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Do something at least once!

Posted by admin (Graham Ellis), 1 December 2002
While and for loops can be skipped over completely if the initial conditions is false when the loop is entered from above, until loops can be skipped over if the initial condition is true, and foreach loops can be skipped over if you run them on an empty list.

So if you want to force a loop to perform at least once (for example, if you want to prompt and read an answer at least once,  and keep prompting until the user enters a valid respone)  how do you do it?   One way is simply to program carefully so that your while loop  always enters with a true condition, but Perl also provides a do ... while loop that will check the condition after running the code in the block rather than before.

Here's an example of do ... while prompring for an input, and then reprompring as many times as necessary until the user enters just a single word response.

sub getplayer {
       $angle = $_[0];
       do {
       $rpt = 0;
       print "Player sitting at $angle is ... ";
       chomp ($response = <STDIN>);
       ($response !~ /^\S+$/) and
                       print "One name please\n" and
               while ($rpt);
       return ($response);

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