sh(1)
NAME
sh, jsh - standard and job control shell and command inter-
preter
SYNOPSIS
/usr/bin/sh [-acefhiknprstuvx] [argument...]
/usr/xpg4/bin/sh [ _ abCefhikmnoprstuvx] [ _ o option...]
[-c string] [arg...]
/usr/bin/jsh [-acefhiknprstuvx] [argument...]
DESCRIPTION
The /usr/bin/sh utility is a command programming language
that executes commands read from a terminal or a file.
The /usr/xpg4/bin/sh utility is a standards compliant shell.
This utility provides all the functionality of ksh(1),
except in cases discussed in ksh(1) where differences in
behavior exist.
The jsh utility is an interface to the shell that provides
all of the functionality of sh and enables job control (see
Job Control section below).
Arguments to the shell are listed in the Invocation section
below.
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 !.
USAGE
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 ter-
minates normally, or (octal) 200+status if it terminates
abnormally. See signal(3HEAD) 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, that is, the shell
waits for the pipeline to finish before executing any com-
mands following the semicolon. An ampersand (&) causes asyn-
chronous execution of the preceding pipeline, that is, 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 zero (non-zero) exit
status. An arbitrary number of newlines may appear in a
list, instead of semicolons, to delimit commands.
A command is either a simple-command or one of the follow-
ing. Unless otherwise stated, the value returned by a com-
mand is that of the last simple-command executed in the com-
mand.
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 section 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 pat-
terns is the same as that used for file-name genera-
tion (see File Name Generation section), 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 section).
The { and } are unnecessary if the body of the func-
tion 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:
if then else elif fi case esac for while until do
done { }
Comments Lines
A word beginning with # causes that word and all the follow-
ing characters up to a newline 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 newlines 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 com-
mand 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 newline character (\new-
line), both the backslash and the newline 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 \, `,
", newline, and $ are left intact when the command string is
read.
Parameter Substitution
The character $ is used to introduce substitutable parame-
ters. There are two types of parameters, positional and key-
word. 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 fol-
lowed 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.
${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 exam-
ple, 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 parame-
ters in this section are also referred to as environment
variables.
HOME The default argument (home directory) for the cd com-
mand, 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 section
below).
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 speci-
fied 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 check before each prompt.
MAILPATH
A colon-separated list of file names. If this parame-
ter 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
newline (see Blank Interpretation section).
SHACCT
If this parameter is set to the name of a file writ-
able 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 section below) for this name.
See environ(5) for descriptions of the following environment
variables that affect the execution of sh: LC_CTYPE and
LC_MESSAGES.
The shell gives default values to PATH, PS1, PS2, MAILCHECK,
and IFS. Default values for 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 char-
acters (those found in IFS) and split into distinct argu-
ments where such characters are found. Explicit null argu-
ments ("" or '') are retained. Implicit null arguments
(those resulting from parameters that have no values) are
removed.
Input/Output Redirection
A command's input and output may be redirected using a spe-
cial 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: 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 EOF.
Otherwise, the file is created.
<>word
Open file word for reading and writing as standard
input.
<<[-]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
EOF. If, however, the hyphen (-) is appended to <<:
1. leading tabs are stripped from word before the
shell input is read (but after parameter and com-
mand 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 EOF.
If any character of word is quoted (see Quoting section
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) \newlines 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 stan-
dard 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 associ-
ated with file descriptor 1.
The order in which redirections are specified is signifi-
cant. The shell evaluates redirections left-to-right. For
example:
... 1>xxx 2>&1
first associates file descriptor 1 with file xxx. It associ-
ates file descriptor 2 with the file associated with file
descriptor 1 (that is, 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 com-
mands, 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, 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.
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 pat-
tern, 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 lexi-
cally between the pair, inclusive. If the first char-
acter following the opening [ is a !, any character
not enclosed is matched.
Notice 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:
; & ( ) | ^ < > newline space tab
A character may be quoted (that is, 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 com-
mand is executed. The pair \newline 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.
Inside a pair of double quote marks (""), parameter and com-
mand 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 \, `, , (comma), and $. The pair \newline is
removed before parameter and command substitution. If a
backslash precedes characters other than \, `, , (comma), $,
and newline, 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 newline is
typed and further input is needed to complete a command, the
secondary prompt (that is, 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 com-
mand is used to bind the shell's parameter to the environ-
ment (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 addi-
tions, 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 command
and
(export TERM; TERM=450; command
are equivalent as far as the execution of command is con-
cerned if command is not a Special Command. If command is a
Special Command, then
TERM=450 command
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 example first prints a=b c and c:
echo a=b c
a=b c
set -k
echo a=b c
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 car-
ried 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 script
files, which require a sub-shell for invocation). 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 argu-
ments 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. 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 loca-
tions 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 com-
mands. 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 section
below).
: No effect; the command does nothing. A zero exit code
is returned.
. filename
Read and execute commands from filename and return.
The search path specified by PATH is used to find the
directory containing filename.
bg [%jobid ...]
When Job Control is enabled, the bg command is added
to the user's environment to manipulate jobs. Resumes
the execution of a stopped job in the background. If
%jobid is omitted the current job is assumed. (See Job
Control section below for more detail.)
break [ n ]
Exit from the enclosing for or while loop, if any. If
n is specified, break n levels.
cd [ argument ]
Change the current directory to argument. The shell
parameter HOME is the default argument. The shell
parameter CDPATH defines the search path for the
directory containing argument. Alternative directory
names are separated by a colon (:). The default path
is <null> (specifying the current directory). Note:
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 argument begins with a / the search
path is not used. Otherwise, each directory in the
path is searched for argument.
chdir [ dir ]
chdir changes the shell's working directory to direc-
tory dir. If no argument is given, change to the home
directory of the user. If dir is a relative pathname
not found in the current directory, check for it in
those directories listed in the CDPATH variable. If
dir is the name of a shell variable whose value starts
with a /, change to the directory named by that value.
continue [ n ]
Resume the next iteration of the enclosing for or
while loop. If n is specified, resume at the n-th
enclosing loop.
echo [ arguments ... ]
The words in arguments are written to the shell's
standard output, separated by space characters. See
echo(1) for fuller usage and description.
eval [ argument ... ]
The arguments are read as input to the shell and the
resulting command(s) executed.
exec [ argument ... ]
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 the calling shell or shell script to exit with
the exit status specified by n. If n is omitted the
exit status is that of the last command executed (an
EOF 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.
fg [%jobid ...]
When Job Control is enabled, the fg command is added
to the user's environment to manipulate jobs. This
command resumes the execution of a stopped job in the
foreground and also moves an executing background job
into the foreground. If %jobid is omitted, the current
job is assumed. (See Job Control section below for
more detail.)
getopts
Use in shell scripts to support command syntax stan-
dards (see intro(1)). This command parses positional
parameters and checks for legal options. See
getoptcvt(1) for usage and description.
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. Com-
mands 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.
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.
(See Job Control section below for more detail.)
kill [ -sig ] %job ...
kill -l
Sends either the TERM (terminate) signal or the speci-
fied signal to the specified jobs or processes. Sig-
nals are either given by number or by names (as given
in signal(3HEAD) stripped of the prefix "SIG" with the
exception that SIGCHD is named CHLD). If the signal
being sent is TERM (terminate) or HUP (hangup), then
the job or process will be sent a CONT (continue) sig-
nal if it is stopped. The argument job can be the pro-
cess id of a process that is not a member of one of
the active jobs. See Job Control section below for a
description of the format of job. In the second form,
kill -l, the signal numbers and names are listed. (See
kill(1)).
login [ argument ... ]
Equivalent to `exec login argument....' See login(1)
for usage and description.
newgrp [ argument ]
Equivalent to exec newgrp argument. See newgrp(1) 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, and so forth, with leftover words
assigned to the last name. Lines can be continued
using \newline. Characters other than newline 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 EOF 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 speci-
fied by n. If n is omitted, the return status is that
of the last command executed.
set [ -aefhkntuvx [ argument ... ] ]
-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.
-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 exe-
cuted.
- 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.
stop pid ...
Halt execution of the process number pid. (see ps(1)).
suspend
Stops the execution of the current shell (but not if
it is the login shell).
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 [ argument n [ n2 ... ]]
The command argument is to be read and executed when
the shell receives numeric or symbolic signal(s) (n).
(Note: argument 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 argument is absent, all
trap(s) n are reset to their original values. If argu-
ment is the null string, this signal is ignored by the
shell and by the commands it invokes. If n is 0, the
command argument 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. (See
su(1M).)
The -H option specifies a hard limit. The -S option
specifies a soft limit. If neither option is speci-
fied, ulimit will set both limits and print the soft
limit.
The following options specify the resource whose lim-
its are to be printed or set. If no option is speci-
fied, 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)
Run the sysdef(1M) command to obtain the maximum possible
limits for your system. The values reported are in hexade-
cimal, but can be translated into decimal numbers using the
bc(1) utility. See swap(1M).)
As an example of ulimit, to limit the size of a core
file dump to 0 Megabytes, type the following:
ulimit -c 0
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, MAIL-
CHECK, 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 char-
acter 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: Unless the -c or -s flag is speci-
fied, 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 (see rsh(1M)).
-s If the -s flag is present or if no arguments remain,
commands are read from the standard input. Any remain-
ing 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 interac-
tive 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(3HEAD)).
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 for-
mats:
% 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.
pref Where pref is a unique prefix of the command name. For
example, if the command ls -l name were running in the
background, it could be referred to as %ls. pref can-
not 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 back-
ground. If %jobid is omitted the current job is
assumed.
fg [%jobid ...]
Resumes the execution of a stopped job in the fore-
ground, 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 direc-
tory 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.
Large File Behavior
See largefile(5) for the description of the behavior of sh
and jsh when encountering files greater than or equal to 2
Gbyte ( 2**31 bytes).
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
$HOME/.profile
/dev/null
/etc/profile
/tmp/sh*
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
/usr/bin/sh, /usr/bin/jsh
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWcsu |
|_____________________________|_____________________________|
| CSI | Enabled |
|_____________________________|_____________________________|
/usr/xpg4/bin/sh
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Availability | SUNWxcu4 |
|_____________________________|_____________________________|
| CSI | Enabled |
|_____________________________|_____________________________|
SEE ALSO
intro(1), bc(1), echo(1), getoptcvt(1), kill(1), ksh(1),
login(1), newgrp(1), ps(1), pwd(1), set(1),
shell_builtins(1), stty(1), test(1), umask(1), wait(1),
rsh(1M), su(1M), swap(1M), sysdef(1M), dup(2), exec(2),
fork(2), getrlimit(2), pipe(2), ulimit(2), setlocale(3C),
signal(3HEAD), passwd(4), profile(4), attributes(5),
environ(5), largefile(5), XPG4(5)
WARNINGS
The use of setuid shell scripts is strongly discouraged.
NOTES
Words used for filenames in input/output redirection are not
interpreted for filename generation (see File Name Genera-
tion section 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 pro-
cess table is probably full or you have too many active
foreground processes. There is a limit to the number of pro-
cess 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.
The Bourne shell has a limitation on the effective UID for a
process. If this UID is less than 100 (and not equal to the
real UID of the process), then the UID is reset to the real
UID of the process.
Because the shell implements both foreground and background
jobs in the same process group, they all receive the same
signals, which can lead to unexpected behavior. It is,
therefore, recommended that other job control shells be
used, especially in an interactive environment.
When the shell executes a shell script that attempts to exe-
cute a non-existent command interpreter, the shell returns
an erroneous diagnostic message that the shell script file
does not exist.
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