Making XHTML file valid using regex

Question

I'm trying to use PHP with SimpleXML to parse an XHTML file, however the file contains < and > signs which are not part of the markup and cause parsing to fail (opening and end tag mismatches).

How can I convert these to HTML entities before parsing without changing the file or affecting the markup?

Example:

<p> a < b </p>

Would become:

<p> a &lt; <b> </p>

you should consider to use php.net/manual/en/domdocument.loadhtmlfile.php — ajreal
– ajreal, Commented Feb 15, 2011 at 7:52
Its generally bad practice to use a xml parser on a xhtml document, as its a rare sight that a page actually is valid xhtml. What is the purpose of wanting to parse the page via xml? — Jan Dragsbaek
– Jan Dragsbaek, Commented Feb 15, 2011 at 7:52
I want to parse a table of products from an xhtml page and store them in a database and wasn't aware of the DOMDocument::loadHTMLFile, however it seems to choke on < as well :( — Simononon
– Simononon, Commented Feb 15, 2011 at 8:05

Martin Jespersen · Accepted Answer · 2011-02-15 07:55:05Z

2

Well the short answer is: you can't parse html with regex.

Maybe you could try using another xml parser that doesnt' choke on the < and > ?

Better yet, don't try to parse an xhtml file as xml, since as you already point out yourself, it isn't really an xml file, and has illegal characters in it.

answered Feb 15, 2011 at 7:55

Martin Jespersen

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Tim Pietzcker · Accepted Answer · 2011-02-15 08:06:29Z

1

As Martin Jespersen already said, there is no good way to parse (invalid or valid) markup with regexes, at least not with PHP regexes.

That said, if you're only looking for a way to remove

unbalanced angle brackets
that are between valid tags
which do not contain angle brackets somewhere inside their attribute values

then you might get away with doing this:

$intermediate = preg_replace('/(>[^<>]*)<([^<>]*<)/', '\1&lt;\2', $subject);
$result = preg_replace('/(>[^<>]*)>([^<>]*<)/', '\1&gt;\2', $intermediate);

but you'd have to run this several times until there are no more matches because this will only catch one stray < or > between tags at a time. It will also fail on pseudo-balanced brackets like <p> a <> b </p>.

answered Feb 15, 2011 at 8:06

Tim Pietzcker

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1 Comment

Simononon Over a year ago

Got away with your suggestion and using DOMDocument::loadHTMLFile instead of SimpleXML and it works a treat, thanks!

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