[TUHS] Were cron and at done at the same time? Or one before the other?

Michael Kjörling michael at kjorling.se
Wed Dec 9 05:20:54 AEST 2020

On 8 Dec 2020 11:05 -0800, from lm at mcvoy.com (Larry McVoy):
> Doesn't it stand to reason that cron would come first, isn't at implemented
> with an entry in a crontab?

I don't know if it is implemented that way, but if you have cron, then
I suspect you could implement some form of at with even a pretty simple
shell script that runs once a minute (via cron) to parse a set of files
to see what should be run now as opposed to later.

If you have at but not cron, then implementing the other doesn't seem
quite as straightforward. It would certainly still be possible, but it
would definitely give rise to the question of "wouldn't it be real nice
if I could set this task up to run on a recurring basis?" followed by
"wouldn't it make more sense for the run-stuff-at-some-time task to run
from the recurring-execution tool, than the other way around?".

Certainly the step from cron to at seems fairly obvious; not all tasks
that are to be executed at some point in time lend themselves well to a
recurring nature. Sometimes you really want to do something just once,
just not right now.

Michael Kjörling • https://michael.kjorling.semichael at kjorling.se
 “Remember when, on the Internet, nobody cared that you were a dog?”

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