Add PrefixedCommandRunner

pre_commit/prefixed_command_runner.py

@@ -0,0 +1,42 @@
+
+import os
+import os.path
+import subprocess
+
+
+def _replace_cmd(cmd, **kwargs):
+    return [part.format(**kwargs) for part in cmd]
+
+
+class PrefixedCommandRunner(object):
+    """A PrefixedCommandRunner allows you to run subprocess commands with
+    comand substitution.
+
+    For instance:
+        PrefixedCommandRunner('/tmp/foo').run(['{prefix}foo.sh', 'bar', 'baz'])
+
+    will run ['/tmpl/foo/foo.sh', 'bar', 'baz']
+    """
+    def __init__(self, prefix_dir, popen=subprocess.Popen):
+        self.prefix_dir = prefix_dir.rstrip(os.sep) + os.sep
+        self.__popen = popen
+
+    def run(self, cmd, stdin=None):
+        replaced_cmd = _replace_cmd(cmd, prefix=self.prefix_dir)
+        proc = self.__popen(
+            replaced_cmd,
+            stdin=subprocess.PIPE,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+        stdout, stderr = proc.communicate(stdin)
+
+        return proc.returncode, stdout, stderr
+
+    @classmethod
+    def from_command_runner(cls, command_runner, prefix_postfix):
+        """Constructs a new command runner from an existing one by appending
+        `prefix_postfix` to the command runner's prefix directory.
+        """
+        new_prefix = os.path.join(command_runner.prefix_dir, prefix_postfix)
+        return cls(new_prefix, popen=command_runner.__popen)