Git post-merge hook to delete merged branch

post-merge.sh

#!/bin/bash

# Based on: https://github.com/brianstorti/git-hooks/blob/master/hooks/post-merge

exec < /dev/tty

# Merge can go three ways:
# * F: fast forward: no commit is created, only a ref is changed
# * A: automatic: true merge (non-ff) without conflicts. A new commit is created
# * C: merge with conflicts: no commit is created but the index is prepared (partially)
#      for a merge commit

# How it appears on reflog:
# eccb159 master@{0}: commit (merge): Merge branch 'qa'   -> When there is a conflict (C)
# d021b0e master@{1}: merge qa: Merge made by recursive.  -> Automatic (A)
# e1cde23 master@{2}: merge qa: Fast-forward              -> Fast-forward (F)

# For cases F and A, the "post-merge" hook is called, but for case C, just the
# "post-commit" is called, so we need to do the verification there, too.

###############################################################################
# Warns if you try
#  * to merge the "qa" branch on any other branch
#  * to merge on master a branch that is not yet merged on qa
###############################################################################

branch_name=$(git branch | grep "*" | sed "s/\* //")
reflog_message=$(git reflog -1)
merged_branch_name=$(echo $reflog_message | cut -d" " -f 4 | sed "s/://")

# if the merge was caused by a "git pull", we can safely ignore it
if [[ $reflog_message =~ "pull" ]]; then
    exit 0
fi

if [[ $branch_name == "master" ]]; then
    read -p "Branch successfully merged on master. Do you want to remove it, both locally and remotely? (y/N) " answer
    if [[ "$answer" == "y" ]]; then
        git branch -D $merged_branch_name
        git remote | grep -q origin
        if [[ $? == 0 ]]; then
            git push origin --delete $merged_branch_name
        fi
    fi
fi