how to get certain content from a file?

I use file_get_contents to get file http://mydomain.com/test.html

inside the html file, I need to get the text between <div id="testing"></div>

<div id="testing">

I need to find out whatever the content here.

/sldfksf
/n
likllsdf
</div>

whats the best way to do it? all i can think about is to read line by line,but I got I have alot pages to process, that will take forever, is there a better way to do it.

 

What I would do is this, assuming that you only have "<div id="testing"></div>" once in your html file...
assuming your file is read into the variable $htmlcontents

$pos1=strpos($htmlcontents, "<div id=\"testing\">");
$pos1=$pos1+18;
$pos2=strpos($htmlcontents, "</div>", $pos1);
$testingvalue=substr($htmlcontents, $pos1, $pos2-$pos1);

Code (markup):

I can't say if that's the best way to do it, but that's what I would do.