Regex to replace substring in given xml node only

Question 1

Description

This expression will find only the /oem/en string if it is inside the target tag

regex: (<target>(?:(?!<\/target>).)*?)(\/oem\/en(?=\/|\"))

replace with: $1~~~~New Value~~~~~

enter image description here

C# code example

Input Text

<?xml version="1.0" encoding="utf-8"?><xliff version="1.2" xmlns="urn:oasis:names:tc:xliff:document:1.2"><file product-version="1.4" original="" source-language="default" target-language="default" datatype="plaintext" category="page_content"><header></header><body><trans-unit id="page_description" datatype="x-System.String" maxwidth="0" minwidth="0"><source><![CDATA[bla bla]]></source><target><![CDATA[translated bla bla]]></target></trans-unit><trans-unit id="f55c4d88-1f2e-4ad9-aaa8-819af4ee7ee8" datatype="x-System.String" resname="PublishingPageContent" maxwidth="0" minwidth="0"><source><![CDATA[<a href="/oem/en/link1">bla bla</a>]]></source><target><![CDATA[<a href="/oem/en/link1/>translated bla bla</a>]]></target></trans-unit><trans-unit id="f55c4d88-1f2e-4ad9-aaa8-819af4ee7ee8" datatype="x-System.String" resname="PublishingPageContent" maxwidth="0" minwidth="0"><source><![CDATA[<a href="/oem/en/link2">bla bla</a>]]></source><target><![CDATA[<a href="/oem/en/link2/>translated bla bla</a>]]></target></trans-unit></body></file></xliff>

Code

using System;
using System.Text.RegularExpressions;
namespace myapp
{
  class Class1
    {
      static void Main(string[] args)
        {
          String sourcestring = "source string to match with pattern";
          String matchpattern = @"(<target>(?:(?!<\/target>).)*?)(\/oem\/en(?=\/|\""))";
          String replacementpattern = @"$1~~~~~new value~~~~~";
          Console.WriteLine(Regex.Replace(sourcestring,matchpattern,replacementpattern,RegexOptions.IgnoreCase));
        }
    }
}

Yields

<?xml version="1.0" encoding="utf-8"?><xliff version="1.2" xmlns="urn:oasis:names:tc:xliff:document:1.2"><file product-version="1.4" original="" source-language="default" target-language="default" datatype="plaintext" category="page_content"><header></header><body><trans-unit id="page_description" datatype="x-System.String" maxwidth="0" minwidth="0"><source><![CDATA[bla bla]]></source><target><![CDATA[translated bla bla]]></target></trans-unit><trans-unit id="f55c4d88-1f2e-4ad9-aaa8-819af4ee7ee8" datatype="x-System.String" resname="PublishingPageContent" maxwidth="0" minwidth="0"><source><![CDATA[<a href="/oem/en/link1">bla bla</a>]]></source><target><![CDATA[<a href="~~~~~new value~~~~~/link1/>translated bla bla</a>]]></target></trans-unit><trans-unit id="f55c4d88-1f2e-4ad9-aaa8-819af4ee7ee8" datatype="x-System.String" resname="PublishingPageContent" maxwidth="0" minwidth="0"><source><![CDATA[<a href="/oem/en/link2">bla bla</a>]]></source><target><![CDATA[<a href="~~~~~new value~~~~~/link2/>translated bla bla</a>]]></target></trans-unit></body></file></xliff>

Question 2

I don't think this would be reliable without requiring the CDATA section.

Below is the regex. It finds the target tag followed by the CDATA. It then matches any character not followed by the CDATA close ]]. /oem/en is matched as long as the ]] isn't encountered. I believe C# supports negated look aheads and non capturing groups. Obviously negated look aheads are essential.

<target><!\[CDATA\[(?:.(?!\]\]))*(/oem/en)

If you need to accommodate target having parameters you can do something like <target[^>]*>. If there is going to be whitespace between target and CDATA, then `\w*

I have a regex editor that's very alpha, but you can test it on: http://rey.gimenez.biz/