Watch command smallest -n interval

watch

What is the smallest interval for the watch command?

The man page and Google searches do not indicate what the smallest interval lower limit is. I found through experimentation it can be smaller than 1 second.

To test, I ran this command run on a firewall:

watch -n 0.1 cat /sys/class/net/eth1/statistics/rx_bytes

It clearly updates faster than one second, but it is not clear if it is really doing 100ms updates.

Best Answer

What platform are you on?

On my Linux (Ubuntu 14.10) the man page says:

 -n, --interval seconds
          Specify  update  interval. The  command will not allow quicker
          than 0.1 second interval, in which the smaller values  are  con‐
          verted.

I just tested this with a script calling a C-program that prints the timestamp with microseconds and it works.

Related Solutions

Cygwin has no watch command

There is watch in cygwin. But it isn't installed by default. You need to install procps-ng package to appear watch. (you can run cygwin installer again and it allows to install only the missed packages without reinstalling the whole cygwin)

Instead of watch you can use simple cycle like:

while true ; do check file ; sleep 2 ; done

where check is your command of choice.

Output of ‘watch’ command as a list

You can use the -t switch to watch which causes it not to print header. However, that will still clear the screen so you might be better off with a simple shell loop:

while sleep 1; do
    wc -l my.log
done

One of the advantages is, that you can easily add other commands (e.g. date) and/or pipe the output through sed to reformat it. By the way, if you swap sleep 1 with wc in the loop, it will automatically terminate on errors.

Best Answer

Related Solutions

Cygwin has no watch command

Output of ‘watch’ command as a list

Related Question