update a GitHub forked repository?

update_forked_repo.sh

# Add the remote, call it "upstream":

git remote add upstream https://github.com/whoever/whatever.git

# Fetch all the branches of that remote into remote-tracking branches

git fetch upstream

# Make sure that you're on your master branch:

git checkout master

# Rewrite your master branch so that any commits of yours that
# aren't already in upstream/master are replayed on top of that
# other branch:

git rebase upstream/master

# If you don't want to rewrite the history of your master branch, (for example because other people may have cloned it) 
# then you should replace the last command with

git merge upstream/master. 

# However, for making further pull requests that are as clean as possible, it's probably better to rebase.

# If you've rebased your branch onto upstream/master you may need to force the push in order to push it to your own
# forked repository on GitHub. You'd do that with:

git push -f origin master

# You only need to use the -f the first time after you've rebased.