Targeting a tag with preg_replace

[dresden_phoenix]

Regex is driving me nuts tonight.

what I am trying to do ( as illogical as this goal may sound ) is to eliminate open/close tag pairs and their content. For example, in the following, I want to eliminate the part in red:

<b class=‘test another’ id=‘x’>hey<i><span class=‘sp’> some more stuff </span><em>

in this example i want to target the open span… its class… its content and then its closing span tags so that I get this :
<b class=‘test another’ id=‘x’>hey<i><em>
( sorry, am being redundant)

I figured this was a job for preg_replace and a GOOD regex expression, this is what I have thus far…

$string=preg_replace(“/(^<(.+)\s*.>).(<\/(?(2)(.+))>)/”,“”,$string)

thinking that the regexp expression I created means the following…
( look for a pattern
^< that begins with “<” and is followed immediately by
(.+) a pattern containing one or more charters ( captured pattern #2)
\s? maybe followed by a space or no space
.* maybe followed by 0 or more charcters
>)and lastly an “>”
.* after that there be 0 or more characters
( then another pattern
</ which starts with “</” and is followed by
(?(2)(.+))a pattern containing one or more charters which MATCH the characters of captured pattern #2 and is followed by
>) / and lastly an “>” , end search…

somewhere I am off… I would appreciate any fresh perspective on this…

thanks in advance

[aamonkey]

maybe something like this:

function removeTagPairs($html)
{
    $c = 0;
    $html = preg_replace('#<([a-z]+)[^>]*>[^<]*</\\1>#s', '', $html, -1, $c);
    return ($c > 0) ? removeTagPairs($html) : $html;
}

It’s recursive so that if you had something like

<b class='test another' id='x'>hey<i><span class='sp'> some <b>more</b> stuff </span><em>

it would first remove the inner <b>more</b> tags, then the outer <span> tags.

It won’t remove things like:
<span class=‘sp’> some <b>more stuff </span>

[TomB]

That will break under two potentially valid conditions.

1. if nesting occurs:

<span class='sp'> 
<span class='sp'> 
test
</span>
</span>

Will break it.

2. Closing </span> tags which don’t belong to the correct pair:

<span class="sp"> 
Will be removed
<span class="foo">
Will be removed
</span>
Should be removed but won't be.
<span>

The best solution? Don’t use regex to alter HTML. Use DomDocument.

[aamonkey]

Hi Tom - I’m not arguing that DomDocument wouldn’t be a safer bet, but to my eyes neither of your examples breaks the regex I posted - it handles nesting (as in your 1st example), and your second example is invalid html and as such shouldn’t be removed if I’m understanding the OP’s goal correctly.

[dresden_phoenix]

Well am not altering the DOM… I am writing a PHP script parser.
the idea kinda 1-upping wordpress, in a way. the data you saw will be reversedd and the tags closed.

so the input is:
“<b class=‘test another’ id=‘x’>hey<i><span class=‘sp’> some more stuff </span><em>”

will output :
"</i></b></em> "

and both of those will be wrapred around some other generated code…

so as to complete a wrap around a script tag. I have got the whole thing works… except when there is an already closed tag pair as shown above…

Am not sure if DOMDoc applies here

Oh one more question cause I like your format…
why did you use ‘#’ instead of’ / ’ to open and close the expression?

and is “/\1” how you reuse a captured pattern?

[aamonkey]

@dresden_phoenix

Oh one more question cause I like your format…
why did you use ‘#’ instead of’ / ’ to open and close the expression?

I like to use symbols that are less likely to occur in the target string - it requires fewer escape characters and therefore becomes easier to read - /'s occur in html often, but not pound signs.

@dresden_phoenix

and is “/\1” how you reuse a captured pattern?

almost - “\1” (without the quotes). the / is part of the closing tag

[dresden_phoenix]

ok, different strategy… is there a way to do a negate… as in any character BUT “>”

[dresden_phoenix]

oops, strike that

[dresden_phoenix]

I am confused for one thing… I have entered your function…

function removeTagPairs($html){
$c = 0;
$html = preg_replace(‘#<([a-z]+)[^>]>[^<]</\1>#s’, ‘’, $html, -1, $c);
if ($c>0) {echo “more!!!”;}
return ($c > 0) ? removeTagPairs($html) : $html;
}

call it from :
$wraped=removeTagPairs($wraped);
( I know it goes to remove tag pairs as I have tested this already)
but the preg_ always returns false…

this now baffles me more as:

1. I have OTHER working preg_s in my code
2. I tested your expression here

did I make some horrible typo…? do I need a version of PHP higher than 5.2.6 for this to work!!!

[TomB]

@aamonkey

Hi Tom - I’m not arguing that DomDocument wouldn’t be a safer bet, but to my eyes neither of your examples breaks the regex I posted - it handles nesting (as in your 1st example), and your second example is invalid html and as such shouldn’t be removed if I’m understanding the OP’s goal correctly.

Ah I thought the OP wanted to remove a specific tag and its contents not every tag.

dresden_phoenix: If your input length is long it’s likely you’re running into this bug: http://bugs.php.net/40846

To get around it use

ini_set('pcre.backtrack_limit', 10000000);
ini_set('pcre.recursion_limit', 10000000);

[dresden_phoenix]

thanks guys… actually it works very well … the hitch was this

#<([a-z]+)[^>]>[^<]</\\1>#s’

I had the same problem earlier, on a javascript. I never knew/keep forgetting to double escape.