Git script to save a snapshot of the current worktree

snapshot.sh

#!/bin/bash

if [ ! -z $1 ]; then
    export GIT_DIR=$1
fi

git rev-parse -q --verify HEAD >/dev/null;

if [ $? -ne 0 ]; then
    exit
fi

# Set the index to a temp file to previous changing the current index.
export GIT_INDEX_FILE=$(mktemp)
# Delete the temp file as git except it to not exist.
rm -f $GIT_INDEX_FILE
# Delete temp file on exit.
trap "rm -f $GIT_INDEX_FILE" 0 1 2 3 15

branch=$(git branch --show-current)
head=$(git rev-parse --short HEAD)
snapshotTag="refs/snapshot/$head"

if ! git rev-parse -q --verify "$snapshotTag" >/dev/null; then
    # No previous snapshot exist, using the head as previous snapshot.
    git update-ref $snapshotTag HEAD
fi

snapshot=$(git rev-parse $snapshotTag)

# Add all changes to the index and build a tree of the index.
git add -A
workdir=`git write-tree 2>/dev/null`

if [ $(git rev-parse $snapshotTag^{tree}) == $workdir ]; then
    echo "'$snapshotTag' is already up to date."
    exit
fi

# Commit with the previous snapshot as parent.
commit=$(git commit-tree -m "Snapshot of $branch" -p $snapshot $workdir 2>/dev/null)

if [ $? -ne 0 ]; then
    echo "Error creating commit."
    exit
fi

# Update references to the new commit.
git update-ref $snapshotTag $commit
echo "'$snapshotTag' updated."
git update-ref refs/heads/snapshot/$branch $commit
echo "'refs/heads/snapshot/$branch' updated."