have ipv6calc &&
_ipv6calc()
{
    local cur prev split=false

    COMPREPLY=()
    _get_comp_words_by_ref -n = cur prev
    #cur=`_get_cword =`
    #prev=`_get_pword`

    _split_longopt && split=true

    case "$prev" in
        -d|--debug)
            return 0
            ;;
        -I|--in|-O|--out|-A|--action)
            # With ipv6calc < 0.73.0, -m does nothing here, so use sed instead.
            COMPREPLY=( $( compgen -W "$( ipv6calc "$prev" -h 2>&1 | \
                sed -ne 's/^[[:space:]]\{1,\}\([^[:space:]:]\{1,\}\)[[:space:]]*:.*/\1/p' )" \
                -- "$cur" ) )
            return 0
            ;;
        --db-geoip|--db-ip2location-ipv4|--db-ip2location-ipv6)
            _filedir
            return 0
            ;;
        --printstart|--printend)
            return 0
            ;;
    esac

    $split && return 0

    if [[ "$cur" == -* ]]; then
        COMPREPLY=( $( compgen -W '--help --debug --quiet --in \
            --out --action --examples --showinfo --show_types \
            --machine_readable --db-geoip --db-geoip-default \
            --db-ip2location-ipv4 --db-ip2location-ipv6 \
            --lowercase --uppercase --printprefix --printsuffix \
            --maskprefix --masksuffix --printstart --printend \
            --printcompressed --printuncompressed \
            --printfulluncompressed --printmirrored' -- "$cur" ) )
        return 0
    fi

    return 0
} &&
complete -F _ipv6calc ipv6calc

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