git-sync-upstream

#!/usr/bin/env bash
#
# Requirements:
#   - git
#
# Author: James Cherti
# URL: https://github.com/jamescherti/bash-stdops
#
# Description:
# ------------
# This script synchronizes the current Git branch with its upstream counterpart
# and force-pushes the result to the 'origin' remote. It is intended for
# workflows where a local branch is kept in sync with an upstream source of
# truth, and the mirror on 'origin' must match upstream exactly.
#
# The script performs the following actions:
#   1. Verifies that both 'origin' and 'upstream' remotes are defined.
#   2. Performs a rebase of the current branch onto its upstream equivalent.
#   3. Displays the diff between the rebased branch and the remote 'origin'.
#   4. Prompts for confirmation unless run in batch mode.
#   5. Merges upstream changes with --ff-only and force-pushes to 'origin'.
#
# Intended for use in CI workflows or manual synchronization where upstream is
# authoritative.
#
# Usage:
#   git-sync-upstream [-h] [-b]
#     -h    Show help message and exit
#     -b    Run in batch mode (no interactive prompts)
#
# License:
# --------
# Copyright (C) 2012-2026 James Cherti
#
# Distributed under terms of the GNU General Public License version 3.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <https://www.gnu.org/licenses/>.
#

set -euo pipefail

# shellcheck disable=SC2317
error_handler() {
  local errno="$?"
  echo "Error: ${BASH_SOURCE[1]}:${BASH_LINENO[0]}" \
    "(${BASH_COMMAND} exited with status $errno)" >&2
  exit "${errno}"
}

show_usage() {
  echo "Usage: $0 [-h] [-b] [-t]" >&2
  echo
  echo "  -h    Show this help message and exit"
  echo "  -b    Run in batch mode (skip interactive confirmations)"
  echo "  -t    Synchronize tags from upstream to origin"
}

main() {
  trap "error_handler" ERR
  set -o errtrace

  BATCH_MODE=0
  SYNC_TAGS=0

  while getopts ":hbt" opt; do
    case "$opt" in
    h)
      show_usage
      exit 0
      ;;
    b)
      BATCH_MODE=1
      ;;
    t)
      SYNC_TAGS=1
      ;;
    \?)
      echo "Invalid option: -$OPTARG" >&2
      exit 1
      ;;
    :)
      echo "Option -$OPTARG requires an argument" >&2
      exit 1
      ;;
    esac
  done

  shift $((OPTIND - 1))

  if ! git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
    echo "Error: Not in a Git repository." >&2
    exit 1
  fi

  for remote in origin upstream; do
    if ! git remote | grep -q "^${remote}$"; then
      echo "Error: Remote '$remote' is not defined." >&2
      exit 1
    fi
  done

  CURRENT_BRANCH=$(git symbolic-ref --short HEAD)
  REMOTE_ORIGIN=$(git config --get remote.origin.url || true)
  echo "[SYNC MIRROR] $REMOTE_ORIGIN (Branch: $CURRENT_BRANCH)"

  if [[ $BATCH_MODE -eq 0 ]]; then
    read -r -p "Synchronize the '${CURRENT_BRANCH}' branch? [y,n] " ANSWER
    [[ "$ANSWER" != "y" ]] && exit 1
  fi

  git pull -q --rebase upstream "$CURRENT_BRANCH"

  if [[ $SYNC_TAGS -eq 1 ]]; then
    git fetch -q upstream --tags
  fi

  if git diff --quiet "origin/$CURRENT_BRANCH" "$CURRENT_BRANCH" 2>/dev/null; then
    if [[ $SYNC_TAGS -eq 1 ]]; then
      git push origin --tags
    else
      echo "Nothing to do."
    fi
    exit 0
  fi

  git diff "origin/$CURRENT_BRANCH" "$CURRENT_BRANCH" || true

  if [[ $BATCH_MODE -eq 0 ]]; then
    read -r -p "Proceed? [y,n] " ANSWER
    [[ "$ANSWER" != "y" ]] && {
      echo "Aborted." >&2
      exit 1
    }
  fi

  git merge "upstream/$CURRENT_BRANCH" --ff-only --quiet
  git push origin "$CURRENT_BRANCH" --force

  if [[ $SYNC_TAGS -eq 1 ]]; then
    git push origin --tags
  fi
}

main "$@"