Cross-platform shell script to change the 'master' branch to 'main' for the local and remote repository

change-master-branch-to-main.sh

#!/bin/sh -eu

# code licensed under BSD 2-Clause "Simplified" License

# see `change-master-branch-to-main.sh --help` for usage
# see twitter thread for more details: https://twitter.com/EdwinKofler/status/1272729160620752898

site="github.com"
oldDefaultBranch="master"
newDefaultBranch="main"
bin="gh" # or set to 'hub'
user="${1:-""}"
repo="${2:-""}"

# ------------------- helper functions ------------------- #
showHelp() {
	echo "change-master-branch-to-main.sh"
	echo
	echo "Description:"
	echo "    Cross-platform shell script to change the 'master' branch to"
	echo "    'main' for the local and remote repository. Should work with"
	echo "    providers besides Github, but I haven't tested that"
	echo
	echo "Usage:"
	echo "    change-master-branch-to-main.sh [username] [repo name]"
	echo "        Rename the 'master' branch to 'main' both for the local"
	echo "        and remote repository with the specified variables. It"
	echo "        also sets the default branch to 'main' if the previous"
	echo "        default was 'master'"
	echo "    change-master-branch-to-main.sh"
	echo "        Same as above, but intelligently guesses (and ask user for"
	echo "        confirmation) the github user and repo names"
	echo
	echo "Requirements:"
	echo "    'jq' and 'gh' are optional dependencies and are only required"
	echo "    when trying to update the GitHub default branch"
	echo
	echo "Examples:"
	echo "    change-master-branch-to-main.sh eankeen deno-babel"
}

# get the GitHub username, if it wasn't already specified
askUser() {
	# return if user is already set (passed as arg)
	test ! -z "$user" && return

	# get github username and strip quotes
	url="$(git config --get remote.origin.url)"

	# if url looks like [email protected]:user/repo
	if [ "$(echo "$url" | cut -d'@' -f1)" = "git" ]; then
		user="$(echo "$url" | sed -E "s/(.*:)(.*)(\/.*)/\2/g")"
	else
		user="$(echo "$url" | sed -E "s/(.*$site\/)(.*)(\/.*)/\2/g")"
	fi

	printInfo "github username (default: %s): " "$user"
	read -r

	# trim whitespace
	REPLY="$(echo "$REPLY" | xargs)"

	user="${REPLY:-$user}"
	printInfo "input: $user\n\n"
}

# get the GitHub repository name, if it wasn't already specified
askRepo() {
	# return if repo is already set (passed as arg)
	test ! -z "$repo" && return

	url="$(git config --get remote.origin.url)"
	repo="$(basename -s .git "$url")"

	printInfo "github repository name (default: %s): " "$repo"
	read -r

	# trim whitespace
	REPLY="$(echo "$REPLY" | xargs)"

	repo="${REPLY:-$repo}"
	printInfo "input: $repo\n\n"
}

remoteMainExists() {
	git show-branch "refs/remotes/origin/$newDefaultBranch" >/dev/null 2>&1
}

remoteMasterExists() {
	git show-branch "refs/remotes/origin/$oldDefaultBranch" >/dev/null 2>&1
}

localMainExists() {
	git rev-parse --verify --quiet "refs/heads/$newDefaultBranch" >/dev/null
}

localMasterExists() {
	git rev-parse --verify --quiet "refs/heads/$oldDefaultBranch" >/dev/null
}

hasColor() {
	test -t 1 && command -v tput >/dev/null && \
		test -n "$(tput colors)" && test "$(tput colors)" -ge 8
}

hasBinAndJq() {
	command -v jq >/dev/null && command -v "$bin" >/dev/null
}

printInfo() {
	if hasColor; then
		printf "\033[0;94m"
		# shellcheck disable=SC2059
		printf "$@"
		printf "\033[0m"
	else
		# shellcheck disable=SC2059
		printf "$@"
	fi
}

# ------------------------- main ------------------------- #
test "${1:-""}" = "--help" && showHelp && exit

git fetch --all
git checkout "$oldDefaultBranch"
git push origin "$oldDefaultBranch"

# ensure 'main' is the default locally
if ! localMainExists; then
	printInfo "renaming '$oldDefaultBranch' to '$newDefaultBranch' locally\n"
	git checkout $oldDefaultBranch
	git branch --move $oldDefaultBranch "$newDefaultBranch"
fi

# ensure 'main' is at remote
if ! remoteMainExists; then
	printInfo "setting '$newDefaultBranch' as default upstream branch\n"
	git checkout "$newDefaultBranch"
	git push --set-upstream origin "$newDefaultBranch"
fi

# remove local 'master' branch
if localMasterExists; then
	printInfo "renaming local $oldDefaultBranch branch\n"
	git branch --delete $oldDefaultBranch
fi

# ensure github default branch is 'main'
if hasBinAndJq; then
	askRepo
	askUser

	beforeNewbranch="$("$bin" api "repos/$user/$repo" -X GET | jq --raw-output ".default_branch")"

	# sets new default branch
	if test "$beforeNewbranch" = "$oldDefaultBranch"; then
		"$bin" api "repos/$user/$repo" -X PATCH -F default_branch="$newDefaultBranch"
	fi

	afterNewbranch="$("$bin" api "repos/$user/$repo" -X GET | jq --raw-output ".default_branch")"

	printInfo "default branch at $user/$repo was: '$beforeNewbranch'\n"
	printInfo "default branch at $user/$repo is now: '$afterNewbranch'\n"
fi

# remove remote 'master' branch
if remoteMasterExists; then
	printInfo "deleting remote $oldDefaultBranch branch\n"

	# if this fails, it may be due to forgetting
	# to reset the default branch to 'main' on github
	git push origin --delete $oldDefaultBranch

	test ! $? && printInfo "this probably errored since '$oldDefaultBranch' is still the 'default branch' on github" \
		&& printInfo "if you install \`gh\` and \`jq\` this will be done for you"
fi

@eankeen it so cool. will this same script work for GITLAB as well ?

Thank you! It should work, provided you set site=gitlab.com near the top - but it's not tested :) I don't think GitLab is fully supported. To get complete support, you'll have to modify the requests starting near line 150 that use the gh or hub utility (basically anything that executes the utility referred to by "$bin")