Preg replace callback validation

Question

So I need to re-write some old code that I found on a library.

    $text = preg_replace("/(<\/?)(\w+)([^>]*>)/e",
                         "'\\1'.strtolower('\\2').'\\3'", $text);

    $text = preg_replace("/<br[ \/]*>\s*/","\n",$text);
    $text = preg_replace("/(^[\r\n]*|[\r\n]+)[\s\t]*[\r\n]+/", "\n",
                         $text);

And for the first one I have tried like this:

 $text = preg_replace_callback(
   "/(<\/?)(\w+)([^>]*>)/",
   function($subs) {
       return strtolower($subs[0]);
   },
   $text);

I'm a bit confused b/c I don't understand this part: "'\\1'.strtolower('\\2').'\\3'" so I'm not sure what should I replace it with.

As far as I understand the first line looks for tags, and makes them lowercase in case I have data like

<B>FOO</B>

Can you guys help me out here with a clarification, and If my code is done properly?

Wiktor Stribiżew · Accepted Answer · 2017-04-25 13:05:37Z

1

The $subs is an array that contains the whole value in the first item and captured texts in the subsequent items. So, Group 1 is in $subs[1], Group 2 value is in $subs[2], etc. The $subs[0] contains the whole match value, and you applied strtolower to it, but the original code left the Group 3 value (captured with ([^>]*>) that may also contain uppercase letters) intact.

Use

$text = preg_replace_callback("~(</?)(\w+)([^>]*>)~", function($subs) {
    return $subs[1] . strtolower($subs[2]) . $subs[3]; 
 }, $text);

See the PHP demo.

answered Apr 25, 2017 at 13:05

Wiktor Stribiżew

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