Regular Expression for adding meta tag, if it does not exist (notepad++)

Question

I'm trying to come up with a regular expression that will be applied for potentially hundreds of files, as a find..replace in notepad++. It's going to be like an if..else.

Here's what I want to do but as a regex:

if title tag exists and <meta http-equiv="X-UA-Compatible" content="IE=edge" /> does not exist on the page, AND an iframe tag exists, then insert <meta http-equiv="X-UA-Compatible" content="IE=edge" /> right after the title tag.

Sample text:

<title>Some Title</title>
<meta name="description" content="Mydescription." />
<meta http-equiv="Content-type" content="text/html; charset=utf-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />

 ...

<iframe src="iframeresource"></iframe>

Regex I have thus far:

(<title>.*<\s*\/title>).*?(?!<meta http-equiv="X-UA-Compatible" content="IE=edge"\s*\/>.*?<iframe)

It uses a negative lookahead. I need something like a conditional negative lookahead but the ability to perform substitution, if and only if <meta http-equiv="X-UA-Compatible" content="IE=edge /> does not exist already. I'm not quite sure how to do this with straight regex.

Any ideas would be most appreciated. Thank you.

Answer 1

HTML parsing is best done with a dedicated DOM parser. A regex can only be used to fix a well-structured, consistent HTML code.

If this is the case, use

(?si)\A(?!.*?<meta\s+http-equiv="X-UA-Compatible"\s+content="IE=edge"\s*/>)(.*?<title>.*?</title>)(.*)

and replace with $1\\n<meta http-equiv="X-UA-Compatible" content="IE=edge" />$2\\n .

(?si) enables . to match linebreaks and makes the pattern case insensitive. \\A matches the start of a file. The (?!.*?<meta\\s+http-equiv="X-UA-Compatible"\\s+content=‌​"IE=e‌​dge"\\s*/>) fails the match if the meta tag pattern is matched. (.*?<‌​title>.*?</title>) consumes and captures text up to and including the first title tag. Then (.*) matches the rest of the document.

See the regex demo