Short Open Tag (<?)

Also Known As

TL;DR

Explanation

PHP supports three open tags: <?php (always works), <?= (short echo, always works since PHP 5.4), and <? (short open tag, requires short_open_tag=On in php.ini). The <? short tag conflicts with XML processing instructions <?xml and is disabled in many shared hosting environments, Docker images, and production configurations. PSR-1 mandates only <?php and <?= tags. Rector can automatically expand <? to <?php across a codebase.

Common Misconception

Why It Matters

Common Mistakes

• Using <? throughout a legacy codebase that runs fine locally but fails on the production server.
• <?= is a short echo tag — unlike <?, this is always available since PHP 5.4 and is PSR-1 compliant.
• Mixing <?php and <? in the same file.
• Not running Rector's ShortOpenTagSniff to find all occurrences automatically.

Code Examples

<? // Short tag — requires short_open_tag=On
$user = getUser($id);
?>
<p>Hello <? echo $user->name; ?></p>

<? if ($user->isAdmin()): ?>
    <p>Admin panel</p>
<? endif; ?>

<?php // Always works — PSR-1 compliant
$user = getUser($id);
?>
<p>Hello <?= htmlspecialchars($user->name) ?></p>

<?php if ($user->isAdmin()): ?>
    <p>Admin panel</p>
<?php endif; ?>

References

• ↗ https://www.php-fig.org/psr/psr-1/#23-side-effects

Tags

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