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.