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Old 12-12-2008, 01:34 PM   #1
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[Bash] Waiting for a process to terminate or stopping it after some time

Hi folks,

I've got a bunch of files to be processed by a program, one after the other.
File processing can take some time. I want the program not to take more than 1 hour for each file.
So I put up the following bash script. It calls iteratively the program and stops it after 1 hour. The program is expected to perform a clean exit upon receiving the SIGHUP signal.
a_program $file & 
sleep 3600
kill -s SIGHUP $!
The problem with the script is that it always waits 1 hour before processing the next file, independently from program termination.
How can I tell the shell to resume the script when the program terminate as well?


Old 12-12-2008, 05:19 PM   #2
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Run both the a_program command and the sleep command in the background. Then issue a wait command to wait for whichever background command completes first.

Steve Stites

P.S. If the program can process the files in parallel then you could start all of the a_programs in the background simultaneously. Then start the sleep in the background. Then wait on all background jobs and keep track of which a_programs have completed. If all a_programs have completed kill the sleep process. If the sleep process completes before all of the a_program processes have completed then kill the remaining a_programs.

Last edited by jailbait; 12-12-2008 at 06:50 PM.
Old 12-12-2008, 06:25 PM   #3
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A dirty way is to check for the elapsed time of the background process using the ps command:
a_program $file &

while [ $(ps -p $! -o etime= | tr -d ": ") -lt 10000 ]
  sleep 60
done 2> /dev/null

kill -s SIGHUP $!
The while loop will end up when the elapsed time is greater than (or equal to) 1 hour or when the process is terminated. The format of the elapsed time is MM:SS or HH:MM:SS with trailing blank spaces, hence the tr command to delete commas and blank spaces, leaving a pure number. The value 10000 corresponds to 1 hour.

If the program terminates before 1 hour, the output of the ps command is null and the shell would give a "unary operator expected" error (redirected to /dev/null). In this case the while loop is broken due to the error.


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