rc/sh/has

#!/usr/bin/env sh
# YES_ZSH
# YES_BASH
# YES_DASH
# YES_ASH

has() ( ### @- print the result of `which` if the program is found, else simply return 1.
    ### ```
    ### export SOLVER="$(has kissat || has picosat || has cadical || has minisat)"
    ### ```
    fancy=0
    [ -z "$ZSH_VERSION" ] && [ -z "$BASH_VERSION" ] || fancy=1

    if [ "${1:-/}" = "${1#*[!A-Za-z_-]}" ]; then # has a simple name?
        # only ash and dash support aliases beginning with hyphens.
        # forcefully unalias it (regardless of if it even was an alias):
        if [ $fancy = 0 ] || [ "${1:-/}" = "${1#-}" ]; then
            alias "$1"=
            unalias -- "$1"
        fi

        # only bash and zsh support function names containing hyphens.
        # forcefully unset it (regardless of if it even was a function):
        if [ "$FANCY" = 1 ]; then
            eval -- "$1() (:)"
            unset -f -- "$1"
        elif [ "${1:-/}" = "${1#*-}" ]; then
            eval "$1() (:)"
            unset -f -- "$1"
        fi
    fi

    which -- "$1" >/dev/null 2>&1 && which -- "$1"
) # this uses parentheses instead of braces so that the function is always run
#   in a subshell. otherwise, the user's aliases and functions may be overwritten.

[ -n "${preload+-}" ] || has "$@"