Script to extract submodules from git repositories. Depends on --split-submodule filter.

git-extract-submodule

#!/bin/bash
# Extract subdirectory into a submodule.

if [ -z "$1" ]; then
    echo "Usage: extract-submodule subdirectory"
    echo "No trailing slash"
    echo "Should be run from the root directory of repository"
    echo "Everything should be clean prior to running this script"
    echo "You need to manually copy submodule somewhere and update .gitmodules file appropriately"
    exit 1;
fi
path="$1"

set -ex
git filter-branch --split-submodule "$path" --tag-name-filter cat -- --branches --tags
git clone . "$path"
pushd .
cd "$path"
set +e
rm -Rf .git/refs/original
set +x
for i in `git show-ref | cut -b 42-`; do
    set -x
    git update-ref -m 'submodule conversion' $i $i:$path || git update-ref -d $i
    set +x
done
set -x
git reset --hard
popd
cat >> .gitmodules <<EOF

[submodule "$path"]
    path = $path
    url = please://fix/me/
EOF
set +x
echo "You should probably do 'git submodule update --init' now"

The --split-submodule patch for git is mirrored at http://vi-server.org/vi/bin/git-extract-submodule.patch

The script itself is mirrored at http://vi-server.org/vi/bin/git-extract-submodule