shell while until

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

echo ""

i=1
#注意while和[[中间得有空格,[[与$i及4与]]之间同样要有空格
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