Regular expression problem

[Dean C]

Hey,

I'm sure this is an easy one for a regex guru

    $string = '[b]hmmz[/b]testing[b]test[/b]';
    $pattern = '/\[b\](.*)\[\/b\]/';
    if(preg_match($pattern, $string, $array))
    {
        //$array[1] = strip_tags($array[1]);
        //echo $array[1];
        $string = preg_replace($pattern, '<b>\1</b>', $string);
        echo $string;
    } 

This outputs:

<b>hmmz[/b]testing[b]test</b>
[/b]

I can see why this happens, but the question is how to stop it happening So it matches the next closing instead of the very last!

Edit:


Hmm it seems changing the pattern to:

$pattern = '/\[b\](.*?)\[\/b\]/'; 

Fixes the problem. Why is this?

Edit:

    $string = '[b][b]hmmz[/b]testing[b]test[/b][/b]';
    $pattern = '/\[b\](.*?)\[\/b\]/';
    if(preg_match_all($pattern, $string, $array))
    {
        //$array[1] = strip_tags($array[1]);
        //echo $array[1];
        $string = preg_replace($pattern, '<b>\1</b>', $string);
        echo $string;
    } 

The problem with this above is it doesn't put surrounding <b></b> around the whole block too

[devil cat]

With something as simple as this, why not just use str_replace?

  $string = '[b]hmmz[/b]testing[b]test[/b]';
  $string = str_replace('[b]', '<b>', $string);
  $string = str_replace('[/b]', '</b>', $string);

  echo $string; 

Is there a specific reason why not?

This function returns a string or an array with all occurrences of search in subject replaced with the given replace value. If you don't need fancy replacing rules (like regular expressions), you should always use this function instead of ereg_replace() or preg_replace().

[Dean C]

Because ideally it should break in certain circumstances e.g:

[b]test[/b][/b]

That should output <b>test[/b]</b>

[Mr_Money]

hey,
it is because in the default use, the regular expression is "greedy" meaning it matches as much as it can while satisfying the pattern.
What you did in the edit portion was add the '?' which means it is a non-greedy quantifier, and will match the minimum amount while still satisfying the pattern.

[devil cat]

I think I know why it is doing this.

It seems to do a progressive search through the string looking for matches. Since the second (b) follows the first without a (/b), it matches the first set and skips that next tag in favor of looking for a start that follows the first matched (/b). I really hope that makes sense. If not, I'll try to explain better. It might help to take a look at which tags are not being used:

This will force it past that, and still leave incomplete pairs untouched:

  $string = '[b][b]hmmz[/b]testing[b]test[/b][/b]';
  $pattern = '/\[b\](.*?)\[\/b\]/';
  while(preg_match_all($pattern, $string, $array))
  {
      //$array[1] = strip_tags($array[1]);
      //echo $array[1];
      $string = preg_replace($pattern, '<b>\1</b>', $string);
  }
  echo $string; 

edit - possibly better explanation:

When it replaces the tags, it starts at the end of the first replacement set (a complete (b)(/b) set) and scans the string from there. Since the second (b) lies within the first set, it gets skipped when it starts looking again.