my @a = ( 1, 2, 3, 4, 2, 5, 7 );

my $last = $#a;
my $i = 0;
while( $i <= $last ){

  if( $a[$i] == 2 ){
    $last --;
    last if $i > $last;
  }

}continue{
  $i ++;
}
$#a = $last;