Regex C# is it possible to use a variable in substitution? -

i got bunch of strings in text, looks this:

h1. header h3. 1 header h111. , 

and got function, suppose process text depends on lets iteration been called

public void processheadersintext(string inputtext, int atlevel = 1) 

so output should 1 below in case of been called

processheadersintext(inputtext, 2) 

output should be:

<h3>this header<h3> <h5>this 1 header too<h5> <h9 , <h9> 

(last 1 looks because of if value after h letter more 9 suppose 9 in output)

so, started think using regex.

here's example https://regex101.com/r/spb3af/1/

(as can see came regex (^(h([\d]+)\.+?)(.+?)$) , tried use substitution on <h$3>$4</h$3>)

its i'm looking need add logic work heading level.

is possible add work variables in substitution?

or need find other way? (extract heading first, replace em considering function variables , value of header, , after use regex wrote?)

the regex may use is

^h(\d+)\.+\s*(.+) 

if need make sure match not span across line, may replace \s [^\s\r\n]. see regex demo.

when replacing inside c#, parse group 1 value int , increment value inside match evaluator inside regex.replace method.

here example code you:

using system; using system.linq; using system.text.regularexpressions; using system.io; public class test {     // demo: https://regex101.com/r/m9iguo/2     public static readonly regex reg = new regex(@"^h(\d+)\.+\s*(.+)", regexoptions.compiled | regexoptions.multiline);       public static void main()     {         var inputtext = "h1. topic 1\r\nblah blah blah, because of bla bla bla\r\nh2. parta\r\nblah blah blah\r\nh3. part a\r\nblah blah blah\r\nh2. part b\r\nblah blah blah\r\nh1. topic 2\r\nand cuz blah blah\r\nfin";         var res = processheadersintext(inputtext, 2);         console.writeline(res);     }     public static string processheadersintext(string inputtext, int atlevel = 1)      {         return reg.replace(inputtext, m =>             string.format("<h{0}>{1}</h{0}>", (int.parse(m.groups[1].value) > 9 ?                 9 : int.parse(m.groups[1].value) + atlevel), m.groups[2].value.trim()));     } } 

see c# online demo

note using .trim() on m.groups[2].value . matches \r. may use trimend('\r') rid of char.