PHP Syntax

PHP Syntax: Tags, Statements, and Case Sensitivity

PHP syntax defines how the PHP parser reads your code inside .php files. Every PHP instruction sits inside <?php ... ?> delimiters, ends with a semicolon ;, and runs sequentially from top to bottom.

How PHP Tags Work

When PHP reads a file, it ignores plain HTML outside the tags and executes everything inside <?php ... ?>. If a file contains only PHP code, leave off the closing ?> tag to prevent accidental whitespace bugs in HTTP headers.

<?php
declare(strict_types=1);

$siteTitle = "KoderSolution Tutorial";
$lessonCount = 60;

echo "Course: " . $siteTitle . PHP_EOL;
echo "Total Lessons: " . $lessonCount . PHP_EOL;

Short echo tags <?= $value ?> provide a clean shortcut when embedding PHP variables inside HTML templates. They work automatically in all modern PHP versions.

Case Sensitivity Rules in PHP

PHP treats variable names differently from keywords and function names. Mixing up casing is a frequent source of subtle bugs for beginners.

• Keywords and functions are case-insensitive: echo, ECHO, strlen(), and STRLEN() behave identically, though lowercase is the community standard.
• Variables are strictly case-sensitive: $userName, $username, and $USERNAME point to three separate variables in memory.
• Class names are case-insensitive, but match file names: Autoloaders like Composer PSR-4 expect exact PascalCase filenames matching your class name.

<?php
$orderTotal = 49.95;
$ordertotal = 12.00;

echo "Primary total: $" . $orderTotal . PHP_EOL;
echo "Secondary total: $" . $ordertotal . PHP_EOL;

Common Mistakes to Avoid

• Missing a semicolon at the end of a line: PHP throws a ParseError: syntax error on the next line if you forget ;.
• Adding a closing ?> in pure PHP files: Trailing spaces or newlines after ?> break header() calls and JSON API responses.
• Using short open tags <?: Short tags <? without php are disabled on most servers. Always write <?php or <?=.

Frequently Asked Questions

When should I omit the closing ?> tag?

Omit the closing ?> tag in files that contain only PHP code, such as classes, helpers, and configuration files. Include it only when switching back to raw HTML.

What does declare(strict_types=1); do at the top of a file?

It forces PHP to check exact parameter and return types instead of silently converting strings or numbers, catching type bugs early.

Are PHP variable names case-sensitive?

Yes. $total and $Total are completely different variables, so stick to consistent camelCase or snake_case naming across your project.