Update a GitHub Forked Repository with his Upstream/Master (and update remote master)

git-sync-upstream.sh

#!/bin/bash

# usage: git-sync-upstream "/your/git/folder/" [rebase/merge]

action="merge"

if [ $# -ge 1 ]; then cd "$1"; fi
if [ $# -eq 2 ]; then if [ "$2" = "rebase" ]; then action="rebase"; fi; fi

clear;
echo "Working on `pwd`"

if [ -d ".git" ]; then
	current_branch="$(git status -b | head -n1 | sed 's/On branch //g')"
	if git remote -v | grep -q upstream; then
		git checkout master
		[ $? -ne 0 ] && { echo -e "\\033[1;31mCan't checkout branch master, aborting\\0033[0;39m"; exit; }
		echo -e "\\033[1;32mFetch upstream repo\\0033[0;39m"
		git fetch upstream
		echo -ne "\\033[1;32mGit $action upstream > master :\\0033[0;39m  "
		git $action upstream/master
		echo -ne "\\033[1;32mGit push master > origin :\\0033[0;39m  "
		git push origin master
		
		[ "$current_branch" != "master" ] && git checkout $current_branch
	else
		echo -e "\\033[1;31mPlease add upstream remote with command:\\0033[0;39m  git remote add upstream [url]"
	fi
else
	echo "Not a git repo!"
fi

By default this bash script fetch upstream/master and merge modifications with master branch, and pull modifications to remote origin/master (stay forked repo in sync with upstream).
💥 Be careful if you choose rebase option that no prompt will tell you if you want to rebase the project and lose local modification !