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I'm running a process and I'm counting the number of threads with
ps huH p <PID_OF_U_PROCESS> | wc -l
I can run this thread with watch like this;
watch -n 1 ps huH p <PID_OF_U_PROCESS> | wc -l
This will output the number of threads the process is running, but usually that number doesn't change.
How can I only print the new number to screen if it changed from the last time the command was run?
For example:
64
65
64
(a few minutes go by)
65
Etc.
You could just pipe to uniq:
while ps -o nlwp= -p "$pid"; do sleep 1; done | uniq
watch is not capable of doing this directly. Although you can highlight differences in the command output (via option -d) or exit when the output changes (via option -g) it is not possible to display the output of more than one run. But you can achieve this via other common tools.
One of many possible solutions:
last=""; while true; do cur="$(ps h -o nlwp -p <PID>)"; if ! [ "$cur" = "$last" ]; then last="$cur"; echo "$(date) $cur"; fi; sleep 1; done
Or more readable:
last=""
while true
do
cur="$(ps h -o nlwp -p <PID>)"
if ! [ "$cur" = "$last" ]
then
last="$cur"
echo "$(date) $cur"
fi
sleep 1
done
Explanation: The ps option -o nlwp directly prints the number of threads, so you don't have to call wc -l. You can also use $(pidof programname) instead of <PID> in order to determine the process ID automatically. I also added the current date via $(date) which seems useful to me. If you don't like it then just remove it.
