Linux: repeatedly run a command to monitor output
If you need to repeatedly run a command and view the output changes over time then check out my cli_watch.pl script. I was watching a RAID array rebuild slowly and needed a way to see the progress over time.
Usage: cli_watch.pl [--delay 15] [--line 3] command
Run my_command every 15 seconds:
cli_watch.pl --delay 15 'my_command | grep stuff'
Filter output to only line 2:
cli_watch.pl --line 2 'ping -c 1 192.168.5.222'
Replies
There is a standard watch command (part of procps on linux, and its own watch package in homebrew on MacOS) which might be lighter weight than running a perl script.
It has options to highlight differences and to set the time between invocations, as well as some other nice flags.
It doesn't have a 'specific line number' option, though you could use awk (... | awk 'NR==12') / sed (.... | sed -n 12p) for that (though I can never remember those syntaxes, I end up looking them up when I need them :) )