Bash function to prompt for yes or no with a single keypress

yes_or_no.sh

#!/usr/bin/env bash

affirmative_response_to() {
  PROMPT=$*

  IFS= read -n 1 -s -p "${PROMPT}? [Y/n]: " answer

  if [ "${answer:-Y}" = "${answer#[Yy]}" ]; then
    # anything other than enter, Y, or y was pressed
    echo "NO"
    return 1
  fi

  # enter, Y, or y was pressed
  echo "YES"
}

if affirmative_response_to "Would you like some cake"; then
  echo "Here is some cake for you!"
else
  echo "FINE! I didn't want to share, anyway."
fi