Question

I have a custom php script that looks through text to find key phrases and replaces them using preg_replace, but I’m having trouble getting a clean regex for the job.

For example this sentence:

The fox jumped over the gated fence
because it did not have hands to open
the gate.

I would want to bold all instances of gate, yet respect oddities like gated. And also preserve original capitalization too if possible.

So the end sentence would read like this:

The fox jumped over the gated fence
because it did not have hands to open
the gate.

Here is the regular expression I’ve created myself, and you will see that it would not account for gate. because of the period following the word. And also the regex does not respect any original capitalization.

$description  = preg_replace("/ $keyphrase /", " <b>$keyphrase</b> ", $description, $limit);

Answer 1

preg_replace_callback('/\b'.preg_quote($keyphrase, '/').'\b/i',
    function ($matches) {
        return "<b>" . $matches[0] . "</b>";
    }, htmlspecialchars($subject));

You need to use word boundaries (\b). Do not forget to:

• Properly escape the key phrase for use in the regex expression (use preg_quote).
• Properly escape for HTML special characters the sentence. This is necessary assuming you’re turning a text string into an HTML string. If the initial string already has HTML, do not use regex.

EDIT PHP < 5.3 must use:

function cb($matches) {
    return "<b>" . $matches[0] . "</b>";
};
preg_replace_callback('/\b'.preg_quote($keyphrase, '/').'\b/i', 'cb',
   htmlspecialchars($subject));