Allow the export_course command to dump results to stdout

lms/djangoapps/courseware/management/commands/export_course.py

 """
 A Django command that exports a course to a tar.gz file.
+
+If <filename> is '-', it pipes the file to stdout
+
 """
 
+import os
 import shutil
 import tarfile
-from tempfile import mkdtemp
+from tempfile import mktemp, mkdtemp
 from textwrap import dedent
 
 from path import path
@@ -25,13 +29,37 @@ class Command(BaseCommand):
     help = dedent(__doc__).strip()
 
     def handle(self, *args, **options):
+        course_id, filename, pipe_results = self._parse_arguments(args)
+
+        export_course_to_tarfile(course_id, filename)
+
+        results = self._get_results(filename) if pipe_results else None
+
+        return results
+
+    def _parse_arguments(self, args):
+        """Parse command line arguments"""
         try:
             course_id = args[0]
             filename = args[1]
         except IndexError:
             raise CommandError("Insufficient arguments")
 
-        export_course_to_tarfile(course_id, filename)
+        # If filename is '-' save to a temp file
+        pipe_results = False
+        if filename == '-':
+            filename = mktemp()
+            pipe_results = True
+
+        return course_id, filename, pipe_results
+
+    def _get_results(self, filename):
+        """Load results from file"""
+        results = None
+        with open(filename) as f:
+            results = f.read()
+            os.remove(filename)
+        return results
 
 
 def export_course_to_tarfile(course_id, filename):

lms/djangoapps/courseware/tests/test_commands.py

@@ -96,10 +96,15 @@ class CommandsTestBase(object):
         finally:
             shutil.rmtree(tmp_dir)
 
+    def test_export_course_stdout(self):
+        output = self.run_export_course('-')
+        with tarfile.open(fileobj=StringIO(output)) as tar_file:
+            self.check_export_file(tar_file)
+
     def run_export_course(self, filename):  # pylint: disable=missing-docstring
         args = ['edX/simple/2012_Fall', filename]
         kwargs = {'modulestore': 'default'}
-        self.call_command('export_course', *args, **kwargs)
+        return self.call_command('export_course', *args, **kwargs)
 
     def check_export_file(self, tar_file):  # pylint: disable=missing-docstring
         names = tar_file.getnames()