Add option to run from alternate config file

pre_commit/main.py

@@ -34,6 +34,10 @@ def _add_color_option(parser):
     )
 
 
+def _add_config_option(parser):
+    parser.add_argument('-c', '--config', help='Path to alternate config file')
+
+
 def main(argv=None):
     argv = argv if argv is not None else sys.argv[1:]
     argv = [five.to_text(arg) for arg in argv]
@@ -89,6 +93,7 @@ def main(argv=None):
         help="Auto-update pre-commit config to the latest repos' versions.",
     )
     _add_color_option(autoupdate_parser)
+    _add_config_option(autoupdate_parser)
 
     run_parser = subparsers.add_parser('run', help='Run hooks.')
     _add_color_option(run_parser)
@@ -119,6 +124,7 @@ def main(argv=None):
         '--hook-stage', choices=('commit', 'push'), default='commit',
         help='The stage during which the hook is fired e.g. commit or push.',
     )
+    _add_config_option(run_parser)
     run_mutex_group = run_parser.add_mutually_exclusive_group(required=False)
     run_mutex_group.add_argument(
         '--all-files', '-a', action='store_true', default=False,
@@ -152,7 +158,10 @@ def main(argv=None):
 
     with error_handler():
         add_logging_handler(args.color)
-        runner = Runner.create()
+        runner_kwargs = {}
+        if hasattr(args, 'config_file'):
+            runner_kwargs['config_file'] = args.config_file
+        runner = Runner.create(**runner_kwargs)
         git.check_for_cygwin_mismatch()
 
         if args.command == 'install':

pre_commit/runner.py

@@ -16,18 +16,19 @@ class Runner(object):
     repository under test.
     """
 
-    def __init__(self, git_root):
+    def __init__(self, git_root, config_file=None):
         self.git_root = git_root
+        self.config_file = config_file or C.CONFIG_FILE
 
     @classmethod
-    def create(cls):
+    def create(cls, config_file=None):
         """Creates a PreCommitRunner by doing the following:
             - Finds the root of the current git repository
             - chdir to that directory
         """
         root = git.get_root()
         os.chdir(root)
-        return cls(root)
+        return cls(root, config_file=config_file)
 
     @cached_property
     def git_dir(self):
@@ -35,7 +36,7 @@ class Runner(object):
 
     @cached_property
     def config_file_path(self):
-        return os.path.join(self.git_root, C.CONFIG_FILE)
+        return os.path.join(self.git_root, self.config_file)
 
     @cached_property
     def repositories(self):