code: def main(filename):
      
      if filename:
          if not os.path.exists(filename):
              logger.error("'%s' doesn't exists!" % filename)
              sys.stderr.write("'%s' doesn't exists!\n" % filename)
              sys.exit(1)
  
          logger.info("Processing '%s'" % filename)
          for ir in process_log(sh.tail("-f", filename, _iter=True)):
              print ir
      else:
          logger.info("Processing stdin.")
          for ir in process_log(_read_stdin()):
              print ir
docs: Open `filename` and start processing it line by line. If `filename` is
      none, process lines from `stdin`.