[SOLVED] Check if user has typed something while script is running

Issue

I have to write a script that prints every three seconds the % of CPU used by user or by system. If the user types a specific string, the output must switch back and forth.

How can I check for input without interrupting the output stream? The read command would stop it, I'm running out of ideas.

Solution

You can use the read command with the timeout option read -t. For example the below script detects the string 'cc'. You can also specify the number of characters to read with -N so that user does not have to press enter.

flag=0
while true; do
    sleep 3
    if [[ $flag -eq 0 ]];then
      echo user
    else
      echo sys
    fi
    read -t 0.25 -N 2 input
    if [[ $input = "cc" ]] ; then
       [[ $flag -eq 0 ]] && flag=1 || flag=0
    fi
done

Answered By - Samik