Learning Perl: 10.2. The until Control Structure

10.2. The until Control Structure

Sometimes,you'll want to reverse the condition of a while loop. To do that,use until:

    until ($j > $i) {
      $j *= 2;
    }

This loop runs until the conditional expression returns true. It's really just a while loop in disguise,except it repeats as long as the conditional is false,rather than true. The conditional expression is evaluated before the first iteration,so this is a zero-or-more-times loop,just like the while loop.^[*] As with if and unless,you could rewrite any until loop to become a while loop by negating the condition. But generally,you'll find it simple and natural to use until from time to time.

^[*] Pascal programmers,take note: in Pascal,the repeat-until always runs at least one iteration,but an until loop in Perl may not run at all if the conditional expression is true before the loop starts.