What are common reasons for file upload via form not functioning in PHP, especially when the form is submitted to the same file?

Common reasons for file upload via form not functioning in PHP when the form is submitted to the same file include not setting the enctype attribute of the form to "multipart/form-data", not checking if the file was successfully uploaded, and not moving the uploaded file to the desired location on the server. To solve this, ensure the form has enctype="multipart/form-data", check if the file was uploaded using $_FILES, and move the uploaded file using move_uploaded_file() function. 

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST" && isset($_FILES["file"])) {
    $file = $_FILES["file"];
    
    if ($file["error"] == UPLOAD_ERR_OK) {
        $target_dir = "uploads/";
        $target_file = $target_dir . basename($file["name"]);
        
        if (move_uploaded_file($file["tmp_name"], $target_file)) {
            echo "File uploaded successfully.";
        } else {
            echo "Error uploading file.";
        }
    } else {
        echo "Error: " . $file["error"];
    }
}
?>

<form method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="Upload">
</form>

Keywords

file upload form submission PHP enctype move_uploaded_file

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