The contribute/git-new-workdir script from the git source. Super useful GitHub pages workflow.

git-new-workdir.sh

#!/bin/sh

usage () {
    echo "usage:" $@
    exit 127
}

die () {
    echo $@
    exit 128
}

failed () {
    die "unable to create new workdir '$new_workdir'!"
}

if test $# -lt 2 || test $# -gt 3
then
    usage "$0 <repository> <new_workdir> [<branch>]"
fi

orig_git=$1
new_workdir=$2
branch=$3

# want to make sure that what is pointed to has a .git directory ...
git_dir=$(cd "$orig_git" 2>/dev/null &&
  git rev-parse --git-dir 2>/dev/null) ||
  die "Not a git repository: \"$orig_git\""

case "$git_dir" in
.git)
    git_dir="$orig_git/.git"
    ;;
.)
    git_dir=$orig_git
    ;;
esac

# don't link to a configured bare repository
isbare=$(git --git-dir="$git_dir" config --bool --get core.bare)
if test ztrue = "z$isbare"
then
    die "\"$git_dir\" has core.bare set to true," \
        " remove from \"$git_dir/config\" to use $0"
fi

# don't link to a workdir
if test -h "$git_dir/config"
then
    die "\"$orig_git\" is a working directory only, please specify" \
        "a complete repository."
fi

# make sure the links in the workdir have full paths to the original repo
git_dir=$(cd "$git_dir" && pwd) || exit 1

# don't recreate a workdir over an existing directory, unless it's empty
if test -d "$new_workdir"
then
    if test $(ls -a1 "$new_workdir/." | wc -l) -ne 2
    then
        die "destination directory '$new_workdir' is not empty."
    fi
    cleandir="$new_workdir/.git"
else
    cleandir="$new_workdir"
fi

mkdir -p "$new_workdir/.git" || failed
cleandir=$(cd "$cleandir" && pwd) || failed

cleanup () {
    rm -rf "$cleandir"
}
siglist="0 1 2 15"
trap cleanup $siglist

# create the links to the original repo.  explicitly exclude index, HEAD and
# logs/HEAD from the list since they are purely related to the current working
# directory, and should not be shared.
for x in config refs logs/refs objects info hooks packed-refs remotes rr-cache svn
do
    # create a containing directory if needed
    case $x in
    */*)
        mkdir -p "$new_workdir/.git/${x%/*}"
        ;;
    esac

    ln -s "$git_dir/$x" "$new_workdir/.git/$x" || failed
done

# commands below this are run in the context of the new workdir
cd "$new_workdir" || failed

# copy the HEAD from the original repository as a default branch
cp "$git_dir/HEAD" .git/HEAD || failed

# the workdir is set up.  if the checkout fails, the user can fix it.
trap - $siglist

# checkout the branch (either the same as HEAD from the original repository,
# or the one that was asked for)
git checkout -f $branch