This is a general-purpose function to ask Yes/No questions in Bash, either with or without a default answer.

ask.sh

#!/bin/bash

# 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.
# http://djm.me/ask
    
while true; do

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

    # Ask the question
    echo -ne "$1 [$prompt] "
    read -n1 REPLY
    echo

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

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

done

ask_example.sh

#/bin/bash

said_yes() { echo "Just said YES!"; }
said_no()  { echo "Just said NO!";  }

# EXAMPLE USAGE:

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

# Colored syntax:
ask "Do you want to do \\033[1;31msuch-and-such\\033[0m?" && said_yes

# 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