git-merge-repo

#!/bin/sh
# merge one repo with another
# http://www.kernel.org/pub/software/scm/git/docs/howto/using-merge-subtree.html

# Check arguments
if [ $# -ne 2 ]; then
    echo 1>&2 Usage: 
	echo 1>&2 "  cd bigrepo"
	echo 1>&2 "  $0 repo /path/to/repo"
    exit 127
fi

REPO=$1
DIR=$2

git remote add -f $REPO $DIR
git merge -s ours --no-commit $REPO/master
git read-tree --prefix=$REPO/ -u $REPO/master
git commit -m "Merge $REPO as our subdirectory"

git pull -s subtree $REPO master