bash scripting: eval and waiting for processes in background

[Matt Iavarone]

On Thu, Feb 25, 2010 at 8:35 AM, Tom H <tomh0665 at gmail.com> wrote:
>> I have a directory with some scripts with similar names, that I would like
>> to run. I would like to run them all from another script, without having
>> to specify their individual names. Because in the future I may add other
>> scripts, and then I don't have to change the master script.
>> I tried this:
>
>> SCRIPTS=`ls /root/bin/hotcopy-*.sh`
>> eval "$SCRIPTS" &
>> wait
>> echo "Continue master script."
>
>> Works great, except for one little detail.
>> I added echo lines at the start and end of each script for debugging
>> purpose. Because the & moves the process to the background, I expected to
>> see the following output:
>
>> Script 1 starting...
>> Script 2 starting...
>> Script 3 starting...
>> Script 4 starting...
>> Script 1 done.
>> Script 4 done.
>> Script 3 done.
>> Script 2 done.
>> Continue master script.
>
>> The real output is:
>
>> Script 1 starting...
>> Script 1 done.
>> Script 2 starting...
>> Script 2 done.
>> Script 3 starting...
>> Script 3 done.
>> Script 4 starting...
>> Script 4 done.
>> Continue master script.
>
>> So this means that the scripts aren't running simultaneous. It's not a big
>> issue, but they are all independent. Each script stops a service, runs
>> some maintenance (seconds to several minutes) and restarts the service, so
>> I'd like to keep the total service downtime as short as possible.
>
>> I suspect that the problem is with the eval command parsing multiple
>> scripts at once. I tried moving the & inside the quotes, but that doesn't
>> make a difference.
>
> eval will only background the last script whether you put the & inside
> or outside the ".
>
> A loop should do the trick.
>
> I am not sure whether it will run the scripts simultaneously, but you
> could also test run-parts rather than use a loop.
>
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This is not exactly my strong point, scripting, but wouldn't you need
some kind of threading to start each script to run independent of the
other?  Something like _thread in python?