rc/sh/confirm

#!/usr/bin/env bash
# YES_ZSH
# YES_BASH
# NO_DASH

### @ confirm
### display a simple yes-or-no prompt and return 0-or-1 respectively.
###
### ```
### $ confirm && echo yay || echo nay
### Continue? [y/N] y
### yay
### $ confirm && echo yay || echo nay
### Continue? [y/N] n
### nay
### ```
###
### a real world example:
###
### ```
### % g1 && confirm && git commit -a --amend --no-edit
### daf84e3 document a ton of stuff
### Continue? [y/N] y
### [master 92bdf76] document a ton of stuff
###  Date: Sun Aug 1 09:27:25 2021 -0700
###  20 files changed, 406 insertions(+), 29 deletions(-)
### ```

if [ -n "$ZSH_VERSION" ]; then
    confirm() {
        [ $# -le 0 ] || { printf "%s\n" "$0: too many arguments" >&2; return 1; }
        read -q '?Continue? [y/N] '
        ret=$?
        echo
        return $ret
    }
else
    confirm() {
        # specify stdin (1) to avoid taking input from pipes
        [ $# -le 0 ] || { printf "%s\n" "$0: too many arguments" >&2; return 1; }
        read -n1 -u 1 -p "Continue? [y/N] " c
        echo
        [ "$c" != 'y' ] && [ "$c" != 'Y' ] && return 1
        return 0
    }
fi

[ "${SOURCING:-0}" -gt 0 ] || confirm "$@"