PHP: Regex match string not preceeded by a dollar sign

In my syntax highlighter, I use regex to parse different terms. Below is how I parse PHP cla开发者_开发知识库sses:

foreach ( PHP::$Classes as $class )
    $code = preg_replace( "/\b{$class}\b/", $this->_getHtmlCode( $class, PHP::$Colors['class'] ), $code );

Now, just ignore the PHP class and the _getHtmlCode function. The regex, "/\b{$class}\b/", matches names such as count. If I make a variable named $count, it matches that was well.

How can I look for class names that are not preceded by a $?

You could use a negative zero-width look-behind to accomplish the same task - basically, to make sure that there isn't a dollar sign before your text: /(?<!\$){$class}/.

(?<!     # Non-capturing look-behind group, captures only if the following regex is NOT found before the text.
  \$)    # Escaped dollar sign
{$class} # Class name

Are you trying to match className? i.e. class className {} or $foo = new className

If so you could check for one or more spaces before the classname:

/[ ]+{$class}\b/

Curious that $ counts as a boundary isn't it. Anyway, one fix is to put this after the \b:

(?<!\$)

See http://www.php.net/manual/en/regexp.reference.assertions.php for what it means

Here was the test script that demonstrates this:

$list=array(
    'class MyClass',
    'class HisClass',
    'var $MyClass',
    );

foreach($list as $s){
    echo $s."\n";
    if(preg_match('/\bMyClass\b/',$s))echo "OK";else echo "Failed";
    echo "\n";
    if(preg_match('/\b(?<!\$)MyClass\b/',$s))echo "OK";else echo "Failed";
    echo "\n";
    }