A script to transform a linear flow in a git repository (all in master) in a flow named "git-flow" (http://nvie.com/posts/a-successful-git-branching-model/) with a master branch, a develop one, and one for each feature, hotfixe and release.

linear-git-to-git-flow.sh

#!/bin/bash

# Explanations : http://bit.ly/gs2qpL

# give optionnaly a revision from where to start
# if not given initial_ref will be the first ref available
initial_ref='757794e524755d2eebc6d881fea026c308a11fd5'

# declare below all the steps whith this format : 
# 'version type name ref' \
#  - version is the tag which will be applied on the future master branch. Can be "-" to no tag it Iit when will be just merged in the develop branch without release and merge to master)
#  - type is the type of branch to create. Can be "feature" or "hotfix".
#  - name is the name of the branch (full name for a feature, but will be prefixed by "hotfix-" in other case)
#    (if no name is provided, the version will be used, usefull for a hotfix)
#  - ref if the ref in the current master branch from which the new branch will start
# dont forget to add a space before the slash at the end of each line, and do not add any space or quote in each parameter

declare -a all_steps=(\
'1.0.1    feature   better-1.0-usability             24be26a54b6a116d5c4843b23e37944ff11a51ea' \
'1.0.2    feature   first-full-rewrite-1.0           a3179cc084536194fcd86297f5134a86c74958c4' \
'1.0.3    feature   base-debug-engine                2c20dbf610eb0536c4f08b948ed441aab19188cf' \
'1.0.4    feature   webkit-long-press-bug            64e7492ebe21513033c37175ec9de917092f3fc6' \
'1.0.5    feature   unicode-categories               6056a7efbadc59718d784cc38a47086eb4e4af28' \
'1.0.6    feature   quick-context-access             a88fdf2f1ecf91a6b2ebd1f7fc65dd9adbd7bf82' \
'1.0.7    feature   simple-gestures                  7581e38bbab36f4bb61f0030820c36f43278fab6' \
'1.0.7-2  hotfix    -                                2fdf164768eafa65a2256534ebc1cb87ad663628' \
'1.0.8    feature   quick-itemview-context-access    74f0d41a8e18c3d8cf42f29bbc0bc9b3118cc68e' \
) # all_steps

# change this to "no" if you don't want branches (features, releases and hotfixes) to be pushed to remote
sync_branches_remotely="no"
# change this to "yes" if you want branches (features, releases and hotfixes) to be deleted after being merged
delete_branches="yes"
# change this to "no" if you don't want the old "master" branch be deleted (will be renamed as "legacy")
delete_old_master="yes"

# you can change some git names here
origin=origin
master=master
newmaster=newmaster
develop=develop
base_release=release-
base_hotfix=hotfix-

########## you should not change anything below this line ##########

# some usefull functions

# return the date of the merge (penultimate one : the one before the merge to have the date of the original last commit)
function git-merge-date {
  echo `git log | grep 'Date:' | head -n 2 | tail -n 1 | sed 's/Date:\s\+//'`
} # git-merge-date

# return the last ref (used to get the one of the last commit)
# if a parameter is given, it's a branch used to restric the list of refs
function git-last-ref {
  local branch="$1"
  echo `git log $branch | grep '^commit' | head -n 1 | sed 's/commit\s\+//'`
} # git-last-ref

# get the current branch
function git-current-branch {
  echo `git branch | grep '^*' | sed 's/^*\s\+//'`
} # git-current-branch

# change the date of a commit
# https://git.wiki.kernel.org/index.php/GitFaq#How_can_I_tweak_the_date_of_a_commit_in_the_repo.3F
# take 2 parameters :
#  - the ref of the commit
#  - the new date (you can use git-rev-date to see the format)
function git-update-commit-date {
  local commit="$1"
  local date="$2"
  if [ "$date" ]
  then
    git filter-branch --env-filter \
      "if test \$GIT_COMMIT = '$commit'
      then
	  export GIT_AUTHOR_DATE
	  export GIT_COMMITTER_DATE
	  GIT_AUTHOR_DATE='$date'
	  GIT_COMMITTER_DATE='$date'
      fi" &&
    rm -fr "$(git rev-parse --git-dir)/refs/original/"
  fi # date
} # git-update-commit-date

# cherry pick a commit and change the date of the new commit to be the same
# you can also pass a branch to get the date (else the current will be used)
function git-cherry-pick-and-date {
  local commit="$1"
  local branch="$2"
  local date=`git log $branch --pretty=format:'%H %cD' | grep "^$commit" | sed "s/^$commit //"`
  git cherry-pick $commit
  last_error=$?
  if [ "$last_error" == 0 ]
  then
    local last_ref=`git-last-ref`
    git-update-commit-date $last_ref "$date"
  fi # error
}

# merge with a branch given as parameter, and set the merge date to the last commit merged
function git-merge {
  local branch="$1"
  local current=`git-current-branch`
  if [ "$current" == "$newmaster" ]
  then
    current=$master
  fi # newmaster
  git merge --no-ff -m "Merge branch '$branch' into '$current'" $branch
  local last_ref=`git-last-ref`
  local merge_date=`git-merge-date`
  git-update-commit-date $last_ref "$merge_date"
}

# create a branch from a starting ref, and optionnaly sync it remotely
# with the help of http://djwonk.com/blog/2009/04/18/tracking-remote-git-branches/
# take 3 parameters :
#  - the branch name
#  - the ref to use as a starting point
#  - "yes" if you want the branch to be sync remotely
# The branch will be the current one after being created
function git-create-branch {
  local branch="$1"
  local start_ref="$2"
  local sync_branch_remotely="$3"
  git checkout -b $branch $start_ref
  if [ "$sync_branch_remotely" == "yes" ]
  then
    git push $origin $branch
    git checkout $master
    git branch -f $branch $origin/$branch
    git checkout $branch
  fi # sync_branch_remotely
}

# start here
echo "==========> START"
git checkout $master
last_error=0

# find existing branches
old_branches=`git branch | grep -v '^*'`

# check initial ref
if [ -z "$initial_ref" ]
then
  initial_ref=`git log | grep ^commit | tail -n 1 | sed 's/commit\s\+//'`
fi # initial_ref

# some configuration
git config branch.autosetupmerge true

# prepare main branches

git-create-branch "$develop" "$initial_ref" "yes"
git-create-branch "$newmaster" "$initial_ref" "yes"

# prepare initial vars
last_develop_ref=$initial_ref
last_master_ref=$initial_ref
prev_ref=$initial_ref

# loop on each step
for i_step in `seq 0 \`expr ${#all_steps[@]} - 1\``
do

  # split fields for this step
  declare -a step=(${all_steps[$i_step]})
  version=${step[0]}
  mode=${step[1]}
  name=${step[2]}
  ref=${step[3]}

  # new branch name
  branch=$name
  source=$develop

  if [ "$mode" == "hotfix" ]
  then
    source=$newmaster
    if [ "$name" == "-" ]
    then
      if [ "$version" == "-" ]
      then
	branch="$base_hotfix$i_step"
      else # version -
	branch="$base_hotfix$version"
      fi # version -
    else # name -
      branch="$base_hotfix$name"
    fi # name -
  fi # hotfix

  echo "==========> Step $i_step: version=$version, mode=$mode, name=$name, ref=$ref => branch $branch"

  # create branch
  git-create-branch "$branch" "$source" "$sync_branches_remotely"

  # cherry pick commits from master 
  for commit in `git rev-list --reverse $prev_ref..$ref`
  do
    git-cherry-pick-and-date $commit $master
    if [ "$last_error" != 0 ]
    then
      read -p "The Cherry pick resulted in an error. You may want to press CTRL-C to abort (or any other key to let the script continue)"
      last_error=0
    fi # last_error
  done # for commit 

  # if hotfix, merge into master
  if [ "$mode" == "hotfix" ]
  then
    if [ "$sync_branches_remotely" == "yes" ]
    then
      git push $origin $branch
    fi # sync_branches_remotely
  fi # hotfix

  # always merge into develop
  git checkout $develop
  git-merge $branch
  git push $origin $develop

  # create a release
  if [ "$version" != "-" ]
  then
    # create the branch
    release_branch="$base_release$version"
    git-create-branch "$release_branch" "$develop" "$sync_branches_remotely"
    if [ "$sync_branches_remotely" == "yes" ]
    then
      git push $origin $release_branch
    fi # sync_branches_remotely

    # merge into master
    git checkout $newmaster
    git-merge $release_branch
    git push $origin $newmaster

    # merge into develop
    git checkout $develop
    git-merge $release_branch
    git push $origin $develop

    # then tag the release
    git tag -a -m "version $version" "$version"
    git push --tags

    # delete the release branch
    if [ "$delete_branches" == "yes" ]
    then
      git branch -d "$release_branch"
    fi # delete_branches

  fi # version

  # delete branch
  if [ "$delete_branches" == "yes" ]
  then
    git branch -d "$branch"
  fi # delete_branches

  # and now the save the ref as the prev_ref
  prev_ref="$ref"

done # for i_step

# recreate old branches
for old_branch in $old_branches
do
  echo "==========> Work on branch $old_branch"

  # ask confirmation to see if we continue with this branch
  echo "Do you want to recreate this branch ("$old_branch") ? Type Y/y to validate (any other key else to cancel)"
  REPLY=""
  read -p "> " -n 1
  echo ""
  if [[ $REPLY =~ ^[Yy]$ ]]
  then
  
    git checkout $master

    # temporary branch name
    branch="gf_new_$old_branch"

    # is the old branch remotely synced ?
    sync_branch_remotely=""
    if [ `git branch -r | grep "$origin/$old_branch"` ]
    then
      sync_branch_remotely="yes"
    fi # git branch

    # find the new start_ref
    old_start_ref=`git merge-base $old_branch $master`
    branch_info=`git log $old_branch --pretty=format:'%H %cD %s' | grep "^$old_start_ref" | sed "s/^$old_start_ref//"`
    start_ref=`git log $develop --pretty=format:'%H %cD %s' | grep "$branch_info" | awk '{ print $1 }'`
    
    # create the branch
    git-create-branch "$branch" "$start_ref" "$sync_branch_remotely"
    # apply all commits
    old_last_ref=`git-last-ref $old_branch`
    for commit in `git rev-list --reverse $old_start_ref..$old_last_ref`
    do
      git-cherry-pick-and-date $commit $old_branch
      if [ "$last_error" != 0 ]
      then
	read -p "The Cherry pick resulted in an error. The work on this branch ($old_branch) will stop and the new branch will be deleted (Press any key to continue)"
	echo ""
	last_error=0
	git checkout $develop
	git branch -D $branch
	git push $origin :$branch
	break
      fi # last_error
    done # for commit

    # sync remotely if needed
    if [ $sync_branch_remotely ]
    then
      git push $origin $branch
    fi # sync_branch_remotely

    git checkout $develop

    # delete old branch
    git branch -D $old_branch
    if [ $sync_branch_remotely ]
    then
      git push $origin :$old_branch
    fi # sync_branch_remotely

    # rename new branch
    git branch -m $branch $old_branch
    if [ $sync_branch_remotely ]
    then
      git push $origin :$branch
      git push $origin $old_branch:$old_branch
    fi # sync_branch_remotely

    git checkout $develop
    git push $origin $develop

  fi # REPLY (manage branch)

done # old_branch

# set newmaster the new master branch
# http://limi.co.uk/posts/renaming-master-branch-on-github
echo "==========> Move $newmaster to $master"
read -p "On Github, change the default branch to \"$newmaster\" (go to \"Admin\"). Then press any key to continue"
git checkout $develop
git branch -m $master legacy
git branch -m $newmaster $master
git push $origin :$master
git push $origin $master:refs/heads/$master
git push $origin legacy:refs/heads/legacy
read -p "On Github, change the default branch to \"$master\" (go to \"Admin\"). Then press any key to continue"
git push $origin :$newmaster

# delete the old master branch if wanted
if [ "$delete_old_master" == "yes" ]
then
  git branch -D legacy
  git push $origin :legacy
fi # $delete_old_master

echo "
==========> DONE !"