c# regex replace string within a specified string with spaces [duplicate]

This resembles XML data. And so i would approach it as such.

It is widely known that regex is not good for structured data like mark up languages.

So I suggest leveraging XDocument for that task:

string SanitizeXmlLikeString(string input, bool writeFullClosingNode = true)
{
    const string openRootNode = "<root>";
    const string closeRootNode = "</root>";
    try
    {
        var xDoc = XDocument.Parse($"{openRootNode}{rawXml}{closeRootNode}");

        // Remove any content that is in "value" nodes
        foreach (var valueNode in xDoc.Descendants("value"))
        {
            valueNode.RemoveAll();
        }

        using var memoryStream = new MemoryStream();
        using var xmlWriter = writeFullClosingNode
            ? new FullElementXmlTextWriter(memoryStream, Encoding.UTF8)
            : new XmlTextWriter(memoryStream, Encoding.UTF8);

        xDoc.Root.WriteTo(xmlWriter);
        xmlWriter.Flush();
        memoryStream.Seek(0, SeekOrigin.Begin);

        var cleanedRawXml = Encoding.UTF8.GetString(memoryStream.ToArray());
        cleanedRawXml = cleanedRawXml
            .Trim('?') // serializer puts ? in front, so we don't want it
            .Trim() // before removing root node, trim any surrounding spaces
            [(openRootNode.Length + 1)..^closeRootNode.Length]; // take substring to remove opening and closing root markup

        return cleanedRawXml;
    }
    catch
    {
        // in case of problems return original string
        return input;
    }
}

Only thing to mention besides inline comments is that XmlTextWriter writes empty nodes as <value /> - self closing, which might be not what you want. For that we can use approach suggested in this SO post to write full element <value></value>, even when empty:

public class FullElementXmlTextWriter : XmlTextWriter
{
    public FullElementXmlTextWriter(TextWriter w) : base(w) { }

    public FullElementXmlTextWriter(Stream w, Encoding encoding) : base(w, encoding) { }

    public FullElementXmlTextWriter(string filename, Encoding encoding) : base(filename, encoding) { }

    public override void WriteEndElement()
    {
        base.WriteFullEndElement();
    }
}