shell command now uses cmd.Cmd.stdout for output

The main advantages of this are that shell command output can now be

- piped to another shell command
- redirected to a file

In the future, I may take it a step further where the output is piped, but using a pipe versus a real terminal changes the behavior of many shell commands, for example by getting rid of ANSI color and various other pretty formatting.

Author: tleonhardt

cmd2.py

@@ -1138,21 +1138,15 @@ def do_pause(self, text):
     Usage:  pause [text]"""
         sm.input(text + '\n')
 
-    # noinspection PyMethodMayBeStatic
     def do_shell(self, command):
         """Execute a command as if at the OS prompt.
 
     Usage:  shell <command> [arguments]"""
         try:
-            out = subprocess.check_output(shlex.split(command))
-        except subprocess.CalledProcessError as e:
-            self.perror(e, traceback_war=False)
+            proc = subprocess.Popen(command, stdout=self.stdout, stderr=sys.stderr, shell=True)
+            proc.communicate()
         except FileNotFoundError as e:
-            self.perror(e, traceback_war=False)
-        else:
-            if six.PY3:
-                out = out.decode()
-            self.stdout.write(out + '\n')
+            self.perror(e.strerror, traceback_war=False)
 
     def path_complete(self, text, line, begidx, endidx, dir_exe_only=False, dir_only=False):
         """Method called to complete an input line by local file system path completion.

tests/test_cmd2.py

@@ -103,12 +103,10 @@ def test_base_set_not_supported(base_app, capsys):
 
 def test_base_shell(base_app, monkeypatch):
     m = mock.Mock()
-    monkeypatch.setattr("os.system", m)
+    monkeypatch.setattr("subprocess.Popen", m)
     out = run_cmd(base_app, 'shell echo a')
     assert out == []
     assert m.called
-    m.assert_called_with('echo a')
-
 
 def test_base_py(base_app, capsys):
     run_cmd(base_app, 'py qqq=3')