wait(1)wait(1)NAMEwait - Awaits process completion
SYNOPSISwait [pid]
Note
The C shell has a built-in version of the wait command. If you are
using the C shell, and want to guarantee that you are using the command
described here, you must specify the full path /usr/bin/wait. See the
csh(1) reference page for a description of the built-in command.
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
wait: XCU5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
OPTIONS
None
OPERANDS
One of the following: The unsigned decimal integer process ID of a com‐
mand, for which the utility is to wait for the termination. A job con‐
trol 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. The exit status of
wait is determined by the last command in the pipeline.
DESCRIPTION
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 exits with
a zero exit status.
If one or more pid operands are specified that represent known process
IDs, the wait utility waits until all of them have terminated. If one
or more pid operands are specified that represent unknown process IDs,
wait treats them as if they were known process IDs 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 operand.
The known process IDs are applicable only for invocations of wait in
the current shell execution environment.
RESTRICTIONS
If wait is called in a subshell or separate utility execution environ‐
ment, such as one of the following, it returns immediately because
there are no known process IDs to wait for in those environments:
(wait) nohup wait ... find . -execwait ... \; If the exit sta‐
tus of wait is greater than 128, there is no way for the appli‐
cation to know if the waited-for process exited with that value
or was killed by a signal. Since most utilities exit with small
values, there is seldom any ambiguity.
EXIT STATUS
If one or more parameters were specified, all of them have terminated
or were not known by the invoking shell, and the status of the last
parameter specified is known, then the exit status of wait is the exit
status information of the command indicated by the last parameter spec‐
ified. If the process terminated abnormally due to the receipt of a
signal, the exit status is greater than 128 and is distinct from the
exit status generated by other signals. (See the kill -l option.) Oth‐
erwise, the wait utility exits with one of the following values: The
wait utility was invoked with no operands and all process IDs known by
the invoking shell have terminated. The wait utility detected an
error. The command identified by the last pid operand specified is
unknown.
EXAMPLES
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 using kill as shown
by the following script:
sleep 1000& pid=$! kill -kill $pid wait $pid echo $pid was ter‐
minated by a SIG$(kill -l $?) signal. If either sequence of
commands shown on the first two lines is run in less than 31
seconds either of the commands shown on lines 3 and 4 will
return the exit status of the second sleep in the pipeline:
sleep 257 | sleep 31 & jobs -l %% wait <pid of sleep 31> wait %%
ENVIRONMENT VARIABLES
The following environment variables affect the execution of wait: Pro‐
vides a default value for the internationalization variables that are
unset or null. If LANG is unset or null, the corresponding value from
the default locale is used. If any of the internationalization vari‐
ables contain an invalid setting, the utility behaves as if none of the
variables had been defined. If set to a non-empty string value, over‐
rides the values of all the other internationalization variables.
Determines the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to multi‐
byte characters in arguments). Determines the locale used to affect
the format and contents of diagnostic messages written to standard
error. Determines the location of message catalogues for the process‐
ing of LC_MESSAGES.
SEE ALSO
Commands: bg(1), csh(1), fg(1), jobs(1), kill(1), ksh(1), sh(1)
Functions: wait(2)
Standards: standards(5)wait(1)
