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This is a short How-to for a while loop which echoes “LOOP!” :

while(true)
do echo "LOOP!"
sleep 3
done

• while: starts the loop (in the brackets there is the constraint). Because an undefined variable is always “true” the loop will restart endless.
• do: Contains what the loop should do. For this example it echoes “Loop!”.
• sleep X – The script wait X second before continuing. (3 seconds here).
• done – Ends the loop

You can save the script and run it in shell using “bash SCRIPTNAME” or use “chmod a+x” to make it runnable and start it by clicking at it.