Build.hx

class Build {
  macro static public function getEnv(s:String)
    return macro $v{Sys.getEnv(s)};
    
  macro static public function exec(cmd:String, ?args:Array<String>) {
    var p = new sys.io.Process(cmd, args),
        pos = haxe.macro.Context.currentPos();
    return
      switch p.exitCode() {
        case 0: 
          var value = 
            switch p.stdout.readAll().toString() {
              case '': p.stderr.readAll().toString();//sometimes output goes to stderr, particularly for --help and --version type of invocations
              case v: v;
            }
          macro @:pos(pos) $v{value};
        case v:
          haxe.macro.Context.fatalError('Command $cmd exited with $v because ${p.stderr.readAll().toString()}', pos);
      }
  }  
}