interpreter) with C-like syntax for DG/UX
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SYNTAX
csh [ -cefinstvVxX ] [ arg ... ]
DESCRIPTION
Csh is an implementation of a command language interpreter
incorporating a history mechanism (see History Substitutions),
job control facilities (see Jobs) , a C-like syntax, and
editread. Editread is an optional interface used for editing
command lines entered from the shell. It also provides a history
facility that saves previously typed commands (see Using the
DG/UX System for more information). To use its job control
facilities, you must use the new tty driver (see newtty(7) and
tty(7) for DG/UX). This new tty driver lets you generate
interrupt characters from the keyboard to tell jobs to stop.
Stty(1) gives details on setting options in the new tty driver.
An instance of csh begins by executing commands from the file
/etc/login.csh, then the file .cshrc in the home directory of the
invoker. If the shell is being invoked as a result of a user
logging on, then it also executes commands from the file .login
there. CRT users usually put an stty command in their .login
files. For a 605x terminal, the command
stty echoe -icrnl -onlcr erase ^? intr ^c kill ^u obs ^y
will set things up appropriately: the erase character is set to
the DEL key, control-c interrupts command or program execution,
and control-u kills the current input (the obs setting is
necessary and unique to 605x terminals).
The shell will usually begin reading commands from the terminal,
prompting with % . Processing arguments and using the shell to
process files containing command scripts are described later.
The shell then repeats these steps: It reads a line of command
input and breaks it into words. The shell places this sequence of
words on the command history list and parses it. Finally, it
executes each command in the current line.
When a login shell terminates, it executes commands from the file
.logout in the user's home directory.
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Lexical structure
The shell splits input lines into words at blanks and tabs with
the following exceptions. The characters &, |, ;, <, >, (, and )
form separate words. If doubled in &&, ||, <<, or >>, these
pairs form single words. To make these parser metacharacters
part of other words, or to prevent their special meaning, precede
them with \. A newline preceded by a \ is equivalent to a blank.
In addition, strings enclosed in matched pairs of quotations ('',
``, or "") form parts of a word; metacharacters in these
strings, including blanks and tabs, do not form separate words.
The rules for these quotations are described below. Within
enquoting characters, a new-line preceded by a \ gives a true
new-line character.
When the shell's input is not a terminal, the character #
introduces a comment that continues to the end of the input line.
It does not have this special meaning when you precede it with \
and in quotations using `, ', and ".
Commands
A simple command is a sequence of words, the first of which
specifies the command to be executed. A simple command or a
sequence of simple commands separated by pipe characters (|)
forms a pipeline. The output of each command in a pipeline is
connected to the input of the next. Sequences of pipelines may
be separated by ;, and are then executed sequentially. To
execute a sequence of pipelines without immediately waiting for
it to terminate, follow it with an &.
Any of the above may be placed in parentheses to form a simple
command (which may be a component of a pipeline, etc.) You can
also separate pipelines with || or && indicating, as in the C
language, that the second is to be executed only if the first
fails or succeeds (see Expressions ).
Jobs
The shell associates a job with each pipeline. It keeps a table
of current jobs, printed by the jobs command, and assigns them
small integer numbers. When a job is started asynchronously with
&, the shell prints a line that looks like:
[1] 1234
indicating that the job started asynchronously was job number 1,
which had one (top-level) process, and whose process id was 1234.
If you are running a job and want to do something else, type ^Z
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(control-Z), which sends a STOP signal to the current job. The
shell should indicate that the job has been stopped, and print
another prompt. You can then manipulate the state of this job,
putting it in the background with the bg command, or run some
other commands and then eventually bring the job back into the
foreground with the foreground command fg. A ^Z takes effect
immediately and is like an interrupt: pending output and unread
input are discarded when it is typed. The special key ^Y does
not generate a STOP signal until a program tries to read(2) it.
This can usefully be typed ahead when you have prepared some
commands for a job that you wish to stop after it has read them.
A job running in the background will stop if it tries to read
from the terminal. Background jobs are normally allowed to
produce output, but this can be disabled by giving the command
stty tostop. If you set this tty option, then background jobs
will stop when they try to produce output like they do when they
try to read input.
There are several ways to refer to jobs in the shell. The
character % introduces a job name. If you wish to refer to job
number 1, you can name it as %1. Just naming a job brings it to
the foreground; thus %1 is a synonym for fg %1, bringing job 1
back into the foreground. Similarly, saying %1 & resumes job 1
in the background. Jobs can also be named by prefixes of the
string typed in to start them, if these prefixes are unambiguous.
Thus, %ex would normally restart a suspended ex(1) job, if there
were only one suspended job whose name began with the string
"ex." You can also specify %?string, for a a job whose text
contains string, if there is only one such job.
The shell maintains a notion of the current and previous jobs.
In output pertaining to jobs, the current job is marked with a +
and the previous job with a -. The abbreviation %+ refers to the
current job and %- refers to the previous job. To follow the
syntax of the history mechanism (described below), %% is also a
synonym for the current job.
Status reporting
This shell learns immediately whenever a process changes state.
It normally informs you whenever a job becomes blocked so that no
further progress is possible, but only just before it prints a
prompt. This is to avoid disturbing your work. However, if you
set the shell variable notify, the shell will notify you
immediately of changes of status in background jobs. There is
also a shell command notify that marks a single process so that
its status changes will be immediately reported. By default,
notify marks the current process; simply say notify after
starting a background job to mark it.
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When you try to leave the shell while jobs are stopped, you will
be warned that you have stopped jobs. The jobs command lets you
see what they are. If you do this or immediately try to exit
again, the shell will not warn you a second time, and the
suspended jobs will be terminated.
Substitutions
We now describe the transformations that the shell performs on
the input, in the order in which they occur.
History substitutions
History substitutions use words from previous command input as
portions of new commands. This makes it easy to repeat commands,
repeat arguments of a previous command in the current command, or
fix spelling mistakes in the previous command. History
substitutions begin with the character ! and may begin anywhere
in the input stream, as long as they do not nest. This ! may be
preceded by a \ to prevent its special meaning; a ! is passed
unchanged when it is followed by a blank, tab, new-line, = or (.
(History substitutions also occur when an input line begins with
↑. This special abbreviation is described later.) Any input line
that contains history substitution is echoed on the terminal
before it is executed as it could have been typed without history
substitution.
Commands input from the terminal that consist of one or more
words are saved on the history list. The history substitutions
reintroduce sequences of words from these saved commands into the
input stream. The size of the input stream is controlled by the
history variable; the previous command is always retained,
regardless of its value. Commands are numbered sequentially from
1.
Consider the following output from the history command:
9 write michael
10 ex write.c
11 cat oldwrite.c
12 diff *write.c
The commands are shown with their event numbers. You do not
usually need to use event numbers, but the current event number
can be made part of the prompt if you place an ! in the prompt
string.
With the current event 13, you can refer to previous events by
event number !11, relatively as in !-2 (referring to the same
event), by a prefix of a command word as in !d for event 12 or
!wri for event 9, or by a string contained in a word in the
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command as in !?mic? also referring to event 9. These forms,
without further modification, simply reintroduce the words of the
specified events, each separated by a blank. As a special case
!! refers to the previous command; thus !! alone is essentially
a redo.
To select words from an event you can follow the event
specification by a : 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,
etc. The basic word designators are:
0 first (command) word
n nth argument
↑ first argument, i.e. 1
$ last argument
% word matched by (immediately preceding) ?s? search
x-y range of words
-y abbreviates 0-y
* abbreviates ↑-$, or nothing if only 1 word in event
x* abbreviates x-$
x- like x* but omitting word $
You can omit the : separating the event specification from the
word designator if the argument selector begins with a ↑, $, * -
or %. A sequence of modifiers can follow the optional word
designator. Precede each with a :. The following modifiers are
defined:
h Remove a trailing pathname component, leaving the head.
r Remove a trailing .xxx component, leaving the root name.
e Remove all but the extension .xxx.
s/l/r/ Substitute l with r
t Remove all leading pathname components, leaving the tail.
& Repeat the previous substitution.
g Apply the change globally, prefixing the above, e.g. g&.
p Print the new command but do not execute it.
q Quote the substituted words (no further substitutions).
x Like q, but break into words at blanks, tabs and new-lines.
Unless preceded by a "g," the modification is applied only to the
first modifiable word. With substitutions, it is an error for no
word to be applicable.
The left-hand side of substitutions are not regular expressions
in the sense of the editors, but rather strings. You can use any
character as the delimiter in place of /; a \ quotes the
delimiter in the l and r strings. The character & in the right-
hand side is replaced by the text from the left. A \ quotes &
also. A null l uses the previous string from a l or from a
contextual scan string s in !?s?. The trailing delimiter in the
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substitution may be omitted if a new-line follows immediately; so
may the trailing ? in a contextual scan.
You can give a history reference without an event specification
with !$. The reference is to the previous command unless a
previous history reference occurred on the same line. In that
case, this form repeats the previous reference. Thus, !?foo?↑ !$
gives the first and last arguments from the command matching
?foo?.
A special abbreviation of a history reference occurs when the
first non-blank character of an input line is a ↑. This is
equivalent to !:s↑ providing a convenient shorthand for
substitutions on the text of the previous line. Thus ↑lb↑lib
fixes the spelling of lib in the previous command. Finally, you
can surround a history substitution with { and } to insulate it
from the characters that follow. Thus, after "ls -ld ~paul," you
might do "!{l}a' to do "ls -ld ~paula," while "!la" would look
for a command starting "la".
Quoting
The following characters have a special meaning and terminate a
word unless quoted:
; & ( ) | ^ < > new-line space tab
You can make a character stand for itself by preceding it with a
\. This is called quoting. The pair \new-line is ignored.
Quotations with ' and "
Enguoting strings with ' and " can prevent all or some of the
remaining substitutions. Strings enclosed in ' are not
interpreted further. Strings enclosed in " will still expand
variables and commands, as described below.
In both cases, the resulting text becomes (all or part of) a
single word; only in one special case (see "Command Substitition"
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 you can establish,
display and modify with the alias and unalias commands. After a
command line is scanned, it is parsed into distinct commands and
the first word of each command, left-to-right, is checked to see
if it has an alias. If it does, then the alias for that command
is reread with the history mechanism available as though that
command were the previous input line. The resulting words
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replace the command and argument list. If no reference is made
to the history list, then the argument list is left unchanged.
Thus, if the alias for "ls" is "ls -l," the command "ls /usr"
would map to "ls -l /usr," and the argument list would stay the
same. Similarly, if the alias for "lookup" was "grep !↑
/etc/passwd", then "lookup bill" would map to "grep bill
/etc/passwd."
If an alias is found, the word transformation of the input text
is performed and the aliasing process begins again on the
reformed input line. Looping is prevented if the first word of
the new text is the same as the old by flagging it to prevent
further aliasing. Other loops are detected and cause an error.
Aliases can introduce parser metasyntax. Thus, we can "alias
print pr \| lp" to make a command print which pr's its arguments
to the line printer.
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 shells argument list, and words of
this variables value are referred to in special ways.
The set and unset commands display and change the values of
variables. Some of the variables referred to by the shell are
toggles; the shell does not care what their value is, only
whether they are set. For instance, the verbose variable is a
toggle that echoes command input. 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. In numeric operations,
the null string is considered to be zero, and the second and
subsequent words of multiword values are ignored.
After the input line is aliased and parsed, and before each
command is executed, variable substitution is performed keyed by
$ characters. This expansion can be prevented by preceding the $
with a \ except within double quotes ("), where it always occurs,
and within right quotes ('), 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.
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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 double quotes or given the :q modifier, the
results of variable substitution may eventually be command and
filename substituted. Within double quotes, a variable whose
value consists of multiple words expands to a single word that
itself is made up of the multiple words separated by blanks.
When the :q modifier is applied to a substitution, the variable
will expand to multiple words with each word separated by a blank
and enquoted. Both methods prevent later command or filename
substitution.
The following metasequences introduce variable values into the
shell input. Except as noted, it is an error to reference an
unset variable.
$name
${name}
Replaced by the words of the value of variable name, each
separated by a blank. Braces insulate name from following
characters that would otherwise be part of it. Shell
variables have names consisting of up to 20 letters and
digits starting with a letter. The underscore character is
considered a letter.
If name is not a shell variable, but is set in the
environment, then that value is returned (but : modifiers
and the other forms given below are not available 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].
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$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 :
modifier on each $ expansion.
The following substitutions may not be modified with : modifiers.
$?name
${?name}
Substitutes the string 1 if name is set, 0 if it is not.
$?0
Substitutes 1 if the current input filename is known, 0 if
it is not.
$$
Substitutes the (decimal) process number of the (parent)
shell.
$<
Substitutes a line from the standard input, with no further
interpretation. It can be used to read from the keyboard in
a shell script.
Command and filename substitution
The remaining substitutions, command and filename substitution,
are applied selectively to the arguments of built-in commands.
This means that unevaluated portions of expressions are not
subjected to these expansions. For commands which are not
internal to the shell, the command name is substituted separately
from the argument list. This occurs very late, after input-
output redirection is performed, and in a child of the main
shell.
Command substitution
Command substitution is indicated by a command enclosed in
"backquotes" (`). The output from such a command is normally
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broken into separate words at blanks, tabs and new-lines. Null
words are discarded, and this text replaces the original string.
Within double quotes, 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.
Filename substitution
If a word contains any of the characters *, ?, [ or { or begins
with the character ~, then that word is a candidate for filename
substitution. This word is then regarded as a pattern, and
replaced with an alphabetically sorted list of filenames that
match the pattern. In a list of words specifying filename
substitution, it is an error for no pattern to match an existing
filename, but not each pattern must match. Only the
metacharacters *, ? and [ imply pattern matching; the characters
~ and { are more akin to abbreviations.
In matching filenames, the character . at the beginning of a
filename or immediately following a /, as well as the character /
must be matched explicitly. The character * matches any string
of characters, including the null string. The character ?
matches any single character. The sequence [...] matches any one
of the characters enclosed. Within [...], a pair of characters
separated by - matches any character lexically between the two.
The character ~ at the beginning of a filename refers to a home
directory. Standing alone, i.e. ~, it expands to your 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 your name and substitutes your home
directory. For example, ~ken might expand to /usr/ken and
~ken/chmach to /usr/ken/chmach. If the character ~ is followed
by a character other than a letter or / or does not appear at the
beginning of a word, it is left undisturbed.
The metanotation a{b,c,d}e is shorthand for abe ace ade. Left-
to-right order is preserved, with results of matches being sorted
separately at a low level to preserve this order. This construct
may be nested. Thus
~source/s1/{oldls,ls}.c
expands to
/usr/source/s1/oldls.c /usr/source/s1/ls.c
whether or not these files exist, without any chance of error if
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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
You can redirect standard input and standard output of a command
with the following syntax:
< name
Open file name (which is first variable-, command- and
filename-expanded) as the standard input.
<< word
Read the shell input up to a line which is identical to
word. Word is not subjected to variable, filename or command
substitution, and each input line is compared to word before
any substitutions are done on this input line. Unless an
enquoting \, ", ' or ` appears in word, variable and command
substitution is performed on the intervening lines, letting
\ enquote $, \ and `. Commands that 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, its 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 (e.g. a terminal or
/dev/null) or an error results. This helps prevent
accidental destruction of files. In this case the ! forms
can be used 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 filenames are.
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>> 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 command in a pipeline. Thus, unlike some previous shells,
commands run from a file of shell commands have no access to the
text of the commands by default; rather they receive the original
standard input of the shell. The << mechanism should be used to
present inline data. This permits shell command scripts to
function as components of pipelines and allows the shell to block
read its input. Note that the default standard input for a
command run detached is not 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 numbers. The
operators =~ and !~ are like != and == except that the right hand
side is a pattern (containing, e.g. *s, ?s and instances of
[...]) against which the left hand operand is matched. This
reduces the need for use of the switch statement in shell scripts
when all that is really needed is pattern matching.
Strings 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
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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 filename expanded and then
tested to see if it has the specified relationship to the real
user. If the file does not exist or is inaccessible then all
enquiries return false, i.e. 0. Command executions succeed,
returning true, i.e. 1, if the command exits with status 0,
otherwise they fail, returning false, i.e. 0. If more detailed
status information is required then the command should be
executed outside 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 gotos will succeed on non-
seekable inputs.)
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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
filename 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 the address of the last location in
the heap. With an argument, alloc 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
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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 executing 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 is 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. This is usually used
to execute commands generated as the result of command or
variable substitution, since parsing occurs before these
substitutions. See tset(1) for an example of using eval.
exec command
The specified command is executed in place of the current
shell.
exit
exit(expr)
The shell exits either with the value of the status variable
(first form) or with the value of the specified expr (second
form).
fg
fg %job ...
Brings the current or specified jobs into the foreground,
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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.)
Use the built-in command continue to continue the loop
prematurely, and the built-in command break to terminate it
prematurely. When this command is read from the terminal,
the loop is read once, prompting with ? before any
statements in the loop are executed. If you make a mistake
typing in a loop at the terminal you use the delete key to
correct it.
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 filename expand a
list of words.
goto word
The specified word is filename and command expanded to yield
a string of the form "label." The shell rewinds its input as
much as possible and searches for a line of the form
"label": possibly preceded by blanks or tabs. Execution
continues after the specified line.
hashstat
Print a statistics line 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
history n
history -r n
history -h n
Display the history event list; if n is given, only the n
most recent events are printed. The -r option reverses the
order of printout to be most recent first rather than oldest
first. The -h option prints the history list without
leading numbers. This produces files suitable for sourcing
using the -h option to source.
if (expr) command
If the specified expression evaluates true, then the single
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command with arguments is executed. Variable substitution
on command happens early, at the same time it does for the
rest of the if command. Command must be a simple command,
not a pipeline, a command list, or a parenthesized command
list. Input/output redirection occurs even if expr is
false, when the 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; 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 option lists process ids
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 number 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, so
just saying kill by itself 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.
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Controllable resources include cputime (the maximum number
of cpu-seconds to be used by each process); filesize (the
largest single file which can be created); datasize (the
maximum growth of the data+stack region via sbrk(2) beyond
the end of the program text), stacksize (the maximum size of
the automatically-extended stack region), and coredumpsize
(the size of the largest core dump that will be created).
The maximum-use can be 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, use 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 sh(1).
logout
Terminate a login shell. Especially useful if ignoreeof is
set.
newgrp
Changes the group identification of the caller; for details
see newgrp(1). A new shell is executed by newgrp so that
the shell state is lost.
nice
nice +number
nice command
nice +number command
Niceness is the willingness to run your job at a lower
priority. The "nice" number is the factor that is added to
your job's default priority. (Priority numbers are ordinal;
that is, a higher priority number means a lower priority.)
The first form sets the nice factor for this shell to 4 (the
default). The second form sets the nice factor to the given
number. The final two forms run command at (default
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 placed on commands in simple if statements
apply.
nohup
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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
nohuped.
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.
The default is to terminate shell scripts or to return to
the terminal command input level. The second form, onintr -
causes all interrupts to be ignored. The final form causes
the shell to execute a goto label when an interrupt is
received or a child process terminates because it was
interrupted.
If the shell is running detached and interrupts are being
ignored, no form of onintr has meaning. 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 an argument +n, the nth entry in the stack
is discarded. 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 (ala cd) 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 numbered from
the top starting at 0.
rehash
Recomputes the internal hash table of the contents of the
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directories in the path variable. This is needed if new
commands are added to directories in the path while you are
logged in. This should only be necessary if you add
commands to one of your own directories, or if a systems
programmer changes the contents of one of the system
directories.
repeat count command
Command is subject to the same restrictions as the command
in the one-line if statement above. It 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 with other than a single word as value
appear 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 indexth 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 filename expanded.
These arguments may be repeated to set multiple values in a
single set command. Note however, that variable expansion
happens for all arguments before any setting occurs.
setenv name value
Sets the value of environment variable name to value, a
single string. The most commonly used environment variable
USER, TERM, and PATH are automatically imported to and
exported from the csh variables user, term, and path; there
is no need to use setenv for these.
shift
shift variable
The members of argv are shifted to the left, discarding
argv[1]. It is an error for argv not to be set or to have
less than one word as value. The second form performs the
same function on the specified variable.
source name
source -h name
The shell reads commands from name. Source commands may be
nested; if they are nested too deeply the shell may run out
of file descriptors. An error in a source at any level
terminates all nested source commands. Normally, input
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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. Do not use stop 0 in a login shell (one that
you are in after logging on). It will hang your terminal.
Also, you must be using the Berkeley line driver (stty line
1) for stop and suspend signals to be handled properly.
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 su(1).
switch (string)
case str1:
...
breaksw
...
default:
...
breaksw
endsw
Each case 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,
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 continues
execution 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 and system resources
used by this shell and its children is printed. If
arguments are given the specified simple command is timed
and a summary of time and system resources used is printed.
The information is printed in seven fields; we show the
example of a "zero consumption" case with each field
description:
0.0u user time in seconds
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0.0s system time in seconds
0:00 real time in minutes and seconds
0% a rough approximation of the percentage of CPU cycles
used during real time, calculated by adding system and
user times and dividing the sum by elapsed real time
0+0k shared and unshared memory-time, in kilobyte-seconds,
separated by +.
0+0io
Number of blocks input and output, separated by +.
0pf+0w
Number of page faults (pf) and number of times the
process was swapped out to disk (w).
If necessary, an extra shell is created to print the time
statistic when the command completes. The time variable,
mentioned below, can be set to a threshold; thereafter, time use
information (system, user, real) is printed whenever any program
or command exceeds that threshold.
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 read and execute access only to users in the
group or others. Note, however, that umask 000 is
effectively umask 111; csh creates files with a default
permission of 666, which means that no one (even the owner)
has execute permission for the file. Use chmod(1) to add
execute permission. (Note that any file of shell or C-shell
commands must have execute permission set in order to run).
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
Disables the internal hash table from speeding up location
of executed programs.
unlimit resource
unlimit
Removes the limitation on resource. If no resource is
specified, then all resource limitations are removed.
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unset pattern
All variables whose names match the specified pattern are
removed. Thus all variables are removed by "unset *"; this
has noticeably bad side-effects. It is not an error for
nothing to be unset.
unsetenv pattern
Removes all variables whose names match the specified
pattern from the environment. See also the setenv command
above and printenv(1).
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 continue can be used to terminate or
continue the loop prematurely. (The while and end must
appear alone on their input lines.) Prompting 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 indexth argument
of name. Both name and its indexth 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
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name respectively, i.e. @ i++.
Pre-defined and environment variables
NOTE:
By convention, environment variables are uppercase, and
local variables are lowercase. 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 the user does it.
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; its
setting in the file .login is sufficient since inferior csh
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, i.e. $1 is replaced by $argv[1], etc.
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 executed. For non-built-in
commands, all expansions occur before echoing.
Built-in commands are echoed before command and
filename 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 that has been
referenced in this many events will not be
discarded. Too-large values of history may run
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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 filename expansion of ~
refers to this variable.
ignoreeof If set, the shell ignores end-of-file from input
devices that are terminals. This prevents shells
from accidentally being killed by control-Ds.
mail The files where the shell checks for mail. This
is done after each command completion that 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
ensure that files are not accidentally destroyed,
and that >> redirections refer to existing files.
noglob If set, filename expansion is inhibited. This is
most useful in shell scripts which are not dealing
with filenames, or after a list of filenames has
been obtained and further expansions are not
desirable.
nonomatch If set, it is not an error for a filename
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,
i.e. echo [ still gives an error.
notify If set, the shell notifies asynchronously of job
completions. The default is to 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 specifies the current
directory. If there is no path variable then only
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full pathnames 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 command with neither the -c nor the -t
option will normally hash the contents of the
directories in the path variable after reading
.cshrc, and each time the path variable is reset.
If new commands are added to these directories
while the shell is active, you may need to give
the rehash in order to find the commands.
prompt The string 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
that 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 logoins. A large value of
savehist slows down the shell during start-up.
shell The file in which the shell resides. This is used
in forking shells to interpret files that 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 that 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 print a line when it terminates
giving user, system, and real times and a
utilization percentage which is the ratio of user
plus system times to real time.
verbose Set by the -v command line option, prints the
words of each command after history substitution.
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Non-built-in command execution
When a command to be executed is not a built-in command, the
shell tries to execute the command via exec(2). Each word in the
variable path names a directory from which the shell will try 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; 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), if the shell
was given a -c or -t argument, or for each directory component of
path which does not begin with a /, the shell concatenates with
the given command name to form a pathname 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 commands 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 pathname of the shell
(e.g. $shell). Note that this is a special, late occurring, case
of alias substitution, and only lets unmodified words be
prepended to the argument list.
Argument list processing
If argument 0 to the shell is - then this is a login shell. The
flag arguments are:
-c Commands are read from the (single) following argument which
must be present. Any remaining arguments are placed in
argv.
-e The shell exits if any invoked command terminates abnormally
or yields a non-zero exit status.
-f The shell will start faster, because it will neither search
for nor execute commands from the file .cshrc in the
invokers home directory.
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-i The shell is interactive and prompts for its top-level
input, even if it appears to not be a terminal. Shells are
interactive without this option if their inputs and outputs
are terminals.
-n Commands are parsed, but not executed. This may aid 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 Sets the verbose variable, with the effect that command
input is echoed after history substitution.
-x Sets the echo variable, so that commands are echoed
immediately before execution.
-V Sets the verbose variable even before .cshrc is executed.
-X Is to -x as -V is to -v.
After processing of flag arguments if arguments remain but none
of the -c, -i, -s, or -t options 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 two characters of a script are not
#!. 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
generated from the keyboard, including hangups. Other signals
have the values which the shell inherited from its parent. The
shell's 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.
FILES
~/.cshrc Read at beginning of execution by each
shell.
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~/.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 #!)
/tmp/sh* Temporary file for <<.
/etc/passwd Source of home directories for ~name.
LIMITATIONS
Words can be no longer than 1024 characters. The system limits
argument lists to 10240 characters. The number of arguments to a
command that involves filename expansion is limited to one-sixth
the number of characters allowed in an argument 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 substititutions on a single line to 20.
SEE ALSO
sh(1).
access(2), exec(2), fork(2), killpg(2), pipe(2), sigsys(2),
umask(2), vlimit(2), wait(2), jobs(3), sigset(3), a.out(4),
environ(5) in the Programmer's Reference for the DG/UX System.
tty(7) in the System Manager's Reference for the DG/UX System.
NOTES
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, since the job may have changed
directories internally.
If a process reading from a pipe ends before the process writing
to the pipe, a harmless "Broken Pipe" error message is printed.
Example: ls -l | head in a large directory.
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. Placing the sequence of
commands in parentheses to force it to a subshell, i.e. ( a ; b
; c ), will suffice.
Control over tty output after processes are started is primitive;
perhaps this will inspire someone to work on a good virtual
terminal interface. In a virtual terminal interface much more
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interesting things could be done with output control.
Alias substitution is most often used to clumsily simulate shell
procedures; shell procedures should be provided rather than
aliases.
Commands within loops, prompted for by ?, are not placed in the
history list. Control structure should be parsed rather than
being recognized as built-in commands. This would let you place
control commands 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. All and more than one : modifier should
be allowed on $ substitutions.
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