I don't often use a do-while loop, but when I was writing my Animals program, I found this to be a useful little trick for interactive input that needs a certain letter.
do {
  print "\nDid I guess your animal?\n\n";
} while ($answer=<STDIN>) !~ /^[YN]/i;

## OR

do {
  print "\nDo you want to <P>lay again or <Q>uit?\n\n";
} while ($answer=<STDIN>) !~ /^[PQ]/i;

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The three newlines help to clear out the users input and make a nicer looking response if they fail to answer with a correct letter. Since $answer has already been set, after the loop you can say: 
if ($answer =~ /^P/i) {
  ## Code for P here
}
## Add some elsifs if > 2 choices
else { 
  ## No need to check the final letter
  ## Code for Q here
}

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In reply to Do/while correct answer loop by turnstep

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