PHP BBCode regex replacement

Question

How can I replace:

<tag attr="z">
    <tag attr="y">
        <tag attr="x"></tag>
    </tag>
</tag>

to:

<tag attr="z">
    [tag=y]
        <tag attr="x"></tag>
    [/tag]
</tag>

Without using extensions?

I unsuccessfully tried:

preg_replace("#<tag attr=\"y\">(.+?)</tag>#i", "[tag=y]\\1[/tag]", $text);

preg_replace("#<tag attr=\"y\">(.+?)</tag>#i", "[tag=y]\\1[/tag]", $text); — Bestudio
– Bestudio, Commented Sep 3, 2012 at 13:33
Click "edit" to update your question with more information, this is easier to read than the comments. — Jocelyn
– Jocelyn, Commented Sep 3, 2012 at 16:54

Bart Kiers · Accepted Answer · 2012-09-03 21:36:42Z

2

Well, PHP's regex implementation supports PCRE's recursive patterns. However, I'd hesitate to use such a feature because of its cryptic nature. However, since you asked:

Without using extensions?

here it is:

<?php

$html = '<tag attr="z">
    <tag attr="y">
        <tag>
            <tag attr="more" stuff="here">
                <tag attr="x"></tag>
            </tag>
        </tag>
    </tag>
</tag>
';

$attr_regex = "(?:\s+\w+\s*=\s*(?:'[^']*'|\"[^\"]*\"))";
$recursive_regex = "@
    <tag\s+attr=\"y\">         # match opening tag with attribute 'y'
    (                          # start match group 1
      \s*                      #   match zero or more white-space chars
      <(\w+)$attr_regex*\\s*>  #   match an opening tag and store the name in group 2
      (                        #   start match group 3
        [^<]+                  #     match one or more chars other than '<'
        |                      #     OR
        (?1)                   #     match whatever the pattern from match group 1 matches (recursive call!)
      )*                       #   end match group 3
      </\\2>                   #   match the closing tag with the same name stored in group 2
      \s*                      #   match zero or more white-space chars
    )                          # end match group 1
    </tag>                     # match closing tag
    @x";

echo preg_replace($recursive_regex, "[tag=y]$1[/tag]", $html);

?>

which will print the following:

<tag attr="z">
    [tag=y]
        <tag>
            <tag attr="more" stuff="here">
                <tag attr="x"></tag>
            </tag>
        </tag>
    [/tag]
</tag>

answered Sep 3, 2012 at 21:36

Bart Kiers

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3 Comments

Bestudio Over a year ago

Why can't I run this Regex Code twice?

Bart Kiers Over a year ago

@Bestudio, you can. Perhaps create another question ?

Bart Kiers Over a year ago

@Bestudio, sorry, I don't know what you mean. I don't know what you meant by "running it twice" and I don't know what you mean by "having an example". As you can see from my answer, the regex works just fine, and my code snippet is self-contained: you can run it and see that it works. If you have another problem, I suggest you create another question for it (as I suggested earlier). Good luck!

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