prepare-commit-msg git hook to add branch name to commit message

prepare-commit-msg

#!/bin/sh
#
# An example hook script to prepare the commit log message.
# Called by "git commit" with the name of the file that has the
# commit message, followed by the description of the commit
# message's source.  The hook's purpose is to edit the commit
# message file.  If the hook fails with a non-zero status,
# the commit is aborted.
#
# To enable this hook, rename this file to "prepare-commit-msg".

### http://hugogiraudel.com/2014/03/17/git-tips-and-tricks-part-2/
COMMIT_MSG=$1
COMMIT_MODE=$2

# This way you can customize which branches should be skipped when
# prepending commit message. 
# http://blog.bartoszmajsak.com/blog/2012/11/07/lazy-developers-toolbox-number-1-prepend-git-commit-messages/
if [ -z "$BRANCHES_TO_SKIP" ]; then
  BRANCHES_TO_SKIP=(master develop temp test)
fi

#BRANCH_NAME=$(git branch | grep '*' | sed 's/* //')
# Converts '_' to '/'. By sample: 'feature/Users_Mail' to 'feature/Users/Mail'
BRANCH_NAME=$(git branch | grep '*' | sed 's/* //' | tr '_' '/')

BRANCH_EXCLUDED=$(printf "%s\n" "${BRANCHES_TO_SKIP[@]}" | grep -c "^$BRANCH_NAME$")
BRANCH_IN_MESSAGE=$(grep -c "\[$BRANCH_NAME\]" $1)
BRACKETS_IN_MESSAGE=$(grep -c "\[.*\]" $1)
REBASING=$(echo $BRANCH_NAME | grep 'rebasing')

# $2 is the commit mode
# if $2 == 'commit'  => user used `git commit`
# if $2 == 'message' => user used `git commit -m '...'`

if [ -n "$BRANCH_NAME" ] && ! [[ $BRANCH_EXCLUDED -eq 1 ]] && ! [[ $BRANCH_IN_MESSAGE -ge 1 ]] && [ -z "$REBASING" ] && ! [[ $BRACKETS_IN_MESSAGE -ge 1 ]] ; then 

	# We check the fist line of the commit message file.
	# If it's an empty string then user didn't use `git commit --amend` so we can fill the commit msg file
    firstline=`head -n1 $COMMIT_MSG`

	if [ "$COMMIT_MODE" = "message" ] || [ -z "$firstline" ] ; then
		sed -i.bak -e "1s:^:[$BRANCH_NAME] :" $COMMIT_MSG
	fi

else

	if [ -z "$BRANCH_NAME" ]; then
		echo 'prepare-commit-msg: Empty branch name'
	fi

	if [ -n "$REBASING" ]; then
		echo 'prepare-commit-msg: Rebasing'
	fi

	if [[ $BRANCH_EXCLUDED -eq 1 ]]; then
		echo 'prepare-commit-msg: Branch excluded from commit message'
	fi

	if [[ $BRANCH_IN_MESSAGE -ge 1 ]]; then
		echo 'prepare-commit-msg: Branch already on commit message'
	fi
fi

if [ -z "$REBASING" ]; then
	# Add one blank line in second line if not exists
	firstline=`head -n1 $COMMIT_MSG`
	secondline=`head -n2 $COMMIT_MSG | tail -1`
	if [ -n "$firstline" ] && [ -n "$secondline" ] && ! [ "$firstline" == "$secondline" ]; then
		echo adding new line
		sed -i '1 a\\' $COMMIT_MSG
	fi
fi

Not use: BRANCH_NAME=$(git rev-parse --abbrev-ref HEAD) because returns 'Head' during a rebase and will add [head] to your new edited rebased commits.

On sed -i.bak -e "1s:^:[$BRANCH_NAME] :" $1 i'm using : as separator because some branch names can have / characters. You can replace : by another character.

Add check to do not modify message if have BRACKETS_IN_MESSAGE
Add Converts '_' to '/' in BRANCH_NAME. By sample: 'feature/Users_Mail' to 'feature/Users/Mail'