File content:

version.cpp

  #include "stdio.h"
  #define VERSION "x.x.x.x"
  void main() {
  }

Create replace.build file to replace version with $BuildNumber:

replace.build

<version="1.0" encoding="utf-8" ?>
<project name="replace.line" default="replace">
  <target name="replace" descripton="replaces a line">
 
<loadfile file="${version.file}" property="version.file.content" />
  <regex
      input="${version.file.content}"
      pattern="(?'BEFORE'[\w\s\W]*)#define\sVERSION\s*&quot;[x][\.][x][\.][x][\.][x]&quot;(?'AFTER'[\w\s\W]*)" />
   <echo
      file="${version.file}"
      message="${BEFORE}#define VERSION &quot;${BuildNumber}&quot;${AFTER}"
      append="false" />
 
</target>
 
</project>
 

Run it with:

nant -buildfile:replace.build -D:version.file=version.cpp -D:BuildNumber=9.1.0.1