WordPress: Moderate comments using regular expressions

While WordPress allows us to moderate and blacklist comments using two nifty text-areas within Settings->Discussion called “Comment Moderation” and “Comment Blacklist” you may need to add some extra functionality so that RegEx or Regular Expressions can also be used to directly approve, moderate, send to spam or blacklist comments.

Fortunately there is the “pre_comment_approved” filter which we can use for this purpose.

Lets setup our scenario, I want to add some moderation so that users don’t add URL’s in comments and I will make a quick check for domain names in the comment content.

Note: The code below would either go in your themes functions.php or a custom plugin.

In order to keep the example simple I am going to use a generic domain matching regex.

Example 1. Lets say we want to moderate the comments.

Here we set $approved to the integer 0(zero)

function te_check_comment($approved, $commentdata){
	if(preg_match('#\b((?=[a-z0-9-]{1,63}\.)[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b#i',$commentdata["comment_content"])){
		$approved = 0;
	}
	return $approved;
}
add_action('pre_comment_approved', 'te_check_comment', 10, 2);

Example 2. Here we want to mark the comments as spam.

$approved is set to the string ‘spam’

function te_check_comment($approved, $commentdata){
	if(preg_match('#\b((?=[a-z0-9-]{1,63}\.)[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b#i',$commentdata["comment_content"])){
		$approved = 'spam';
	}
	return $approved;
}
add_action('pre_comment_approved', 'te_check_comment', 10, 2);

Example 3. Here we want to send the comments directly to trash.

$approved is set to the string ‘trash’

function te_check_comment($approved, $commentdata){
	if(preg_match('#\b((?=[a-z0-9-]{1,63}\.)[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b#i',$commentdata["comment_content"])){
		$approved = 'trash';
	}
	return $approved;
}
add_action('pre_comment_approved', 'te_check_comment', 10, 2);

Example 4. We want to bypass everything and Approve the comment if it matches our string.

$approved to the integer 1(one)

function te_check_comment($approved, $commentdata){
	if(preg_match('#\b((?=[a-z0-9-]{1,63}\.)[a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,63}\b#i',$commentdata["comment_content"])){
		$approved = 1;
	}
	return $approved;
}
add_action('pre_comment_approved', 'te_check_comment', 10, 2);

Keep in mind that all the comments submitted will be saved in the WordPress comments table with the appropriate approved status.