Proof of concept for .cd command

Proposed in awslabs#76.

Still needs discussion for whether or not this
should be a dot command.  If we go with this
approach the only thing left is tests.

Author: jamesls

awsshell/app.py

@@ -45,6 +45,19 @@ class InputInterrupt(Exception):
     pass
 
 
+class ChangeDirHandler(object):
+    def run(self, command, application):
+        # command is a list of parsed commands
+        if len(command) != 2:
+            sys.stderr.write("invalid syntax, must be: .cd dirname\n")
+            return
+        dirname = os.path.expandvars(os.path.expanduser(command[1]))
+        try:
+            os.chdir(dirname)
+        except OSError as e:
+            sys.stderr.write("cd: %s\n" % e)
+
+
 class EditHandler(object):
     def __init__(self, popen_cls=None, env=None):
         if popen_cls is None:
@@ -85,6 +98,7 @@ def run(self, command, application):
 class DotCommandHandler(object):
     HANDLER_CLASSES = {
         'edit': EditHandler,
+        'cd': ChangeDirHandler,
     }
 
     def __init__(self, output=sys.stdout, err=sys.stderr):