This script takes a directory and creates a new commit in the gh-pages branch that represent the state of that directoy. This is used in my own project Roby to generate the documentation using webgen and rdoc, and automatically (and cheaply) update the gh

export_dir_to_gh_pages.sh

PAGES_BRANCH=gh-pages
DOC_DIR=doc/html

set -e

git reset -q HEAD

# Create the tree object
git add -f $DOC_DIR
tree=$(git write-tree --prefix=$DOC_DIR)

# Get the parent commit for the tree. If the branch does not yet exist, create
# it
msg="generated from $(git show-ref HEAD | awk '{print $1}')"
parent=$(git show-ref refs/heads/$PAGES_BRANCH | awk '{ print $1 }')
if test -n "$parent"; then
    # Check that some things changes since last time
    last_tree=$(git cat-file commit $PAGES_BRANCH | grep tree | awk '{print $2}')
    if test "x$last_tree" = "x$tree"; then
        echo "no changes to commit"
    else
        commit=$(echo $msg | git commit-tree $tree -p $parent)
    fi
else
    commit=$(echo $msg | git commit-tree $tree)
fi

if test -n "$commit"; then
    # And finally update the tip of the branch
    echo $commit > .git/refs/heads/$PAGES_BRANCH
fi

git reset -q HEAD