WAIT(1) User Commands WAIT(1)

NAME

wait - await process completion

SYNOPSIS

/bin/sh
wait [pid]...


/bin/jsh /bin/ksh /usr/xpg4/bin/sh
wait [pid]...


wait [% jobid...]


/bin/csh
wait


ksh93
wait [job...]

DESCRIPTION

The shell itself executes wait, without creating a new process. If you
get the error message cannot fork,too many processes, try using the wait
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.


Not all the processes of a pipeline with three or more stages are
children of the shell, and thus cannot be waited for.

/bin/sh, /bin/jsh
Wait for your background process whose process ID is pid and report its
termination status. If pid is omitted, all your shell's currently active
background processes are waited for and the return code is 0. The wait
utility accepts a job identifier, when Job Control is enabled (jsh), and
the argument, jobid, is preceded by a percent sign (%).


If pid is not an active process ID, the wait utility returns immediately
and the return code is 0.

csh
Wait for your background processes.

ksh
When an asynchronous list is started by the shell, the process ID of the
last command in each element of the asynchronous list becomes known in
the current shell execution environment.


If the wait utility is invoked with no operands, it waits until all
process IDs known to the invoking shell have terminated and exit with an
exit status of 0.


If one or more pid or jobid operands are specified that represent known
process IDs (or jobids), the wait utility waits until all of them have
terminated. If one or more pid or jobid operands are specified that
represent unknown process IDs (or jobids), wait treats them as if they
were known process IDs (or jobids) that exited with exit status 127. The
exit status returned by the wait utility is the exit status of the
process requested by the last pid or jobid operand.


The known process IDs are applicable only for invocations of wait in the
current shell execution environment.

ksh93
wait with no operands, waits until all jobs known to the invoking shell
have terminated. If one or more job operands are specified, wait waits
until all of them have completed. Each job can be specified as one of the
following:

number
number refers to a process ID.


-number
number refers to a process group ID.


%number
number refers to a job number


%string
Refers to a job whose name begins with string


%?string
Refers to a job whose name contains string


%+
%%
Refers to the current job


%-
Refers to the previous job


If one or more job operands is a process id or process group id not known
by the current shell environment, wait treats each of them as if it were
a process that exited with status 127.

OPERANDS

The following operands are supported:

pid
The unsigned decimal integer process ID of a command, for which
the utility is to wait for the termination.


jobid
A job control job ID that identifies a background process group
to be waited for. The job control job ID notation is applicable
only for invocations of wait in the current shell execution
environment, and only on systems supporting the job control
option.

USAGE

On most implementations, wait is a shell built-in. If it is called in a
subshell or separate utility execution environment, such as one of the
following,

(wait)
nohup wait ...
find . -exec wait ... \;


it returns immediately because there is no known process IDs to wait for
in those environments.

EXAMPLES

Example 1: Using A Script To Identify The Termination Signal

Although the exact value used when a process is terminated by a signal is
unspecified, if it is known that a signal terminated a process, a script
can still reliably figure out which signal is using kill, as shown by the
following (/bin/ksh and /usr/xpg4/bin/sh):


sleep 1000&
pid=$!
kill -kill $pid
wait $pid
echo $pid was terminated by a SIG$(kill -l $(($?-128))) signal.

Example 2: Returning The Exit Status Of A Process

If the following sequence of commands is run in less than 31 seconds
(/bin/ksh and /usr/xpg4/bin/sh):


sleep 257 | sleep 31 &

jobs -l %%


then either of the following commands returns the exit status of the
second sleep in the pipeline:


wait <pid of sleep 31>
wait %%

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment variables
that affect the execution of wait: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES,
and NLSPATH.

EXIT STATUS

ksh93
The following exit values are returned by the wait built-in in ksh93:

0
wait was invoked with no operands. All processes known by the
invoking process have terminated.


127
job is a process id or process group id that is unknown to the
current shell environment.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

csh(1), jobs(1), ksh(1), ksh93(1), sh(1), attributes(7), environ(7),
standards(7)

May 17, 2020 WAIT(1)