PHP Regex Question

Question

I have a series of urls in a web doc, something like this:

<a href="somepage.php?x=some_document.htm">click here</a>

What I want to do is replace the bold piece:

<a href="somepage.php?x=some_document.htm">click here</a>

.. with some sort of encrypted variation (lets just say base64_encoding) .. something like this:

for each match, turn it into base64_encode(match)

Notes:

1.the phrase href="somepage.php?x= will always precede the phrase.
2.a double-quote (") will always follow the phrase.

I am not a regex guru -- but I know some of you are. Any easy way to do this?

UPDATE:

I solved this by using a modified version of what Chris submitted, here it is:

function encrypt_param( $in_matches ) {    
  return   'href="somepage.php?x=' . base64_encode( $in_matches[1] ) . '"';
}

$webdoc = preg_replace_callback( '/href="somepage.php\?x=([^"]+)"/',
                                 'encrypt_param', 
                                 $webdoc );

Answer 1

I would consider using the PHP DOM parser. Anything less is a hack. (Not that hacks are always bad, just know the difference between a simple regex and a DOM parser.) getElementsByTagName() will get your <a> tags, getAttribute() will get your href attributes, and setAttribute() modifies.

Answer 2

preg_replace('/href="somepage.php\?x=([^"]*)"/e', "somepage.php?x='.base64_encode("$1").'"', $url)

(not tested). The /e means you can use an expression in the replacement string

Answer 3

I think you are looking for something like this:

function doSomething($matches) {
   return base64_encode($matches[1]);
}

preg_replace_callback('/href="somepage.php?x=([^"]+)"/', 'doSomething', $webdoc);

The preg_replace answer works similarly. If you want to do something more elaborate, the callback would allow you do to that

Answer 4

It seems like you might be conflating a multi-step task, which may ultimately create more trouble in the long run. You'd basically like to do three things:

1. Find all anchor tags on a page
2. Extract the URL in the href attribute from these tags
3. Extract a specific variable in the query string from that URL

There is a number of ways to do this in PHP. Yes, one direct way is using a regular expression, but it's less transparent. For this particular case, you're really data fitting a very small problem, reduces the scalability of your code for future applications.

My suggestion is the implementation of a light DOM parser available from Source Forge called SimpleHTMLDom. Using this parser, you can write much clearer code for the task you're undertaking.

foreach ($dom_object->find('a') as $anchor){
    $url = $anchor->href;
    $queryArray = array();
    parse_str(parse_url($url, PHP_URL_QUERY), $queryArray);
    $myVariable = $queryArr['x'];
}

And then of course $myVariable will be the value you're looking to get with that regex.

Answer 5

Regexes are fundamentally bad at parsing HTML (see Can you provide some examples of why it is hard to parse XML and HTML with a regex? for why). What you need is an HTML parser. See Can you provide an example of parsing HTML with your favorite parser? for examples using a variety of parsers.