while (1) {
  # use a block for structuring things
  {
     print "do something, then leave the loop\n";
     last;
  }
}

##</code><code>##

while (1) {
  # use a block for structuring things (a bit unconventionally)
  if (1) {
     print "do something, then leave the loop\n";
     last;
  }
}