rts the UNIX <code>cat</code> utility, which when given no
command-line arguments, echos its input.
The program writes to the process's standard input stream
and prints data from its standard output stream.</p>
<pre class="language-dart"><code>import 'dart:io';
import 'dart:convert';

main() {
  Process.start('cat', []).then((Process process) {
    process.stdout
        .transform(utf8.decoder)
        .listen((data) { print(data); });
    process.stdin.writeln('Hello, world!');
    process.stdin.writeln('