I am confused how this works. I would assume `SECONDS` would just be a shell variable and it was first assigned `0` and then it should stay same, why did it kee

I am confused how this works. I would assume `SECONDS` would just be a shell variable and it was first assigned `0` and then it should stay same, why did it keep counting the seconds? > SECONDS bash: SECONDS: command not found > SECONDS=0; sleep 5; echo $SECONDS; 5 > echo "Your command completed after $SECONDS seconds"; Your command completed after 41 seconds > echo "Your command completed after $SECONDS seconds"; Your command completed after 51 seconds > echo "Your command completed after $SECONDS seconds"; Your command completed after 53 seconds