<?php
$file = "data.txt";

function get_data()
{
    global $file;
    $data = "";
    if( !file_exists($file) )
    {
        return $data;
    }

    $data = file_get_contents($file);

    return $data;
}

var_dump(get_data());

function add_new_item( $txt )
{
    global $file;
    $data = get_data();
    $data = $data . $txt . "<br>\r\n";

    $fp = fopen($file, "w");
    fwrite($fp, $data );
    fclose($fp);
}

if( isset( $_POST['submit'] ) )
{
    $txt = $_POST['item'];
    add_new_item( $txt );
}
?>
<form action="" method="post">
    Name : <input type="text" name="item" />
    <input type="submit" name="submit" value="Save" />
</form>

<h3>All Data</h3>

<?php
echo get_data();
?>