git-force-pull

#!/usr/bin/env bash

app_name="$(basename "${BASH_SOURCE[0]}")"

print_help() {
	expand -t 4 << EOF
Usage:
	$app_name [--all]
		Fetch and force pull remote tracking branch(es) by doing a hard reset.

Options:
	--all
		Force pull all branches instead of just the currently checked out one.

	-?, --help
		Show this help information and exit.
EOF
}

all=0

while [[ $# -gt 0 ]]; do
	case "$1" in
		--all)
			all=1
			shift
			;;
		-\?|--help)
			print_help
			exit 0
			;;
		-*)
			echo "$app_name: [Error] Unknown option: $1" >&2
			exit 1
			;;
		*)
			echo "$app_name: [Error] Unexpected argument: $1" >&2
			exit 1
			;;
	esac
done

force_pull() {
	local branch_full_name="$1"
	local branch="${branch_full_name#refs/heads/}"
	local upstream="$(git rev-parse --quiet --verify --abbrev-ref "$branch@{upstream}")"
	local has_upstream=$?
	if [[ has_upstream -eq 0 ]]; then
		if git merge-base --is-ancestor "$upstream" "$branch"; then
			local abbrev="${upstream%/$branch}"
			echo "${branch@Q} is already up to date with ${abbrev@Q}."
		else
			branch_sha_short="$(git rev-parse --quiet --short --verify "$branch")" &&
			upstream_sha_short="$(git rev-parse --quiet --short --verify "$upstream")" &&
			if [[ "$branch" == "$current_branch" ]]; then
				git reset --quiet --hard "$upstream"
			else
				git update-ref "$branch_full_name" "$upstream"
			fi &&
			echo "Update ${branch@Q} ("$branch_sha_short") to ${upstream@Q} ("$upstream_sha_short"): $(git show --no-patch --format="%s" "$upstream")"
		fi
	fi
}

current_branch="$(git rev-parse --abbrev-ref HEAD)" &&

git fetch --all &&
if [[ all -eq 1 ]]; then
	for branch_full_name in $(git for-each-ref --format='%(refname)' refs/heads); do
		force_pull "$branch_full_name"
	done
else
	current_branch_full_name="$(git symbolic-ref --quiet HEAD)"
	is_head_attached=$?
	if [[ is_head_attached -eq 0 ]]; then
		force_pull "$current_branch_full_name"
	fi
fi