Generic Syntax Highlighting with Regular Expressions in pure PHP

class SyntaxHighlight {

   
    static $tokens = array();// This array will be filled from the regexp-callback

 
    public static function process($s) {

        $s = htmlspecialchars($s);

 
        // Workaround for escaped backslashes

        $s = str_replace('\\\\','\\\\<e>', $s); 
 
        $regexp = array(

 
            // Punctuations

            '/([\-\!\%\^\*\(\)\+\|\~\=\`\{\}\[\]\:\"\'<>\?\,\.\/]+)/'

            => '<span class="P">$1</span>',

 
            // Numbers (also look for Hex)

            '/(?<!\w)(

                (0x|\#)[\da-f]+|
                \d+|
                \d+(px|em|cm|mm|rem|s|\%)
            )(?!\w)/ix'
            => '<span class="N">$1</span>',

 
            // Make the bold assumption that an

            // all uppercase word has a special meaning

            '/(?<!\w|>|\#)(

                [A-Z_0-9]{2,}
            )(?!\w)/x'
            => '<span class="D">$1</span>',

 
            // Keywords

            '/(?<!\w|\$|\%|\@|>)(

                and|or|xor|for|do|while|foreach|as|return|die|exit|if|then|else|
                elseif|new|delete|try|throw|catch|finally|class|function|string|
                array|object|resource|var|bool|boolean|int|integer|float|double|
                real|string|array|global|const|static|public|private|protected|
                published|extends|switch|true|false|null|void|this|self|struct|
                char|signed|unsigned|short|long
            )(?!\w|=")/ix'
            => '<span class="K">$1</span>',

 
            // PHP/Perl-Style Vars: $var, %var, @var

            '/(?<!\w)(

                (\$|\%|\@)(\->|\w)+
            )(?!\w)/ix'
            => '<span class="V">$1</span>'

 
        );      
        
        $s = preg_replace_callback( '/(

                \/\*.*?\*\/|
                \/\/.*?\n|
                \#.[^a-fA-F0-9]+?\n|
                \<\!\-\-[\s\S]+\-\-\>|
                (?<!\\\)&quot;.*?(?<!\\\)&quot;|
                (?<!\\\)\'(.*?)(?<!\\\)\'

            )/isx' , array('SyntaxHighlight', 'replaceId'),$s);

                        
        $s = preg_replace(array_keys($regexp), array_values($regexp), $s);

 
        // Paste the comments and strings back in again

        $s = str_replace(array_keys(SyntaxHighlight::$tokens), array_values(SyntaxHighlight::$tokens), $s);

 
        // Delete the "Escaped Backslash Workaround Token" (TM)

        // and replace tabs with four spaces.

        $s = str_replace(array('<e>', "\t"), array('', '    '), $s);

 
        return '<pre>'.$s.'</pre>' ;

    }

 
    // Regexp-Callback to replace every comment or string with a uniqid and save

    // the matched text in an array

    // This way, strings and comments will be stripped out and wont be processed

    // by the other expressions searching for keywords etc.

     static function replaceId($match) {

        $id = "##r" . uniqid() . "##";

        
        // String or Comment?

        if(substr($match[1], 0, 2) == '//' || substr($match[1], 0, 2) == '/*' || substr($match[1], 0, 2) == '##' || substr($match[1], 0, 7) == '<!--') {

            SyntaxHighlight::$tokens[$id] = '<span class="C">' . $match[1] . '</span>';

        } else {

           SyntaxHighlight::$tokens[$id] = '<span class="S">' . $match[1] . '</span>';

        }

                
        return $id;

    }

}

pre { 
        font-family: 'Courier New', 'Bitstream Vera Sans Mono', 'monospace'; 
        font-size: 9pt;

        border-top: 1px solid #333;

        border-bottom: 1px solid #333;

        padding: 0.4em;

        color: #fff;

}
pre span.N{ color:#f2c47f; } /* Numbers */

pre span.S{ color:#42ff00; } /* Strings */

pre span.C{ color:#838383; } /* Comments */

pre span.K{ color:#ff0078; } /* Keywords */

pre span.V{ color:#70d6ff; } /* Vars */

pre span.D{ color:#ff9a5d; } /* Defines */

echo SyntaxHighlight::process( $your_code );