Split a subtree of a git repository into a separate repo.

git-split-subpath.bash

#########################################################
#
# classes is a git repository with many class projects
# I want to split one of those projects into its own repo
# and I want preserve the commit history
#
# The super top-level repo is classes.git
# Within classes.git is a sub-directory "networks/project2" 
# we want to create a new repository with just the history of 
# "networks/project2"
#
#########################################################

# the subtree 
SUBDIR = "networks/project2"

# the top level git repository
SUPER_REPO = "~/projects/classes.git"

# new project name
NEW_REPO = "project2.git"

# first clone the super class repo, because we will be removing all other commits
# that are not related to subtree 
git clone $SUPER_REPO $NEW_REPO

# cd into new repository clone
cd $NEW_REPO

# now filter-branch and remove all history unrelated to networks/project2 
git filter-branch --prune-empty --subdirectory-filter $SUBDIR master

# now all that remains is commit history of sub-directory