Out of band syncing to a local git branch.

README.md

git-snapshot

Out of band syncing to a local git branch.

This started as an experiment to see how commits could be created without modifying the working directory, the index, or the state of HEAD. The end result is like a cross between rsync and git stash using a specified branch.

Benefits

This allows you to deploy your current working directory:

• without polluting your master branch with build artifacts
• without modifying your current checkout at all:
  • no branch switching
  • no index clobbering
  • no complaining about clobbering unstaged changes

Example

Here's how you would use it to push your current working directory to a git push based hosting provider (like Heroku):

$ git-snapshot production
Creating branch 'production' if it doesn't exist...
Creating index... (this can take a while)
Creating tree from index...
Created tree 1e035b51027ba785c74155025cd616bbd20d8d17
Creating commit...
Created commit f2527eb28622d7a17403f723d36584027e595723
$ git push hosting production:master

References

In order of appearance:

• http://git-scm.com/docs/git-branch
• http://git-scm.com/docs/git-rev-parse
• http://git-scm.com/docs/git-ls-files
• http://git-scm.com/docs/git-hash-object
• http://git-scm.com/docs/git-update-index
• http://git-scm.com/docs/git-write-tree
• http://git-scm.com/docs/git-commit-tree
• http://git-scm.com/docs/git-update-ref

TODO

• Option to create tag instead of branch
• Specify commit message
• Don't do empty commits, it means the branch is already up to date
• Find portable replacement for stat

git-snapshot.sh

#!/usr/bin/env bash

# Fail fast, we're messing with git internals!
#set -x

BRANCH=${1:-deploy}

# Don't interfere with the real index, which means we are immune to "dirty" working copies
TMPDIR=`mktemp -d -t deploy-indexXXXXXX`
export GIT_INDEX_FILE=$TMPDIR/index

# This is where we would want to "Do stuff" like 'npm install --production`

echo "Creating branch '$BRANCH' if it doesn't exist..."
git branch $BRANCH 2> /dev/null || echo "using existing"
PARENT=`git rev-parse refs/heads/$BRANCH`

# Start building our new index
echo "Creating index... (this can take a while)"

# Every file that is tracked or untracked
git ls-files --cached --other | while read f; do
    # Create a new git blob object, writing it to .git/objects
    if test -L "$f"; then
        # Symlinks are hashes of the path pointed to
        OBJ=`readlink "$f" | git hash-object -w --stdin`
    else
        # Everything else is a hash of the file contents
        OBJ=`git hash-object -w "$f"`
    fi
    MODE=`stat -c %a "$f"`

    # Add the object to the index as a file with a name and mode
    git update-index --add --replace --cacheinfo $MODE $OBJ "$f"
done

# At this point we've got a giant index representing the current state of every file under $CWD

echo "Creating tree from index..."
TREE=`git write-tree --missing-ok`
echo "Created tree $TREE"

# Create a new commit object decending from the $BRANCH branch containing out new tree
echo "Creating commit..."
SHA1=`git commit-tree -p $PARENT -m "Deploy snapshot $(date)" $TREE`
echo "Created commit $SHA1"

# We now have a commit, but nothing is pointing to it

# Update our "$BRANCH" branch to point to the new commit, which is a child of the $BRANCH branch head
git update-ref refs/heads/$BRANCH $SHA1

# Clean up after ourselves, or echo the name of our temp file if $DEBUG is set
test -n "$DEBUG" && ls -l $GIT_INDEX_FILE || rm -rf $TMPDIR