Syncs a forked repository against its upstream.

forksync.sh

#!/bin/sh

git_repo=$1
[ -z "$git_repo" ] && git_repo="."
cd $git_repo > /dev/null 2>&1
if [ $? -ne 0 ]; then
    printf "Invalid directory path.\n" 
    exit 1
fi

RED=$(tput setaf 1)
GREEN=$(tput setaf 2)
NORMAL=$(tput sgr0)
col=$(tput cols)

git status > /dev/null 2>&1
git fetch upstream > /dev/null 2>&1

if [ $? -ne 0 ]; then
    printf "Not a git repository or no upstream found for %s.\n" "$git_repo"
    exit 1
fi

upstream_branches=`git branch -r | grep upstream | cut -c3-`

for branch_name in $upstream_branches
do
    printf "Syncing branch %s of %s... " "$branch_name" "$git_repo" 
    local_name=`echo $branch_name | cut -c10-`
    git checkout -b $local_name $branch_name > /dev/null 2>&1
    git checkout $local_name
    git merge $branch_name
    git push origin $local_name
    
    if [ $? -eq 0 ]; then
        printf '%s%*s%s' "$GREEN" $col "[OK]" "$NORMAL"
    else
        printf '%s%*s%s' "$RED" $col "[FAIL]" "$NORMAL"
    fi
done

Usage: ./forksync.sh [repository_path]

Put it on your crontab and be happy!