Bash waits for background processes
This article explains how to wait for background processes in Bash.
Bash waits for background processes
The wait command in Bash can be used to wait for all background processes to complete. This command will wait for the process and return the exit status.
waitCommands affect the current shell execution environment, which is why they are built into shells such as Bash.
waitThe syntax of the command is:
wait [Options] BackgroundProcessID
Where BackgroundProcessID id is a process or job. The wait command will wait until all processes and subprocesses of the given ID have completed.
A simple example of a wait command could be:
wait 1234
The above command will wait for the background process 1234. We can also give multiple processes, and then the wait command will wait for all the background processes.
Now let's run a process in the background:
rsync -a /mn/c/Users/Sheeraz &
The above command will run a process in the background and return the job and process ID. See the output:
[1] 37
The job ID is 1 and the process ID is 37.
Now to wait for the job, we run the following command:
wait %1
where 1 is the job ID. The output of this command is:
[1]+ Exit 23 rsync -a /mn/c/Users/Sheeraz
To wait for this process, we use the following command:
wait 37
The above command will wait for the background process 37 to complete. Most of the time, waitthe command is used in Bash script files to spawn background processes for parallel execution.
The following is an example of a script file:
#!/bin/bash
sleep 30 &
ProcessId=$!
echo "PID: $ProcessId"
wait $ProcessId
echo "Exit status: $?"
Running this script will output the process ID and exit status of the background process. View the output:
PID: 50
Exit status: 0
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