Syncs your repo fork with the upstream master and then pushes the synced master to origin. Presumes you have an 'upstream' remote which is from whence your fork was created. Put on your path and chmod a+x it then do: git fork-sync. Use -h for usage help.

git-fork-sync

#!/usr/bin/env bash

set -Eeuo pipefail

VERSION="20200421.1"

_usage() {
    cat << __EOF
$0 usage:

    $0 [options]

Where [options] include:

    -h|--help                   Show this help
    -v|--version                Show the version and exit
    -r|--remote REMOTE_NAME     Fetch only this remote
    -m|--merge                  Merge instead of rebase. Interaction
                                required. (Only for -t or --topic)
    -X|--merge-strategy         Merge strategy used for rebasing or
                                merging (only for -t or --topic)
                                Defaults to "ours" for rebasing,
                                "theirs" for merges
    -t|--topic  TOPIC_BRANCH    And rebase MAIN_BRANCH onto this
                                topic branch after syncing unless
                                -m or --merge is specified
    -g|--origin-reset           Reset topic branches specified using
                                -t or --topic to the origin version when
                                rebasing or merging
    -u|--upstream REMOTE_NAME   And push synced MAIN_BRANCH here too
    -c|--checkout TOPIC_BRANCH  When done, checkout this branch
    -s|--mine-only              Only sync with your origin
    -a|--fetch-all              With -s, also fetch all remotes
    -n|--no-deploy-branches     Do not sync up deployment branches if found.
                                If qa|stage|staging|prod|production are found
                                they will be reset to their upstream versions
                                and pushed to your origin (if applicable)
    -b|--main-branch BRANCH     Use BRANCH instead of master for the repos
                                MAIN_BRANCH

MAIN_BRANCH is defaulted to master if -b or --main-branch is not specified.

If remote is not specified, all remotes are fetched
and your local MAIN_BRANCH is rebased with upstream/MAIN_BRANCH
then pushed to your origin.

If remote is specified, only that remote is fetched
and your local MAIN_BRANCH is rebased to remote/MAIN_BRANCH
then pushed to your origin.

-t|--topic       may be used multiple times
-u|--upstream    may be used multiple times
-s|--mine-only   will ignore other options except -a

If you only have an origin, git fork-sync will only sync with
your origin as if you specified -s or --mine-only.

If topics are specified (-t or --topic) and you specify -m or --merge, a
non-fast-forward merge will be performed which will require interaction.
In any case, this will attempt to reset the local topic branch to the
version from origin unless -g or --no-origin-reset is specified.

git fork-sync will fail if you do not have at least origin defined
as a remote.

__EOF

    exit 1
}

_die() {
    echo "$*" >&2
    exit 1
}

bold=$(tput bold)
normal=$(tput sgr0)

GIT_VER=`git --version | cut -f 3 -d ' '`
REBASE_ARG="-p"
PULL_REBASE_ARG="--rebase=preserve"
REMOTE=""
MINE_ONLY=""
FETCH_ALL=""
NO_REBASE=""
MERGE_STRATEGY=""
TOPICS=()
DO_ORIGIN_RESET=""
UPSTREAMS=()
CHECKOUT=""
NO_DEPLOY_BRANCHES=""
MAIN_BRANCH="master"

while [ $# -ge 1 ]
do
    key="$1"
    shift

    case $key in
    -h|--help)
        _usage
        exit 1
        ;;
    -v|--version)
        echo "git-fork-sync version $VERSION"
        echo""
        exit 0
        ;;
    -r|--remote)
        REMOTE="$1"
        shift
        ;;
    -m|--merge)
        NO_REBASE="yes"
        ;;
    -X|--merge-strategy)
        MERGE_STRATEGY="$1"
        shift
        ;;
    -t|--topic)
        TOPICS+=("$1")
        shift
        ;;
    -g|--origin-reset)
        DO_ORIGIN_RESET="yes"
        ;;
    -u|--upstream)
        UPSTREAMS+=("$1")
        shift
        ;;
    -c|--checkout)
        CHECKOUT="$1"
        shift
        ;;
    -s|--mine-only)
        MINE_ONLY="yes"
        ;;
    -a|--fetch-all)
        FETCH_ALL="yes"
        ;;
    -n|--no-deploy-branches)
        NO_DEPLOY_BRANCHES="yes"
        ;;
    -b|--main-branch)
        MAIN_BRANCH="$1"
        shift
        ;;
    *)
        _usage
        exit 1
        ;;
    esac
done

if [ -z "$MERGE_STRATEGY" ]
then
    if [ -z "$NO_REBASE" ]
    then
        MERGE_STRATEGY="ours"
    else
        MERGE_STRATEGY="theirs"
    fi
fi

if [ "$GIT_VER" \> "2.26.0" ]
then
    REBASE_ARG="-r"
    PULL_REBASE_ARG="--rebase=merges"
else
    echo "You are using an older version of git, will use the older preserve"
    echo "merges flag."
    echo ""
fi

if output=$(git status --untracked-files=no --porcelain) && [ -z "$output" ]
then
    echo "${bold}Working directory is clean.${normal}"
else
    _die "You have uncommitted changes."
fi

echo "${bold}Checking connectivity:${normal}"

all_remotes=`git remote`
cr=($all_remotes)
have_origin=""
have_upstream=""

for r in $all_remotes
do
    echo -n "   $r... "

    if [ "origin" == "$r" ]
    then
        have_origin="yes"
    elif [ "upstream" == "$r" ]
    then
        have_upstream="yes"
    fi

    if git ls-remote --exit-code $r &>/dev/null
    then
        echo "ok"
    else
        _die "FAILED!"
    fi
done

if [ -z "$have_origin" ]
then
    _die "You do not have an origin defined."
fi

if [ 1 == ${#cr[@]} ]
then
    echo "${bold}You only have an origin, falling back to single mode.${normal}"
    MINE_ONLY="yes"
fi

if [ -z "$have_upstream" ]
then
    echo "${bold}You do not have an upstream, falling back to single mode and fetching all.${normal}"
    MINE_ONLY="yes"
    FETCH_ALL="yes"
fi

echo "${bold}Using $MAIN_BRANCH as the main branch.${normal}"

git checkout $MAIN_BRANCH

if ! [ -z "$MINE_ONLY" ]
then
    if [ -z "$FETCH_ALL" ]
    then
        echo "${bold}Only syncing with your origin.${normal}"
        git pull $PULL_REBASE_ARG --tags

        echo -n "Now pruning remote origin... "
        git remote prune origin && echo "done."
    else
        echo "${bold}Getting all remote history and syncing only with your origin.${normal}"
        git pull $PULL_REBASE_ARG --all --tags

        echo "${bold}Pruning all remotes:${normal}"

        for r in $all_remotes
        do
            echo -n "   $r... "
            git remote prune $r && echo "done"
        done
    fi

    exit 0
elif [ -z "$REMOTE" ]
then
    echo "${bold}Getting all remote history.${normal}"
    git pull $PULL_REBASE_ARG --all --tags

    echo "${bold}Syncing with upstream.${normal}"
    git rebase $REBASE_ARG upstream/$MAIN_BRANCH
    git push origin $MAIN_BRANCH

    echo "${bold}Pruning all remotes:${normal}"

    for r in $all_remotes
    do
        echo -n "   $r... "
        git remote prune $r && echo "done"
    done
else
    echo "${bold}Only syncing $REMOTE with $MAIN_BRANCH.${normal}"

    git pull $PULL_REBASE_ARG --tags
    git fetch $REMOTE
    git rebase $REMOTE/$MAIN_BRANCH
    git push origin $MAIN_BRANCH
    git remote prune $REMOTE
fi

if [ ${#TOPICS[@]} -gt 0 ]
then
    if ! [ -z "$NO_REBASE" ]
    then
        echo "${bold}Merging $MAIN_BRANCH with topic branches:${normal}"
    else
        echo "${bold}Rebasing topic branches with history from $MAIN_BRANCH:${normal}"
    fi

    for t in ${TOPICS[@]}
    do
        if ! [ -z "$NO_REBASE" ]
        then
            echo "   ${bold}with $t${normal}"
            git checkout $t

            if ! [ -z "$DO_ORIGIN_RESET" ]
            then
                git reset --hard origin/$t
            fi

            git merge --no-ff -X$MERGE_STRATEGY $MAIN_BRANCH
        else
            echo "   ${bold}onto $t${normal}"
            git checkout $t

            if ! [ -z "$DO_ORIGIN_RESET" ]
            then
                git reset --hard origin/$t
            fi

            git rebase $REBASE_ARG -X$MERGE_STRATEGY $MAIN_BRANCH
        fi
    done

    git checkout $MAIN_BRANCH
fi

if [ ${#UPSTREAMS[@]} -gt 0 ]
then
    echo "${bold}Pushing synced $MAIN_BRANCH:${normal}"

    for u in ${UPSTREAMS[@]}
    do
        echo "   ${bold}to $u${normal}"
        git push $u $MAIN_BRANCH
    done
fi

if [ -z "$NO_DEPLOY_BRANCHES" ]
then
    echo "${bold}Checking for deployment branches to sync.${normal}"

    all_branches=`git branch | sed -E "s/\*? +//g"`

    for b in $all_branches
    do
        if [ "qa" == "$b" ] || [ "stage" == "$b" ] || [ "staging" == "$b" ] || [ "prod" == "$b" ] || [ "production" == "$b" ]
        then
            if ! [ -z "$MINE_ONLY" ]
            then
                echo "${bold}Syncing $b with your origin.${normal}"
                git checkout $b
                git reset --hard origin/$b
            elif [ -z "$REMOTE" ]
            then
                echo "${bold}Syncing $b with your upstream.${normal}"
                git checkout $b
                git reset --hard upstream/$b
                git push origin $b
            else
                echo "${bold}Only syncing $b with $REMOTE.${normal}"
            fi
        fi
    done

    git checkout $MAIN_BRANCH
fi

if ! [ -z "$CHECKOUT" ]
then
    git checkout $CHECKOUT
fi

echo "${bold}Done.${normal}"

exit 0