Bash General-Purpose Yes/No Prompt Function ("ask")

_README.md

This is 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.

ask.sh

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)
        printf '%s%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
}

examples.sh

# EXAMPLE USAGE:

if ask "Do you want to do such-and-such?"; then
    printf '%s\n' "Yes"
else
    printf '%s\n' "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
    printf '%s\n' "Yes"
else
    printf '%s\n' "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
    printf '%s\n' "Yes"
else
    printf '%s\n' "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