watch to remember its last zero exit output

Question

I run a process that takes lot of time. Time is not a problem actually but I would like to know how much RAM memory it requires. Process is already running so /usr/bin/time is not an option. I found the pid of my process and run

watch -n 1 grep VmHWM /proc/3100/status

it works nice, I can leave it, do some other work, and just check later what was the value recorded with 1 seconds intervals. The problem starts if/when a process terminates (either finish job, or get killed because of OOM) because watch replace the last valid output with

grep: /proc/3100/status: No such file or directory

using option -e does not help. Is there a way to make watch not refresh output on non-zero exit? or show two most recent ones, so the previous zero exit can still be seen?

If you know what your process is called, you could incorporate pgrep into that. I'm not posting this as an answer as I don't have a Linux system to test properly on at the moment. — Kusalananda
– Kusalananda ♦, Commented Dec 5, 2019 at 12:54
@Kusalananda I used pgrep to find process id. I don't understand how pgrep would help me more, if process terminates then pgrep won't list it anyway, isn't? — jangorecki
– jangorecki, Commented Dec 5, 2019 at 13:23
Oh, I'm sorry. I misinterpreted what you were writing and though that you were watching a particular PID, and that the process later restarted with a new PID, and that you wanted to follow that instead. — Kusalananda
– Kusalananda ♦, Commented Dec 5, 2019 at 13:33
I would just use a shell while loop for this. while grep VmHWM /proc/3100/status; do sleep 1; done. — Mikel
– Mikel, Commented Dec 5, 2019 at 13:35
@Mikel thanks, you suggestion does the job well. Yet I find it strange that watch -e cannot handle that in better way. — jangorecki
– jangorecki, Commented Dec 5, 2019 at 13:40

Mikel · Accepted Answer · 2019-12-05 13:47:09Z

1

I would use a shell while loop for this.

pid=3100
while out=$(grep VmHWM /proc/$pid/status); do
  printf "\r$out     "
  sleep 1
done
printf "\n"

edited Dec 5, 2019 at 13:47

answered Dec 5, 2019 at 13:39

Mikel

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