Add identity meta hook

pre_commit/meta_hooks/identity.py

@@ -0,0 +1,13 @@
+import sys
+
+from pre_commit import output
+
+
+def main(argv=None):
+    argv = argv if argv is not None else sys.argv[1:]
+    for arg in argv:
+        output.write_line(arg)
+
+
+if __name__ == '__main__':
+    exit(main())

pre_commit/repository.py

@@ -237,6 +237,7 @@ class MetaRepository(LocalRepository):
         # The hooks are imported here to prevent circular imports.
         from pre_commit.meta_hooks import check_hooks_apply
         from pre_commit.meta_hooks import check_useless_excludes
+        from pre_commit.meta_hooks import identity
 
         def _make_entry(mod):
             """the hook `entry` is passed through `shlex.split()` by the
@@ -260,6 +261,13 @@ class MetaRepository(LocalRepository):
                 'language': 'system',
                 'entry': _make_entry(check_useless_excludes),
             },
+            {
+                'id': 'identity',
+                'name': 'identity',
+                'language': 'system',
+                'verbose': True,
+                'entry': _make_entry(identity),
+            },
         ]
 
         return {

tests/meta_hooks/identity_test.py

@@ -0,0 +1,6 @@
+from pre_commit.meta_hooks import identity
+
+
+def test_identity(cap_out):
+    assert not identity.main(('a', 'b', 'c'))
+    assert cap_out.get() == 'a\nb\nc\n'