Simple Syntax highlighting

Shows how to create a simple syntax highlighting function for PHP code.

Warning: This function is very simple and may not handle complicated or obfuscated PHP code ;-)

function syntax_highlight($code){

    // this matches --> "foobar" <--
    $code = preg_replace(
        '/"(.*?)"/U',
        '&quot;<span style="color: #007F00">$1</span>&quot;', $code
    );

    // hightlight functions and other structures like --> function foobar() <---
    $code = preg_replace(
        '/(\s)\b(.*?)((\b|\s)\()/U',
        '$1<span style="color: #0000ff">$2</span>$3',
        $code
    );

    // Match comments (like /* */):
    $code = preg_replace(
        '/(\/\/)(.+)\s/',
        '<span style="color: #660066; background-color: #FFFCB1;"><i>$0</i></span>',
        $code
    );

    $code = preg_replace(
        '/(\/\*.*?\*\/)/s',
        '<span style="color: #660066; background-color: #FFFCB1;"><i>$0</i></span>',
        $code
    );

    // hightlight braces:
    $code = preg_replace('/(\(|\[|\{|\}|\]|\)|\->)/', '<strong>$1</strong>', $code);

    // hightlight variables $foobar
    $code = preg_replace(
        '/(\$[a-zA-Z0-9_]+)/', '<span style="color: #0000B3">$1</span>', $code
    );

    /* The \b in the pattern indicates a word boundary, so only the distinct
    ** word "web" is matched, and not a word partial like "webbing" or "cobweb"
    */

    // special words and functions
    $code = preg_replace(
        '/\b(print|echo|new|function)\b/',
        '<span style="color: #7F007F">$1</span>', $code
    );

    return $code;
}


/*example-start*/

/*
** Create some example PHP code:
*/

$example_php_code = '
// some code comment:
$example = "foobar";

print $_SERVER["REMOTE_ADDR"];

$array = array(1, 2, 3, 4, 5);

function example_function($str) {
    // reverse string
    echo strrev($obj);
}

print example_function("foo");

/*
** A multiple line comment
*/

print "Something: " . $example;';


// output the formatted code:
print '<pre>';
print syntax_highlight($example_php_code);
print '</pre>';

/*example-end*/