post-checkout Git hook for switching branches

post-checkout

#!/bin/bash

set -e  # Stop execution of script if a command or pipeline has an error
printf '\nExample post-checkout hook\n'

# These are the parameters given to the hook
# https://git-scm.com/docs/githooks.html#_post_checkout
oldHEAD=$1       # ref of the previous (old) HEAD
newHEAD=$2       # ref of the new HEAD 
checkoutType=$3  # checkout type flag: 1 = changing branches, 
                 #                     0 = retrieving a file from the index 

# If checkoutType is 0, exit
if [[ $checkoutType -eq 0 ]]; then
    exit 0
fi

# Since $1 and $2 are the 40-character SHA-1,
# it is not possible to unambiguously determine old- and new branch names
# [[ $checkoutType == 1 ]] && checkoutType='branch' ||  checkoutType='file' ;
# echo 'Checkout type: '$checkoutType
# echo '     old HEAD: '`git name-rev --name-only $oldHEAD`
# echo '     new HEAD: '`git name-rev --name-only $newHEAD`
# https://stackoverflow.com/q/25590267/4859684

# Get branch names from git-reflog
oldBRANCH=`git reflog | awk 'NR==1{ print $6; exit }'`
newBRANCH=`git reflog | awk 'NR==1{ print $8; exit }'`
echo "Old branch: $oldBRANCH"
echo "New branch: $newBRANCH"
echo ""

# If any of the branches is empty, it's rebase
if [ -z "$oldBRANCH" ] || [ -z "$newBRANCH" ]; then
    exit 0
fi

exists_in_list() {
# Function for determine if a word is in a space-separated list
# https://www.baeldung.com/linux/check-variable-exists-in-list
    LIST=$1
    WORD=$2
    if [[ "$LIST" =~ (" "|^)$WORD(" "|$) ]]; then
        echo 1
    else
        echo 0
    fi
}

starts_with(){
# Function to check if a word start with a given prefix
    WORD=$1
    PREF=$2
    if [[ $WORD =~ ^$PREF* ]]; then
        echo 1
    else
        echo 0
    fi
}

# ACTION IF NEW BRANCH IS IN A GIVEN LIST
# Determine if NEW branch name belongs to a list of names
listBranches="dev tmp test"
isNewList="$(exists_in_list "$listBranches" "$newBRANCH")"
# NEW branch was in list
if [[ $isNewList -eq 1 ]]; then
    printf "New branch: $newBRANCH was in list\n"
    printf ' Do something 0\n'
    exit 0
fi

# ACTION ACCORDING THE NAMES OF OLD TO NEW BRANCH
# Determine if OLD and NEW branch names have a given prefix
isOldFtr="$(starts_with "$oldBRANCH" "ftr-")"
isNewFtr="$(starts_with "$newBRANCH" "ftr-")"

# If any of the branches is empty, it's rebase
if [ -z "$oldBRANCH" ] || [ -z "$newBRANCH" ]; then
    exit 0
fi

# NoFeature branch to Feature branch
if [[ $isOldFtr -eq 0 ]] && [[ $isNewFtr -eq 1 ]]; then
    printf "Branch switch: $oldBRANCH -> $newBRANCH\n"
    printf ' Do something 1\n'
    exit 0
fi

# Feature branch to NoFeature branch
if [[ $isOldFtr -eq 1 ]] && [[ $isNewFtr -eq 0 ]]; then
    printf "Branch switch: $oldBRANCH -> $newBRANCH\n"
    printf ' Do something 2\n'
    exit 0
fi

# No change in type of branch
if ([[ $isOldFtr -eq 0 ]] && [[ $isNewFtr -eq 0 ]]) || ([[ $isOldFtr -eq 1 ]] && [[ $isNewFtr -eq 1 ]]); then
    printf "Branch switch: $oldBRANCH -> $newBRANCH\n"
    printf ' Do something 3\n'
    exit 0
fi

exit 0