anchor.diff:      if(showTabs) lines = lines.map((str) => str.replaceAll('\t', '^I'));
   
       // TODO: Show non-printing characters.
  +    // See http://docstore.mik.ua/orelly/unix3/upt/ch12_04.htm
       if(showNonprinting) {}
   
  -    lines.forEach(print);
  +    return lines.forEach(print);
     });
   }
   
  
positive.code:   if (files.isEmpty) {
      // Default to stdin.
      files = [Input.parse('-')];
    }
  
    files.forEach((Input input) {
  
      var bytesToLines = UTF8.decoder.fuse(const LineSplitter());
      var lines = input.stream.transform(bytesToLines);
  
negative.code: @Command(help: 'Concatenate FILE(s), or standard input, to standard output.')
  @ArgExample('f - g', help: "Output f's contents, then standard input, then g's contents.")
  @ArgExample('', help: 'Copy standard input to standard output.')
  /// A dart implementation of the unix utility [cat][cat_wiki].
  /// [cat_wiki]: http://en.wikipedia.org/wiki/Cat_(Unix)
  cat(
      List<Input> files,
      {@Flag(abbr: 'n', help: 'number all output lines')
       bool number,
  