shell while until

i=1
while((i<=3))
do
  echo -n $i
  let i=i+1
done

echo ""

i=1
#Note that there must be a space between while and [[, and there must also be a space between [[ and $i and 4 and ]]
while [[ $i != 4 ]]
do
  echo -n $i
  let i=i+1
done

echo ""

i=1
until [[ $i > 3 ]]
do
  echo -n $i
  let i=i+1
done

123
123
123