anchor.diff:  @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(
  -    @Rest(parser: Input.parse)
       List<Input> files,
       {@Flag(abbr: 'n', help: 'number all output lines')
        bool number,
  
positive.code:     if(showTabs) lines = lines.map((str) => str.replaceAll('\t', '^I'));
  
      // TODO: Show non-printing characters.
      if(showNonprinting) {}
  
      lines.forEach(print);
    });
  }
  
  
negative.code:   if (files.isEmpty) {
      // Default to stdin.
      files = [Input.parse('-')];
    } else {
      // TODO: If there are multiple stdin files ('-') does cat store the
      // stdin content for the later ones?
    }
  
    forEachAsync(files, (Input input) {
  
      var bytesToLines = UTF8.decoder.fuse(const LineSplitter());
      var lines = input.stream.transform(bytesToLines);
  