4.3BSD-Reno/share/man/cat1/stop.0
CSH(1) UNIX Reference Manual CSH(1)
NNAAMMEE
ccsshh - a shell (command interpreter) with C-like syntax
SSYYNNOOPPSSIISS
ccsshh [--cceeff^^iinnssttvvVVxxXX] [arg ...]
DDEESSCCRRIIPPTTIIOONN
The CCsshh is a command language interpreter incorporating a history mechan-
ism (see HHiissttoorryy SSuubbssttiittuuttiioonnss), job control facilities (see JJoobbss), in-
teractive file name and user name completion (see FFiillee NNaammee CCoommpplleettiioonn),
and a C-like syntax. It is used both as an interactive login shell and a
shell script command processor.
AArrgguummeenntt lliisstt pprroocceessssiinngg
If the first argument (argument 0) to the shell is `--' then this is a
login shell. The flag arguments are interpreted as follows:
--bb 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.
--cc Commands are read from the (single) following argument which must be
present. Any remaining arguments are placed in _a_r_g_v.
--ee The shell exits if any invoked command terminates abnormally or
yields a non-zero exit status.
--ff The shell will start faster, because it will neither search for nor
execute commands from the file ._c_s_h_r_c in the invoker's home directo-
ry.
--ii 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.
--nn Commands are parsed, but not executed. This aids in syntactic
checking of shell scripts.
--ss Command input is taken from the standard input.
--tt 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.
--vv Causes the _v_e_r_b_o_s_e variable to be set, with the effect that command
input is echoed after history substitution.
--xx Causes the _e_c_h_o variable to be set, so that commands are echoed im-
mediately before execution.
--VV Causes the _v_e_r_b_o_s_e variable to be set even before ._c_s_h_r_c _i_s
_e_x_e_c_u_t_e_d.
--XX Is to --xx as --VV is to --vv.
After processing of flag arguments, if arguments remain but none of the
--cc, --ii, --ss, or --tt options were 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 sys-
tems 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.
An instance of ccsshh begins by executing commands from the file
/_e_t_c/_c_s_h._c_s_h_r_c and, if this is a login shell, /_e_t_c/_c_s_h._l_o_g_i_n. It then
executes commands from ._c_s_h_r_c in the _h_o_m_e directory of the invoker, and,
if this is a login shell, the file ._l_o_g_i_n in the same location. 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 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 com-
mand 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 files ._l_o_g_o_u_t
in the user's _h_o_m_e directory and /_e_t_c/_c_s_h._l_o_g_o_u_t.
LLeexxiiccaall ssttrruuccttuurree
The shell splits input lines into words at blanks and tabs with the fol-
lowing 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 separate words. These quotations have se-
mantics to be described subsequently. Within pairs of `'' or `"' charac-
ters a newline preceded by a `\' gives a true newline character.
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 `"'.
CCoommmmaannddss
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 com-
mands 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 respective-
ly. (See _E_x_p_r_e_s_s_i_o_n_s.)
JJoobbss
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 ^^ZZ (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 com-
mands and then eventually bring the job back into the foreground with the
foreground command _f_g. A ^^ZZ takes effect immediately and is like an in-
terrupt in that pending output and unread input are discarded when it is
typed. There is another special key ^^YY 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 output, but
this can be disabled by giving the command ``stty tostop''. If you set
this tty option, then background jobs will stop when they try to produce
output like they do when they try to read input.
There are several ways to refer to jobs in the shell. The character `%'
introduces a job name. If you wish to refer to job number 1, you can
name it as `%1'. Just naming a job brings it to the foreground; thus
`%1' is a synonym for `fg %1', bringing job 1 back into the foreground.
Similarly saying `%1 &' resumes job 1 in the background. Jobs can also
be named by prefixes of the string typed in to start them, if these pre-
fixes 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 _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.
The job control mechanism requires that the stty(1) option nneeww be set. It
is an artifact from a _n_e_w implementation of the tty driver which 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.
SSttaattuuss rreeppoorrttiinngg
This shell learns immediately whenever a process changes state. It nor-
mally informs you whenever a job becomes blocked so that no further pro-
gress 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 immediately 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; sim-
ply 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 second time, and the suspended jobs will be
terminated.
FFiillee NNaammee CCoommpplleettiioonn
When the file name completion feature is enabled by setting the shell
variable _f_i_l_e_c (see sseett), ccsshh 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 exam-
ple, 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>
ccsshh will complete the prefix ``ch'' to the only matching file name
``chaosnet'', changing the input line to
% vi chaosnet
However, given
% vi D<escape>
ccsshh will only expand the input to
% vi DSC.
and will sound the terminal bell to indicate that the expansion is incom-
plete, since there are two file names matching the prefix ``D''.
If a partial file name is followed by the end-of-file character (usually
control-D), then, instead of completing the name, ccsshh 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 par-
tial user names, if the word to be completed (or listed) begins with the
character ``~''. For example, typing
cd ~ro<escape>
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 candidates for name
completion. Files with certain suffixes can be excluded from considera-
tion by setting the variable _f_i_g_n_o_r_e to the list of suffixes to be ig-
nored. Thus, if _f_i_g_n_o_r_e is set by the command
% set fignore = (.o .out)
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 comple-
tion possible requires not ignoring these suffixes, then they are not ig-
nored. 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.
SSuubbssttiittuuttiioonnss
We now describe the various transformations the shell performs on the in-
put in the order in which they occur.
HHiissttoorryy ssuubbssttiittuuttiioonnss
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 _a_n_y_w_h_e_r_e
in the input stream (with the proviso that they ddoo nnoott nest.) This `!'
may be preceded by an `\' to prevent its special meaning; for conveni-
ence, 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 substi-
tution.
Commands input from the terminal which consist of one or more words are
saved on the history list. The history substitutions reintroduce se-
quences of words from these saved commands into the input stream. The
size of which is controlled by the _h_i_s_t_o_r_y 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 _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 `!' 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 reintro-
duce 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 _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 preceded 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 line but do not execute it.
q Quote the substituted words, preventing further substitu-
tions.
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 previ-
ous 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'.
QQuuoottaattiioonnss wwiitthh '' aanndd ""
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 ex-
panded 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.
AAlliiaass ssuubbssttiittuuttiioonn
The shell maintains a list of aliases which can be established, 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.
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 per-
formed 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.
VVaarriiaabbllee ssuubbssttiittuuttiioonn
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 special 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 --vv command line option.
Other operations treat variables numerically. The `@' command permits
numeric calculations to be performed and the result assigned to a vari-
able. Variable values are, however, 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 _a_l_w_a_y_s occurs, and within `''s where it _n_e_v_e_r oc-
curs. Strings quoted by ``' are interpreted later (see CCoommmmaanndd
ssuubbssttiittuuttiioonn 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 substituted. Within
`"', a variable whose value consists of multiple words expands to a (por-
tion of) a single word, with the words of the variables value separated
by blanks. When the `:q' modifier is applied to a substitution the vari-
able 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 _n_a_m_e, each
separated by a blank. Braces insulate _n_a_m_e from following charac-
ters 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 : modifiers and the other forms
given below are not available in this case).
$name[selector]
${name[selector]}
May be used to select only some of the words from the value of
_n_a_m_e. The selector is subjected to `$' substitution and may con-
sist 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
${#name}
Gives the number of words in the variable. This is useful for
later use in a `$argv[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 `:e', `:h', `:t', `:r',
`:q' and `:x' may be applied to the substitutions above as may
`:gh', `:gt' and `:gr'. If braces `{' '}' appear in the command
form then the modifiers must appear within the braces. The current
implementation allows only one `:' modifier on each `$' expansion.
The following substitutions may not be modified with `:' modifiers.
$?name
${?name}
Substitutes the string `1' if name is set, `0' if it is not.
$?0 Substitutes `1' if the current input filename is known, `0' if it
is not.
$$ 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.
CCoommmmaanndd aanndd ffiilleennaammee ssuubbssttiittuuttiioonn
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 redirection is performed, and in a
child of the main shell.
CCoommmmaanndd ssuubbssttiittuuttiioonn
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.
FFiilleennaammee ssuubbssttiittuuttiioonn
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 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 consisting of letters, digits and `-' characters the shell
searches for a user with that name and substitutes their home directory;
thus `~ken' might expand to `/usr/ken' and `~ken/chmach' to
`/usr/ken/chmach'. If the character `~' is followed by a character other
than a letter or `/' or appears not at the beginning of a word, it is
left undisturbed.
The metanotation `a{b,c,d}e' is a shorthand for `abe ace ade'. Left to
right order is preserved, with results of matches being sorted 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.
IInnppuutt//oouuttppuutt
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 ex-
panded) 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 ``' ap-
pears in _w_o_r_d variable and command substitution is performed on the
intervening lines, allowing `\' to quote `$', `\' and ``'. Com-
mands 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 ex-
ist 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 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 speci-
fied file as well as the standard output. _N_a_m_e is expanded in the
same way as `<' input filenames are.
>> 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. Otherwise similar to `>'.
A command receives the environment in which the shell was invoked as
modified by the input-output parameters and the presence of the command
in a pipeline. Thus, unlike some previous shells, commands run from a
file of shell commands have no access to the text of the commands by de-
fault; 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 _n_o_t modified to be the empty file /_d_e_v/_n_u_l_l;
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 _J_o_b_s above).
Diagnostic output may be directed through a pipe with the standard out-
put. Simply use the form `|&' rather than just `|'.
EExxpprreessssiioonnss
A number of the builtin commands (to be described subsequently) take ex-
pressions, in which the operators are similar to those of C, with the
same precedence. These expressions appear in the @@,, _e_x_i_t, _i_f, and _w_h_i_l_e
commands. The following operators are available:
|| && | *(ua & == != =~ !~ <= >= < >
<< >> + - * / % ! ~ ( )
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 matching.
Strings which begin with `0' are considered octal numbers. Null or miss-
ing arguments are considered `0'. The result of all expressions are
strings, which represent decimal numbers. It is important to note that
no two components of an expression can appear in the same word; except
when adjacent to components of expressions which are syntactically signi-
ficant to the parser (`&' `|' `<' `>' `(' `)') they should be surrounded
by spaces.
Also available in expressions as primitive operands are command execu-
tions enclosed in `{' and `}' and file enquiries of the form --ll _n_a_m_e
where ll 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 com-
mand 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.
CCoonnttrrooll ffllooww
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 use-
ful ways) from terminal input. These commands all operate by forcing the
shell to reread or skip in its input and, due to the implementation, res-
trict the placement of some of the commands.
The ffoorreeaacchh, sswwiittcchh, and wwhhiillee statements, as well as the iiff--tthheenn--eellssee
form of the iiff statement require that the major keywords appear in a sin-
gle 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 accom-
plish the rereading implied by the loop. (To the extent that this al-
lows, backward goto's will succeed on non-seekable inputs.)
BBuuiillttiinn ccoommmmaannddss
Builtin commands are executed within the shell. If a builtin command oc-
curs as any component of a pipeline except the last then it is executed
in a subshell.
aalliiaass
aalliiaass _n_a_m_e
aalliiaass _n_a_m_e _w_o_r_d_l_i_s_t
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.
aalllloocc
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
system types, since systems other than the VAX may use a different
memory allocator.
bbgg
bbgg %%_j_o_b ...
Puts the current or specified jobs into the background, continuing
them if they were stopped.
bbrreeaakk
Causes execution to resume after the eenndd of the nearest enclosing
ffoorreeaacchh or wwhhiillee. The remaining commands on the current line are
executed. Multi-level breaks are thus possible by writing them all
on one line.
bbrreeaakkssww
Causes a break from a sswwiittcchh, resuming after the eennddssww.
ccaassee _l_a_b_e_l:
A label in a sswwiittcchh statement as discussed below.
ccdd
ccdd _n_a_m_e
cchhddiirr
cchhddiirr _n_a_m_e
Change the shell's working directory to directory _n_a_m_e. If no ar-
gument is given then change to the home directory of the user. If
_n_a_m_e is not found as a subdirectory of the current directory (and
does not begin with `/', `./' or `../'), then each component of the
variable ccddppaatthh 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.
ccoonnttiinnuuee
Continue execution of the nearest enclosing wwhhiillee or ffoorreeaacchh. The
rest of the commands on the current line are executed.
ddeeffaauulltt:
Labels the default case in a sswwiittcchh statement. The default should
come after all ccaassee labels.
ddiirrss
Prints the directory stack; the top of the stack is at the left,
the first directory in the stack being the current directory.
eecchhoo _w_o_r_d_l_i_s_t
eecchhoo --nn _w_o_r_d_l_i_s_t
The specified words are written to the shells standard output,
separated by spaces, and terminated with a newline unless the --nn
option is specified.
eellssee
eenndd
eennddiiff
eennddssww
See the description of the ffoorreeaacchh, iiff, sswwiittcchh, and wwhhiillee state-
ments below.
eevvaall _a_r_g ...
(As in sh(1).) The arguments are read as input to the shell and the
resulting command(s) executed in the context of the current shell.
This is usually used to execute commands generated as the result of
command or variable substitution, since parsing occurs before these
substitutions. See tset(1) for an example of using eevvaall.
eexxeecc _c_o_m_m_a_n_d
The specified command is executed in place of the current shell.
eexxiitt
eexxiitt (_e_x_p_r)
The shell exits either with the value of the ssttaattuuss variable (first
form) or with the value of the specified eexxpprr (second form).
ffgg
ffgg %%_j_o_b ...
Brings the current or specified jobs into the foreground,
continuing them if they were stopped.
ffoorreeaacchh _n_a_m_e (_w_o_r_d_l_i_s_t)
...
eenndd The variable nnaammee is successively set to each member of wwoorrddlliisstt
and the sequence of commands between this command and the matching
eenndd are executed. (Both ffoorreeaacchh and eenndd must appear alone on
separate lines.) The builtin command ccoonnttiinnuuee may be used to con-
tinue the loop prematurely and the builtin command bbrreeaakk to ter-
minate it prematurely. When this command is read from the termi-
nal, the loop is read up once prompting with `?' before any state-
ments in the loop are executed. If you make a mistake typing in a
loop at the terminal you can rub it out.
gglloobb _w_o_r_d_l_i_s_t
Like eecchhoo 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.
ggoottoo _w_o_r_d
The specified wwoorrdd 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 pre-
ceded by blanks or tabs. Execution continues after the specified
line.
hhaasshhssttaatt
Print a statistics line indicating how effective the internal hash
table has been at locating commands (and avoiding eexxeecc's). An eexxeecc
is attempted for each component of the _p_a_t_h where the hash function
indicates a possible hit, and in each component which does not be-
gin with a `/'.
hhiissttoorryy
hhiissttoorryy _n
hhiissttoorryy --rr _n
hhiissttoorryy --hh _n
Displays the history event list; if _n is given only the _n most re-
cent events are printed. The --rr option reverses the order of prin-
tout to be most recent first rather than oldest first. The --hh op-
tion causes the history list to be printed without leading numbers.
This is used to produce files suitable for sourceing using the -h
option to ssoouurrccee.
iiff (_e_x_p_r)
_c_o_m_m_a_n_d 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
iiff _c_o_m_m_a_n_d. _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 nnoott exe-
cuted (this is a bug).
iiff (_e_x_p_r) _t_h_e_n
...
eellssee iiff (_e_x_p_r_2) tthheenn
...
eellssee
...
eennddiiff
If the specified _e_x_p_r is true then the commands to the first eellssee
are executed; otherwise if _e_x_p_r_2 is true then the commands to the
second eellssee are executed, etc. Any number of eellssee--iiff pairs are
possible; only one eennddiiff is needed. The eellssee part is likewise op-
tional. (The words eellssee and eennddiiff must appear at the beginning of
input lines; the iiff must appear alone on its input line or after an
eellssee.)
jjoobbss
jjoobbss --ll
Lists the active jobs; given the --ll options lists process id's in
addition to the normal information.
kkiillll %%_j_o_b
kkiillll _p_i_d
kkiillll --ssiigg_p_i_d ...
kkiillll --ll
Sends either the TERM (terminate) signal or the specified signal to
the specified jobs or processes. Signals are either given by
number or by names (as given in /_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 process will be sent a CONT (contin-
ue) signal as well.
lliimmiitt
lliimmiitt _r_e_s_o_u_r_c_e
lliimmiitt _r_e_s_o_u_r_c_e _m_a_x_i_m_u_m-_u_s_e
lliimmiitt --hh
lliimmiitt --hh _r_e_s_o_u_r_c_e
lliimmiitt --hh _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 --hh flag is given, the hard limits are used instead of the
current limits. The hard limits impose a ceiling 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 process), _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 sbrk(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.
llooggiinn
Terminate a login shell, replacing it with an instance of
/_b_i_n/_l_o_g_i_n. This is one way to log off, included for compatibility
with sh(1).
llooggoouutt
Terminate a login shell. Especially useful if iiggnnoorreeeeooff is set.
nniiccee
nniiccee +_n_u_m_b_e_r
nniiccee _c_o_m_m_a_n_d
nniiccee +_n_u_m_b_e_r _c_o_m_m_a_n_d
The first form sets the scheduling priority for this shell to 4.
The second form sets the priority to the given _n_u_m_b_e_r. 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 simple iiff statements apply.
nnoohhuupp
nnoohhuupp _c_o_m_m_a_n_d
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 nnoohhuupp'ed.
nnoottiiffyy
nnoottiiffyy %% _j_o_b ...
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
nnoottiiffyy is set.
oonniinnttrr
oonniinnttrr --
oonniinnttrr _l_a_b_e_l
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 oonniinnttrr have no meaning and interrupts
continue to be ignored by the shell and all invoked commands.
ppooppdd
ppooppdd +_n
Pops the directory stack, returning to the new top directory. With
an argument `+_n' discards the _n'th entry in the stack. The
elements of the directory stack are numbered from 0 starting at the
top.
ppuusshhdd
ppuusshhdd _n_a_m_e
ppuusshhdd _n
With no arguments, ppuusshhdd exchanges the top two elements of the
directory stack. Given a _n_a_m_e argument, ppuusshhdd changes to the new
directory (ala ccdd) and pushes the old current working directory (as
in ccssww) onto the directory stack. With a numeric argument, rotates
the _n'th 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.
rreehhaasshh
Causes the internal hash table of the contents of the directories
in the ppaatthh variable to be recomputed. This is needed if new com-
mands are added to directories in the ppaatthh 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.
rreeppeeaatt _c_o_u_n_t _c_o_m_m_a_n_d
The specified _c_o_m_m_a_n_d which is subject to the same restrictions as
the _c_o_m_m_a_n_d in the one line iiff 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.
sseett
sseett _n_a_m_e
sseett _n_a_m_e=_w_o_r_d
sseett _n_a_m_e[index]=_w_o_r_d
sseett _n_a_m_e=(_w_o_r_d_l_i_s_t)
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 nnaammee to
the null string. The third form sets nnaammee to the single wwoorrdd. The
fourth form sets the _i_n_d_e_x'th 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.
sseetteennvv
sseetteennvv _n_a_m_e _v_a_l_u_e
sseetteennvv _n_a_m_e
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
automatically imported to and exported from the ccsshh variables _u_s_e_r,
[_t_e_r_m], and _p_a_t_h; there is no need to use sseetteennvv for these.
sshhiifftt
sshhiifftt _v_a_r_i_a_b_l_e
The members of aarrggvv are shifted to the left, discarding aarrggvv[1].
It is an error for aarrggvv not to be set or to have less than one word
as value. The second form performs the same function on the speci-
fied variable.
ssoouurrccee _n_a_m_e
ssoouurrccee --hh _n_a_m_e
The shell reads commands from nnaammee. SSoouurrccee commands may be nested;
if they are nested too deeply the shell may run out of file
descriptors. An error in a ssoouurrccee at any level terminates all
nested ssoouurrccee commands. Normally input during ssoouurrccee commands is
not placed on the history list; the -h option causes the commands
to be placed in the history list without being executed.
ssttoopp
ssttoopp %%_j_o_b ...
Stops the current or specified job which is executing in the
background.
ssuussppeenndd
Causes the shell to stop in its tracks, much as if it had been sent
a stop signal with ^^ZZ. This is most often used to stop shells
started by su(1).
sswwiittcchh (_s_t_r_i_n_g)
ccaassee _s_t_r_1:
...
bbrreeaakkssww
...
ddeeffaauulltt:
...
bbrreeaakkssww
eennddssww
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 de-
fault label. Each case label and the default label must appear at
the beginning of a line. The command bbrreeaakkssww causes execution to
continue after the eennddssww. 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 eennddssww.
ttiimmee
ttiimmee _c_o_m_m_a_n_d
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 summary as described under the ttiimmee
variable is printed. If necessary, an extra shell is created to
print the time statistic when the command completes.
uummaasskk
uummaasskk _v_a_l_u_e
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.
uunnaalliiaass _p_a_t_t_e_r_n
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 uunnaalliiaasseedd.
uunnhhaasshh
Use of the internal hash table to speed location of executed pro-
grams is disabled.
uunnlliimmiitt
uunnlliimmiitt _r_e_s_o_u_r_c_e
uunnlliimmiitt --hh
uunnlliimmiitt --hh _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 --hh is given, the
corresponding hard limits are removed. Only the super-user may do
this.
uunnsseett _p_a_t_t_e_r_n
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
uunnsseett.
uunnsseetteennvv _p_a_t_t_e_r_n
Removes all variables whose name match the specified pattern from
the environment. See also the sseetteennvv command above and prin-
tenv(1).
wwaaiitt
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.
wwhhiillee (_e_x_p_r)
...
eenndd While the specified expression evaluates non-zero, the commands
between the wwhhiillee and the matching end are evaluated. BBrreeaakk and
ccoonnttiinnuuee may be used to terminate or continue the loop prematurely.
(The wwhhiillee and eenndd must appear alone on their input lines.) Prompt-
ing occurs here the first time through the loop as for the ffoorreeaacchh
statement if the input is a terminal.
%% _j_o_b
Brings the specified job into the foreground.
%% _j_o_b &&
Continues the specified job in the background.
@@
@@ _n_a_m_e = _e_x_p_r
@@ _n_a_m_e[index] =expr
The first form prints the values of all the shell variables. 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 as-
signs the value of _e_x_p_r to the _i_n_d_e_x'th argument of _n_a_m_e. Both
_n_a_m_e and its _i_n_d_e_x'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 _e_x_p_r which would oth-
erwise be single words.
Special postfix `++' and `--' operators increment and decrement _n_a_m_e
respectively, i.e. `@ i++'.
PPrree--ddeeffiinneedd aanndd eennvviirroonnmmeenntt vvaarriiaabblleess
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 initializa-
tion; these variables will not then be modified unless this is done ex-
plicitly 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 en-
vironment 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 ccsshh processes will im-
port the definition of _p_a_t_h from the environment, and re-export it if you
then change it.
aarrggvv Set to the arguments to the shell, it is from this variable
that positional parameters are substituted, i.e. `$1' is re-
placed by `$argv[1]', etc.
ccddppaatthh Gives a list of alternate directories searched to find sub-
directories in _c_h_d_i_r commands.
ccwwdd The full pathname of the current directory.
eecchhoo Set when the --xx command line option is given. Causes each com-
mand 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 substi-
tution, since these substitutions are then done selectively.
ffiilleecc Enable file name completion.
hhiissttcchhaarrss
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.
hhiissttoorryy 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 al-
ways saved on the history list.
hhoommee The home directory of the invoker, initialized from the en-
vironment. The filename expansion of `~' refers to this
variable.
iiggnnoorreeeeooff
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.
mmaaiill 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 _m_a_i_l is numeric it specifies
a different mail checking interval, in seconds, than the de-
fault, 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.
nnoocclloobbbbeerr
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 ac-
cidentally destroyed, and that `>>' redirections refer to ex-
isting files.
nnoogglloobb 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.
nnoonnoommaattcchh
If set, it is not an error for a filename expansion to not
match any existing files; rather the primitive pattern is re-
turned. It is still an error for the primitive pattern to be
malformed, i.e. `echo [' still gives an error.
nnoottiiffyy If set, the shell notifies asynchronously of job completions.
The default is to rather present job completions just before
printing a prompt.
ppaatthh 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 variable then only
full path names will execute. The usual search path is `.',
`/bin' and `/usr/bin', but this may vary from system to system.
For the super-user the default search path is `/etc', `/bin'
and `/usr/bin'. A shell which is given neither the --cc nor the
--tt 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
variable is reset. If new commands are added to these direc-
tories 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.
pprroommpptt 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.
ssaavveehhiisstt
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.
sshheellll 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.
ssttaattuuss The status returned by the last command. If it terminated ab-
normally, then 0200 is added to the status. Builtin commands
which fail return exit status `1', all other builtin commands
set status `0'.
ttiimmee Controls automatic timing of commands. If set, then any com-
mand which takes more than this many cpu seconds will cause a
line giving user, system, and real times and a utilization per-
centage which is the ratio of user plus system times to real
time to be printed when it terminates.
vveerrbboossee Set by the --vv command line option, causes the words of each
command to be printed after history substitution.
NNoonn--bbuuiillttiinn ccoommmmaanndd eexxeeccuuttiioonn
When a command to be executed is found to not be a builtin command the
shell attempts to execute the command via execve(2). Each word in the
variable _p_a_t_h names a directory from which the shell will attempt to exe-
cute the command. If it is given neither a --cc nor a --tt option, the shell
will hash the names in these directories into an internal table so that
it will only try an eexxeecc 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 uunnhhaasshh), or if the shell was given a
--cc or --tt 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 exe-
cute.
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 cchhddiirr from affecting the current shell.
If the file has execute permissions but is not an executable binary to
the system, then it is assumed to be a file containing shell commands and
a new shell is spawned to read it.
If there is an aalliiaass for sshheellll then the words of the alias will be
prepended to the argument list to form the shell command. The first word
of the aalliiaass should be the full path name of the shell (e.g. `$shell').
Note that this is a special, late occurring, case of aalliiaass substitution,
and only allows words to be prepended to the argument list without modif-
ication.
SSiiggnnaall hhaannddlliinngg
The shell normally ignores _q_u_i_t signals. Jobs running detached (either
by && or the bbgg or %%...... && commands) are immune to signals generated from
the keyboard, including hangups. Other signals have the values which the
shell inherited from its parent. The shell's handling of interrupts and
terminate signals in shell scripts can be controlled by oonniinnttrr. Login
shells catch the _t_e_r_m_i_n_a_t_e signal; otherwise this signal is passed on to
children from the state in the shell's parent. In no case are interrupts
allowed when a login shell is reading the file ._l_o_g_o_u_t.
AAUUTTHHOORR
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 completion code written by Ken Greer, HP Labs.
FFIILLEESS
~/._c_s_h_r_c Read at beginning of execution by each shell.
~/._l_o_g_i_n Read by login shell, after `.cshrc' at login.
~/._l_o_g_o_u_t Read by login shell, at logout.
/_b_i_n/_s_h Standard shell, for shell scripts not starting with a `#'.
/_t_m_p/_s_h* Temporary file for `<<'.
/_e_t_c/_p_a_s_s_w_d Source of home directories for `~name'.
LLIIMMIITTAATTIIOONNSS
Word lengths - 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 aalliiaass substitutions on
a single line to 20.
SSEEEE AALLSSOO
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),
_A_n _i_n_t_r_o_d_u_c_t_i_o_n _t_o _t_h_e _C _s_h_e_l_l
HHIISSTTOORRYY
CCsshh Appeared in 3 BSD. It was a first implementation of a command
language interpreter incorporating a history mechanism (see HHiissttoorryy
SSuubbssttiittuuttiioonnss), job control facilities (see JJoobbss), interactive file name
and user name completion (see FFiillee NNaammee CCoommpplleettiioonn), and a C-like syntax.
There are now many shells which also have these mechanisms, plus a few
more (and maybe some bugs too), which are available thru the internet, or
as contributed software such as the ksh(korn shell).
BBUUGGSS
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 inter-
nally.
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
_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 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 pro-
cedures; shell procedures should be provided rather than aliases.
Commands within loops, prompted for by `?', are not placed in the hhiissttoorryy
list. Control structure should be parsed rather than being recognized as
built-in commands. This would allow control commands to be placed any-
where, 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 `:' modifier should be allowed on
`$' substitutions.
The way the ffiilleecc facility is implemented is ugly and expensive.