PSR-1: Basic Coding Standard

Also Known As

TL;DR

Explanation

PSR-1 establishes baseline rules all PHP code should follow: files must use only <?php or <?= tags, use UTF-8 without BOM, and either declare symbols (classes, functions, constants) or cause side effects (output, config changes) — but not both in the same file. Class names must be in PascalCase, class constants in UPPER_SNAKE_CASE, and method names in camelCase. These rules underpin PSR-4 autoloading and PSR-12 style and are enforced by PHP_CodeSniffer. PSR-1 compliance is a prerequisite for all PHP-FIG standards.

Common Misconception

Why It Matters

Common Mistakes

• Mixing class definitions and side effects (echo, function calls) in the same file.
• Using short open tags <? instead of <?php — not all servers have short_open_tag enabled.
• Files with BOM (byte order mark) before <?php — causes 'headers already sent' errors.
• StudlyCaps class names vs camelCase method names — PSR-1 requires both.

Code Examples

<?php
// PSR-1 violation — side effect (echo) and symbol declaration in same file:
echo 'Loading...'; // Side effect

class UserRepository { // Symbol declaration
    public function find(int $id): User {}
}
// Fix: move the echo to the caller, keep this file declaration-only

<?php
// PSR-1 Basic Coding Standard — key rules:

// 1. Files MUST use only <?php or <?= tags (not short <? tags)
// 2. PHP files MUST use only UTF-8 without BOM
// 3. Files SHOULD either declare symbols OR cause side effects — not both

// Side effects: echo, require, config changes
// Declarations: class, function, const

// Bad: declarations + side effects in same file
<?php
echo 'Loading...'; // side effect
class MyClass {}    // declaration — these shouldn't mix

// Good: separate files
// src/MyClass.php       — declarations only
// public/bootstrap.php  — side effects only

// 4. Namespaces and classes MUST follow an autoloading PSR (PSR-4)
// 5. Class names MUST be in StudlyCaps
// 6. Method names MUST be in camelCase

References

• ↗ https://www.php-fig.org/psr/psr-1/

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