在PHP中，要实现文件上传，可以使用$_FILES全局数组来处理上传的文件。以下是一个简单的示例，展示了如何使用file_upload()函数进行文件上传：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>File Upload</title>
</head>
<body>
<form action="upload.php" method="post" enctype="multipart/form-data">
<label for="fileToUpload">Choose a file to upload:</label>
<input type="file" name="fileToUpload" id="fileToUpload">
<input type="submit" value="Upload File" name="submit">
</form>
</body>
</html>
注意enctype="multipart/form-data"属性，它允许在表单中上传文件。
upload.php的PHP文件，用于处理文件上传：<?php
if (isset($_FILES['fileToUpload'])) {
$target_file = "uploads/" . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($target_file, PATHINFO_EXTENSION));
// Check if the file already exists
if (file_exists($target_file)) {
echo "Sorry, file already exists.";
$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"], $target_file)) {
echo "The file ". htmlspecialchars(basename($_FILES["fileToUpload"]["name"])). " has been uploaded.";
} else {
echo "Sorry, there was an error uploading your file.";
}
}
} else {
echo "No file selected.";
}
?>
这个PHP脚本首先检查$_FILES数组中是否存在名为fileToUpload的文件。如果存在，它将检查文件是否已经存在于服务器上，然后尝试将文件移动到uploads目录。如果上传成功，它将显示一条成功消息；否则，它将显示一条错误消息。
确保在运行此示例之前在服务器上创建一个名为uploads的目录，并设置适当的权限，以便PHP可以将文件上传到该目录。
