Provide method to run multiple commands w/o a cmdloop.

runcmds_plus_hooks can accept multiple commands process the command queue to
 deal with subsequent commands loaded from scripts without requiring a command
 loop. This better supports a one-off batch processing scenario.

Also fixed the insertion order of commands placed in the command queue by load
and _relative_load so that script commands are run in the expected order.

Minor tweak to setup instructions in CONTRIBUTING.md to include pyperclip in
prerequisites.

Author: alevy03

CONTRIBUTING.md

@@ -192,7 +192,7 @@ Once you have cmd2 cloned, before you start any cmd2 application, you first need
 
 ```bash
 # Install cmd2 prerequisites
-pip install -U six pyparsing
+pip install -U six pyparsing pyperclip
 
 # Install prerequisites for running cmd2 unit tests
 pip install -U pytest mock

cmd2.py

@@ -789,6 +789,44 @@ def onecmd_plus_hooks(self, line):
         finally:
             return self.postparsing_postcmd(stop)
 
+    def runcmds_plus_hooks(self, cmds):
+        """Convenience method to run multiple commands by onecmd_plus_hooks.
+
+        This method adds the given cmds to the command queue and processes the
+        queue until completion or an error causes it to abort. Scripts that are
+        loaded will have their commands added to the queue. Scripts may even
+        load other scripts recursively. This means, however, that you should not
+        use this method if there is a running cmdloop or some other event-loop.
+        This method is only intended to be used in "one-off" scenarios.
+
+        NOTE: You may need this method even if you only have one command. If
+        that command is a load, then you will need this command to fully process
+        all the subsequent commands that are loaded from the script file. This
+        is an improvement over onecmd_plus_hooks, which expects to be used
+        inside of a command loop which does the processing of loaded commands.
+
+        Example: cmd_obj.runcmds_plus_hooks(['load myscript.txt'])
+
+        :param cmds: list - Command strings suitable for onecmd_plus_hooks.
+        :return: bool - True implies the entire application should exit.
+
+        """
+        stop = False
+        self.cmdqueue = list(cmds) + self.cmdqueue
+        try:
+            while self.cmdqueue and not stop:
+                stop = self.onecmd_plus_hooks(self.cmdqueue.pop(0))
+        finally:
+            # Clear out the command queue and script directory stack, just in
+            # case we hit an error and they were not completed.
+            self.cmdqueue = []
+            self._script_dir = []
+            # NOTE: placing this return here inside the finally block will
+            # swallow exceptions. This is consistent with what is done in
+            # onecmd_plus_hooks and _cmdloop, although it may not be
+            # necessary/desired here.
+            return stop
+
     def _complete_statement(self, line):
         """Keep accepting lines of input until the command is complete."""
         if not line or (not pyparsing.Or(self.commentGrammars).setParseAction(lambda x: '').transformString(line)):
@@ -1775,18 +1813,13 @@ def do_load(self, file_path):
             return
 
         try:
-            # Specify file encoding in Python 3, but Python 2 doesn't allow that argument to open()
-            if six.PY3:
-                # Add all commands in the script to the command queue
-                with open(expanded_path, encoding='utf-8') as target:
-                    self.cmdqueue.extend(target.read().splitlines())
-            else:
-                # Add all commands in the script to the command queue
-                with open(expanded_path) as target:
-                    self.cmdqueue.extend(target.read().splitlines())
-
-            # Append in an "end of script (eos)" command to cleanup the self._script_dir list
-            self.cmdqueue.append('eos')
+            # Read all lines of the script and insert into the head of the
+            # command queue. Add an "end of script (eos)" command to cleanup the
+            # self._script_dir list when done. Specify file encoding in Python
+            # 3, but Python 2 doesn't allow that argument to open().
+            kwargs = {'encoding' : 'utf-8'} if six.PY3 else {}
+            with open(expanded_path, **kwargs) as target:
+                self.cmdqueue = target.read().splitlines() + ['eos'] + self.cmdqueue
         except IOError as e:
             self.perror('Problem accessing script from {}:\n{}'.format(expanded_path, e))
             return

tests/scripts/nested.txt

@@ -0,0 +1,4 @@
+_relative_load precmds.txt
+help
+shortcuts
+_relative_load postcmds.txt

tests/scripts/postcmds.txt

@@ -0,0 +1,2 @@
+set abbrev off
+set colors off

tests/scripts/precmds.txt

@@ -0,0 +1,2 @@
+set abbrev on
+set colors on

tests/test_cmd2.py

@@ -401,6 +401,61 @@ def test_load_with_utf8_file(base_app, capsys, request):
     assert base_app._current_script_dir == sdir
 
 
+def test_load_nested_loads(base_app, request):
+    # Verify that loading a script with nested load commands works correctly,
+    # and loads the nested script commands in the correct order. The recursive
+    # loads don't happen all at once, but as the commands are interpreted. So,
+    # we will need to drain the cmdqueue and inspect the stdout to see if all
+    # steps were executed in the expected order.
+    test_dir = os.path.dirname(request.module.__file__)
+    filename = os.path.join(test_dir, 'scripts', 'nested.txt')
+    assert base_app.cmdqueue == []
+
+    # Load the top level script and then run the command queue until all
+    # commands have been exhausted.
+    initial_load = 'load ' + filename
+    run_cmd(base_app, initial_load)
+    while base_app.cmdqueue:
+        base_app.onecmd_plus_hooks(base_app.cmdqueue.pop(0))
+
+    # Check that the right commands were executed.
+    expected = """
+%s
+_relative_load precmds.txt
+set abbrev on
+set colors on
+help
+shortcuts
+_relative_load postcmds.txt
+set abbrev off
+set colors off""" % initial_load
+    assert run_cmd(base_app, 'history -s') == normalize(expected)
+
+
+def test_base_runcmds_plus_hooks(base_app, request):
+    # Make sure that runcmds_plus_hooks works as intended. I.E. to run multiple
+    # commands and process any commands added, by them, to the command queue.
+    test_dir = os.path.dirname(request.module.__file__)
+    prefilepath = os.path.join(test_dir, 'scripts', 'precmds.txt')
+    postfilepath = os.path.join(test_dir, 'scripts', 'postcmds.txt')
+    assert base_app.cmdqueue == []
+
+    base_app.runcmds_plus_hooks(['load ' + prefilepath,
+                                 'help',
+                                 'shortcuts',
+                                 'load ' + postfilepath])
+    expected = """
+load %s
+set abbrev on
+set colors on
+help
+shortcuts
+load %s
+set abbrev off
+set colors off""" % (prefilepath, postfilepath)
+    assert run_cmd(base_app, 'history -s') == normalize(expected)
+
+
 def test_base_relative_load(base_app, request):
     test_dir = os.path.dirname(request.module.__file__)
     filename = os.path.join(test_dir, 'script.txt')