sh(1) (Essential Utilities) sh(1)
NAME
sh, jsh, rsh - shell, the standard, job control, and restricted
command interpreter
SYNOPSIS
sh [ -acefhiknprstuvx ] [ args ]
jsh [ -acefhiknprstuvx ] [ args ]
rsh [ -acefhiknprstuvx ] [ args ]
DESCRIPTION
sh is a command programming language that executes commands read from
a terminal or a file. The command jsh is an interface to the shell
which provides all of the functionality of sh and enables Job Control
(see ``Job Control,'' below). rsh is a restricted version of the
standard command interpreter sh; It is used to restrict logins to
execution environments whose capabilities are more controlled than
those of the standard shell. See ``Invocation,'' below for the
meaning of arguments to the shell.
Definitions
A blank is a tab or a space. A name is a sequence of ASCII letters,
digits, or underscores, beginning with a letter or an underscore. A
parameter is a name, a digit, or any of the characters *, @, #, ?, -,
$, and !\^.
Commands
A simple-command is a sequence of non-blank words separated by
blanks. The first word specifies the name of the command to be
executed. Except as specified below, the remaining words are passed
as arguments to the invoked command. The command name is passed as
argument 0 [see exec(2)]. The value of a simple-command is its exit
status if it terminates normally, or (octal) 200+status if it
terminates abnormally; see signal(5) for a list of status values.
A pipeline is a sequence of one or more commands separated by |. The
standard output of each command but the last is connected by a
pipe(2) to the standard input of the next command. Each command is
run as a separate process; the shell waits for the last command to
terminate. The exit status of a pipeline is the exit status of the
last command in the pipeline.
A list is a sequence of one or more pipelines separated by ;, &, &&,
or ||, and optionally terminated by ; or &. Of these four symbols, ;
and & have equal precedence, which is lower than that of && and ||.
The symbols && and || also have equal precedence. A semicolon (;)
causes sequential execution of the preceding pipeline (i.e., the
shell waits for the pipeline to finish before executing any commands
following the semicolon); an ampersand (&) causes asynchronous
execution of the preceding pipeline (i.e., the shell does not wait
for that pipeline to finish). The symbol && (||) causes the list
following it to be executed only if the preceding pipeline returns a
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zero (non-zero) exit status. An arbitrary number of new-lines may
appear in a list, instead of semicolons, to delimit commands.
A command is either a simple-command or one of the following. Unless
otherwise stated, the value returned by a command is that of the last
simple-command executed in the command.
for name [ in word ... ] do list done
Each time a for command is executed, name is set to the next
word taken from the in word list. If in word ... is omitted,
then the for command executes the do list once for each
positional parameter that is set (see ``Parameter
Substitution,'' below). Execution ends when there are no more
words in the list.
case word in [ pattern [ | pattern ] ... ) list ;; ] ... esac
A case command executes the list associated with the first
pattern that matches word. The form of the patterns is the
same as that used for file-name generation (see ``File Name
Generation'') except that a slash, a leading dot, or a dot
immediately following a slash need not be matched explicitly.
if list then list [ elif list then list ] ... [ else list ] fi
The list following if is executed and, if it returns a zero
exit status, the list following the first then is executed.
Otherwise, the list following elif is executed and, if its
value is zero, the list following the next then is executed.
Failing that, the else list is executed. If no else list or
then list is executed, then the if command returns a zero exit
status.
while list do list done
A while command repeatedly executes the while list and, if the
exit status of the last command in the list is zero, executes
the do list; otherwise the loop terminates. If no commands in
the do list are executed, then the while command returns a zero
exit status; until may be used in place of while to negate the
loop termination test.
(list)
Execute list in a sub-shell.
{ list;}
list is executed in the current (that is, parent) shell. The {
must be followed by a space.
name () { list;}
Define a function which is referenced by name. The body of the
function is the list of commands between { and }. The { must
be followed by a space. Execution of functions is described
below (see ``Execution''). The { and } are unnecessary if the
body of the function is a command as defined above, under
``Commands.''
The following words are only recognized as the first word of a
command and when not quoted:
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if then else elif fi case esac for while until do done { }
Comments
A word beginning with # causes that word and all the following
characters up to a new-line to be ignored.
Command Substitution
The shell reads commands from the string between two grave accents
(``) and the standard output from these commands may be used as all
or part of a word. Trailing new-lines from the standard output are
removed.
No interpretation is done on the string before the string is read,
except to remove backslashes (\) used to escape other characters.
Backslashes may be used to escape a grave accent (`) or another
backslash (\) and are removed before the command string is read.
Escaping grave accents allows nested command substitution. If the
command substitution lies within a pair of double quotes (" ...` ...`
... "), a backslash used to escape a double quote (\") will be
removed; otherwise, it will be left intact.
If a backslash is used to escape a new-line character (\new-line),
both the backslash and the new-line are removed (see the later
section on ``Quoting''). In addition, backslashes used to escape
dollar signs (\$) are removed. Since no parameter substitution is
done on the command string before it is read, inserting a backslash
to escape a dollar sign has no effect. Backslashes that precede
characters other than \, `, ", new-line, and $ are left intact when
the command string is read.
Parameter Substitution
The character $ is used to introduce substitutable parameters. There
are two types of parameters, positional and keyword. If parameter is
a digit, it is a positional parameter. Positional parameters may be
assigned values by set. Keyword parameters (also known as variables)
may be assigned values by writing:
name=value [ name=value ] ...
Pattern-matching is not performed on value. There cannot be a
function and a variable with the same name.
${parameter}
The value, if any, of the parameter is substituted. The braces
are required only when parameter is followed by a letter,
digit, or underscore that is not to be interpreted as part of
its name. If parameter is * or @, all the positional
parameters, starting with $1, are substituted (separated by
spaces). Parameter $0 is set from argument zero when the shell
is invoked.
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${parameter:-word}
If parameter is set and is non-null, substitute its value;
otherwise substitute word.
${parameter:=word}
If parameter is not set or is null set it to word; the value of
the parameter is substituted. Positional parameters may not be
assigned in this way.
${parameter:?word}
If parameter is set and is non-null, substitute its value;
otherwise, print word and exit from the shell. If word is
omitted, the message ``parameter null or not set'' is printed.
${parameter:+word}
If parameter is set and is non-null, substitute word; otherwise
substitute nothing.
In the above, word is not evaluated unless it is to be used as the
substituted string, so that, in the following example, pwd is
executed only if d is not set or is null:
echo ${d:-`pwd`}
If the colon (:) is omitted from the above expressions, the shell
only checks whether parameter is set or not.
The following parameters are automatically set by the shell.
# The number of positional parameters in decimal.
- Flags supplied to the shell on invocation or by the set
command.
? The decimal value returned by the last synchronously
executed command.
$ The process number of this shell.
! The process number of the last background command
invoked.
The following parameters are used by the shell. The parameters in
this section are also referred to as environment variables.
HOME The default argument (home directory) for the cd command,
set to the user's login directory by login(1) from the
password file [see passwd(4)].
PATH The search path for commands (see ``Execution,'' below).
The user may not change PATH if executing under rsh.
CDPATH
The search path for the cd command.
MAIL If this parameter is set to the name of a mail file and
the MAILPATH parameter is not set, the shell informs the
user of the arrival of mail in the specified file.
MAILCHECK
This parameter specifies how often (in seconds) the shell
will check for the arrival of mail in the files specified
by the MAILPATH or MAIL parameters. The default value is
600 seconds (10 minutes). If set to 0, the shell will
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check before each prompt.
MAILPATH
A colon (:) separated list of file names. If this
parameter is set, the shell informs the user of the
arrival of mail in any of the specified files. Each file
name can be followed by % and a message that will be
printed when the modification time changes. The default
message is you have mail.
PS1 Primary prompt string, by default ``$ ''.
PS2 Secondary prompt string, by default ``> ''.
IFS Internal field separators, normally space, tab, and new-
line (see ``Blank Interpretation'').
LANG If this parameter is set, the shell will use it to
determine the current locale; see environ(5),
setlocale(3C).
SHACCT
If this parameter is set to the name of a file writable
by the user, the shell will write an accounting record in
the file for each shell procedure executed.
SHELL When the shell is invoked, it scans the environment (see
``Environment,'' below) for this name. If it is found
and rsh is the file name part of its value, the shell
becomes a restricted shell.
The shell gives default values to PATH, PS1, PS2, MAILCHECK, and IFS.
HOME and MAIL are set by login(1).
Blank Interpretation
After parameter and command substitution, the results of substitution
are scanned for internal field separator characters (those found in
IFS) and split into distinct arguments where such characters are
found. Explicit null arguments ("" or '') are retained. Implicit
null arguments (those resulting from parameters that have no values)
are removed.
Input/Output
A command's input and output may be redirected using a special
notation interpreted by the shell. The following may appear anywhere
in a simple-command or may precede or follow a command and are not
passed on as arguments to the invoked command. Note that parameter
and command substitution occurs before word or digit is used.
<word Use file word as standard input (file descriptor 0).
>word Use file word as standard output (file descriptor 1).
If the file does not exist, it is created; otherwise,
it is truncated to zero length.
>>word Use file word as standard output. If the file exists,
output is appended to it (by first seeking to the end-
of-file); otherwise, the file is created.
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<<[-]word After parameter and command substitution is done on
word, the shell input is read up to the first line that
literally matches the resulting word, or to an end-of-
file. If, however, - is appended to <<:
1) leading tabs are stripped from word before the
shell input is read (but after parameter and
command substitution is done on word),
2) leading tabs are stripped from the shell input as
it is read and before each line is compared with
word, and
3) shell input is read up to the first line that
literally matches the resulting word, or to an
end-of-file.
If any character of word is quoted (see ``Quoting,''
later), no additional processing is done to the shell
input. If no characters of word are quoted:
1) parameter and command substitution occurs,
2) (escaped) \new-lines are removed, and
3) \ must be used to quote the characters \, $, and `.
The resulting document becomes the standard input.
<&digit Use the file associated with file descriptor digit as
standard input. Similarly for the standard output
using >&digit.
<&- The standard input is closed. Similarly for the
standard output using >&-.
If any of the above is preceded by a digit, the file descriptor which
will be associated with the file is that specified by the digit
(instead of the default 0 or 1). For example:
... 2>&1
associates file descriptor 2 with the file currently associated with
file descriptor 1.
The order in which redirections are specified is significant. The
shell evaluates redirections left-to-right. For example:
... 1>xxx 2>&1
first associates file descriptor 1 with file xxx. It associates file
descriptor 2 with the file associated with file descriptor 1 (i.e.,
xxx). If the order of redirections were reversed, file descriptor 2
would be associated with the terminal (assuming file descriptor 1 had
been) and file descriptor 1 would be associated with file xxx.
Using the terminology introduced on the first page, under
``Commands,'' if a command is composed of several simple commands,
redirection will be evaluated for the entire command before it is
evaluated for each simple command. That is, the shell evaluates
redirection for the entire list, then each pipeline within the list,
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then each command within each pipeline, then each list within each
command.
If a command is followed by & the default standard input for the
command is the empty file /dev/null. Otherwise, the environment for
the execution of a command contains the file descriptors of the
invoking shell as modified by input/output specifications.
Redirection of output is not allowed in the restricted shell.
File Name Generation
Before a command is executed, each command word is scanned for the
characters *, ?, and [. If one of these characters appears the word
is regarded as a pattern. The word is replaced with alphabetically
sorted file names that match the pattern. If no file name is found
that matches the pattern, the word is left unchanged. The character
. at the start of a file name or immediately following a /, as well
as the character / itself, must be matched explicitly.
* Matches any string, including the null string.
? Matches any single character.
[...] Matches any one of the enclosed characters. A pair of
characters separated by - matches any character lexically
between the pair, inclusive. If the first character
following the opening [ is a !, any character not
enclosed is matched.
Note that all quoted characters (see below) must be matched
explicitly in a filename.
Quoting
The following characters have a special meaning to the shell and
cause termination of a word unless quoted:
; & ( ) | ^ < > new-line space tab
A character may be quoted (i.e., made to stand for itself) by
preceding it with a backslash (\) or inserting it between a pair of
quote marks ('' or ""). During processing, the shell may quote
certain characters to prevent them from taking on a special meaning.
Backslashes used to quote a single character are removed from the
word before the command is executed. The pair \new-line is removed
from a word before command and parameter substitution.
All characters enclosed between a pair of single quote marks (''),
except a single quote, are quoted by the shell. Backslash has no
special meaning inside a pair of single quotes. A single quote may
be quoted inside a pair of double quote marks (for example, "'"), but
a single quote can not be quoted inside a pair of single quotes.
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Inside a pair of double quote marks (""), parameter and command
substitution occurs and the shell quotes the results to avoid blank
interpretation and file name generation. If $* is within a pair of
double quotes, the positional parameters are substituted and quoted,
separated by quoted spaces ("$1 $2 ..."); however, if $@ is within a
pair of double quotes, the positional parameters are substituted and
quoted, separated by unquoted spaces ("$1" "$2" ... ). \ quotes the
characters \, `, ", and $. The pair \new-line is removed before
parameter and command substitution. If a backslash precedes
characters other than \, `, ", $, and new-line, then the backslash
itself is quoted by the shell.
Prompting
When used interactively, the shell prompts with the value of PS1
before reading a command. If at any time a new-line is typed and
further input is needed to complete a command, the secondary prompt
(i.e., the value of PS2) is issued.
Environment
The environment [see environ(5)] is a list of name-value pairs that
is passed to an executed program in the same way as a normal argument
list. The shell interacts with the environment in several ways. On
invocation, the shell scans the environment and creates a parameter
for each name found, giving it the corresponding value. If the user
modifies the value of any of these parameters or creates new
parameters, none of these affects the environment unless the export
command is used to bind the shell's parameter to the environment (see
also set -a). A parameter may be removed from the environment with
the unset command. The environment seen by any executed command is
thus composed of any unmodified name-value pairs originally inherited
by the shell, minus any pairs removed by unset, plus any
modifications or additions, all of which must be noted in export
commands.
The environment for any simple-command may be augmented by prefixing
it with one or more assignments to parameters. Thus:
TERM=450 cmd and
(export TERM; TERM=450; cmd)
are equivalent as far as the execution of cmd is concerned if cmd is
not a Special Command. If cmd is a Special Command, then
TERM=450 cmd
will modify the TERM variable in the current shell.
If the -k flag is set, all keyword arguments are placed in the
environment, even if they occur after the command name. The
following first prints a=b c and c:
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echo a=b c
set -k
echo a=b c
Signals
The INTERRUPT and QUIT signals for an invoked command are ignored if
the command is followed by &; otherwise signals have the values
inherited by the shell from its parent, with the exception of signal
11 (but see also the trap command below).
Execution
Each time a command is executed, the command substitution, parameter
substitution, blank interpretation, input/output redirection, and
filename generation listed above are carried out. If the command
name matches the name of a defined function, the function is executed
in the shell process (note how this differs from the execution of
shell procedures). If the command name does not match the name of a
defined function, but matches one of the Special Commands listed
below, it is executed in the shell process. The positional
parameters $1, $2, .... are set to the arguments of the function.
If the command name matches neither a Special Command nor the name of
a defined function, a new process is created and an attempt is made
to execute the command via exec(2).
The shell parameter PATH defines the search path for the directory
containing the command. Alternative directory names are separated by
a colon (:). The default path is /usr/bin. The current directory is
specified by a null path name, which can appear immediately after the
equal sign, between two colon delimiters anywhere in the path list,
or at the end of the path list. If the command name contains a / the
search path is not used; such commands will not be executed by the
restricted shell. Otherwise, each directory in the path is searched
for an executable file. If the file has execute permission but is
not an a.out file, it is assumed to be a file containing shell
commands. A sub-shell is spawned to read it. A parenthesized
command is also executed in a sub-shell.
The location in the search path where a command was found is
remembered by the shell (to help avoid unnecessary execs later). If
the command was found in a relative directory, its location must be
re-determined whenever the current directory changes. The shell
forgets all remembered locations whenever the PATH variable is
changed or the hash -r command is executed (see below).
Special Commands
Input/output redirection is now permitted for these commands. File
descriptor 1 is the default output location. When Job Control is
enabled, additional Special Commands are added to the shell's
environment (see ``Job Control'').
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: No effect; the command does nothing. A zero exit code is
returned.
. file
Read and execute commands from file and return. The search
path specified by PATH is used to find the directory containing
file.
break [ n ]
Exit from the enclosing for or while loop, if any. If n is
specified, break n levels.
continue [ n ]
Resume the next iteration of the enclosing for or while loop.
If n is specified, resume at the n-th enclosing loop.
cd [ arg ]
Change the current directory to arg. The shell parameter HOME
is the default arg. The shell parameter CDPATH defines the
search path for the directory containing arg. Alternative
directory names are separated by a colon (:). The default path
is <null> (specifying the current directory). Note that the
current directory is specified by a null path name, which can
appear immediately after the equal sign or between the colon
delimiters anywhere else in the path list. If arg begins with
a / the search path is not used. Otherwise, each directory in
the path is searched for arg. The cd command may not be
executed by rsh.
echo [ arg ... ]
Echo arguments. See echo(1) for usage and description.
eval [ arg ... ]
The arguments are read as input to the shell and the resulting
command(s) executed.
exec [ arg ... ]
The command specified by the arguments is executed in place of
this shell without creating a new process. Input/output
arguments may appear and, if no other arguments are given,
cause the shell input/output to be modified.
exit [ n ]
Causes a shell to exit with the exit status specified by n. If
n is omitted the exit status is that of the last command
executed (an end-of-file will also cause the shell to exit.)
export [ name ... ]
The given names are marked for automatic export to the
environment of subsequently executed commands. If no arguments
are given, variable names that have been marked for export
during the current shell's execution are listed. (Variable
names exported from a parent shell are listed only if they have
been exported again during the current shell's execution.)
Function names are not exported.
getopts
Use in shell scripts to support command syntax standards [see
intro(1)]; it parses positional parameters and checks for legal
options. See getopts(1) for usage and description.
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hash [ -r ] [ name ... ]
For each name, the location in the search path of the command
specified by name is determined and remembered by the shell.
The -r option causes the shell to forget all remembered
locations. If no arguments are given, information about
remembered commands is presented. Hits is the number of times
a command has been invoked by the shell process. Cost is a
measure of the work required to locate a command in the search
path. If a command is found in a "relative" directory in the
search path, after changing to that directory, the stored
location of that command is recalculated. Commands for which
this will be done are indicated by an asterisk (*) adjacent to
the hits information. Cost will be incremented when the
recalculation is done.
newgrp [ arg ]
Equivalent to exec newgrp arg. See newgrp(1M) for usage and
description.
pwd Print the current working directory. See pwd(1) for usage and
description.
read name ...
One line is read from the standard input and, using the
internal field separator, IFS (normally space or tab), to
delimit word boundaries, the first word is assigned to the
first name, the second word to the second name, etc., with
leftover words assigned to the last name. Lines can be
continued using \new-line. Characters other than new-line can
be quoted by preceding them with a backslash. These
backslashes are removed before words are assigned to names, and
no interpretation is done on the character that follows the
backslash. The return code is 0, unless an end-of-file is
encountered.
readonly [ name ... ]
The given names are marked readonly and the values of the these
names may not be changed by subsequent assignment. If no
arguments are given, a list of all readonly names is printed.
return [ n ]
Causes a function to exit with the return value specified by n.
If n is omitted, the return status is that of the last command
executed.
set [ --aefhkntuvx [ arg ... ] ]
-a Mark variables which are modified or created for export.
-e Exit immediately if a command exits with a non-zero exit
status.
-f Disable file name generation
-h Locate and remember function commands as functions are
defined (function commands are normally located when the
function is executed).
-k All keyword arguments are placed in the environment for a
command, not just those that precede the command name.
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-n Read commands but do not execute them.
-t Exit after reading and executing one command.
-u Treat unset variables as an error when substituting.
-v Print shell input lines as they are read.
-x Print commands and their arguments as they are executed.
-- Do not change any of the flags; useful in setting $1 to
-.
Using + rather than - causes these flags to be turned off.
These flags can also be used upon invocation of the shell. The
current set of flags may be found in $-. The remaining
arguments are positional parameters and are assigned, in order,
to $1, $2, .... If no arguments are given the values of all
names are printed.
shift [ n ]
The positional parameters from $n+1 ... are renamed $1 ... .
If n is not given, it is assumed to be 1.
test
Evaluate conditional expressions. See test(1) for usage and
description.
times
Print the accumulated user and system times for processes run
from the shell.
trap [ arg ] [ n ] ...
The command arg is to be read and executed when the shell
receives numeric or symbolic signal(s) (n). (Note that arg is
scanned once when the trap is set and once when the trap is
taken.) Trap commands are executed in order of signal number
or corresponding symbolic names. Any attempt to set a trap on
a signal that was ignored on entry to the current shell is
ineffective. An attempt to trap on signal 11 (memory fault)
produces an error. If arg is absent all trap(s) n are reset to
their original values. If arg is the null string this signal
is ignored by the shell and by the commands it invokes. If n
is 0 the command arg is executed on exit from the shell. The
trap command with no arguments prints a list of commands
associated with each signal number.
type [ name ... ]
For each name, indicate how it would be interpreted if used as
a command name.
ulimit [ -[HS][a | cdfnstv] ]
ulimit [ -[HS][c | d | f | n | s | t | v] ] limit
ulimit prints or sets hard or soft resource limits. These
limits are described in getrlimit(2).
If limit is not present, ulimit prints the specified limits.
Any number of limits may be printed at one time. The -a option
prints all limits.
If limit is present, ulimit sets the specified limit to limit.
The string unlimited requests the largest valid limit. Limits
may be set for only one resource at a time. Any user may set a
soft limit to any value below the hard limit. Any user may
lower a hard limit. Only a super-user may raise a hard limit;
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see su(1).
The -H option specifies a hard limit. The -S option specifies
a soft limit. If neither option is specified, ulimit will set
both limits and print the soft limit.
The following options specify the resource whose limits are to
be printed or set. If no option is specified, the file size
limit is printed or set.
-c maximum core file size (in 512-byte blocks)
-d maximum size of data segment or heap (in kbytes)
-f maximum file size (in 512-byte blocks)
-n maximum file descriptor plus 1
-s maximum size of stack segment (in kbytes)
-t maximum CPU time (in seconds)
-v maximum size of virtual memory (in kbytes)
umask [ nnn ]
The user file-creation mask is set to nnn [see umask(1)]. If
nnn is omitted, the current value of the mask is printed.
unset [ name ... ]
For each name, remove the corresponding variable or function
value. The variables PATH, PS1, PS2, MAILCHECK, and IFS cannot
be unset.
wait [ n ]
Wait for your background process whose process id is n and
report its termination status. If n is omitted, all your
shell's currently active background processes are waited for
and the return code will be zero.
Invocation
If the shell is invoked through exec(2) and the first character of
argument zero is -, commands are initially read from /etc/profile and
from $HOME/.profile, if such files exist. Thereafter, commands are
read as described below, which is also the case when the shell is
invoked as /usr/bin/sh. The flags below are interpreted by the shell
on invocation only. Note that unless the -c or -s flag is specified,
the first argument is assumed to be the name of a file containing
commands, and the remaining arguments are passed as positional
parameters to that command file:
-c string If the -c flag is present commands are read from string.
-i If the -i flag is present or if the shell input and output
are attached to a terminal, this shell is interactive. In
this case TERMINATE is ignored (so that kill 0 does not
kill an interactive shell) and INTERRUPT is caught and
ignored (so that wait is interruptible). In all cases,
QUIT is ignored by the shell.
-p If the -p flag is present, the shell will not set the
effective user and group IDs to the real user and group
IDs.
-r If the -r flag is present the shell is a restricted shell.
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-s If the -s flag is present or if no arguments remain,
commands are read from the standard input. Any remaining
arguments specify the positional parameters. Shell output
(except for Special Commands) is written to file descriptor
2.
The remaining flags and arguments are described under the set command
above.
Job Control (jsh)
When the shell is invoked as jsh, Job Control is enabled in addition
to all of the functionality described previously for sh. Typically
Job Control is enabled for the interactive shell only. Non-
interactive shells typically do not benefit from the added
functionality of Job Control.
With Job Control enabled every command or pipeline the user enters at
the terminal is called a job. All jobs exist in one of the following
states: foreground, background or stopped. These terms are defined
as follows: 1) a job in the foreground has read and write access to
the controlling terminal; 2) a job in the background is denied read
access and has conditional write access to the controlling terminal
[see stty(1)]; 3) a stopped job is a job that has been placed in a
suspended state, usually as a result of a SIGTSTP signal [see
signal(5)].
Every job that the shell starts is assigned a positive integer,
called a job number which is tracked by the shell and will be used as
an identifier to indicate a specific job. Additionally the shell
keeps track of the current and previous jobs. The current job is the
most recent job to be started or restarted. The previous job is the
first non-current job.
The acceptable syntax for a Job Identifier is of the form:
%jobid
where, jobid may be specified in any of the following formats:
% or + for the current job
- for the previous job
?<string> specify the job for which the command line uniquely
contains string.
n for job number n, where n is a job number
pref where pref is a unique prefix of the command name
(for example, if the command ls -l foo were running
in the background, it could be referred to as %ls);
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pref cannot contain blanks unless it is quoted.
When Job Control is enabled, the following commands are added to the
user's environment to manipulate jobs:
bg [%jobid ...]
Resumes the execution of a stopped job in the background. If
%jobid is omitted the current job is assumed.
fg [%jobid ...]
Resumes the execution of a stopped job in the foreground, also
moves an executing background job into the foreground. If
%jobid is omitted the current job is assumed.
jobs [-p|-l] [%jobid ...]
jobs -x command [arguments]
Reports all jobs that are stopped or executing in the
background. If %jobid is omitted, all jobs that are stopped or
running in the background will be reported. The following
options will modify/enhance the output of jobs:
-l Report the process group ID and working directory of the
jobs.
-p Report only the process group ID of the jobs.
-x Replace any jobid found in command or arguments with the
corresponding process group ID, and then execute command
passing it arguments.
kill [-signal] %jobid
Builtin version of kill to provide the functionality of the
kill command for processes identified with a jobid.
stop %jobid ...
Stops the execution of a background job(s).
suspend
Stops the execution of the current shell (but not if it is the
login shell).
wait [%jobid ...]
wait builtin accepts a job identifier. If %jobid is omitted
wait behaves as described above under Special Commands.
Restricted Shell (rsh) Only
rsh is used to set up login names and execution environments whose
capabilities are more controlled than those of the standard shell.
The actions of rsh are identical to those of sh, except that the
following are disallowed:
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changing directory [see cd(1)],
setting the value of $PATH,
specifying path or command names containing /,
redirecting output (> and >>).
The restrictions above are enforced after .profile is interpreted.
A restricted shell can be invoked in one of the following ways: (1)
rsh is the file name part of the last entry in the /etc/passwd file
[see passwd(4)]; (2) the environment variable SHELL exists and rsh is
the file name part of its value; (3) the shell is invoked and rsh is
the file name part of argument 0; (4) the shell is invoke with the -r
option.
When a command to be executed is found to be a shell procedure, rsh
invokes sh to execute it. Thus, it is possible to provide to the
end-user shell procedures that have access to the full power of the
standard shell, while imposing a limited menu of commands; this
scheme assumes that the end-user does not have write and execute
permissions in the same directory.
The net effect of these rules is that the writer of the .profile [see
profile(4)] has complete control over user actions by performing
guaranteed setup actions and leaving the user in an appropriate
directory (probably not the login directory).
The system administrator often sets up a directory of commands (i.e.,
/usr/rbin) that can be safely invoked by a restricted shell. Some
systems also provide a restricted editor, red.
EXIT STATUS
Errors detected by the shell, such as syntax errors, cause the shell
to return a non-zero exit status. If the shell is being used non-
interactively execution of the shell file is abandoned. Otherwise,
the shell returns the exit status of the last command executed (see
also the exit command above).
jsh Only
If the shell is invoked as jsh and an attempt is made to exit the
shell while there are stopped jobs, the shell issues one warning:
There are stopped jobs.
This is the only message. If another exit attempt is made, and there
are still stopped jobs they will be sent a SIGHUP signal from the
kernel and the shell is exited.
FILES
/etc/profile
$HOME/.profile
/tmp/sh*
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/dev/null
SEE ALSO
cd(1), echo(1), getopts(1), intro(1), login(1), pwd(1), stty(1),
test(1), umask(1), wait(1).
dup(2), exec(2), fork(2), getrlimit(2), pipe(2), ulimit(2),
setlocale(3C), profile(4), environ(5), signal(5) in the Programmer's
Reference Manual.
newgrp(1M), in the System Administrator's Reference Manual.
NOTES
Words used for filenames in input/output redirection are not
interpreted for filename generation (see ``File Name Generation,''
above). For example, cat file1 >a* will create a file named a*.
Because commands in pipelines are run as separate processes,
variables set in a pipeline have no effect on the parent shell.
If you get the error message cannot fork, too many processes, try
using the wait(1) command to clean up your background processes. If
this doesn't help, the system process table is probably full or you
have too many active foreground processes. (There is a limit to the
number of process ids associated with your login, and to the number
the system can keep track of.)
Only the last process in a pipeline can be waited for.
If a command is executed, and a command with the same name is
installed in a directory in the search path before the directory
where the original command was found, the shell will continue to exec
the original command. Use the hash command to correct this
situation.
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