A quick bash script for changing the "master" branch of your github repo(s) to an alternative of your choosing.

no_masters.sh

#!/bin/bash
# There's a better way to do this! Use:
# https://github.com/dfm/rename-github-default-branch
# instead.
#
# Also: don't change the default branch name on your gists! Github appears to have them
# locked to master; it will break your gist.

set -e

usage(){
	echo "Usage: $0 [--user USERNAME] [--owner OWNER] [--token TOKEN] NEW_DEFAULT [PATH ...]"
    echo "Replace the 'master' branch of a github project with NEW_DEFAULT."
    echo "Suggested replacements: 'main', 'trunk', 'root', 'default', 'canon'"
    echo "If no path or paths to repositories are provided, operates on the"
    echo "current working directory."
    echo ""
    echo "  -u, --user     The github user (defaults to current username)"
    echo "  -o, --owner    The github project owner (defaults to user)"
    echo "  -t, --token    The github API token (defaults to pw auth)"
    echo "  --no-delete    Do not delete the 'master' branch from origin"
    echo ""
    echo "If no token is provided, (deprecated) password authentication will be used."
	exit 1
}

DEFAULT=""
OWNER=$USER
REPO_PATHS=()
while [ $# -gt 0 ]; do
  case "$1" in
    -t|--token)
        shift
        if [ -n "$1" ] && [ ${1:0:1} != "-" ]; then
            TOKEN="$1"
            shift
        else
            echo "Error: no token provided" >&2
            usage
        fi
        ;;
    --no-delete)
        shift
        NO_DELETE=1
        ;;
    -u|--user)
        shift
        if [ -n "$1" ] && [ ${1:0:1} != "-" ]; then
            USER="$1"
            shift
        else
            echo "Error: no user provided" >&2
            usage
        fi
        ;;
        
    -o|--owner)
        shift
        if [ -n "$1" ] && [ ${1:0:1} != "-" ]; then
            OWNER="$1"
            shift
        else
            echo "Error: no owner provided" >&2
            usage
        fi
        ;;
    -*|--*=) 
        echo "Error: unknown flag $1" >&2
        usage
        ;;
    *) # preserve positional arguments
        if [ -z "${DEFAULT}" ]; then
            DEFAULT="$1"
        else
            REPO_PATHS+=("$1")
        fi
        shift
        ;;
  esac
done
if [ -z "${REPO_PATHS[*]}" ]; then
    REPO_PATHS="."
fi
#echo "user ${USER} owner ${OWNER} default ${DEFAULT} paths ${REPO_PATHS[*]}"

if [ -z "${DEFAULT}" ]; then
    echo "Error: new default branch name not provided!" >&2
    usage
fi

if [ -n "${TOKEN}" ]; then
    USER=${USER}:${TOKEN}
fi

change_current_master() {
    git checkout master
    git branch -m ${DEFAULT}
    git push origin -u ${DEFAULT}
    curl -i -u ${USER} --header "Content-Type: application/json" --request PATCH --data "{\"name\":\"${REPO}\", \"default_branch\": \"${DEFAULT}\" }" https://api.github.com/repos/${OWNER}/${REPO}
    if [ -z "${NO_DELETE}" ]; then
        git push origin --delete master
    fi
}

for REPO_PATH in "${REPO_PATHS[@]}"; do
    pushd ${REPO_PATH} >/dev/null
    TL=`git rev-parse --show-toplevel`
    REPO=`basename ${TL}`
    echo "Transitioning ${REPO} from master -> ${DEFAULT} (in `pwd`)"
    change_current_master
    popd >/dev/null
done

TODOs:

• use a token instead of deprecated password challenge
• ignore repos that already have a non-master default
• add option to scan all of a user's repos and do bulk updates
• document/usage examples