wait - await process completion
wait [pid]...
wait [% jobid...]
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.
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.
Wait for your background processes.
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.
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.
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.
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.
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 %%
See environ(5) for descriptions of the following environment variables
that affect the execution of wait: LANG, LC_ALL,
LC_CTYPE, LC_MESSAGES, and NLSPATH.
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.
See attributes(5) for descriptions of the following attributes:
| ATTRIBUTE
TYPE |
ATTRIBUTE VALUE |
| Interface Stability |
Committed |
| Standard |
See standards(5). |
csh(1), jobs(1), ksh(1), ksh93(1), sh(1),
attributes(5), environ(5), standards(5)