Bash script to sync a forked project with its upstream repository

sync-upstream.sh

#/bin/bash

red=`tput setaf 1`
green=`tput setaf 2`
yellow=`tput setaf 3`
upstream=$1
branch=$2

# checks if there is a remote repo called upstream
check_upstream() {
    git remote -v | grep upstream
    # if there are no remote repository called upstream
    if [ $? -ne 0  ]; then
        printf "${red}Upstream not configured\n"
        # if the url was passed as an parameter, adds a remote repo called upstream pointing to that url
        if [[ $upstream ]]; then
            printf "${yellow}Upstream URL will be set to ${upstream}\n"
            git remote add upstream $upstream
        else
            # if there is no remote called upstream and no url was passed aborts the whole thing
            printf "${red}Upstream parameter not informed, please inform it like this:\n\n${yellow}--> bash sync-upstream <upstream-url> <branch-to-sync-from>\n\n"
            printf "${yellow}This is an one time configuration (for each forked repository)\n\n"
            exit 1
        fi
    else
        printf "${green}Upstream seems to be configured\n"
    fi
}

# check if a branch was passed as parameter and if not it makes the master as the default branch
check_branch() {
    if [[ $branch ]]; then
        printf "${green}Branch to sync to is set to {$branch}\n"
    else
        printf "${yellow}Branch to sync to not supplied, using *master* as the default branch to sync to\n"
        branch="master"
    fi
}

# fetch updates from upstream
# merges upstream with a given branch
# push the changes
sync() {
    printf "${green}Fetching its updates...\n"
    git fetch upstream
    if [ $? -eq 0 ]; then
        printf "${green}Merging updates with ${branch}\n"
        git merge upstream/$branch
        git push
    else
        printf "${red}"
    fi
}


check_upstream
check_branch
sync

Usage example:

1. Find a cool project you are willing to contribute to, for instance this one https://github.com/Juraci/swamp
2. Fork it!
3. Clone your forked repository
4. Copy this bash script to the root folder of that repository
5. bash sync-upstream
   example: bash sync-upstream git@github.com:Juraci/swamp.git master
6. Create a branch and submit your changes by pushing it and opening a pull request in the original repository

All made with help from this links:
https://help.github.com/articles/fork-a-repo/
https://help.github.com/articles/syncing-a-fork/
https://help.github.com/articles/using-pull-requests/

Why does git remote update --prune not work?

sync out of git repo
https://gist.github.com/klkyy2020/7d98fb91fa410f0eb05ad6b6aebf178a