Tribblix: manual page: wait.1

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