CSH(1) GENIX Programmer's Manual CSH(1)
NAME
csh - a shell (command interpreter) with C-like syntax
SYNOPSIS
csh [ -cefinstvVxX ] [ arg ... ]
DESCRIPTION
Csh is a first implementation of a command language interpreter
incorporating a history mechanism (see History Substitutions) job
control facilities (see Jobs) and a C-like syntax. So as to be able
to use its job control facilities, users of csh must (and automati-
cally) use the new tty driver summarized in newtty(4) and fully
described in tty(4). This new tty driver allows generation of
interrupt characters from the keyboard to tell jobs to stop. See
stty(1) for details on setting options in the new tty driver.
An instance of csh begins by executing commands from the file
`.cshrc' in the home directory of the invoker. If this is a login
shell then it also executes commands from the file `.login' there.
It is typical for users on crt's to put the command ``stty crt'' in
their .login file, and to also invoke tset(1) there.
In the normal case, the shell will then begin reading commands from
the terminal, prompting with `% '. Processing of arguments and the
use of the shell to process files containing command scripts will be
described later.
The shell then repeatedly performs the following actions: a line of
command input is read and broken into words. This sequence of words
is placed on the command history list and then parsed. Finally each
command in the current line is executed.
When a login shell terminates it executes commands from the file
`.logout' in the user's home directory.
Lexical structure
The shell splits input lines into words at blanks and tabs with the
following exceptions. The characters `&' `|' `;' `<' `>' `(' `)'
form separate words. If doubled in `&&', `||', `<<' or `>>' these
pairs form single words. These parser metacharacters may be made
part of other words, or prevented their special meaning, by preced-
ing 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. These quota-
tions have semantics to be described subsequently. Within pairs of
`'' or `"' characters a newline preceded by a `\' gives a true new-
line character.
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When the shell's input is not a terminal, the character `#' intro-
duces a comment which continues to the end of the input line. It is
prevented this special meaning when preceded by `\' and in quota-
tions using ``', `'', and `"'.
Commands
A simple command is a sequence of words, the first of which speci-
fies the command to be executed. A simple command or a sequence of
simple commands separated by `|' characters forms a pipeline. The
output of each command in a pipeline is connected to the input of
the next. Sequences of pipelines may be separated by `;', and are
then executed sequentially. A sequence of pipelines may be executed
without immediately waiting for it to terminate by following it with
an `&'.
Any of the above may be placed in `(' `)' to form a simple command
(which may be a component of a pipeline, etc.) It is also possible
to separate pipelines with `||' or `&&' indicating, as in the C
language, that the second is to be executed only if the first fails
or succeeds respectively. (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 which looks like:
[1] 1234
indicating that the jobs which was started asynchronously was job
number 1 and had one (top-level) process, whose process id was 1234.
If you are running a job and wish to do something else you may hit
the key ^Z (control-Z) which sends a STOP signal to the current job.
The shell will then normally 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 in that pending output
and unread input are discarded when it is typed. There is another
special key ^Y which does not generate a STOP signal until a program
attempts to read(2) it. This can usefully be typed ahead when you
have prepared some commands for a job which you wish to stop after
it has read them.
A job being run in the background will stop if it tries to read from
the terminal. Background jobs are normally allowed to produce out-
put, but this can be disabled by giving the command ``stty tostop''.
If you set this tty option, then background jobs will stop when they
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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 fore-
ground; thus `%1' is a synonym for `fg %1', bringing job 1 back into
the foreground. Similarly saying `%1 &' resumes job 1 in the back-
ground. Jobs can also be named by prefixes of the string typed in
to start them, if these prefixes are unambiguous, thus `%ex' would
normally restart a suspended ex(1) job, if there were only one
suspended job whose name began with the string `ex'. It is also
possible to say `%?string' which specifies a job whose text contains
string, if there is only one such job.
The shell maintains a notion of the current and previous jobs. In
output 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. For close analogy
with 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 done so that it does not otherwise disturb your
work. If, however, you set the shell variable notify, the shell
will notify you immediately of changes of status in background jobs.
There is also a shell command notify which marks a single process so
that its status changes will be immediately reported. By default
notify marks the current process; simply say `notify' after starting
a background job to mark it.
When you try to leave the shell while jobs are stopped, you will be
warned that `You have stopped jobs.' You may use the jobs command
to see what they are. If you do this or immediately try to exit
again, the shell will not warn you a second time, and the suspended
jobs will be terminated.
Substitutions
We now describe the various transformations the shell performs on
the input in the order in which they occur.
History substitutions
History substitutions place words from previous command input as
portions of new commands, making it easy to repeat commands, repeat
arguments of a previous command in the current command, or fix spel-
ling mistakes in the previous command with little typing and a high
degree of confidence. History substitutions begin with the
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character `!' and may begin anywhere in the input stream (with the
proviso that they do not nest.) This `!' may be preceded by an `\'
to prevent its special meaning; for convenience, a `!' is passed
unchanged when it is followed by a blank, tab, newline, `=' or `('.
(History substitutions also occur when an input line begins with
`↑'. This special abbreviation will be described later.) Any input
line which 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 which consist of one or more words
are saved on the history list. The history substitutions reintro-
duce sequences of words from these saved commands into the input
stream. The size of which is controlled by the history variable;
the previous command is always retained, regardless of its value.
Commands are numbered sequentially from 1.
For definiteness, consider the following output from the history
command:
9 write michael
10 ex write.c
11 cat oldwrite.c
12 diff *write.c
The commands are shown with their event numbers. It is not usually
necessary to use event numbers, but the current event number can be
made part of the prompt by placing an `!' in the prompt string.
With the current event 13 we can refer to previous events by event
number `!11', relatively as in `!-2' (referring to the same event),
by a prefix of a command word as in `!d' for event 12 or `!wri' for
event 9, or by a string contained in a word in the command as in
`!?mic?' also referring to event 9. These forms, without further
modification, simply reintroduce the words of the specified events,
each separated by a single blank. As a special case `!!' refers to
the previous command; thus `!!' alone is essentially a redo.
To select words from an event we can follow the event specification
by a `:' and a designator for the desired words. The words of 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 n'th argument
↑ first argument, i.e. `1'
$ last argument
% word matched by (immediately preceding) ?s? search
x-y range of words
-y abbreviates `0-y'
* abbreviates `↑-$', or nothing if only 1 word in event
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x* abbreviates `x-$'
x- like `x*' but omitting word `$'
The `:' separating the event specification from the word designator
can be omitted if the argument selector begins with a `↑', `$', `*'
`-' or `%'. After the optional word designator can be placed a
sequence of modifiers, each preceded by a `:'. The following modif-
iers 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, e.g. `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 newlines.
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 newline follows immediately as may the trailing
`?' in a contextual scan.
A history reference may be given without an event specification,
e.g. `!$'. In this case the reference is to the previous command
unless a previous history reference occurred on the same line in
which case this form repeats the previous reference. Thus `!?foo?↑
!$' gives the first and last arguments from the command matching
`?foo?'.
A special abbreviation of a history reference occurs when the first
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, 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 command
starting `la'.
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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 `"' are
yet variable and command 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 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 which can be established,
displayed and modified by the alias and unalias commands. After a
command line is scanned, it is parsed into distinct commands and the
first word of each command, left-to-right, is checked to see if it
has an alias. If it does, then the text which is the alias for that
command is reread with the history mechanism available as though
that command were the previous input line. The resulting words
replace the command and argument list. If no reference is made to
the history list, then the argument list is left unchanged.
Thus if the alias for `ls' is `ls -l' the command `ls /usr' would
map to `ls -l /usr', the argument list here being undisturbed.
Similarly if the alias for `lookup' was `grep !↑ /etc/passwd' then
`lookup bill' would map to `grep bill /etc/passwd'.
If an alias is found, the word transformation of the input text is
performed and the aliasing process begins again on the reformed
input line. Looping is prevented if the first word of the new text
is the same as the old by flagging it to prevent further aliasing.
Other loops are detected and cause an error.
Note that the mechanism allows aliases to introduce parser metasyn-
tax. Thus we can `alias print 'pr \!* | lpr'' to make a command
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 shell's argument list, and words of this variable's
value are referred to in special ways.
The values of variables may be displayed and changed by using the
set and unset commands. Of the variables referred to by the shell a
number are toggles; the shell does not care what their value is,
only whether they are set or not. For instance, the verbose vari-
able is a toggle which causes command input to be echoed. The
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setting of this variable results from the -v command line option.
Other operations treat variables numerically. The `@' command per-
mits 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 filename substi-
tuted. Within `"' a variable whose value consists of multiple words
expands to a (portion of) a single word, with the words of the vari-
ables value separated by blanks. When the `:q' modifier is applied
to a substitution the variable will expand to multiple words with
each word separated by a blank and quoted to prevent later command
or filename substitution.
The following metasequences are provided for introducing variable
values into the shell input. Except as noted, it is an error to
reference a variable which is not set.
$name
${name}
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 vari-
ables 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).
$name[selector]
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${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 `:' 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 know, `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.
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Command and filename substitution
The remaining substitutions, command and filename substitution, are
applied selectively to the arguments of builtin commands. This
means that portions of expressions which are not evaluated are not
subjected to these expansions. For commands which are not internal
to the shell, the command name is substituted separately from the
argument list. This occurs very late, after input-output redirec-
tion is performed, and in a child of the main shell.
Command substitution
Command substitution is indicated by a command enclosed in ``'. The
output from such a command is normally broken into separate words at
blanks, tabs and newlines, with null words being discarded, this
text then replacing the original string. Within `"'s, only newlines
force new words; blanks and tabs are preserved.
In any case, the single final newline does not force a new word.
Note that it is thus possible for a command substitution to yield
only part of a word, even if the command outputs a complete line.
Filename substitution
If a word contains any of the characters `*', `?', `[' or `{' or
begins with the character `~', then that word is a candidate for
filename substitution, also known as `globbing'. This word is then
regarded as a pattern, and replaced with an alphabetically sorted
list of file names which match the pattern. In a list of words
specifying filename substitution it is an error for no pattern to
match an existing file name, but it is not required for each pattern
to match. Only the metacharacters `*', `?' and `[' imply pattern
matching, the characters `~' and `{' being more akin to abbrevia-
tions.
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 is used to refer to
home directories. Standing alone, i.e. `~' it expands to the invok-
ers home directory as reflected in the value of the variable home.
When followed by a name consisting of letters, digits and `-' char-
acters 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 fol-
lowed by a character other than a letter or `/' or appears not at
the beginning of a word, it is left undisturbed.
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The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'. Left
to right order is preserved, with results of matches being sorted
separately at a low level to preserve this order. This construct
may be nested. Thus `~source/s1/{oldls,ls}.c' expands to
`/usr/source/s1/oldls.c /usr/source/s1/ls.c' 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 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 substi-
tution, and each input line is compared to word before any sub-
stitutions are done on this input line. Unless a quoting `\',
`"', `'' or ``' appears in word variable and command substitu-
tion is performed on the intervening lines, allowing `\' to
quote `$', `\' and ``'. Commands which are substituted have
all blanks, tabs, and newlines preserved, except for the final
newline which is dropped. The resultant text is placed in an
anonymous temporary file which is given to the command as stan-
dard 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 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 builtin 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 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
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syntactically significant to the parser (`&' `|' `<' `>' `(' `)')
they should be surrounded by spaces.
Also available in expressions as primitive operands are command exe-
cutions 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 expres-
sion and the variable status examined.
Control flow
The shell contains a number of commands which can be used to regu-
late 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 com-
mands.
The foreach, switch, and while statements, as well as the
if-then-else form of the if statement require that the major key-
words 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.)
Builtin commands
Builtin commands are executed within the shell. If a builtin com-
mand occurs as any component of a pipeline except the last then it
is executed in a subshell.
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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 substi-
tuted. 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 modi-
fied version of the system memory allocator.
bg
bg %job ...
Puts the current or specified jobs into the background, con-
tinuing them if they were stopped.
break
Causes execution to resume after the end of the nearest enclos-
ing 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 com-
ponent 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.
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CSH(1) GENIX Programmer's Manual CSH(1)
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 direc-
tory.
echo wordlist
echo -n wordlist
The specified words are written to the shells standard output,
separated by spaces, and terminated with a newline unless the
-n option is specified.
else
end
endif
endsw
See the description of the foreach, if, switch, and while
statements below.
eval arg ...
(As in sh(1).) The arguments are read as input to the shell and
the resulting command(s) executed. 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, con-
tinuing 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.)
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CSH(1) GENIX Programmer's Manual CSH(1)
The builtin command continue may be used to continue the loop
prematurely and the builtin command break to terminate it
prematurely. When this command is read from the terminal, the
loop is read up once prompting with `?' before any statements
in the loop are executed. 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 del-
imited 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 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
Displays the history event list; if n is given only the n most
recent events are printed. The -r option reverses the order of
printout to be most recent first rather than oldest first.
if (expr) command
If the specified expression evaluates true, then the single
command with arguments is executed. Variable substitution on
command happens early, at the same time it does for the rest of
the if command. Command must be a simple command, not a pipe-
line, 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
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CSH(1) GENIX Programmer's Manual CSH(1)
are possible; only one endif is needed. The else part is like-
wise 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 sig-
nal 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, 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 each process created by the current
process 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.
Resources controllable currently 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 may be given as an 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 scal-
ing 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.
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CSH(1) GENIX Programmer's Manual CSH(1)
login
Terminate a login shell, replacing it with an instance of
/bin/login. This is one way to log off, included for compati-
bility 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
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 terminate shell scripts or to return to the terminal command
input level. The second form `onintr -' causes all interrupts
to be ignored. The final form causes the shell to execute a
`goto label' when an interrupt is received or a child process
terminates because it was interrupted.
In any case, if the shell is running detached and interrupts
are being ignored, all forms of onintr have no meaning and
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CSH(1) GENIX Programmer's Manual CSH(1)
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 (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
Causes the internal hash table of the contents of the direc-
tories in the path variable to be recomputed. This is needed
if new commands are added to directories in the path while you
are logged in. This should only be necessary if you add com-
mands to one of your own directories, or if a systems program-
mer 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 sin-
gle 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 filename expanded.
These arguments may be repeated to set multiple values in a
single set command. Note however, that variable expansion hap-
pens for all arguments before any setting occurs.
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CSH(1) GENIX Programmer's Manual CSH(1)
setenv name value
Sets the value of environment variable name to be value, a sin-
gle 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
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. Input during source commands is
never placed on the history list.
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 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 com-
mand breaksw causes execution to continue after the endsw. Oth-
erwise control may fall through case labels and default labels
as in C. If no label matches and there is no default, execu-
tion continues after the endsw.
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CSH(1) GENIX Programmer's Manual CSH(1)
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 sim-
ple command 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 dis-
carded. 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 speci-
fied, 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
printenv(1).
wait
All background jobs are waited for. It the shell is interac-
tive, then an interrupt can disrupt the wait, at which time the
shell prints names and job numbers of all jobs known to be out-
standing.
while (expr)
...
end
While the specified expression evaluates non-zero, the commands
between the while and the matching end are evaluated. Break
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CSH(1) GENIX Programmer's Manual CSH(1)
and continue may 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 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, i.e. `@ 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 .cshrc as inferior
csh processes will import the definition of path from the environ-
ment, and re-export it if you then change it. (It could be set once
in the .login except that commands through net(1) would not see the
definition.)
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.
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CSH(1) GENIX Programmer's Manual CSH(1)
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-builtin commands all
expansions occur before echoing. Builtin commands
are echoed before command and filename substitution,
since these substitutions are then done selectively.
history Can be given a numeric value to control the size of
the history list. Any command which has been refer-
enced 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 filename expansion of `~'
refers to this variable.
ignoreeof If set the shell ignores end-of-file from input dev-
ices 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, restric-
tions are placed on output redirection to insure 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.
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CSH(1) GENIX Programmer's Manual CSH(1)
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 com-
pletions. The default is to rather present job com-
pletions 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 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 nei-
ther 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 direc-
tories 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.
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-builtin Command Execution
below.) Initialized to the (system-dependent) home of
the shell.
status The status returned by the last command. If it ter-
minated abnormally, then 0200 is added to the status.
Builtin commands which fail return exit status `1',
all other builtin 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.
verbose Set by the -v command line option, causes the words
of each command to be printed after history
Printed 11/16/83 23
CSH(1) GENIX Programmer's Manual CSH(1)
substitution.
Non-builtin command execution
When a command to be executed is found to not be a builtin command
the shell attempts to execute the command via exec(2). 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 component 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 (e.g.
`$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 Commands are read from the (single) following argument which
must be present. Any remaining arguments are placed in argv.
-e The shell exits if any invoked command terminates abnormally or
yields a non-zero exit status.
-f The shell will start faster, because it will neither search for
nor execute commands from the file `.cshrc' in the invoker's
home directory.
-i The shell is interactive and prompts for its top-level input,
even if it appears to not be a terminal. Shells are
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CSH(1) GENIX Programmer's Manual CSH(1)
interactive without this option if their inputs and outputs are
terminals.
-n Commands are parsed, but not executed. This may aid in syntac-
tic 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 newline at the end of this line and continue onto
another line.
-v Causes the verbose variable to be set, with the effect that
command input is echoed after history substitution.
-x Causes the echo variable to be set, so that commands are echoed
immediately before execution.
-V Causes the verbose variable to be set even before `.cshrc' is
executed.
-X Is to -x as -V is to -v.
After processing of flag arguments if arguments remain but none of
the -c, -i, -s, or -t options 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 `#', i.e. if the script does not start with a com-
ment. 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 shells
handling of interrupts and terminate signals in shell scripts can be
controlled by onintr. Login shells catch the terminate signal; oth-
erwise 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'.
AUTHOR
William Joy. Job control and directory stack features first imple-
mented by J.E. Kulp of I.I.A.S.A, Laxenburg, Austria, with different
syntax than that used now.
FILES
~/.cshrc Read at beginning of execution by each shell.
Printed 11/16/83 25
CSH(1) GENIX Programmer's Manual CSH(1)
~/.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'.
LIMITATIONS
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 filename expansion is limited to 1/6'th the
number of characters allowed in an argument list. Command substitu-
tions may substitute no more characters than are allowed in an argu-
ment list. To detect looping, the shell restricts the number of
alias substititutions on a single line to 20.
SEE ALSO
sh(1), newcsh(1), access(2), exec(2), fork(2), killpg(2), pipe(2),
sigsys(2), umask(2), vlimit(2), wait(2), jobs(3), sigset(3), tty(4),
a.out(5), environ(5), `An introduction to the C shell'
BUGS
When a command is restarted from a stop, the shell prints the direc-
tory it started in if this is different from the current directory;
this can be misleading (i.e. wrong) as the job may have changed
directories internally.
Shell builtin 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, i.e. `( a ; b ; c )'.
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 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 allow control commands
to be placed anywhere, to be combined with `|', and to be used with
`&' and `;' metasyntax.
It should be possible to use the `:' modifiers on the output of com-
mand substitutions. All and more than one `:' modifier should be
allowed on `$' substitutions.
Printed 11/16/83 26