Errors and warnings are printed to stderr.

CHANGELOG.rst

@@ -9,6 +9,9 @@ Next Release (TBD)
   ``aws configure set`` command now write out all credential
   variables to the shared credentials file ``~/.aws/credentials``
   (`issue 847 <https://github.com/aws/aws-cli/issues/847>`__)
+* bugfix:``aws s3``: Write warnings and errors to standard error as
+  opposed to standard output.
+  (`issue 919 <https://github.com/aws/aws-cli/pull/919>`__)
 
 
 1.4.4

awscli/customizations/s3/executor.py

@@ -274,13 +274,15 @@ def run(self):
 
     def _process_print_task(self, print_task):
         print_str = print_task.message
+        print_to_stderr = False
         if print_task.error:
             self.num_errors_seen += 1
+            print_to_stderr = True
         warning = False
         if print_task.warning:
-            if print_task.warning:
-                warning = True
-                self.num_warnings_seen += 1
+            warning = True
+            self.num_warnings_seen += 1
+            print_to_stderr = True
         final_str = ''
         if warning:
             final_str += print_str.ljust(self._progress_length, ' ')
@@ -309,6 +311,12 @@ def _process_print_task(self, print_task):
                 self._num_parts += 1
             self._file_count += 1
 
+        # If the message is an error or warning, print it to standard error.
+        if print_to_stderr == True and not self._quiet:
+            uni_print(final_str, sys.stderr)
+            sys.stderr.flush()
+            final_str = ''
+
         is_done = self._total_files == self._file_count
         if not is_done:
             prog_str = "Completed %s " % self._num_parts

awscli/customizations/s3/utils.py

@@ -223,24 +223,26 @@ def __init__(self):
         self.count = 0
 
 
-def uni_print(statement):
+def uni_print(statement, out_file=None):
     """
-    This function is used to properly write unicode to stdout.  It
-    ensures that the proper encoding is used if the statement is
-    not in a version type of string.  The initial check is to
-    allow if ``sys.stdout`` does not use an encoding
+    This function is used to properly write unicode to a file, usually
+    stdout or stdderr.  It ensures that the proper encoding is used if the
+    statement is not a string type.  The initial check is to allow if
+    ``out_file`` does not use an encoding.
     """
-    encoding = getattr(sys.stdout, 'encoding', None)
+    if out_file is None:
+        out_file = sys.stdout
+    encoding = getattr(out_file, 'encoding', None)
     if encoding is not None and not PY3:
-        sys.stdout.write(statement.encode(sys.stdout.encoding))
+        out_file.write(statement.encode(out_file.encoding))
     else:
         try:
-            sys.stdout.write(statement)
+            out_file.write(statement)
         except UnicodeEncodeError:
             # Some file like objects like cStringIO will
             # try to decode as ascii.  Interestingly enough
             # this works with a normal StringIO.
-            sys.stdout.write(statement.encode('utf-8'))
+            out_file.write(statement.encode('utf-8'))
 
 
 def guess_content_type(filename):

tests/integration/customizations/s3/test_plugin.py

@@ -164,10 +164,10 @@ def assert_no_errors(self, p):
         self.assertEqual(
             p.rc, 0,
             "Non zero rc (%s) received: %s" % (p.rc, p.stdout + p.stderr))
-        self.assertNotIn("Error:", p.stdout)
-        self.assertNotIn("failed:", p.stdout)
-        self.assertNotIn("client error", p.stdout)
-        self.assertNotIn("server error", p.stdout)
+        self.assertNotIn("Error:", p.stderr)
+        self.assertNotIn("failed:", p.stderr)
+        self.assertNotIn("client error", p.stderr)
+        self.assertNotIn("server error", p.stderr)
 
 
 class TestMoveCommand(BaseS3CLICommand):
@@ -458,7 +458,7 @@ def test_download_non_existent_key(self):
         expected_err_msg = (
             'A client error (NoSuchKey) occurred when calling the '
             'HeadObject operation: Key "foo.txt" does not exist')
-        self.assertIn(expected_err_msg, p.stdout)
+        self.assertIn(expected_err_msg, p.stderr)
 
 
 class TestSync(BaseS3CLICommand):
@@ -645,7 +645,7 @@ def testFailWithoutRegion(self):
         p2 = aws('s3 sync s3://%s/ s3://%s/ --region %s' % 
                  (self.src_bucket, self.dest_bucket, self.src_region))
         self.assertEqual(p2.rc, 1, p2.stdout)
-        self.assertIn('PermanentRedirect', p2.stdout)
+        self.assertIn('PermanentRedirect', p2.stderr)
 
     def testCpRegion(self):
         self.files.create_file('foo.txt', 'foo')
@@ -695,9 +695,9 @@ def extra_setup(self):
     def test_no_exist(self):
         filename = os.path.join(self.files.rootdir, "no-exists-file")
         p = aws('s3 cp %s s3://%s/' % (filename, self.bucket_name))
-        self.assertEqual(p.rc, 2, p.stdout)
+        self.assertEqual(p.rc, 2, p.stderr)
         self.assertIn('warning: Skipping file %s. File does not exist.' % 
-                      filename, p.stdout)
+                      filename, p.stderr)
 
     @unittest.skipIf(platform.system() not in ['Darwin', 'Linux'],
                      'Read permissions tests only supported on mac/linux')
@@ -711,9 +711,9 @@ def test_no_read_access(self):
         permissions = permissions ^ stat.S_IREAD
         os.chmod(filename, permissions)
         p = aws('s3 cp %s s3://%s/' % (filename, self.bucket_name))
-        self.assertEqual(p.rc, 2, p.stdout)
+        self.assertEqual(p.rc, 2, p.stderr)
         self.assertIn('warning: Skipping file %s. File/Directory is '
-                      'not readable.' % filename, p.stdout)
+                      'not readable.' % filename, p.stderr)
 
     @unittest.skipIf(platform.system() not in ['Darwin', 'Linux'],
                      'Special files only supported on mac/linux')
@@ -723,10 +723,10 @@ def test_is_special_file(self):
         sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
         sock.bind(file_path)
         p = aws('s3 cp %s s3://%s/' % (file_path, self.bucket_name))
-        self.assertEqual(p.rc, 2, p.stdout)
+        self.assertEqual(p.rc, 2, p.stderr)
         self.assertIn(("warning: Skipping file %s. File is character "
                        "special device, block special device, FIFO, or "
-                       "socket." % file_path), p.stdout)
+                       "socket." % file_path), p.stderr)
 
 
 @unittest.skipIf(platform.system() not in ['Darwin', 'Linux'],
@@ -806,10 +806,10 @@ def test_follow_symlinks_default(self):
 
     def test_bad_symlink(self):
         p = aws('s3 sync %s s3://%s/' % (self.files.rootdir, self.bucket_name))
-        self.assertEqual(p.rc, 2, p.stdout)
+        self.assertEqual(p.rc, 2, p.stderr)
         self.assertIn('warning: Skipping file %s. File does not exist.' % 
                       os.path.join(self.files.rootdir, 'b-badsymlink'),
-                      p.stdout)
+                      p.stderr)
 
 
 class TestUnicode(BaseS3CLICommand):
@@ -945,7 +945,7 @@ def test_mb_rb(self):
     def test_fail_mb_rb(self):
         # Choose a bucket name that already exists.
         p = aws('s3 mb s3://mybucket')
-        self.assertIn("BucketAlreadyExists", p.stdout)
+        self.assertIn("BucketAlreadyExists", p.stderr)
         self.assertEqual(p.rc, 1)
 
 

tests/integration/customizations/s3/test_s3handler.py

@@ -163,12 +163,12 @@ def setUp(self):
         self.s3_files = [self.bucket + '/text1.txt',
                          self.bucket + '/another_directory/text2.txt']
         self.output = StringIO()
-        self.saved_stdout = sys.stdout
-        sys.stdout = self.output
+        self.saved_stderr = sys.stderr
+        sys.stderr = self.output
 
     def tearDown(self):
         self.output.close()
-        sys.stdout = self.saved_stdout
+        sys.stderr = self.saved_stderr
         clean_loc_files(self.loc_files)
         s3_cleanup(self.bucket, self.session)
 
@@ -215,7 +215,7 @@ def setUp(self):
         self.session = botocore.session.get_session(EnvironmentVariables)
         self.service = self.session.get_service('s3')
         self.endpoint = self.service.get_endpoint('us-east-1')
-        params = {'region': 'us-east-1', 'acl': ['private']}
+        params = {'region': 'us-east-1', 'acl': ['private'], 'quiet': True}
         self.s3_handler = S3Handler(self.session, params)
         self.bucket = make_s3_files(self.session, key1=u'\u2713')
         self.bucket2 = create_bucket(self.session)

tests/unit/customizations/s3/test_executor.py

@@ -90,12 +90,20 @@ def __call__(self):
             executor.wait_until_shutdown()
             self.assertEqual(open(f.name, 'rb').read(), b'foobar')
 
+
 class TestPrintThread(unittest.TestCase):
+    def test_print_error(self):
+        result_queue = queue.Queue()
+        print_task = PrintTask(message="Fail File.", error=True)
+        thread = PrintThread(result_queue, False)
+        with mock.patch('sys.stderr', new=six.StringIO()) as mock_stderr:
+            thread._process_print_task(print_task)
+            self.assertIn("Fail File.", mock_stderr.getvalue())
+
     def test_print_warning(self):
         result_queue = queue.Queue()
         print_task = PrintTask(message="Bad File.", warning=True)
         thread = PrintThread(result_queue, False)
-        with mock.patch('sys.stdout', new=six.StringIO()) as mock_stdout:
+        with mock.patch('sys.stderr', new=six.StringIO()) as mock_stderr:
             thread._process_print_task(print_task)
-            self.assertIn("Bad File.", mock_stdout.getvalue())
-
+            self.assertIn("Bad File.", mock_stderr.getvalue())

tests/unit/customizations/s3/test_s3handler.py

@@ -140,7 +140,7 @@ def setUp(self):
         self.session = FakeSession()
         self.service = self.session.get_service('s3')
         self.endpoint = self.service.get_endpoint('us-east-1')
-        params = {'region': 'us-east-1', 'acl': ['private']}
+        params = {'region': 'us-east-1', 'acl': ['private'], 'quiet': True}
         self.s3_handler = S3Handler(self.session, params)
         self.s3_handler_multi = S3Handler(self.session, multi_threshold=10,
                                           chunksize=2,
@@ -275,7 +275,7 @@ def setUp(self):
         self.session = FakeSession(True, True)
         self.service = self.session.get_service('s3')
         self.endpoint = self.service.get_endpoint('us-east-1')
-        params = {'region': 'us-east-1'}
+        params = {'region': 'us-east-1', 'quiet': True}
         self.s3_handler_multi = S3Handler(self.session, params,
                                           multi_threshold=10, chunksize=2)
         self.bucket = create_bucket(self.session)

tests/unit/customizations/s3/test_subcommands.py

@@ -114,12 +114,17 @@ def setUp(self):
         self.bucket = make_s3_files(self.session)
         self.loc_files = make_loc_files()
         self.output = StringIO()
+        self.err_output = StringIO()
         self.saved_stdout = sys.stdout
+        self.saved_stderr = sys.stderr
         sys.stdout = self.output
+        sys.stderr = self.err_output
 
     def tearDown(self):
         self.output.close()
+        self.err_output.close()
         sys.stdout = self.saved_stdout
+        sys.stderr = self.saved_stderr
 
         super(CommandArchitectureTest, self).tearDown()
         clean_loc_files(self.loc_files)
@@ -222,7 +227,7 @@ def test_error_on_same_line_as_status(self):
         output_str = (
             "upload failed: %s to %s Error: Bucket does not exist\n" % (
                 rel_local_file, s3_file))
-        self.assertIn(output_str, self.output.getvalue())
+        self.assertIn(output_str, self.err_output.getvalue())
 
     def test_run_cp_get(self):
         # This ensures that the architecture sets up correctly for a ``cp`` get
@@ -362,7 +367,7 @@ def test_run_rb_nonzero_rc(self):
         cmd_arc.create_instructions()
         rc = cmd_arc.run()
         output_str = "remove_bucket failed: %s" % s3_prefix
-        self.assertIn(output_str, self.output.getvalue())
+        self.assertIn(output_str, self.err_output.getvalue())
         self.assertEqual(rc, 1)