[Toybox] Would someone please explain what bash is doing here?

[Chet Ramey]

On 5/28/20 6:41 PM, Rob Landley wrote:

>> If you support job control IDs, you're already supporting `%' as a special
>> prefix. What's the difference?
> 
> I meant we've resolved that % is one prefix and %? is another prefix with
> similar but distinct meaning. I.E. %? is, itself, a special prefix.

I suppose. But it's the `%' that marks the argument as a job identifier.
The rest of the string is what's interpreted.



>> If you're worried about leaving stray background jobs around, end your
>> test script with `wait'.
> 
> Which will hang if the background job is hung.

It's pretty easy to send yourself a signal from a subshell after a period
of time as a cheap alarm.

> 
>> But you can always save a background job's pid
>> by saving $!, so you can always have a handle to the background jobs you
>> create.
> 
> In theory jobs -p should do it, in practice I've hit background-from-subshell
> cases where it wasn't in the list...

Sure, you can defeat anything. I've done stuff like that myself to avoid
processes being killed by the shell at exit.

> 
>> Bash-5.1 will change the way it does $SECONDS to use gettimeofday(), btw.
> 
> Meanwhile, I'm fielding:
> 
> https://github.com/landley/toybox/pull/210

Ironically, gettimeofday() is more portable.

Chet
-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
		 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    chet at case.edu    http://tiswww.cwru.edu/~chet/