check_dotfiles_variable.sh

#! /usr/bin/env bash

# get path to dotfiles repo root (should be same as $DOTFILES)
#
# Returns:
#   {string} `_COMPUTED_DOTFILES` - path to this repo root
get_dotfiles_repo_root() {
  local dir

  dir="$(cd "$(dirname "${BASH_SOURCE[0]}")" > /dev/null 2>&1 && pwd)"
  cd "$dir" || return

  git rev-parse --show-toplevel
}

# checks if DOTFILES environment variable is set, sets it or quits based on user
# input if not
#
# Returns:
#   {string} `DOTFILES` - exports DOTFILES environment variable if user chooses
#     to set it
check_dotfiles_variable() {
  local computed_dotfiles

  computed_dotfiles="$(get_dotfiles_repo_root)"

  # bail if $DOTFILES already set
  [[ -z $DOTFILES ]] || return 0

  # interactively confirm $DOTFILES path when not headless
  if [[ -z $DOTFILES_SETUP_HEADLESS ]]; then
    printf "This script requires a \$DOTFILES environment variable holding the \
path\nto the repo this script is running from. This path appears to be\n\
'%s'.\n\nIs this correct (y/any other key)? " "$computed_dotfiles"
    # `-r` treats backslash as a literal, `-n` accepts one character of input
    read -r -n 1 maybe_continue

    if [[ $maybe_continue == 'y' ]]; then
      export DOTFILES="$computed_dotfiles"
      printf "\n\nDOTFILES set to '%s'. Note that this export exists\
\nonly within this script.\n" "$DOTFILES"
    else
      printf "\n\nTo continue, set DOTFILES \
(\`export DOTFILES=<path-to-dotfiles-repo>\`),\nthen rerun this script.\n\
Goodbye.\n"
      exit
    fi
  else
    export DOTFILES="$computed_dotfiles"
  fi
}

check_dotfiles_variable "$@"