Sleep while process uses more than n% CPU

Question

I am on macOS. I want to write a bash script which pauses for 0.5 seconds (i.e. sleeps) while a certain process (which I know by command name only) uses more than, say 5% CPU. I could

pgrep command_name

and then

ps -p PID -o %cpu | tail -1 | cut -c 3-5

to get the CPU usage and use this number in a while loop. Can this be done more elegantly (ideally in one line of code)?

Sure you want to use CPU usage from ps? I.e. man ps | less +/'NOTES' and https://unix.stackexchange.com/q/58539/140633 — ibuprofen, Jul 05 '21 at 14:49
by the way, what's the process you're watching there? (And: I don't know how or how much OS X smooths the CPU load, but this looks like something that might go wrong when your script happens to look in the wrong moments, when the process is e.g. limited by IO load) — Marcus Müller, Jul 05 '21 at 16:39

score 1 · Accepted Answer · answered Jul 05 '21 at 19:24

1

You can make it simpler by using command substitution:

ps -p $(pgrep firefox) -o %cpu | tail -1 | cut -c 3-5

I am afraid I don't have a mac to test on, so the following might not work on your system, but on Linux, we can use %cpu= to avoid printing the header:

$ ps -p $(pgrep firefox) -o %cpu 
%CPU
23.3
$ ps -p $(pgrep firefox) -o %cpu= 
23.3

Which means that ps -p $(pgrep firefox) -o %cpu= is enough to give you the number only.

answered Jul 05 '21 at 19:24

terdon

242,166

Works indeed. Many thanks! – 220284 Jul 05 '21 at 20:10
@220284 you're welcome. Out of curiosity, which one worked? Does the = trick work with your ps? – terdon Jul 05 '21 at 20:55
ps -p $(pgrep firefox) -o %cpu= works on macOS as well – 220284 Jul 06 '21 at 08:25
Ah good, I was afraid that was a GNU thing. Thanks! – terdon Jul 06 '21 at 08:32

Sleep while process uses more than n% CPU

1 Answers1