File handling allows PHP to create, read, update, delete, and manage files on the server.

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📂 1. Opening Files (fopen())

Syntax:

fopen(filename, mode);

Modes:

Mode	Description
r	Read only
w	Write (overwrite)
a	Append
x	Create new file
r+	Read + Write

Example:

$file = fopen("test.txt", "r");

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📖 2. Reading Files (fread())

Example:

$file = fopen("test.txt", "r");
$content = fread($file, filesize("test.txt"));
echo $content;
fclose($file);

Line by Line:

while(!feof($file)) {
    echo fgets($file);
}

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✍️ 3. Writing Files (fwrite())

Example:

$file = fopen("test.txt", "w");
fwrite($file, "Hello World!");
fclose($file);

Append Mode:

$file = fopen("test.txt", "a");
fwrite($file, "New Line\n");
fclose($file);

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❌ 4. Closing File (fclose())

fclose($file);

👉 Always close files to free memory.

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📤 5. File Upload System

HTML Form:

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

PHP Code:

if(isset($_POST['upload'])) {
    $fileName = $_FILES['file']['name'];
    $tempName = $_FILES['file']['tmp_name'];
    $folder = "uploads/" . $fileName;    if(move_uploaded_file($tempName, $folder)) {
        echo "File uploaded successfully!";
    } else {
        echo "Upload failed!";
    }
}

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🔒 File Upload Validation (IMPORTANT)

$allowed = ['jpg','png','pdf'];
$ext = pathinfo($fileName, PATHINFO_EXTENSION);if(in_array($ext, $allowed)) {
    // upload
}

👉 Always validate:

• File type
• File size
• Rename file (avoid overwrite)

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📁 6. Directory Handling

Create Directory:

mkdir("new_folder");

Delete Directory:

rmdir("new_folder");

List Files:

$files = scandir("uploads");
print_r($files);

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🔍 Check File Exists

if(file_exists("test.txt")) {
    echo "File exists";
}

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🧠 Important Functions Summary

Function	Use
fopen()	Open file
fread()	Read file
fwrite()	Write file
fclose()	Close file
feof()	End of file check
fgets()	Read line
file_exists()	Check file
move_uploaded_file()	Upload file
mkdir()	Create folder
scandir()	List directory

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⚠️ Best Practices

• Always close files
• Use file permissions carefully
• Validate uploads (security)
• Avoid storing sensitive data in plain text

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💡 Mini Practice Task

👉 Create a system that:

1. Uploads a file
2. Saves file name in log.txt
3. Displays all uploaded files