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

Question

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//some

Answer 1

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' -> ''
  [[ $BASH_VERSION ]] && 
# Usage: confirm "Dangerous. Are you sure?" && rm *
function confirm {
  local prompt="${*:-Are you sure} [y/N]? "
  get_yes_keypress "$prompt" 1
}    

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