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I compiled a short bash one-liner to focus a running application or launch it if it isn't running:

#!/bin/bash
#intellilaunch.sh

wmctrl -a $1 || $1 & disown
exit 1

The command exits perfectly fine when run directly from the command line:

:~$ wmctrl -a firefox || firefox & disown
[1] 32505

A quick check with the system monitor shows that only firefox is running.

However, when I launch firefox via the script (./intellilaunch.sh firefox) it spawns a persisting new process called intellilaunch.sh firefox, which only exits after closing firefox.

What am I doing wrong?

Edit:

I modified my script according to michas' suggestion:

#!/bin/bash

program=$(basename $1)

if ! wmctrl -a "$program"; then
  "$1"&
fi

Not a one-liner anymore but it works perfectly fine now!

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does it work with another program? Eg.: xclock? – jippie Dec 25 '12 at 22:15
@jippie Same exact behaviour: script launches xclock but then stays open instead of exiting; only exits after I close xclock – Glutanimate Dec 25 '12 at 22:38
Strange, I copied your script and works fine here. Only difference is that I didn't use an exit 1 – jippie Dec 25 '12 at 22:42
I just tried it out without exit 1. Same result. How did you launch the script? Did you use ./intellilaunch.sh xclock or something else? – Glutanimate Dec 25 '12 at 22:53
yup. What OS / distribution are you on? – jippie Dec 25 '12 at 22:57
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1 Answer

up vote 2 down vote accepted

I cannot reproduce this behavior on my system. From your description is sounds like there is a process not properly set to background.

Try to run as bash -x intellilaunch.sh xclock, this should show, what is going on.

Also || binds stronger than &, therefore you send the whole pipe in background. Maybe an explicit if would be a good idea.

Your 

wmctrl -a firefox || firefox & disown ; exit 1

is interpreted as

( wmctrl -a firefox || firefox ) & disown ; exit 1

whereas you probably meant

wmctrl -a firefox || ( firefox & disown ) ; exit 1

Beause of that, bash will start two jobs one with wmctl and firefox - and another one with disown and exit. As the background job needs a short time to launch it will probably start the commands slighly later, that is why the output of bash -x seems to be in the wrong order.

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Do you really need the disown? Does your script show the same blocking behavior without the disown? – michas Dec 25 '12 at 23:50
bash -x intellilaunch.sh xclock displayed the same behaviour, i.e. the process just wouldn't exit (the disown was superfluous, I think). I followed your suggestion and dropped the || for an if statement (see above). Everything works perfectly fine now. Thank you! – Glutanimate Dec 26 '12 at 0:09
That still leaves the question why it did not work before. - Running bash with -x lets bash print out all the executed commands. What was the output in your case? - Did just leaving out the disown change the situation? – michas Dec 26 '12 at 0:32
I pasted the outputs both with and without disown here. Look as if everything is out of order. Is it due to the ||? – Glutanimate Dec 26 '12 at 0:45
1  
No, it's because of the &. (See extended answer.) – michas Dec 26 '12 at 21:35
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