On Mon, Jul 17, 2006 at 06:36:55AM -0400, Gary R. Leaf wrote:
> >hi
> >
> >I find that in many cases I need my background tasks to be executed in
> >sequence. Ie, I need background task-b to start right after background
> >task-a has properly started.
> >
> >So far I haven't found a good way to do it. I used
> >
> >task-a & sleep 2; task-b &
> >
> >but that 'sleep 2' has changed to 'sleep 5' and still sometimes task-b
> >starts before task-a. I can raise the wait time, but it means that task-b
> >would normally start too late...
> >
> >Any good way?
> >
> >thanks
> >
> >
> >
> Set up a script that checks the return codes.
>
> if return code of task A is 0 then
> task B
> else
> do something else
>
> if rturn code of task B is 0 then
> task C
> else
> do something else
>
> and so on
>
> execute the controlling script in the background
You don't need a script - just use the 'conditional and' operator
of the shell:
(cmd1 && cmd2 && cmd3)&
will execute cmd1 to cmd3 in sequence, aborting if any fail. If you
don't want to abort on error, use ';' to separate the commands...
from the 'sh' manpage:
``&&'' and ``||'' are AND-OR list operators. ``&&'' exe-
cutes the first command, and then executes the second com-
mand iff the exit status of the first command is zero.
``||'' is similar, but executes the second command iff the
exit status of the first command is nonzero. ``&&'' and
``||'' both have the same priority.
DigbyT
--
Digby R. S. Tarvin digbyt(at)digbyt.com
http://www.digbyt.com
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