RegEx to extract first XML element name with optional namespace prefix

Question

I have to extract with regEx first element name in the xml (ignoring optional namespace prefix.

Here is the sample XML1:

<ns1:Monkey xmlns="http://myurlisrighthereheremonkey.com/monkeynamespace">
 <foodType>
  <vegtables>
   <carrots>1</carrots>
  </vegtables>
 <foodType>   
</ns1:Monkey>

And here is similar XML that is without namespace, XML2:

 <Monkey xmlns="http://myurlisrighthereheremonkey.com/monkeynamespace">
 <foodType>
  <vegtables>
   <carrots>1</carrots>
  </vegtables>
 <foodType>   
</Monkey>

I need a regEx that will return me "Monkey" for either XML1 or XML2

So far I tried HERE this regEx <(\w+:)(\w+) that works for XML1 .... but I don't know how to make it work for XML2

<(\w+:)?(\w+)(?=\s*xmlns="http://myurlisrighthereheremonkey\.com/monkeynamespace") or ^\s*<(\w+:)?(\w+), but why regex? — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Aug 31, 2015 at 21:07
Thank you! That helps! The code I've got can't use xml parsing.... all I need is to check what "xml type" is it based on the element name. Please add it as an answer, so I can rate it. — user1697575
– user1697575, Commented Aug 31, 2015 at 21:07

Wiktor Stribiżew · Accepted Answer · 2015-08-31 21:13:15Z

Since it seems to be a one-time job and you really do not have access to XML parser, you can use either of the 2 regexps (that will work only for the XML files like you provided as samples):

<(\w+:)?(\w+)(?=\s*xmlns="http://myurlisrighthereheremonkey\.com/monkeynamespace")

Demo 1

Or (if you check the whole single file contents with the regex):

^\s*<(\w+:)?(\w+)

Demo 2

The main changes are 2:

(\w+:)? - adding ? modifier makes the first capturing group optional
^\s* makes the regex match at the beginning of the string (guess you do not have XML declaration there), or (?=\s*xmlns="http://myurlisrighthereheremonkey.com/monkeynamespace") look-ahead forcing the match only if followed by optional spaces and literal xmlns="http://myurlisrighthereheremonkey.com/monkeynamespace".

However, you really need to think about changing to code supporting XML parsing, it will make your life and lives of those who will be in charge of maintaining code easier.

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