G Code Manipulation

[TimLewicki]

I want to write code that will take a .txt file that may look like:

N1 G1 G90 X0 Y0 Z3. 
N2 X1.2751 Y1.82

(G Code - can be thousands of lines long. Each new line starts with N__. Leading and trailing zeros are omitted.)

Find every instance of X(and the value attached to it) and add a U(with the same value) afterward. For example, after running the software, the above will now look like:

N1 G1 G90 X0 U0 Y0 Z3.

N2 X1.2751 U1.2751 Y1.82

If been chasing various ideas and haven’t gotten very far.

[Funce]

You might be able to use Regular Expressions. 
Find:

X(\d+\.?\d*)

Replace:

$& U$1