Check for the existence of git before running commands

gclient_scm.py

 # Copyright (c) 2009 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Gclient-specific SCM-specific operations."""
 
 import logging
 import os
 import posixpath
 import re
@@ skipping 268 matching lines @@
     # TODO(maruel): Merge with Capture?
     if cwd is None:
         cwd = self.checkout_path
     stdout=None
     if redirect_stdout:
       stdout=subprocess.PIPE
     if cwd == None:
       cwd = self.checkout_path
     cmd = [self.COMMAND]
     cmd.extend(args)
-    sp = subprocess.Popen(cmd, cwd=cwd, stdout=stdout)
-    output = sp.communicate()[0]
+    logging.debug(cmd)
+    try:
+      sp = subprocess.Popen(cmd, cwd=cwd, stdout=stdout)
+      output = sp.communicate()[0]
+    except OSError:
+      raise gclient_utils.Error("git command '%s' failed to run." %
+              ' '.join(cmd) + "\nCheck that you have git installed.")
     if checkrc and sp.returncode:
       raise gclient_utils.Error('git command %s returned %d' %
                                 (args[0], sp.returncode))
     if output is not None:
       return output.strip()
 
 
 class SVNWrapper(SCMWrapper, scm.SVN):
   """ Wrapper for SVN """
 
@@ skipping 215 matching lines @@
     command = ['status']
     command.extend(args)
     if not os.path.isdir(path):
       # svn status won't work if the directory doesn't exist.
       print("\n________ couldn't run \'%s\' in \'%s\':\nThe directory "
             "does not exist."
             % (' '.join(command), path))
       # There's no file list to retrieve.
     else:
       self.RunAndGetFileList(options, command, path, file_list)