PHP preg_match ignore within certain elements

Question

I'm writing a regex where I need to filter content to format it's typography. So far, my code seems to be filtering out my content properly using preg_replace, but I can't figure out how to avoid this for content wrapped within certain tags, say <pre>.

As a reference, this is to be used within WordPress's the_content filter, so my current code looks like so:

function my_typography( $str ) {
    $ignore_elements = array("code", "pre");

    $rules = array(
        "?" => array("before"=> "&thinsp;", "after"=>""),
        // the others are stripped out for simplicity
    );

    foreach($rules as $rule=>$params) {
        // Pseudo :
        //    if( !in_array( $parent_tag, $ignore_elements) {
        // /Pseudo


        $formatted = $params['before'] . $rule . $params['after'];
        $str = preg_replace( $rule, $formatted, $str );


        // Pseudo :
        //    }
        // /Pseudo
    }

    return $str;
}
add_filter( 'the_content',  'my_typography' );

Basically:

<p>Was this filtered? I hope so</p>
<pre>Was this filtered? I hope not.</pre>

should become

<p>Was this filtered&thinsp;? I hope so</p>
<pre>Was this filtered? I hope not.</pre>

anubhava · Accepted Answer · 2019-02-06 15:19:57Z

1

You need to wrap search regex with regex delimiter in preg_replace and must call preg_quote to escape all special regex characters such ?, ., *, + etc:

$str = preg_replace( '~' . preg_quote($rule, '~') . '~', $formatted, $str );

Full Code:

function my_typography( $str ) {
    $ignore_elements = array("code", "pre");

    $rules = array(
        "?" => array("before"=> "&thinsp;", "after"=>""),
        // the others are stripped out for simplicity
    );

    foreach($rules as $rule=>$params) {
        // Pseudo :
        //    if( !in_array( $parent_tag, $ignore_elements) {
        // /Pseudo


        $formatted = $params['before'] . $rule . $params['after'];
        $str = preg_replace( '~' . preg_quote($rule, '~') . '~', $formatted, $str );


        // Pseudo :
        //    }
        // /Pseudo
    }

    return $str;
}

Output:

<p>Was this filtered&thinsp;? I hope so</p>
<pre>Was this filtered&thinsp;? I hope not.</pre>

answered Feb 6, 2019 at 15:19

anubhava

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3 Comments

Dadou Over a year ago

Thanks for the feedback. This does in fact manage the rules properly; however, my HTML is "broken" in the sense that in the expected output, </p> is returned as < / p > which breaks my page. Is there something I am missing?

anubhava Over a year ago

Your sample data doesn't have </a> anywhere but this code is just replacing ? with something. Can you update the question that recreates this problem?

Dadou Over a year ago

turns out my breaking HTML was one of the rules, had a rule for "/" -- sorry about that! here'S the checkmark, thanks for your time !

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