Clean up how the environments work.

pre_commit/languages/helpers.py

@@ -1,6 +1,37 @@
 
+from plumbum import local
+
+
 def run_hook(env, hook, file_args):
     return env.run(
         ' '.join([hook['entry']] + hook.get('args', []) + list(file_args)),
         retcode=None,
-    )
+    )
+    return env.run(
+        ' '.join(['xargs |', hook['entry']] + hook.get('args', [])),
+        retcode=None,
+        stdin='\n'.join(file_args) + '\n',
+    )
+
+
+class Environment(object):
+    @property
+    def env_prefix(self):
+        """env_prefix is a value that is prefixed to the command that is run.
+
+        Usually this is to source a virtualenv, etc.
+
+        Commands basically end up looking like:
+
+        bash -c '{env_prefix} {cmd}'
+
+        so you'll often want to end your prefix with &&
+        """
+        raise NotImplementedError
+
+    def run(self, cmd, **kwargs):
+        """Returns (returncode, stdout, stderr)."""
+        return local['bash'][
+            '-c',
+            ' '.join([self.env_prefix, cmd])
+        ].run(**kwargs)