How to write a simple file upload and download function via PHP

How to write a simple file upload and download function through PHP

With the development of Internet technology, file upload and download functions have become essential functions for many websites one. By writing a simple file upload and download function, users can easily upload and download files and improve user experience. This article will introduce how to use PHP to write a simple file upload and download function, and provide specific code examples.

1. Implementation of the file upload function

1. Create a form
   First, create a form on the HTML page for users to upload files. The code of the form is as follows:

   <form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="上传">
   </form>

   Among them, the action attribute of the form tag specifies the processing script after the form is submitted as upload.php, method The attribute specifies the form submission method as POST, and the enctype attribute specifies the form encoding type as multipart/form-data to support file upload.

2. Write the upload script
   In the upload.php file, write the PHP code to handle the file upload. The code is as follows:

   <?php
   $targetDir = "uploads/";  // 上传文件存储目录
   $targetFile = $targetDir . basename($_FILES["file"]["name"]);  // 上传文件的路径
   
   // 检查文件类型
   $fileType = strtolower(pathinfo($targetFile, PATHINFO_EXTENSION));
   $allowedTypes = array("jpg", "jpeg", "png", "gif");
   if (!in_array($fileType, $allowedTypes)) {
    echo "只允许上传图片文件！";
    exit;
   }
   
   // 将文件从临时目录移动到指定目录
   if (move_uploaded_file($_FILES["file"]["tmp_name"], $targetFile)) {
    echo "文件上传成功！";
   } else {
    echo "文件上传失败！";
   }
   ?>

   In the above code, a variable $targetDir is first defined to specify the storage directory after the file is uploaded, and then the basename() function is used Get the path of the uploaded file, then use the strtolower() function to convert the file type to lowercase, use the pathinfo() function to get the extension of the file, then check if the file extension is allowed within the type range. If the file type does not meet the requirements, a prompt message is output and the program is terminated. If the file type meets the requirements, use the move_uploaded_file() function to move the file from the temporary directory to the specified directory.

2. Implementation of the file download function

1. Create a file list
   First, you need to display a list of files available for download on the page . The code is as follows:

   <?php
   $files = glob("uploads/*");  // 获取上传文件的列表
   
   foreach ($files as $file) {
    $fileName = basename($file);
    echo "<a href='download.php?file={$fileName}'>{$fileName}</a><br>";
   }
   ?>

   In the above code, use the glob() function to get the list of uploaded files, then use the basename() function to get the file name, and finally Use echo to output a list of files and generate a download link for each file.

2. Write download script
   In the download.php file, write PHP code to download the file. The code is as follows:

   <?php
   $fileName = $_GET["file"];  // 获取要下载的文件名
   $filePath = "uploads/" . $fileName;  // 要下载的文件路径
   
   if (file_exists($filePath)) {
    header("Content-Type: application/octet-stream");
    header("Content-Disposition: attachment; filename={$fileName}");
    readfile($filePath);
   } else {
    echo "文件不存在！";
   }
   ?>

   In the above code, the $_GET super global array is first used to obtain the file name to be downloaded, and then the path of the file is spliced ​​based on the file name. Next, use the file_exists() function to check whether the file exists. If the file exists, set the HTTP header information so that the browser downloads the file as an attachment, and then use the readfile() function to The file is output to the browser. If the file does not exist, a prompt message is output.

The above is a sample code for writing a simple file upload and download function through PHP. Through these codes, we can easily implement file upload and download functions and improve the user experience of the website. Of course, this is just a simple example, and more security and performance optimization issues may need to be considered in actual development, but these sample codes can serve as the basis for getting started and learning, helping beginners quickly master the principles and implementation of file upload and download. Way.

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