File Handling 📂

Read, write, and manage files on the server — essential for logging, data persistence, file uploads, and CSV processing.

What You'll Learn in This Lesson

• Writing files with file_put_contents() and fopen()
• Reading files as strings, arrays, or line-by-line
• File modes: read, write, append, create
• Directory operations: create, list, scan
• CSV processing and file security best practices

Note: PHP runs on a server. Our examples simulate PHP logic using JavaScript. To run real PHP, install PHP.

🎯 Real-World Analogy: File handling is like working with a filing cabinet. file_put_contents() is placing a document in a folder (overwriting what was there). FILE_APPEND is adding a page to an existing document. file_get_contents() is pulling the entire document out to read. fopen() is opening the folder and reading one page at a time.

1️⃣ Quick vs Detailed File Access

Approach	Functions	Best For
Quick (one-liner)	file_get/put_contents()	Small files, simple ops
Handle-based	fopen, fgets, fclose	Large files, streaming

Try It: Reading & Writing Files

Write, read, and append to files using PHP's file functions

Try it Yourself »

JavaScript

// PHP File Handling (simulated in JavaScript)
console.log("=== Writing Files ===");
console.log();

// file_put_contents — the simplest way to write
console.log("file_put_contents('data.txt', 'Hello, World!');");
console.log("  → Writes 'Hello, World!' to data.txt");
console.log("  → Creates the file if it doesn't exist");
console.log("  → OVERWRITES existing content!");
console.log();

// Append mode
console.log("file_put_contents('log.txt', 'New entry', FILE_APPEND);");
console.log("  → Adds 
...

Try It: File Operations & Directories

Check file info, manage directories, and process CSV data

Try it Yourself »

JavaScript

// File Operations & Directory Handling
console.log("=== File Information ===");
console.log();

// Simulated file stats
let stats = {
    exists: true,
    size: 2048,
    modified: "2024-12-15 14:30:22",
    permissions: "0644",
    type: "file",
    extension: "txt",
};

console.log("file_exists('data.txt')  → " + stats.exists);
console.log("filesize('data.txt')     → " + stats.size + " bytes");
console.log("filemtime('data.txt')    → " + stats.modified);
console.log("pathinfo('data.txt')['ex
...

⚠️ Common Mistakes

⚠️

Forgetting to close files — always call fclose($handle) or use file_put_contents() which handles this automatically.

⚠️

Using 'w' mode by accident — fopen('file.txt', 'w') truncates (erases) the file! Use 'a' for append.

⚠️

Not checking file_exists() — reading a non-existent file throws a warning. Always check first.

💡

Pro Tip: For log files, use file_put_contents($file, $msg . PHP_EOL, FILE_APPEND | LOCK_EX) — LOCK_EX prevents race conditions in concurrent writes.

📋 Quick Reference — File Handling

Function	Purpose
file_get_contents()	Read entire file as string
file_put_contents()	Write string to file
file()	Read file into array of lines
fopen() / fclose()	Open/close file handle
fgets() / fwrite()	Read/write line by line
scandir() / mkdir()	List/create directories

🎉 Lesson Complete!

You've mastered PHP file handling! Next, learn how to process HTML forms and handle user input securely.