#git checkout 9332ca9 /usr/local/Library/Formula/erlang.rb
#brew install erlang
git checkout [-p|--patch]  [--] …When or --patch are given, git checkout does not switch branches. It updates the named paths in the working tree from the index file or from a named (most often a commit). In this case, the -b and --track options are meaningless and giving either of them results in an error. The argument can be used to specify a specific tree-ish (i.e. commit, tag or tree) to update the index for the given paths before updating the working tree.