How to use PHP to implement file upload and replacement

In web development, file upload is one of the common functions. After the user uploads the file to the server, we need to process the file, and sometimes we need to replace the file with the same name that already exists on the server. This article will introduce how to use PHP to implement file upload and replacement.

1. File upload basics

In PHP, file upload is implemented through the $_FILES global variable. $_FILES contains the name, type, size, temporary path, error information, etc. of the uploaded file. The following are possible key values ​​for $_FILES:

• name: The name of the uploaded file
• type: The type of the uploaded file
• size: The size of the uploaded file
• tmp_name: The temporary path of the uploaded file
• error: The error code of the uploaded file

In the HTML form, you need to add the enctype="multipart/form-data" attribute to upload files. The following is a sample HTML form for file upload:

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

2. File Upload and Rename

After obtaining the uploaded file information through $_FILES, we need to change the file from temporary The directory is moved to the specified directory. At the same time, since there may be naming conflicts in the uploaded files, we also need to rename the file names. The following is an example to implement basic file upload:

<?php
$uploadDir = &#39;/path/to/upload/dir&#39;; // 上传文件目录
$fileName = $_FILES[&#39;upload_file&#39;][&#39;name&#39;];
$tmpName = $_FILES[&#39;upload_file&#39;][&#39;tmp_name&#39;];
if (move_uploaded_file($tmpName, "{$uploadDir}/{$fileName}")) {
  echo "文件已上传并保存到：{$uploadDir}/{$fileName}";
} else {
  echo "上传失败：{$_FILES[&#39;upload_file&#39;][&#39;error&#39;]}";
}
?>

In the above example, we use the move_uploaded_file() function to move the uploaded file from the temporary path to the specified directory. Please note that move_uploaded_file() will return false if the specified directory does not exist.

In addition to moving files, renaming is also necessary. When renaming, we need to avoid naming conflicts. For example, we can prepend the filename with a timestamp. Here is an example of renaming an uploaded file:

<?php
$uploadDir = &#39;/path/to/upload/dir&#39;; // 上传文件目录
$fileName = time() . &#39;_&#39; . $_FILES[&#39;upload_file&#39;][&#39;name&#39;];
$tmpName = $_FILES[&#39;upload_file&#39;][&#39;tmp_name&#39;];
if (move_uploaded_file($tmpName, "{$uploadDir}/{$fileName}")) {
  echo "文件已上传并保存到：{$uploadDir}/{$fileName}";
} else {
  echo "上传失败：{$_FILES[&#39;upload_file&#39;][&#39;error&#39;]}";
}
?>

3. File replacement

Sometimes, we need to replace a file with the same name that already exists on the server. In order to implement the file replacement function, we need to first determine whether the file with the same name exists, and if it exists, delete the original file. The following is an example of implementing file replacement:

<?php
$uploadDir = &#39;/path/to/upload/dir&#39;; // 上传文件目录
$fileName = time() . &#39;_&#39; . $_FILES[&#39;upload_file&#39;][&#39;name&#39;];
$tmpName = $_FILES[&#39;upload_file&#39;][&#39;tmp_name&#39;];
$existingFile = "{$uploadDir}/{$fileName}";
if (file_exists($existingFile) && !is_dir($existingFile)) {
  unlink($existingFile); // 如果存在同名文件则删除
}
if (move_uploaded_file($tmpName, $existingFile)) {
  echo "文件已上传并保存到：{$uploadDir}/{$fileName}";
} else {
  echo "上传失败：{$_FILES[&#39;upload_file&#39;][&#39;error&#39;]}";
}
?>

In the above example, we use the file_exists() function to check whether the file with the same name exists, and use the unlink() function to delete the file with the same name. Please note that !is_dir() is used to determine whether $file is a file (not a folder).

4. Summary

In this article, we introduced how to use PHP to implement file upload and replacement. You need to pay attention to security when uploading files, such as checking file type, size, black and white lists, etc. to prevent uploading of malicious files and excessively large files. When replacing files, you should first check whether the file with the same name exists to avoid file overwriting and file omission.

Finally, it should be noted that file upload and replacement are highly secure functions, so it is recommended to use professional third-party libraries to implement related functions, which will ensure code security and stability. .

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