PHP字符串比较无法按预期工作

I have the following snippet of code that I am trying to use to read a file that can have some lines repeated two or more times. The goal of this script is to only write unique lines (no duplicates) but for some reason it appears that it is not detecting equality. Any thoughts?

$handle = @fopen("Old.csv", "r");
$new = @fopen("New.csv", "w");
$last_line = null;

if ($handle && $new) {
    while (($buffer = fgets($handle, 4096)) !== false) {
        if( $last_line != $buffer ) fwrite( $new, $buffer );
        $last_line = $buffer;
    }
    if (!feof($handle)) {
        echo "Error: unexpected fgets() fail
";
    }
    fclose($handle);
    fclose($new);
}

Here is an example of "Old.csv"

 apple
 apple
 orange
 grapes
 grapes
 grapes

"New.csv" should be:

apple
orange
grapes

But it ends up being an exact copy of "Old.csv".