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@kapatheus
Created March 30, 2021 05:52
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Bash General-Purpose Yes/No Prompt Function ("ask")

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() {
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
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