Configure Git credentials for when using multipe GitHub accounts.

config_git_credentials.sh

git_config_author(){
  git config --local user.name "${1}"
  git config --local user.email "${2}"
}

git_config_sshkey(){
  # get ssh hosts
  local ssh_hosts="$(grep "github.com-[a-Z]*" ~/.ssh/config | \
                     awk '{print $2}' | sed 's/github\.com-//g' | tr '\n' ' ')"

  # check for argument
  if [ -z "${1}" ]; then
    echo "Please provide appropriate ssh-host (e.g. github.com-USERNAME):" \
         "${ssh_hosts}"
  else
    # determine authorship
    if ! grep -sq "${1}" ~/.ssh/config; then
      echo "Author ${1} not found amongst: ${ssh_hosts}"
    else
      # get remote URL
      local remote_url=$(git remote -v | awk '{print $2}' | tail -n 1)

      # set remote URL
      git remote set-url origin \
          $(echo ${remote_url} | sed "s/github\.com.*:/github\.com-${1}:/g")

      # setup author credentials
      case ${1} in
         GITHUB_USER_1)
          git_config_author 'John Doe' 'johndoe@example.com'
          ;;

        GITHUB_USER_2)
          git_config_author 'Jane Doe' 'janedoe@gmail.com'
          ;;
      esac
    fi
  fi
}