Find and Replace a section of a string with wildcard type search using RegEx (while retaining some text)

Question

I am trying to replace some text in a string with different text while retaining some of the text and I am having trouble doing it.

My code is:

StreamReader reader = new StreamReader(fDialog.FileName.ToString());
string content = reader.ReadToEnd();
reader.Close();

/Replace M2 with M3 (this works fine)
content = Regex.Replace(content, "M2", "M3");

I want to replace a string that contains this:

Z0.1G0H1E1

and turn it into:

G54G43Z.1H1M08
(Note the Z value and the H value contain the same numeric value before the text change)

The trouble I am having is that when I replace the values, I need to retain the H value and the Z value from the first set of text.

For example,

Z0.5G0H5E1

I need to add the new text, but also add the H5 and Z0.5 back into the text such as:

G54G43Z0.5H5M08

But the Z values and H values will be different every time, so I need to capture those values and reinsert them back into the string when add the new G54G43 values.

Can someone please show me how to do this using Regex.Replace?

Answer 1

If the string contains nothing but the serial number ^_(?), it is easiest to extract the parameters one by one, and building them into a string. (you may want to create a function for the Regex.Match lines, they are almost identical). This version doesn't assume any order between Z and H:

string s = "Z0.5G0H5E1";
string zValue = Regex.Match(s, @"Z(\d*\.)?\d+").Value;
string hValue = Regex.Match(s, @"H(\d*\.)?\d+").Value;
s = String.Format("G54G43{0}{1}M08", zValue, hValue);

If you have a string with serial numbers ^_(?) in it, you may also use Regex.Replace:

string s = "hello world Z0.5G0H5E1 this is a string";
s = Regex.Replace(s, @"(Z(?:\d*\.)?\d+)[^H]*(H(?:\d*\.)?\d+)\w*",
                      "G54G43$1$2M08");

That regex basically means: (Z) (number) (not H...) (H) (number) (some more letters...)