do
(tab)statement(s)
until boolean_expression

Execute the statement(s) inside the do loop until the boolean_expression evaluates to true. Do / Until executes the statements one or more times. The test is done after each time the code in the loop is executed.

t = 1
do
  print t
  t = t + 1
until t > 5

will print

1
2
3
4
5