PHP file reading and writing

        $handle  = @ fopen ( "demo.txt" ,  "r" );
    if ( $handle ) {
        while (( $buffer  =  fgets ( $handle ,  4096 )) !==  false ) {
            echo  $buffer ;
        }
        if (! feof ( $handle )) {
            echo  "Error: unexpected fgets() failn" ;
        }
        fclose ( $handle );
    }

    echo '';

    $length= readfile("demo.txt");

    echo '';

    $file_str = 'demo.txt';

    if(file_exists($file_str))
    {
        echo file_get_contents($file_str);

    }

    ?>

PHP