-C <path>
Run as if git was started in <path> instead of the current working directory.
When multiple -C options are given, each subsequent non-absolute -C <path> is interpreted relative to the preceding -C <path>.
This option affects options that expect path name like --git-dir and --work-tree in that their interpretations of the path names would be made relative to the working directory caused by the -Coption.
For example the following invocations are equivalent:
git --git-dir=a.git --work-tree=b -C c status git --git-dir=c/a.git --work-tree=c/b status
原文：http://www.cnblogs.com/chucklu/p/5837692.html