#!/usr/bin/env sh
# compat: +ash +bash +dash +hush -ksh +mksh +oksh +osh +posh +yash +zsh

isup() { ### @-
    ### return 0 if a given website returns a 2xx HTTP code.
    ###
    ### ```
    ### $ isup google.com && echo yay || echo nay
    ### yay
    ### $ isup fdhafdslkjgfjs.com && echo yay || echo nay
    ### nay
    ### ```
    local c="$(curl -sLI -w '%{http_code}' -o /dev/null "$1")"
    [ -z "${c#2[0-9][0-9]}" ]
}

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