base58=({1..9} {A..H} {J..N} {P..Z} {a..k} {m..z})
bitcoinregex="^[$(printf "%s" "${base58[@]}")]{34}$"

decodeBase58() {
    local s=$1
    for i in {0..57}
    do s="${s//${base58[i]}/ $i}"
    done
    dc <<< "16o0d${s// /+58*}+f"
}

checksum() {
    xxd -p -r <<<"$1" |
    openssl dgst -sha256 -binary |
    openssl dgst -sha256 -binary |
    xxd -p -c 80 |
    head -c 8
}

checkBitcoinAddress() {
    if [[ "$1" =~ $bitcoinregex ]]
    then
        h=$(decodeBase58 "$1")
        checksum "00${h::${#h}-8}" |
        grep -qi "^${h: -8}$"
    else return 2
    fi
}