#! /bin/zsh

unit () {
    # check for 3 args, e.g.
    # $ unit 5 miles km
    local args=$#
    local req_args=3
    if (( $args != $req_args )); then
        wrong-number-of-arguments-message $args $req_args
        return
    fi

    # get args
    local quant=$1
    local src_unit=$2
    local dst_unit=$3

    # use bc to get significant digits of the input quantity
    local sig=$(echo "length($quant)" | bc)

    # compute
    local quant_dest=$(units -t -d $sig "$quant $src_unit" $dst_unit)

    # output with unit
    echo $quant_dest $dst_unit
}