File Storage

Quick Introduction

File Storage is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only file storage — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the Login System. After a user signs in, you need file storage working correctly before storing data or showing a dashboard.

Without understanding File Storage, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• File Storage is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (Login System) uses file storage in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

sequenceDiagram
  Client->>Nginx: HTTP Request
  Nginx->>PHP-FPM: FastCGI
  PHP-FPM->>App: Route Handler
  App->>Session: Read/Write Session
  App-->>Client: HTML / Redirect

Syntax

Core syntax for File Storage. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

use League\Flysystem\Filesystem;
use League\Flysystem\Local\LocalFilesystemAdapter;

$adapter = new LocalFilesystemAdapter(__DIR__ . '/storage');
$fs      = new Filesystem($adapter);

$key = 'uploads/' . date('Y/m/') . bin2hex(random_bytes(8)) . '.json';
$fs->write($key, json_encode(['userId' => 42, 'ts' => time()], JSON_THROW_ON_ERROR), [
    'visibility' => 'private',
]);

if ($fs->fileExists($key)) {
    echo 'Stored at: ' . $key . PHP_EOL;
    echo $fs->read($key);
}

Line by line

1. — part of the file storage example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. use League\Flysystem\Filesystem; — part of the file storage example; run the file to see the result.
4. use League\Flysystem\Local\LocalFilesystemAdapter; — part of the file storage example; run the file to see the result.
5. $adapter = new LocalFilesystemAdapter(__DIR__ . '/storage'); — part of the file storage example; run the file to see the result.

File Storage OK

Real-World Example

In the Login System, file storage appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: File Storage exercise for Login System