Shell script to extract a folder from a git repository to make a new repository with only the history for that folder.

gistfile1.sh

# param 1 is path to root of repository to clone
# param 2 is folder to clone to. The folder's name must be the
# same as the folder to be extracted from the repository at param 1.

GIT='/Applications/Xcode.app/Contents/Developer/usr/bin/git'

$GIT clone --no-hardlinks "$1" "$2"

cd "$2"
$GIT filter-branch --subdirectory-filter "`basename $2`" HEAD #-- --all
# "-- --all" copies along tags and branches

$GIT reset --hard
$GIT gc --aggressive
$GIT prune

$GIT remote rm origin
$GIT update-ref -d refs/original/refs/heads/master
$GIT reflog expire --expire=now --all
$GIT repack -ad