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The Best Way(s) to Comment out PHP/HTML Code

PHP supports various styles of comments. Please check the following example:

<?php

// Single line comment
code();

# Single line Comment
code2();

/*
Multi Line comment

code();

The code inside doesn't run
*/

// /* This doesn NOT start a multi-line comment block

/*
Multi line comment block

The following line still ends the multi-line comment block
//*/

The "#" comment style, though, is rarely used.

Do note, in the example, that anything (even a multi-block comment /*) after a "//" or "#" is a comment, and /* */ around any single-line comment overrides it. This information will come in handy when we learn about some neat tricks next.

Comment out PHP Code Blocks

Check the following code

<?php

//* Toggle line
if (1) {
    
//
} else {
    
//
}
//*/

//* Toggle line
if (2) {
    
//
} else {
    
//
}
//*/

Now see how easy it is to toggle a part of PHP code by just removing or adding a single "/" from the "toggle line":

Comment out PHP Code from a PHP/HTML File

Since PHP and HTML go along, you'll be editing files with PHP and HTML codes mixed together a lot of times (for example template/theme file for WordPress).

Let's see some ways we can comment out blocks of HTML/PHP code, do remember there is no "best" way, though there are best practices and methods that would be suitable for your use-case.

First Method: Use PHP Multi-line comment block

This requires that there is no PHP multi-line comment inside the block that you're trying to comment out:

<form action="save.php" method="post">
    <div>
        <label for="fname">First Name</label><br />
        <input type="text" id="fname" name="fname">
    </div>
    <div>
        <label for="lname">Last Name</label><br />
        <input type="text" id="lname" name="lname">
    </div>
    <div>
        <label for="lname">Phone Number</label><br /> <!-- ddd -->
        <input type="text" id="phonenumber" name="phonenumber">
    </div>
    <?php /*
    <div>
        <label for="lname">Email Address</label><br />
        <input type="text" id="email" name="email">
    </div>
    <?php
    echo 'Text';
    ?>
    <input type="submit" name="save" value="Save">
     */ 
?>
</form>

Notice how a multi-line comment within the block of code to be commented out prevents this from working as expected:

Second Method: Use HTML Multi-line comment block

HTML multi-line comments start with "<!--" and end with "-->".

In this case, the PHP code will not necessarily be commented out or won't run, it's just that any output from PHP (along with the HTML) will not be shown. This is helpful when you actually want to see the output of PHP code (in the source code) but do not want the block shown in the browser. Or you're just doing a quick and dirty comment out for testing since the first method won't work. Do note, however, that this method requires that there are no HTML comment codes inside the block that you're trying to comment out.

<form action="save.php" method="post">
    <div>
        <label for="fname">First Name</label><br />
        <input type="text" id="fname" name="fname">
    </div>
    <div>
        <label for="lname">Last Name</label><br />
        <input type="text" id="lname" name="lname">
    </div>
    <div>
        <label for="lname">Phone Number</label><br /> <!-- ddd -->
        <input type="text" id="phonenumber" name="phonenumber">
    </div>
    <!-- The following block of code will not show in browser
    <div>
        <label for="lname">Email Address</label><br />
        <input type="text" id="email" name="email">
    </div>
    <?php
    
/* 
     * Multi-line comment 
     */
    
echo 'Text';
    
?>
    <input type="submit" name="save" value="Save">
    -->
</form>

Third Method: Use PHP if Statement

This method used the PHP if statement to make a block of code not execute. 

<form action="save.php" method="post">
    <?php if (0) : // Commente-out starts ?>
    <!--
    <div>
        <label for="fname">First Name</label><br />
        <input type="text" id="fname" name="fname">
    </div>
    <div>
        <label for="lname">Last Name</label><br />
        <input type="text" id="lname" name="lname">
    </div>
    <div>
        <label for="lname">Phone Number</label><br /> <!-- ddd -->
        <input type="text" id="phonenumber" name="phonenumber">
        <?php /* */ ?>
    </div>
    <div>
        <?php if ($code) :?>
        <label for="lname">Email Address</label><br />
        <input type="text" id="email" name="email">
        <?php endif ?>
    </div>
    <?php
    
echo 'Text';
    
?>
    <input type="submit" name="save" value="Save">
    -->
    <?php endif; // Comment-out ends ?>
</form>
It would be helpful to mark where your comment-outs start and end like in the example above.

The above PHP if statement method of "commenting out" code can be nested with HTML (and HTML comments) and other PHP code blocks (and PHP comments).

The following code doesn't actually "comment out" the block of PHP and HTML code but only makes it so that it doesn't execute. Note the difference. 

If you're editing a lot of PHP/HTML code like WordPress theme files you'll soon realize that they almost always contain a lot of both PHP and HTML comments and the first two methods will not always work, but this final method though not very intuitive to someone who doesn't know much PHP is perhaps the only method which will work regardless of any nested comments or if..else..endifs that may be inside the block of code you want to comment out.

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