Linux – How to run two different long running commands at the same time in a bash script

bashlinuxscripting

I have to chmod and chown hundreds of thousands of files as part of a migration script. Each command takes about an hour and a half to complete. I realized these two operations can be run at the same time which cuts down on running time, which I confirmed by testing in the shell.

I know the trick of pushing commands into the background with '&', but I need to make sure both processes finish before proceeding with the rest of the script.

Thanks

Best Answer

Use the wait command.

This demo:

#!/bin/bash
echo $SECONDS
sleep 12&
sleep 15&
jobs
wait
echo $SECONDS
echo "jobs are done"

Produces this output:

0
[1]-  Running                 sleep 12 &
[2]+  Running                 sleep 15 &
15
jobs are done

There's a fifteen second pause before the last two lines are output.

Related Solutions

Bash – How to Output Two Commands to File

Something like this? (In a loop, cron, or whatever you're currently using.)

(date; my_sensor_command) >> log_file

Linux – Redirect output of Python program to /dev/null

The program may be writing to the tty instead of stdout. You may be able to use the unbuffer script that comes with expect or some other technique using expect or something similar.

Here's a demonstration. Create this script and call it "writetty". Then do chmod u+x writetty:

#!/bin/bash
date > /dev/tty

Now try it out:

$ ./writetty
Tue Jun  8 12:24:36 CDT 2010
$ ./writetty > /dev/null
Tue Jun  8 12:24:46 CDT 2010
$ var=$(./writetty)
Tue Jun  8 12:24:56 CDT 2010
$ unbuffer ./writetty > /tmp/writetty.out
$ cat /tmp/writetty.out
Tue Jun  8 12:25:06 CDT 2010
$ var=$(unbuffer ./writetty)
$ echo $var
Tue Jun  8 12:25:16 CDT 2010

You could use expect to respond to the program's request for input instead of killing it.

Best Answer

Related Solutions

Bash – How to Output Two Commands to File

Linux – Redirect output of Python program to /dev/null

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