In Bash, how to add "Are you sure [Y/n]" to any command or alias?

user_325418 0
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In this particular case, I'd like to add a confirm in Bash for

Are you sure? [Y/n]

for Mercurial's hg push ssh://username@www.example.com//somepath/morepath, which is actually an alias. Is there a standard command that can be added to the alias to achieve it?

The reason is that hg push and hg out can sound similar and sometimes when I want hgoutrepo, I may accidentlly type hgpushrepo (both are aliases).

Update: if it can be something like a built-in command with another command, such as: confirm && hg push ssh://... that'd be great... just a command that can ask for a yes or no and continue with the rest if yes.

confirmation alias bash
18 Answers

No pressing enter required

Here's a longer, but reusable and modular approach:

  • Returns 0=yes and 1=no
  • No pressing enter required - just a single character
  • Can press enter to accept the default choice
  • Can disable default choice to force a selection
  • Works for both zsh and bash.

Defaulting to "no" when pressing enter

Note that the N is capitalsed. Here enter is pressed, accepting the default:

$ confirm "Show dangerous command" && echo "rm *"
Show dangerous command [y/N]?

Also note, that [y/N]? was automatically appended. The default "no" is accepted, so nothing is echoed.

Re-prompt until a valid response is given:

$ confirm "Show dangerous command" && echo "rm *"
Show dangerous command [y/N]? X
Show dangerous command [y/N]? y
rm *

Defaulting to "yes" when pressing enter

Note that the Y is capitalised:

$ confirm_yes "Show dangerous command" && echo "rm *"
Show dangerous command [Y/n]?
rm *

Above, I just pressed enter, so the command ran.

No default on enter - require y or n

$ get_yes_keypress "Here you cannot press enter. Do you like this"
Here you cannot press enter. Do you like this [y/n]? k
Here you cannot press enter. Do you like this [y/n]?
Here you cannot press enter. Do you like this [y/n]? n
$ echo $?
1

Here, 1 or false was returned. Note no capitalisation in [y/n]?

Code

# Read a single char from /dev/tty, prompting with "$*"
# Note: pressing enter will return a null string. Perhaps a version terminated with X and then remove it in caller?
# See https://unix.stackexchange.com/a/367880/143394 for dealing with multi-byte, etc.
function get_keypress {
  local REPLY IFS=
  >/dev/tty printf '%s' "$*"
  [[ $ZSH_VERSION ]] && read -rk1  # Use -u0 to read from STDIN
  # See https://unix.stackexchange.com/q/383197/143394 regarding '\n' -> ''
  [[ $BASH_VERSION ]] && </dev/tty read -rn1
  printf '%s' "$REPLY"
}

# Get a y/n from the user, return yes=0, no=1 enter=$2
# Prompt using $1.
# If set, return $2 on pressing enter, useful for cancel or defualting
function get_yes_keypress {
  local prompt="${1:-Are you sure} [y/n]? "
  local enter_return=$2
  local REPLY
  # [[ ! $prompt ]] && prompt="[y/n]? "
  while REPLY=$(get_keypress "$prompt"); do
    [[ $REPLY ]] && printf '\n' # $REPLY blank if user presses enter
    case "$REPLY" in
      Y|y)  return 0;;
      N|n)  return 1;;
      '')   [[ $enter_return ]] && return "$enter_return"
    esac
  done
}
    
# Credit: http://unix.stackexchange.com/a/14444/143394
# Prompt to confirm, defaulting to NO on <enter>
# Usage: confirm "Dangerous. Are you sure?" && rm *
function confirm {
  local prompt="${*:-Are you sure} [y/N]? "
  get_yes_keypress "$prompt" 1
}    

# Prompt to confirm, defaulting to YES on <enter>
function confirm_yes {
  local prompt="${*:-Are you sure} [Y/n]? "
  get_yes_keypress "$prompt" 0
}
user_53534610

This version allows you to have more than one case y or Y, n or N

  1. Optionally: Repeat the question until an approve question is provided

  2. Optionally: Ignore any other answer

  3. Optionally: Exit the terminal if you want

    confirm() {
    echo -n "Continue? y or n? "
    read REPLY
    case $REPLY in
    [Yy]) echo 'yup y' ;; # you can change what you do here for instance
    [Nn]) break ;;        # exit case statement gracefully
    # Here are a few optional options to choose between
    # Any other answer:

    # 1. Repeat the question
    *) confirm ;;

    # 2. ignore
    # *) ;;

    # 3. Exit terminal
    # *) exit ;;

    esac
    # REPLY=''
}

Notice this too: On the last line of this function clear the REPLY variable. Otherwise if you echo $REPLY you will see it is still set until you open or close your terminal or set it again.

user_17835880

Below code is combining two things

  1. shopt -s nocasematch that will take care of case insensitive

  2. and if condition that will accept both the input either you pass yes,Yes,YES,y.

    shopt -s nocasematch

    if [[ sed-4.2.2.$LINE =~ (yes|y)$ ]]

    then exit 0

    fi

user_15436480

Here is my solution that using localised regex. So in german also "j" for "Ja" would be interpreted as yes.

First argument is the question, if the second argument is "y" than yes would be the default answer otherwise no would be the default answer. The return value is 0 if the answer was "yes" and 1 if the answer was "no".

function shure(){
    if [ $# -gt 1 ] && [[ "$2" =~ ^[yY]*$ ]] ; then
        arg="[Y/n]"
        reg=$(locale noexpr)
        default=(0 1)
    else
        arg="[y/N]"
        reg=$(locale yesexpr)
        default=(1 0)
    fi
    read -p "$1 ${arg}? : " answer
    [[ "$answer" =~ $reg ]] && return ${default[1]} || return ${default[0]}
}

Here is a basic usage

# basic example default is no
shure "question message" && echo "answer yes" || echo "answer no"
# print "question message [y/N]? : "

# basic example default set to yes
shure "question message" y && echo "answer yes" || echo "answer no"
# print "question message [Y/n]? : "
user_12102720

I know this is an old question but this might help someone, it hasn't been addressed here.

I have been asked how to use rm -i in a script which is receiving input from a file. As file input to a script is normally received from STDIN we need to change it, so that only the response to the rm command is received from STDIN. Here's the solution:

#!/bin/bash
while read -u 3 line
do
 echo -n "Remove file $line?"
 read -u 1 -n 1 key
 [[ $key = "y" ]] &&  rm "$line"
 echo
done 3<filelist

If ANY key other than the "y" key (lower case only) is pressed, the file will not be deleted. It is not necessary to press return after the key (hence the echo command to send a new line to the display). Note that the POSIX bash "read" command does not support the -u switch so a workaround would need to be sought.

user_21453780
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