Add git-submodule command

This command can be used to initialize, update and inspect submodules. It
uses a .gitmodules file, readable by git-config, in the top level directory
of the 'superproject' to specify a mapping between submodule paths and
repository url.

Example .gitmodules layout:

[module "git"]
	url = git://git.kernel.org/pub/scm/git/git.git

With this entry in .gitmodules (and a commit reference in the index entry for
the path "git"), the command 'git submodule init' will clone the repository
at kernel.org into the directory "git".

Known issues
============
There is currently no way to override the url found in the .gitmodules file,
except by manually creating the subproject repository. The place to fix this
in the script has a rather long comment about a possible plan.

Funny paths will be quoted in the output from git-ls-files, but git-submodule
does not attempt to unquote (or even detect the presence of) such paths.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>
Signed-off-by: Junio C Hamano <junkio@cox.net>

2 files changed, 66 insertions, 0 deletions

diff --git a/Documentation/cmd-list.perl b/Documentation/cmd-list.perl
index 443802a9a3..51dc6b4105 100755
--- a/Documentation/cmd-list.perl
+++ b/Documentation/cmd-list.perl
@@ -180,6 +180,7 @@ git-ssh-fetch                           synchingrepositories
 git-ssh-upload                          synchingrepositories
 git-status                              mainporcelain
 git-stripspace                          purehelpers
+git-submodule                           mainporcelain
 git-svn                                 foreignscminterface
 git-svnimport                           foreignscminterface
 git-symbolic-ref                        plumbingmanipulators
diff --git a/Documentation/git-submodule.txt b/Documentation/git-submodule.txt
new file mode 100644
index 0000000000..cb0424f77b
--- /dev/null
+++ b/Documentation/git-submodule.txt
@@ -0,0 +1,65 @@
+git-submodule(1)
+================
+
+NAME
+----
+git-submodule - Initialize, update or inspect submodules
+
+
+SYNOPSIS
+--------
+'git-submodule' [--quiet] [--cached] [status|init|update] [--] [<path>...]
+
+
+COMMANDS
+--------
+status::
+	Show the status of the submodules. This will print the SHA-1 of the
+	currently checked out commit for each submodule, along with the
+	submodule path and the output of gitlink:git-describe[1] for the
+	SHA-1. Each SHA-1 will be prefixed with `-` if the submodule is not
+	initialized and `+` if the currently checked out submodule commit
+	does not match the SHA-1 found in the index of the containing
+	repository. This command is the default command for git-submodule.
+
+init::
+	Initialize the submodules, i.e. clone the git repositories specified
+	in the .gitmodules file and checkout the submodule commits specified
+	in the index of the containing repository. This will make the
+	submodules HEAD be detached.
+
+update::
+	Update the initialized submodules, i.e. checkout the submodule commits
+	specified in the index of the containing repository. This will make
+	the submodules HEAD be detached.
+
+
+OPTIONS
+-------
+-q, --quiet::
+	Only print error messages.
+
+--cached::
+	Display the SHA-1 stored in the index, not the SHA-1 of the currently
+	checked out submodule commit. This option is only valid for the
+	status command.
+
+<path>::
+	Path to submodule(s). When specified this will restrict the command
+	to only operate on the submodules found at the specified paths.
+
+FILES
+-----
+When cloning submodules, a .gitmodules file in the top-level directory
+of the containing repository is used to find the url of each submodule.
+This file should be formatted in the same way as $GIR_DIR/config. The key
+to each submodule url is "module.$path.url".
+
+
+AUTHOR
+------
+Written by Lars Hjemli <hjemli@gmail.com>
+
+GIT
+---
+Part of the gitlink:git[7] suite