What are PHP tags (), and why are they used?
Jun 20, 2025 am 12:50 AM
The PHP tag (<?php ?>) is a tag that the server recognizes PHP code. Its core function is to tell the server that "this area is PHP code, it must be executed first and then output to the browser." 1. They are used to embed dynamic content into HTML; 2. Support conditional rendering and data looping; 3. It helps to separate logic from the interface to a certain extent; 4. It is often used to generate dynamic HTML, process forms, include files, set sessions and other scenarios. When using it, you should be careful to avoid errors caused by missing closed tags, short tag compatibility and whitespace characters after closed tags.
PHP tags ( <?php ?> ) are like markers that tell the server, "Hey, everything inside here is PHP code—run it before sending the page to the browser." Without these tags, the server wouldn't know where your PHP starts and ends, and it would just treat it all as plain text.
What Exactly Are <?php ?> Tags?
These tags are called PHP opening and closing tags . The most common ones are <?php (opening) and ?> (closing). Anything between them is parsed as PHP code. For example:
<?php echo "Hello, world!"; ?>
In this case, the server processes the echo statement and sends "Hello, world!" to the browser. If you left out the tags, the PHP code would be displayed as text instead of being executed.
There are also short tags like <?= for echoing variables, but they may not always be enabled on every server, so it's safer to stick with <?php .
Why Do We Need PHP Tags?
The main reason we use <?php ?> is to mix PHP with HTML . Since PHP is a server-side language, it needs a way to jump in and out of regular HTML content. Here's how it helps:
- You can embed dynamic data into static HTML pages.
- It allows conditional rendering or looping through data.
- It separates logic from presentation to some extent.
For example:
<p>Welcome back, <?php echo $username; ?>!</p>
Here, the PHP tag lets you insert a user-specific name dynamically into the HTML paragraph.
You'll often see PHP files start with <?php and sometimes end without a closing tag if it's pure PHP code. That's a common practice to avoid accidental whitespace or output after the tag.
Common Mistakes and Things to Watch Out For
- Forgetting to close the tag – Not a big deal in pure PHP files, but if you're switching back to HTML, forgetting
?>might cause issues. - Extra spaces or lines after
?>– This can lead to “headers already sent” errors in PHP. - Using short tags (
<?or<?=) without checking server settings – Some servers don't support short tags by default, which breaks your site.
A few quick tips:
- Always use
<?phpinstead of<?unless you're sure about server settings. - Avoid ending PHP-only files with
?>to prevent unwanted output. - Make sure there's no space or line break before
<?phpor after?>if headers are involved.
Where Are They Used Most Often?
You'll find PHP tags in any .php file where dynamic behavior is needed. Common scenarios include:
- Generating HTML based on database queries
- Handling form submissions
- Including or requiring other files
- Setting cookies or sessions
- Performing redirects
For example:
<?php
if ($isLoggedIn) {
echo "<p>You're logged in.</p>";
} else {
echo "<p>Please log in.</p>";
}
?>This kind of conditional logic is only possible when PHP code is properly enclosed within its tags.
So, basically, <?php ?> tags are essential for letting the server know where to run PHP code. They make it possible to mix dynamic logic with HTML and keep your web apps flexible and interactive.
The above is the detailed content of What are PHP tags (), and why are they used?. For more information, please follow other related articles on the PHP Chinese website!
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