If you have several projects in one git tree, perhaps something like:

repo/
    .git/
    proj1/
    proj2/

And you want several individual git repos:

proj1/
    .git/
proj2/
    .git/

Then to take all sub-folders from ~/git/src and create new git repos in ~/git:

set -e
srcrepo=~/git/src
cd git_tmp
git clone $srcrepo ./orig
mkdir new
cd new
for dir in ../orig/*;
do
    dir=$(basename $dir)
    git clone ../orig $dir
    pushd $dir
    git filter-branch --subdirectory-filter $dir HEAD -- --all
    git reset --hard
    git gc --aggressive
    git prune
    popd
    git clone --bare $dir ~/git/$dir
done
rm -rf ~/git_tmp/*