I am trying to get a regular expression to work, but not having a whole lot of luck.
the source file I am reading(poorly formatted, but nothing I can do there) has the following in its source between elements
<BR>
<BR>
<BR>
how do I match this with a php regular expression?
Something like this:
preg_match('/(<br>\s*){3}/i', $str, $matches);
This is a bit more lenient than your example - it does a case-insensitive match and matches any whitespace between the <br>s, not just newlines.
To match 3 or more instead of 3:
preg_match('/(<br>\s*){3,}/i', $str, $matches);
If you just want to replace the <BR> instances then you're better off doing a string replacement. It is a lot faster then regex.
$newstr = str_replace('<BR>', 'replacement...', $str);
My take on it
<?php
$html = <<<HTML
<BR>
<BR>
<BR>
<p>^^ Replace 3 consecutive BR tags with nothing</p>
<BR>
<BR>
<p>^^ those should stay, there's only 2 of them</p>
<BR>
<BR>
<BR>
<p>^^ But those should go, whitespace and newlines shouldn't matter
HTML;
echo preg_replace( "/(?:<br>\s*){3}/i", '', $html );