ask

#!/bin/bash

###############################################################################
# Handle options
###############################################################################

# Display the help
if [ "${1:-}" = "-h" ] || [ "${1:-}" = "--help" ]; then
  echo -e "
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.
https://gist.github.com/davejamesmiller/1965569

\e[33mUsage:\e[0m
  ask [-h] <question> {-y|-n}

\e[33mArguments:\e[0m
  question  The question that should be answered

\e[33mOptions:\e[0m
\e[32m  -h, --help \e[0m Display this help message
\e[32m  -y         \e[0m Make Yes the default answer [Y/n]
\e[32m  -n         \e[0m Make No the default answer [y/N]

\e[33mExamples:\e[0m
  \e[37m// Only do something if you say yes, defaults to yes\e[0m
  if ask \"Do you want to do such-and-such?\" -y; then
    said_yes
  fi

  \e[37m// Shorter versions\e[0m
  ask \"Do you want to do such-and-such?\" && said_yes

  ask \"Do you want to do such-and-such?\" || said_no
"
  exit 0;
fi

# Handle what answer to be default
if [ "${2:-}" = "-y" ]; then
    prompt="Y/n"
    default=Y
elif [ "${2:-}" = "-n" ]; then
    prompt="y/N"
    default=N
else
    prompt="y/n"
    default=
fi


###############################################################################
# Script
###############################################################################

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 reply </dev/tty

    # Set the default if we didn't answer the question
    if [ -z "$reply" ]; then
        reply=${default}
    fi

    # Exit with 0 or 1 depending on the reply
    case "${reply}" in
        Y*|y*) exit 0 ;;
        N*|n*) exit 1 ;;
    esac
done