git-submodule: work with GIT_DIR/GIT_WORK_TREE

The combination of GIT_DIR and GIT_WORK_TREE can be used to manage files in one directory hierarchy while keeping the repository that keeps track of them outside the directory hierarchy. For example: git init --bare /path/to/there alias dotfiles="GIT_DIR=/path/to/there GIT_WORK_TREE=/path/to/here git" cd /path/to/here dotfiles add file dotfiles commit -a -m "add /path/to/here/file" ... lets you manage files under /path/to/here/ in the repository located at /path/to/there. git-submodule however fails to add submodules, as it is confused by GIT_DIR and GIT_WORK_TREE environment variables when it tries to work in the submodule, like so: dotfiles submodule add http://path.to/submodule fatal: working tree '/path/to/here' already exists. Simply unsetting the environment where the command works on the submodule is sufficient to fix this, as it has set things up so that GIT_DIR and GIT_WORK_TREE do not even have to point at the repository and the working tree of the submodule. Signed-off-by: Daniel Graña <dangra@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>