Making a system call

A fairly common use case is that you need to call another program from your Dart app, or an operating system command. For this, the abstract class Process in the dart:io package is created.

How to do it...

Use the run method to begin an external program as shown in the following code snippet, where we start Notepad on a Windows system, which shows the question to open a new file tst.txt (refer to make_system_call\bin\ make_system_call.dart):

import 'dart:io';

main() {
  // running an external program process without interaction:
  Process.run('notepad', ['tst.txt']).then((ProcessResult rs){
    print(rs.exitCode);
    print(rs.stdout);
    print(rs.stderr);
  });
}

If the process is an OS command, use the runInShell argument, as shown in the following code:

Process.run('dir',[], runInShell:true).then((ProcessResult 
rs)
{ … }

How it works...

The Run command returns a Future of type ProcessResult, which you can interrogate for its exit code or any messages. The exit code is OS-specific, but usually a negative value indicates an execution problem.

Use the start method if your Dart code has to interact with the process by writing to its stdin stream or listening to its stdout stream.

Note

Both methods work asynchronously; they don't block the main app. If your code has to wait for the process, use runSync.