Upload image with unique name

Question

So I am trying to upload some images to a folder on my server with the script below,but it saves every image as "image.jpg" and it overwrites the last uploaded image if I try to upload multiple ones.As you can see I commented the part that checks if the file already exists to let me upload a file and overwrite the latest one.Help!I need something modified to just randomize the name or get the original image name.

<?php
$target_dir = "wp/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = pathinfo($target_file,PATHINFO_EXTENSION);

// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
    if($check !== false) {
        echo "File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "File is not an image.";
        $uploadOk = 0;
    }
}
// Check if file already exists
/*if (file_exists($target_file)) {
    echo "Sorry, file already exists.";
    $uploadOk = 0;
}*/
// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
}
// Allow certain file formats
if($imageFileType != "png" && $imageFileType != "jpg") {
    echo "Sorry, only PNG and JPG files are allowed.";
    $uploadOk = 0;
}
// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
    echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
    if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
        echo "The file ". basename( $_FILES["fileToUpload"]["name"]). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}
?>

Answer 1

A simple way to get a unique filename is to get the current Unix time in milliseconds and append (or prepend) that to the filename. The command to use is microtime() .

For example:

$target_file = $target_dir . microtime() . basename($_FILES["fileToUpload"]["name"]);

You could also try things like hashing the file to get a unique hash with low probability of collisions, but this is faster and just as effective.

Answer 2

You can implement something like Windows's auto-file-renaming:

$try = 1;
while($file_exists($target_file)) {
    $target_file = preg_replace('/(\(\\d+\))*(\.[^\\(\\)]+)$/',
        "({$try})\\2", $target_file);
    $try++;
}

This will replace the file "duplicate.jpg" with "duplicate(1).jpg", then "duplicate(2).jpg", and so on.

It will still be prone to unlikely race conditions, just as using uniqid() or microtime() (which, conflict-wise, are both better).

Otherwise, always use tempnam() . You can check out this answer .