PHP file_put_contents，根据日期失败生成文件名动态

I'm trying to accomplish the following: Generate textfile with response to different time. Example "example_17/2/2016_22:25:49.txt"

I try using &filename.&date but cannot work. Is it any simple and good solution? Thanks a lot for help ~

The code is attach below

<?php
$timezone = date_default_timezone_get();
$date  = date('Y/m/d H:i:s');
$fileName = $_FILES["file1"]["name"].$date; // The file name


if(isset($_POST['myselect']) && isset($_POST['textarea'])) {
$data = $_POST['myselect'] . "
" . $_POST['textarea'] . "
";
$ret = file_put_contents('/home/pi/Desktop/DMixer_Webinterface_Downloadfile/$fileName.$date', $data);


if($ret === false) {
    die('There was an error writing this file');
}
else {
    echo "$ret bytes written to file";
echo "The".$date;
}
}
else {
   die('no post data to process');
}

Try

    $date  = date('Y-m-d H:i:s');
    $fileName = 'abc';
    $fileName = $fileName.'_'.$date;
    $data = 'Hi';
    $path = '/home/pi/Desktop/DMixer_Webinterface_Downloadfile/'.$fileName.'.txt';
    $ret = file_put_contents($path, $data);

The date format before will be treated as directory ,dont forget to add write permission.