4.3BSD-UWisc/man/cat1/csh.1
CSH(1) UNIX Programmer's Manual CSH(1)
NAME
csh - a shell (command interpreter) with C-like syntax
SYNOPSIS
csh [ -cefinstvVxX ] [ arg ... ]
DESCRIPTION
_C_s_h is a first implementation of a command language inter-
preter incorporating a history mechanism (see History Sub-
stitutions), job control facilities (see Jobs), interactive
file name and user name completion (see File Name Comple-
tion), and a C-like syntax. So as to be able to use its job
control facilities, users of _c_s_h must (and automatically)
use the new tty driver fully described in _t_t_y(4). This new
tty driver allows generation of interrupt characters from
the keyboard to tell jobs to stop. See _s_t_t_y(1) for details
on setting options in the new tty driver.
An instance of _c_s_h begins by executing commands from the
file `.cshrc' in the _h_o_m_e 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 ._l_o_g_i_n file, and to
also invoke _t_s_e_t(1) there.
In the normal case, the shell will then begin reading com-
mands from the terminal, prompting with `% '. Processing of
arguments and the use of the shell to process files contain-
ing command scripts will be described later.
The shell then repeatedly performs the following actions: a
line of command input is read and broken into _w_o_r_d_s. 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 users 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 preceding 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
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separate words. These quotations have semantics to be
described subsequently. Within pairs of `'' or `"' charac-
ters a newline preceded by a `\' gives a true newline char-
acter.
When the shell's input is not a terminal, the character `#'
introduces a comment which continues to the end of the input
line. It is prevented this special meaning when preceded by
`\' 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 `|' characters
forms a pipeline. The output of each command in a pipeline
is connected to the input of the next. Sequences of pipe-
lines may be separated by `;', and are then executed sequen-
tially. 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 `&&' indi-
cating, as in the C language, that the second is to be exe-
cuted only if the first fails or succeeds respectively. (See
_E_x_p_r_e_s_s_i_o_n_s.)
Jobs
The shell associates a _j_o_b with each pipeline. It keeps a
table of current jobs, printed by the _j_o_b_s 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 job which was started asynchronously was
job number 1 and had one (top-level) process, whose process
id was 1234.
If you are running a job and wish to do something else you
may hit 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 _b_g command, or run some other commands
and then eventually bring the job back into the foreground
with the foreground command _f_g. A ^Z takes effect immedi-
ately and is like an interrupt in that pending output and
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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 _r_e_a_d(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 output, but this can be disabled by giv-
ing the command ``stty tostop''. If you set this tty
option, then background jobs will stop when they try to pro-
duce 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 _e_x(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 _s_t_r_i_n_g, 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 _h_i_s_t_o_r_y 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 _n_o_t_i_f_y, the shell will notify you immedi-
ately of changes of status in background jobs. There is
also a shell command _n_o_t_i_f_y which marks a single process so
that its status changes will be immediately reported. By
default _n_o_t_i_f_y 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 _j_o_b_s command to see what they are. If you do this or
immediately try to exit again, the shell will not warn you a
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second time, and the suspended jobs will be terminated.
File Name Completion
When the file name completion feature is enabled by setting
the shell variable _f_i_l_e_c (see set), _c_s_h will interactively
complete file names and user names from unique prefixes,
when they are input from the terminal followed by the escape
character (the escape key, or control-[). For example, if
the current directory looks like
DSC.OLD bin cmd lib xmpl.c
DSC.NEW chaosnet cmtest mail xmpl.o
bench class dev mbox xmpl.out
and the input is
% vi ch<escape>
_c_s_h will complete the prefix ``ch'' to the only matching
file name ``chaosnet'', changing the input line to
% vi chaosnet
However, given
% vi D<escape>
_c_s_h will only expand the input to
% vi DSC.
and will sound the terminal bell to indicate that the expan-
sion is incomplete, since there are two file names matching
the prefix ``D''.
If a partial file name is followed by the end-of-file char-
acter (usually control-D), then, instead of completing the
name, _c_s_h will list all file names matching the prefix. For
example, the input
% vi D<control-D>
causes all files beginning with ``D'' to be listed:
DSC.NEW DSC.OLD
while the input line remains unchanged.
The same system of escape and end-of-file can also be used
to expand partial user names, if the word to be completed
(or listed) begins with the character ``~''. For example,
typing
cd ~ro<control-D>
may produce the expansion
cd ~root
The use of the terminal bell to signal errors or multiple
matches can be inhibited by setting the variable _n_o_b_e_e_p.
Normally, all files in the particular directory are candi-
dates for name completion. Files with certain suffixes can
be excluded from consideration by setting the variable _f_i_g_-
_n_o_r_e to the list of suffixes to be ignored. Thus, if _f_i_g_-
_n_o_r_e is set by the command
% set fignore = (.o .out)
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then typing
% vi x<escape>
would result in the completion to
% vi xmpl.c
ignoring the files "xmpl.o" and "xmpl.out". However, if the
only completion possible requires not ignoring these suf-
fixes, then they are not ignored. In addition, _f_i_g_n_o_r_e does
not affect the listing of file names by control-D. All
files are listed regardless of their suffixes.
Substitutions
We now describe the various transformations the shell per-
forms 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 spelling mistakes in the previous
command with little typing and a high degree of confidence.
History substitutions begin with the character `!' and may
begin anywhere in the input stream (with the proviso that
they do not nest.) This `!' may be preceded by an `\' to
prevent its special meaning; for convenience, 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 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 sub-
stitutions reintroduce sequences of words from these saved
commands into the input stream. The size of which is con-
trolled by the _h_i_s_t_o_r_y variable; the previous command is
always retained, regardless of its value. Commands are num-
bered sequentially from 1.
For definiteness, consider the following output from the
_h_i_s_t_o_r_y 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 _p_r_o_m_p_t by placing an
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`!' 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 rein-
troduce the words of the specified events, each separated by
a single blank. As a special case `!!' refers to the previ-
ous command; thus `!!' alone is essentially a _r_e_d_o.
To select words from an event we can follow the event
specification by a `:' and a designator for the desired
words. The words of an input line are numbered from 0, the
first (usually command) word being 0, the second word (first
argument) being 1, etc. The basic word designators are:
0 first (command) word
_n _n'th argument
^ first argument, i.e. `1'
$ last argument
% word matched by (immediately preceding) ?_s? search
_x-_y range of words
-_y abbreviates `0-_y'
* abbreviates `^-$', or nothing if only 1 word in event
_x* abbreviates `_x-$'
_x- like `_x*' but omitting word `$'
The `:' separating the event specification from the word
designator can be omitted if the argument selector begins
with a `^', `$', `*' `-' or `%'. After the optional word
designator can be placed a sequence of modifiers, each pre-
ceded by a `:'. The following modifiers are defined:
h Remove a trailing pathname component, leaving the head.
r Remove a trailing `.xxx' component, leaving the root name.
e Remove all but the extension `.xxx' part.
s/_l/_r/ Substitute _l for _r
t Remove all leading pathname components, leaving the tail.
& Repeat the previous substitution.
g Apply the change 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 expres-
sions in the sense of the editors, but rather strings. Any
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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 substitu-
tion 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 specifica-
tion, e.g. `!$'. In this case the reference is to the pre-
vious command unless a previous history reference occurred
on the same line in which case this form repeats the previ-
ous reference. Thus `!?foo?^ !$' 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 short-
hand 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 char-
acters 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'.
Quotations with ' and "
The quotation of strings by `'' and `"' can be used to
prevent all or some of the remaining substitutions. Strings
enclosed in `'' are prevented any further interpretation.
Strings enclosed in `"' may be expanded as described below.
In both cases the resulting text becomes (all or part of) a
single word; only in one special case (see _C_o_m_m_a_n_d _S_u_b_s_t_i_t_i_-
_t_i_o_n 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 esta-
blished, displayed and modified by the _a_l_i_a_s and _u_n_a_l_i_a_s
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.
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Thus if the alias for `ls' is `ls -l' the command `ls /usr'
would map to `ls -l /usr', the argument list here being
undisturbed. Similarly if the alias for `lookup' was `grep
!^ /etc/passwd' then `lookup bill' would map to `grep bill
/etc/passwd'.
If an alias is found, the word transformation of the input
text is performed and the aliasing process begins again on
the reformed input line. Looping is prevented if the first
word of the new text is the same as the old by flagging it
to prevent further aliasing. Other loops are detected and
cause an error.
Note that the mechanism allows aliases to introduce parser
metasyntax. Thus we can `alias print 'pr \!* | lpr'' to
make a command which _p_r'_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 _a_r_g_v variable is an image of the shell's argument list,
and words of this variable's value are referred to in spe-
cial ways.
The values of variables may be displayed and changed by
using the _s_e_t and _u_n_s_e_t 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 _v_e_r_b_o_s_e variable is a toggle which causes
command input to be echoed. The setting of this variable
results from the -v command line option.
Other operations treat variables numerically. The `@' com-
mand permits numeric calculations to be performed and the
result assigned to a variable. Variable values are, how-
ever, always represented as (zero or more) strings. For the
purposes of numeric operations, the null string is con-
sidered 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 `"'s where it
always occurs, and within `''s where it never occurs.
Strings quoted by ``' are interpreted later (see _C_o_m_m_a_n_d
_s_u_b_s_t_i_t_u_t_i_o_n below) so `$' substitution does not occur there
until later, if at all. A `$' is passed unchanged if fol-
lowed 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 `"' or given the `:q' modifier the
results of variable substitution may eventually be command
and filename substituted. Within `"', a variable whose
value consists of multiple words expands to a (portion of) a
single word, with the words of the variables value separated
by blanks. When the `:q' modifier is applied to a substitu-
tion the variable will expand to multiple words with each
word separated by a blank and quoted to prevent later com-
mand 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
_n_a_m_e, each separated by a blank. Braces insulate _n_a_m_e
from following characters which would otherwise be part
of it. Shell variables have names consisting of up to
20 letters and digits starting with a letter. The
underscore character is considered a letter.
If _n_a_m_e is not a shell variable, but is set in the
environment, then that value is returned (but : modif-
iers and the other forms given below are not available
in this case).
$name[selector]
${name[selector]}
May be used to select only some of the words from the
value of _n_a_m_e. The selector is subjected to `$' substi-
tution and may consist of a single number or two
numbers separated by a `-'. The first word of a vari-
ables 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 omit-
ted 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 modif-
iers must appear within the braces. The current implementa-
tion allows only one `:' modifier on each `$' expansion.
The following substitutions may not be modified with `:'
modifiers.
$?name
${?name}
Substitutes the string `1' if name is set, `0' if it is
not.
$?0
Substitutes `1' if the current input filename is known,
`0' if it is not.
$$
Substitute the (decimal) process number of the (parent)
shell.
$<
Substitutes a line from the standard input, with no
further interpretation thereafter. It can be used to
read from the keyboard in a shell script.
Command and filename substitution
The remaining substitutions, command and filename substitu-
tion, 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 redirection is per-
formed, and in a child of the main shell.
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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 substitu-
tion to yield only part of a word, even if the command out-
puts 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 `glob-
bing'. 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 pat-
tern to match. Only the metacharacters `*', `?' and `['
imply pattern matching, the characters `~' and `{' being
more akin to abbreviations.
In matching filenames, the character `.' at the beginning of
a filename or immediately following a `/', as well as the
character `/' must be matched explicitly. The character `*'
matches any string of characters, including the null string.
The character `?' matches any single character. The
sequence `[...]' matches any one of the characters enclosed.
Within `[...]', a pair of characters separated by `-'
matches any character lexically between the two.
The character `~' at the beginning of a filename is used to
refer to home directories. Standing alone, i.e. `~' it
expands to the invokers home directory as reflected in the
value of the variable _h_o_m_e. When followed by a name consist-
ing of letters, digits and `-' characters the shell searches
for a user with that name and substitutes their home direc-
tory; thus `~ken' might expand to `/usr/ken' and
`~ken/chmach' to `/usr/ken/chmach'. If the character `~' is
followed by a character other than a letter or `/' or
appears not at the beginning of a word, it is left undis-
turbed.
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
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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 spe-
cial 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 _n_a_m_e (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
_w_o_r_d. _W_o_r_d is not subjected to variable, filename or
command substitution, and each input line is compared
to _w_o_r_d before any substitutions are done on this input
line. Unless a quoting `\', `"', `'' or ``' appears in
_w_o_r_d variable and command substitution 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 standard input.
> name
>! name
>& name
>&! name
The file _n_a_m_e 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 _n_o_c_l_o_b_b_e_r is set, then the file must
not exist or be a character special file (e.g. a termi-
nal 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.
_N_a_m_e is expanded in the same way as `<' input filenames
are.
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>> name
>>& name
>>! name
>>&! name
Uses file _n_a_m_e as standard output like `>' but places
output at the end of the file. If the variable
_n_o_c_l_o_b_b_e_r is set, then it is an error for the file not
to exist unless one of the `!' forms is given. Other-
wise 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 com-
mand run detached is not modified to be the empty file
`/dev/null'; rather the standard input remains as the origi-
nal 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 subse-
quently) take expressions, in which the operators are simi-
lar to those of C, with the same precedence. These expres-
sions appear in the @, _e_x_i_t, _i_f, and _w_h_i_l_e 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 _p_a_t_t_e_r_n (containing, e.g. `*'s, `?'s and instances
of `[...]') against which the left hand operand is matched.
This reduces the need for use of the _s_w_i_t_c_h statement in
shell scripts when all that is really needed is pattern
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CSH(1) UNIX Programmer's Manual CSH(1)
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 adja-
cent 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 com-
mand 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 execu-
tions 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 _s_t_a_t_u_s 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 _f_o_r_e_a_c_h, _s_w_i_t_c_h, and _w_h_i_l_e statements, as well as the
_i_f-_t_h_e_n-_e_l_s_e form of the _i_f statement require that the major
keywords appear in a single simple command on an input line
as shown below.
If the shell's input is not seekable, the shell buffers up
input whenever a loop is being read and performs seeks in
this internal buffer to accomplish the rereading implied by
the loop. (To the extent that this allows, backward goto's
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CSH(1) UNIX Programmer's Manual CSH(1)
will succeed on non-seekable inputs.)
Builtin commands
Builtin commands are executed within the shell. If a buil-
tin 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 _w_o_r_d_l_i_s_t as the alias of _n_a_m_e; _w_o_r_d_l_i_s_t is
command and filename substituted. _N_a_m_e is not allowed
to be _a_l_i_a_s or _u_n_a_l_i_a_s.
alloc
Shows the amount of dynamic memory acquired, broken
down into used and free memory. With an argument shows
the number of free and used blocks in each size
category. The categories start at size 8 and double at
each step. This command's output may vary across sys-
tem types, since systems other than the VAX may use a
different memory allocator.
bg
bg %job ...
Puts the current or specified jobs into the background,
continuing them if they were stopped.
break
Causes execution to resume after the _e_n_d of the nearest
enclosing _f_o_r_e_a_c_h or _w_h_i_l_e. 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 _s_w_i_t_c_h, resuming after the _e_n_d_s_w.
case label:
A label in a _s_w_i_t_c_h statement as discussed below.
cd
cd name
chdir
chdir name
Change the shell's working directory to directory _n_a_m_e.
If no argument is given then change to the home direc-
tory of the user.
If _n_a_m_e is not found as a subdirectory of the current
directory (and does not begin with `/', `./' or `../'),
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CSH(1) UNIX Programmer's Manual CSH(1)
then each component of the variable _c_d_p_a_t_h is checked
to see if it has a subdirectory _n_a_m_e. Finally, if all
else fails but _n_a_m_e 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 _w_h_i_l_e or
_f_o_r_e_a_c_h. The rest of the commands on the current line
are executed.
default:
Labels the default case in a _s_w_i_t_c_h statement. The
default should come after all _c_a_s_e labels.
dirs
Prints the directory stack; the top of the stack is at
the left, the first directory in the stack being the
current directory.
echo wordlist
echo -n wordlist
The specified words are written to the shells 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 _f_o_r_e_a_c_h, _i_f, _s_w_i_t_c_h, and
_w_h_i_l_e statements below.
eval arg ...
(As in _s_h(1).) The arguments are read as input to the
shell and the resulting command(s) executed in the con-
text of the current shell. This is usually used to
execute commands generated as the result of command or
variable substitution, since parsing occurs before
these substitutions. See _t_s_e_t(1) for an example of
using _e_v_a_l.
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 _s_t_a_t_u_s
variable (first form) or with the value of the speci-
fied _e_x_p_r (second form).
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CSH(1) UNIX Programmer's Manual CSH(1)
fg
fg %job ...
Brings the current or specified jobs into the fore-
ground, continuing them if they were stopped.
foreach name (wordlist)
...
end
The variable _n_a_m_e is successively set to each member of
_w_o_r_d_l_i_s_t and the sequence of commands between this com-
mand and the matching _e_n_d are executed. (Both _f_o_r_e_a_c_h
and _e_n_d must appear alone on separate lines.)
The builtin command _c_o_n_t_i_n_u_e may be used to continue
the loop prematurely and the builtin command _b_r_e_a_k to
terminate it prematurely. When this command is read
from the terminal, the loop is read up once prompting
with `?' before any statements in the loop are exe-
cuted. If you make a mistake typing in a loop at the
terminal you can rub it out.
glob wordlist
Like _e_c_h_o 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 _w_o_r_d 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 _e_x_e_c's). An _e_x_e_c is attempted for each com-
ponent of the _p_a_t_h where the hash function indicates a
possible hit, and in each component which does not
begin with a `/'.
history
history _n
history -r _n
history -h _n
Displays the history event list; if _n is given only the
_n most recent events are printed. The -r option rev-
erses the order of printout to be most recent first
rather than oldest first. The -h option causes the
history list to be printed without leading numbers.
This is used to produce files suitable for sourceing
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CSH(1) UNIX Programmer's Manual CSH(1)
using the -h option to _s_o_u_r_c_e.
if (expr) command
If the specified expression evaluates true, then the
single _c_o_m_m_a_n_d with arguments is executed. Variable
substitution on _c_o_m_m_a_n_d happens early, at the same time
it does for the rest of the _i_f command. _C_o_m_m_a_n_d must
be a simple command, not a pipeline, a command list, or
a parenthesized command list. Input/output redirection
occurs even if _e_x_p_r is false, when command is not exe-
cuted (this is a bug).
if (expr) then
...
else if (expr2) then
...
else
...
endif
If the specified _e_x_p_r is true then the commands to the
first _e_l_s_e are executed; otherwise if _e_x_p_r_2 is true
then the commands to the second _e_l_s_e are executed, etc.
Any number of _e_l_s_e-_i_f pairs are possible; only one
_e_n_d_i_f is needed. The _e_l_s_e part is likewise optional.
(The words _e_l_s_e and _e_n_d_i_f must appear at the beginning
of input lines; the _i_f must appear alone on its input
line or after an _e_l_s_e.)
jobs
jobs -l
Lists the active jobs; given the -l options lists pro-
cess 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 speci-
fied signal to the specified jobs or processes. Sig-
nals are either given by number or by names (as given
in /_u_s_r/_i_n_c_l_u_d_e/_s_i_g_n_a_l._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 pro-
cess will be sent a CONT (continue) signal as well.
limit
limit _r_e_s_o_u_r_c_e
limit _r_e_s_o_u_r_c_e _m_a_x_i_m_u_m-_u_s_e
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CSH(1) UNIX Programmer's Manual CSH(1)
limit -h
limit -h _r_e_s_o_u_r_c_e
limit -h _r_e_s_o_u_r_c_e _m_a_x_i_m_u_m-_u_s_e
Limits the consumption by the current process and each
process it creates to not individually exceed _m_a_x_i_m_u_m-
_u_s_e on the specified _r_e_s_o_u_r_c_e. If no _m_a_x_i_m_u_m-_u_s_e is
given, then the current limit is printed; if no
_r_e_s_o_u_r_c_e is given, then all limitations are given. If
the -h flag is given, the hard limits are used instead
of the current limits. The hard limits impose a ceil-
ing on the values of the current limits. Only the
super-user may raise the hard limits, but a user may
lower or raise the current limits within the legal
range.
Resources controllable currently include _c_p_u_t_i_m_e (the
maximum number of cpu-seconds to be used by each pro-
cess), _f_i_l_e_s_i_z_e (the largest single file which can be
created), _d_a_t_a_s_i_z_e (the maximum growth of the
data+stack region via _s_b_r_k(2) beyond the end of the
program text), _s_t_a_c_k_s_i_z_e (the maximum size of the
automatically-extended stack region), and _c_o_r_e_d_u_m_p_s_i_z_e
(the size of the largest core dump that will be
created).
The _m_a_x_i_m_u_m-_u_s_e may be given as a (floating point or
integer) number followed by a scale factor. For all
limits other than _c_p_u_t_i_m_e the default scale is `k' or
`kilobytes' (1024 bytes); a scale factor of `m' or
`megabytes' may also be used. For _c_p_u_t_i_m_e 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 _r_e_s_o_u_r_c_e names and scale factors, unambiguous
prefixes of the names suffice.
login
Terminate a login shell, replacing it with an instance
of /bin/login. This is one way to log off, included for
compatibility with _s_h(1).
logout
Terminate a login shell. Especially useful if
_i_g_n_o_r_e_e_o_f is set.
nice
nice +number
nice command
nice +number command
The first form sets the scheduling priority for this
shell to 4. The second form sets the priority to the
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CSH(1) UNIX Programmer's Manual CSH(1)
given number. The final two forms run command at
priority 4 and _n_u_m_b_e_r respectively. The greater the
number, the less cpu the process will get. The super-
user may specify negative priority by using `nice
-number ...'. Command is always executed in a sub-
shell, and the restrictions placed on commands in sim-
ple _i_f 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 _n_o_h_u_p'_e_d.
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 _n_o_t_i_f_y 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 _o_n_i_n_t_r have
no meaning and interrupts continue to be ignored by the
shell and all invoked commands.
popd
popd +n
Pops the directory stack, returning to the new top
directory. With an 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, _p_u_s_h_d exchanges the top two elements
of the directory stack. Given a _n_a_m_e argument, _p_u_s_h_d
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CSH(1) UNIX Programmer's Manual CSH(1)
changes to the new directory (ala _c_d) and pushes the
old current working directory (as in _c_s_w) 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
directories in the _p_a_t_h variable to be recomputed.
This is needed if new commands are added to directories
in the _p_a_t_h while you are logged in. This should only
be necessary if you add commands to one of your own
directories, or if a systems programmer changes the
contents of one of the system directories.
repeat count command
The specified _c_o_m_m_a_n_d which is subject to the same res-
trictions as the _c_o_m_m_a_n_d in the one line _i_f statement
above, is executed _c_o_u_n_t times. I/O redirections occur
exactly once, even if _c_o_u_n_t 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 _n_a_m_e to the null string.
The third form sets _n_a_m_e to the single _w_o_r_d. The fourth
form sets the _i_n_d_e_x'_t_h component of name to word; this
component must already exist. The final form sets _n_a_m_e
to the list of words in _w_o_r_d_l_i_s_t. 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
setenv name value
setenv name
The first form lists all current environment variables.
The last form sets the value of environment variable
_n_a_m_e to be _v_a_l_u_e, a single string. The second form
sets _n_a_m_e to an empty string. The most commonly used
environment variable USER, TERM, and PATH are automati-
cally imported to and exported from the _c_s_h variables
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CSH(1) UNIX Programmer's Manual CSH(1)
_u_s_e_r, _t_e_r_m, and _p_a_t_h; there is no need to use _s_e_t_e_n_v
for these.
shift
shift variable
The members of _a_r_g_v are shifted to the left, discarding
_a_r_g_v[_1]. It is an error for _a_r_g_v not to be set or to
have less than one word as value. The second form per-
forms the same function on the specified variable.
source name
source -h name
The shell reads commands from _n_a_m_e. _S_o_u_r_c_e commands may
be nested; if they are nested too deeply the shell may
run out of file descriptors. An error in a _s_o_u_r_c_e at
any level terminates all nested _s_o_u_r_c_e commands. Nor-
mally input during _s_o_u_r_c_e commands is not placed on the
history list; the -h option causes the commands to be
placed in the history list without being executed.
stop
stop %job ...
Stops the current or specified job which is executing
in the background.
suspend
Causes the shell to stop in its tracks, much as if it
had been sent a stop signal with ^Z. This is most
often used to stop shells started by _s_u(1).
switch (string)
case str1:
...
breaksw
...
default:
...
breaksw
endsw
Each case label is successively matched, against the
specified _s_t_r_i_n_g 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 _b_r_e_a_k_s_w causes execution to continue after
the _e_n_d_s_w. 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
_e_n_d_s_w.
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time
time command
With no argument, a summary of time used by this shell
and its children is printed. If arguments are given
the specified simple command is timed and a time sum-
mary as described under the _t_i_m_e variable is printed.
If necessary, an extra shell is created to print the
time statistic when the command completes.
umask
umask value
The file creation mask is displayed (first form) or set
to the specified value (second form). The mask is
given in octal. Common values for the mask are 002
giving all access to the group and read and execute
access to others or 022 giving all access except no
write access for users in the group or others.
unalias pattern
All aliases whose names match the specified pattern are
discarded. Thus all aliases are removed by `unalias
*'. It is not an error for nothing to be _u_n_a_l_i_a_s_e_d.
unhash
Use of the internal hash table to speed location of
executed programs is disabled.
unlimit
unlimit _r_e_s_o_u_r_c_e
unlimit -h
unlimit -h _r_e_s_o_u_r_c_e
Removes the limitation on _r_e_s_o_u_r_c_e. If no _r_e_s_o_u_r_c_e is
specified, then all _r_e_s_o_u_r_c_e limitations are removed.
If -h is given, the corresponding hard limits are
removed. Only the super-user may do this.
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 _u_n_s_e_t.
unsetenv pattern
Removes all variables whose name match the specified
pattern from the environment. See also the _s_e_t_e_n_v com-
mand above and _p_r_i_n_t_e_n_v(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.
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CSH(1) UNIX Programmer's Manual CSH(1)
while (expr)
...
end
While the specified expression evaluates non-zero, the
commands between the _w_h_i_l_e and the matching end are
evaluated. _B_r_e_a_k and _c_o_n_t_i_n_u_e may be used to terminate
or continue the loop prematurely. (The _w_h_i_l_e and _e_n_d
must appear alone on their input lines.) Prompting
occurs here the first time through the loop as for the
_f_o_r_e_a_c_h 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 vari-
ables. The second form sets the specified _n_a_m_e to the
value of _e_x_p_r. If the expression contains `<', `>', `&'
or `|' then at least this part of the expression must
be placed within `(' `)'. The third form assigns the
value of _e_x_p_r to the _i_n_d_e_x'_t_h argument of _n_a_m_e. Both
_n_a_m_e and its _i_n_d_e_x'_t_h 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 _e_x_p_r which would otherwise
be single words.
Special postfix `++' and `--' operators increment and
decrement _n_a_m_e respectively, i.e. `@ i++'.
Pre-defined and environment variables
The following variables have special meaning to the shell.
Of these, _a_r_g_v, _c_w_d, _h_o_m_e, _p_a_t_h, _p_r_o_m_p_t, _s_h_e_l_l and _s_t_a_t_u_s
are always set by the shell. Except for _c_w_d and _s_t_a_t_u_s 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 _u_s_e_r, TERM into _t_e_r_m, and HOME into _h_o_m_e, 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 ._c_s_h_r_c as inferior _c_s_h
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CSH(1) UNIX Programmer's Manual CSH(1)
processes will import the definition of _p_a_t_h 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 _c_h_d_i_r com-
mands.
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 selec-
tively.
filec Enable file name completion.
histchars Can be given a string value to change the
characters used in history substitution. The
first character of its value is used as the
history substitution character, replacing the
default character !. The second character of
its value replaces the character |^ in quick
substitutions.
history Can be given a numeric value to control the
size of the history list. Any command which
has been referenced in this many events will
not be discarded. Too large values of _h_i_s_-
_t_o_r_y 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, initial-
ized from the environment. The filename
expansion of `~' refers to this variable.
ignoreeof If set the shell ignores end-of-file from
input devices which are terminals. This
prevents shells from accidentally being
killed by control-D's.
mail The files where the shell checks for mail.
This is done after each command completion
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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 _m_a_i_l is
numeric it specifies a different mail check-
ing interval, in seconds, than the default,
which is 10 minutes.
If multiple mail files are specified, then
the shell says `New mail in _n_a_m_e' when there
is mail in the file _n_a_m_e.
noclobber As described in the section on _I_n_p_u_t/_o_u_t_p_u_t,
restrictions 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.
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 rather
present job completions just before printing
a prompt.
path Each word of the path variable specifies a
directory in which commands are to be sought
for execution. A null word specifies the
current directory. If there is no _p_a_t_h vari-
able then only full path names will execute.
The usual search path is `.', `/bin' and
`/usr/bin', but this may vary from system to
system. For the super-user the default
search path is `/etc', `/bin' and `/usr/bin'.
A shell which is given neither the -c nor the
-t option will normally hash the contents of
the directories in the _p_a_t_h variable after
reading ._c_s_h_r_c, and each time the _p_a_t_h vari-
able is reset. If new commands are added to
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CSH(1) UNIX Programmer's Manual CSH(1)
these directories while the shell is active,
it may be necessary to give the _r_e_h_a_s_h or the
commands may not be found.
prompt The string which is printed before each com-
mand is read from an interactive terminal
input. If a `!' appears in the string it
will be replaced by the current event number
unless a preceding `\' is given. Default is
`% ', or `# ' for the super-user.
savehist is given a numeric value to control the
number of entries of the history list that
are saved in ~/.history when the user logs
out. Any command which has been referenced
in this many events will be saved. During
start up the shell sources ~/.history into
the history list enabling history to be saved
across logins. Too large values of _s_a_v_e_h_i_s_t
will slow down the shell during start up.
shell The file in which the shell resides. This is
used in forking shells to interpret files
which have execute bits set, but which are
not executable by the system. (See the
description of _N_o_n-_b_u_i_l_t_i_n _C_o_m_m_a_n_d _E_x_e_c_u_t_i_o_n
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. 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 giv-
ing user, system, and real times and a utili-
zation 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 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
_e_x_e_c_v_e(2). Each word in the variable _p_a_t_h names a directory
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CSH(1) UNIX Programmer's Manual CSH(1)
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 _e_x_e_c 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 _u_n_h_a_s_h), or if the shell was given a -c or
-t argument, and in any case for each directory component of
_p_a_t_h 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 _h_o_m_e directory; leaving
you where you were (printing this after the home directory),
while `cd ; pwd' leaves you in the _h_o_m_e directory.
Parenthesized commands are most often used to prevent _c_h_d_i_r
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 con-
taining shell commands and a new shell is spawned to read
it.
If there is an _a_l_i_a_s for _s_h_e_l_l then the words of the alias
will be prepended to the argument list to form the shell
command. The first word of the _a_l_i_a_s should be the full
path name of the shell (e.g. `$shell'). Note that this is a
special, late occurring, case of _a_l_i_a_s 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:
-b This flag forces a ``break'' from option processing,
causing any further shell arguments to be treated as
non-option arguments. The remaining arguments will not
be interpreted as shell options. This may be used to
pass options to a shell script without confusion or
possible subterfuge. The shell will not run a set-user
ID script without this option.
-c Commands are read from the (single) following argument
which must be present. Any remaining arguments are
placed in _a_r_g_v.
-e The shell exits if any invoked command terminates
abnormally or yields a non-zero exit status.
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-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 interactive without this option if their inputs and
outputs are terminals.
-n Commands are parsed, but not executed. This aids in
syntactic checking of shell scripts.
-s Command input is taken from the standard input.
-t A single line of input is read and executed. A `\' may
be used to escape the newline at the end of this line
and continue onto another line.
-v Causes the _v_e_r_b_o_s_e variable to be set, with the effect
that command input is echoed after history substitu-
tion.
-x Causes the _e_c_h_o variable to be set, so that commands
are echoed immediately before execution.
-V Causes the _v_e_r_b_o_s_e 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 comment. Remaining arguments initialize the variable
_a_r_g_v.
Signal handling
The shell normally ignores _q_u_i_t signals. Jobs running
detached (either by `&' or the _b_g 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 inter-
rupts and terminate signals in shell scripts can be con-
trolled by _o_n_i_n_t_r. Login shells catch the _t_e_r_m_i_n_a_t_e signal;
otherwise this signal is passed on to children from the
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CSH(1) UNIX Programmer's Manual CSH(1)
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
implemented by J.E. Kulp of I.I.A.S.A, Laxenburg, Austria,
with different syntax than that used now. File name comple-
tion code written by Ken Greer, HP Labs.
FILES
~/.cshrc Read at beginning of execution by each shell.
~/.login Read by login shell, after `.cshrc' at login.
~/.logout Read by login shell, at logout.
/bin/sh Standard shell, for shell scripts not starting with a `#'.
/tmp/sh* Temporary file for `<<'.
/etc/passwd Source of home directories for `~name'.
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 substitutions may substitute no more
characters than are allowed in an argument list. To detect
looping, the shell restricts the number of _a_l_i_a_s substitu-
tions on a single line to 20.
SEE ALSO
sh(1), access(2), execve(2), fork(2), killpg(2), pipe(2),
sigvec(2), umask(2), setrlimit(2), wait(2), tty(4),
a.out(5), environ(7), `An introduction to the C shell'
BUGS
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 (i.e. wrong) as
the job may have changed directories internally.
Shell builtin functions are not stoppable/restartable. Com-
mand 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 espe-
cially noticeable if this expansion results from an _a_l_i_a_s.
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 prim-
itive; 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 con-
trol.
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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 _h_i_s_t_o_r_y 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 `;' metasyn-
tax.
It should be possible to use the `:' modifiers on the output
of command substitutions. All and more than one `:' modif-
ier should be allowed on `$' substitutions.
The way the filec facility is implemented is ugly and expen-
sive.
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