General-purpose Yes/No prompt function

#!/usr/bin/env bash

#
# A general-purpose function to ask Yes/No questions in Bash, either with
# or without a default answer. It keeps repeating the question until it
# gets a valid answer.
#
# https://jonlabelle.com/snippets/view/shell/general-purpose-yesno-prompt-function
# https://gist.github.com/davejamesmiller/1965569
ask() {
    local prompt default reply

    if [[ ${2:-} = 'Y' ]]; then
        prompt='Y/n'
        default='Y'
    elif [[ ${2:-} = 'N' ]]; then
        prompt='y/N'
        default='N'
    else
        prompt='y/n'
        default=''
    fi

    while true; do

        # Ask the question (not using "read -p" as it uses stderr not stdout)
        echo -n "$1 [$prompt] "

        # Read the answer (use /dev/tty in case stdin is redirected from somewhere else)
        read -r reply < /dev/tty

        # Default?
        if [[ -z $reply ]]; then
            reply=$default
        fi

        # Check if the reply is valid
        case "$reply" in
            Y* | y*) return 0 ;;
            N* | n*) return 1 ;;
        esac

    done
}

# EXAMPLE USAGE:

if ask "Do you want to do such-and-such?"; then
    echo "Yes"
else
    echo "No"
fi

# Default to Yes if the user presses enter without giving an answer:
if ask "Do you want to do such-and-such?" Y; then
    echo "Yes"
else
    echo "No"
fi

# Default to No if the user presses enter without giving an answer:
if ask "Do you want to do such-and-such?" N; then
    echo "Yes"
else
    echo "No"
fi

# Only do something if you say Yes
if ask "Do you want to do such-and-such?"; then
    said_yes
fi

# Only do something if you say No
if ! ask "Do you want to do such-and-such?"; then
    said_no
fi

# Or if you prefer the shorter version:
ask "Do you want to do such-and-such?" && said_yes

ask "Do you want to do such-and-such?" || said_no