while( CONDITION_A ) {
  if( CONDITION_B ) {
    # DO SOMETHING
    last; # Exits loop immediately.
  }
}

##</code><code>##

my $found = 0;
while( CONDITION_A && ! $found ) {
  if( CONDITION_B ) {
    # DO_SOMETHING
    $found = 1;
  }
  else {
    # BLAH BLAH
  }
}