How to Prompt For Yes/No/Cancel Input in a Linux Shell Script

How do I prompt for Yes/No/Cancel input in a Linux shell script?

The simplest and most widely available method to get user input at a shell prompt is the read command. The best way to illustrate its use is a simple demonstration:

while true; do
    read -p "Do you wish to install this program? " yn
    case $yn in
        [Yy]* ) make install; break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
    esac
done

Another method, pointed out by Steven Huwig, is Bash's select command. Here is the same example using select:

echo "Do you wish to install this program?"
select yn in "Yes" "No"; do
    case $yn in
        Yes ) make install; break;;
        No ) exit;;
    esac
done

With select you don't need to sanitize the input – it displays the available choices, and you type a number corresponding to your choice. It also loops automatically, so there's no need for a while true loop to retry if they give invalid input.

Also, Léa Gris demonstrated a way to make the request language agnostic in her answer. Adapting my first example to better serve multiple languages might look like this:

set -- $(locale LC_MESSAGES)
yesexpr="$1"; noexpr="$2"; yesword="$3"; noword="$4"

while true; do
    read -p "Install (${yesword} / ${noword})? " yn
    if [[ "$yn" =~ $yesexpr ]]; then make install; exit; fi
    if [[ "$yn" =~ $noexpr ]]; then exit; fi
    echo "Answer ${yesword} / ${noword}."
done

Obviously other communication strings remain untranslated here (Install, Answer) which would need to be addressed in a more fully completed translation, but even a partial translation would be helpful in many cases.

Finally, please check out the excellent answer by F. Hauri.

Bash prompt with yes, no and cancel

I believe it would be just overall simpler to work the same way as read works. Remember to pick a unique name for the namereference.

ask() {
  declare -n _ask_var=$2
  local _ask_answer
  while true; do
    read -p "$1 [Y/n/a] " _ask_answer
    case "${_ask_answer,,}" in
      y|yes|"" ) _ask_var="true" ; break; ;;
      n|no     ) _ask_var="false"; break; ;;
      a|abort  ) exit 1; ;;
    esac
  done
}

ask "Are you happy?" answer
if "$answer"; then echo "Yay! Me too!"; fi

How do I prompt for Yes/No/Cancel input in a Linux shell script?

The simplest and most widely available method to get user input at a shell prompt is the read command. The best way to illustrate its use is a simple demonstration:

while true; do
    read -p "Do you wish to install this program? " yn
    case $yn in
        [Yy]* ) make install; break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
    esac
done

Another method, pointed out by Steven Huwig, is Bash's select command. Here is the same example using select:

echo "Do you wish to install this program?"
select yn in "Yes" "No"; do
    case $yn in
        Yes ) make install; break;;
        No ) exit;;
    esac
done

With select you don't need to sanitize the input – it displays the available choices, and you type a number corresponding to your choice. It also loops automatically, so there's no need for a while true loop to retry if they give invalid input.

Also, Léa Gris demonstrated a way to make the request language agnostic in her answer. Adapting my first example to better serve multiple languages might look like this:

set -- $(locale LC_MESSAGES)
yesexpr="$1"; noexpr="$2"; yesword="$3"; noword="$4"

while true; do
    read -p "Install (${yesword} / ${noword})? " yn
    if [[ "$yn" =~ $yesexpr ]]; then make install; exit; fi
    if [[ "$yn" =~ $noexpr ]]; then exit; fi
    echo "Answer ${yesword} / ${noword}."
done

Obviously other communication strings remain untranslated here (Install, Answer) which would need to be addressed in a more fully completed translation, but even a partial translation would be helpful in many cases.

Finally, please check out the excellent answer by F. Hauri.

How to prompt for yes or no in bash?

I like to use the following function:

function yes_or_no {
    while true; do
        read -p "$* [y/n]: " yn
        case $yn in
            [Yy]*) return 0  ;;  
            [Nn]*) echo "Aborted" ; return  1 ;;
        esac
    done
}

So in your script you can use like this:

yes_or_no "$message" && do_something

In case the user presses any key other than [yYnN] it will repeat the message.

How do I prompt for Yes/No/Cancel input in a Linux shell script?

The simplest and most widely available method to get user input at a shell prompt is the read command. The best way to illustrate its use is a simple demonstration:

while true; do
    read -p "Do you wish to install this program? " yn
    case $yn in
        [Yy]* ) make install; break;;
        [Nn]* ) exit;;
        * ) echo "Please answer yes or no.";;
    esac
done

Another method, pointed out by Steven Huwig, is Bash's select command. Here is the same example using select:

echo "Do you wish to install this program?"
select yn in "Yes" "No"; do
    case $yn in
        Yes ) make install; break;;
        No ) exit;;
    esac
done

With select you don't need to sanitize the input – it displays the available choices, and you type a number corresponding to your choice. It also loops automatically, so there's no need for a while true loop to retry if they give invalid input.

Also, Léa Gris demonstrated a way to make the request language agnostic in her answer. Adapting my first example to better serve multiple languages might look like this:

set -- $(locale LC_MESSAGES)
yesexpr="$1"; noexpr="$2"; yesword="$3"; noword="$4"

while true; do
    read -p "Install (${yesword} / ${noword})? " yn
    if [[ "$yn" =~ $yesexpr ]]; then make install; exit; fi
    if [[ "$yn" =~ $noexpr ]]; then exit; fi
    echo "Answer ${yesword} / ${noword}."
done

Obviously other communication strings remain untranslated here (Install, Answer) which would need to be addressed in a more fully completed translation, but even a partial translation would be helpful in many cases.

Finally, please check out the excellent answer by F. Hauri.

How do I prompt a user for confirmation in bash script?

read -p "Are you sure? " -n 1 -r
echo    # (optional) move to a new line
if [[ $REPLY =~ ^[Yy]$ ]]
then
    # do dangerous stuff
fi

I incorporated levislevis85's suggestion (thanks!) and added the -n option to read to accept one character without the need to press Enter. You can use one or both of these.

Also, the negated form might look like this:

read -p "Are you sure? " -n 1 -r
echo    # (optional) move to a new line
if [[ ! $REPLY =~ ^[Yy]$ ]]
then
    [[ "$0" = "$BASH_SOURCE" ]] && exit 1 || return 1 # handle exits from shell or function but don't exit interactive shell
fi

However, as pointed out by Erich, under some circumstances such as a syntax error caused by the script being run in the wrong shell, the negated form could allow the script to continue to the "dangerous stuff". The failure mode should favor the safest outcome so only the first, non-negated if should be used.

Explanation:

The read command outputs the prompt (-p "prompt") then accepts one character (-n 1) and accepts backslashes literally (-r) (otherwise read would see the backslash as an escape and wait for a second character). The default variable for read to store the result in is $REPLY if you don't supply a name like this: read -p "my prompt" -n 1 -r my_var

The if statement uses a regular expression to check if the character in $REPLY matches (=~) an upper or lower case "Y". The regular expression used here says "a string starting (^) and consisting solely of one of a list of characters in a bracket expression ([Yy]) and ending ($)". The anchors (^ and $) prevent matching longer strings. In this case they help reinforce the one-character limit set in the read command.

The negated form uses the logical "not" operator (!) to match (=~) any character that is not "Y" or "y". An alternative way to express this is less readable and doesn't as clearly express the intent in my opinion in this instance. However, this is what it would look like: if [[ $REPLY =~ ^[^Yy]$ ]]

If statements accepting yes or no in bash script?

There are several problems with your code:

1. Failure to put spaces around [ (which is a command name) and ] (which is a mandatory but functionless argument to ]).
2. Treating the contents of a variable as a command; use functions instead.

---

yesdebug () { echo "Will run in debug mode"; }

nodebug () { echo "Will not run in debug mode"; }

echo "Would you like to run script in debug mode? (yes or no)"

read yesorno

if [ "$yesorno" = yes ]; then
    yesdebug

elif [ "$yesorno" = no ]; then
    nodebug
else
    echo "Not a valid answer."
    exit 1
fi

bypass Yes/No in Shell Script

If you just need to answer "Yes" to everything, you can use

yes Yes | ./ittp-update.sh

How this works:

1. The program yes prints the string you give it (or "y" if you don't give it anything, since this is the default way to give a positive answer in *nix programs) repeatedly on standard output until it receives SIGPIPE.
2. The pipe (|) connects standard output of the preceding command (yes) to the standard input of the following command (./ittp-update.sh).
3. When ./ittp-update.sh finishes, the shell automatically sends SIGPIPE to any commands connected to it by pipes (only yes in this case).
4. Upon receiving SIGPIPE, yes exits.

See man yes for more information.

---

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