Store the output of date and watch command to a file

Question

I am a newbie to linux and I am trying to watch a command and try to log it into a file. I tried

watch -t -n 10 "(date '+TIME:%H:%M:%S' ; ps aux | grep "pattern" | wc -l)" >> logfile

and am expecting a result like

TIME: 10:32:30    12
TIME: 10:32:40    18
TIME: 10:32:50    2

to be stored in logfile. However, when the logfile has unprintable characters in in. How do I get this kind of output from the command li

Answer 1

In order to do what you are looking for, a simple script (as @Ignacio pointed out) should do the trick:

while true
do
    echo "$(date '+TIME:%H:%M:%S') $(ps aux | grep "pattern" | wc -l)" | tee -a logfile
    sleep 2
done

I use tee instead of >> so that you can see the output on your terminal as well as capture it in your log.

Answer 2

watch is an ncurses program, and is designed to be run in a console window (not redirected), which is why it's creating a bunch of unprintable characters (those are the control characters that manage and move the cursor around for redrawing the screen).

You might try moving the date / grep commands into a script, and then call that script from a cronjob.

Answer 3

watch is meant for output to a display. If you simply want to run a command every X seconds then you should just use a delay loop for that.

while true ; do somecommand ; sleep 2 ; done

Answer 4

This can easily be done using watch too without using any scripts.

watch -t -n 10 "(date '+TIME:%H:%M:%S' ; ps aux | grep "pattern" | wc -l) | tee -a logfile"

Answer 5

Ok, so I put it in a script and have the following code:

#!/bin/sh
NOW=$(date '+%Y%m%d%H%M%S')
LOGFILE="log.$NOW"

while true
do
    echo $(date '+[TIME: %H:%M:%S]   Output: ' ; ps aux | grep "pattern" | wc -l ) | tee -a $LOGFILE
    sleep 2
done