_nft()
{
    local cur prev
    COMPREPLY=()
    cur="${COMP_WORDS[COMP_CWORD]}"
    prev="${COMP_WORDS[COMP_CWORD-1]}"

    local families="ip ip6 arp bridge inet netdev"
    local sets=$(nft list sets | grep -i "set" | awk '{print $2 }' | tr -d ' ')

    if [ $COMP_CWORD -eq 1 ]; then
        COMPREPLY=( $(compgen -W "add flush list" -- $cur) )
    elif [ $COMP_CWORD -eq 2 ]; then
        case "$prev" in
            "add")
                command="${prev}"
                COMPREPLY=( $(compgen -W "element map table set" -- $cur) )
                ;;
            "list")
                COMPREPLY=( $(compgen -W "chains ruleset set sets table tables" -- $cur) )
                ;;
            "flush")
                COMPREPLY=( $(compgen -W "table" -- $cur) )
                ;;
            *)
                ;;
        esac
    elif [ $COMP_CWORD -eq 3 ]; then
        case "$prev" in
            "table")
                COMPREPLY=( $(compgen -W "${families}" -- $cur) )
                ;;
            "set"|"element"|"map")
                local tables=$(nft list tables | awk '{print $3 }' | tr -d ' ')
                COMPREPLY=( $(compgen -W "${tables}" -- $cur) )
                ;;
            *)
                ;;
        esac
    elif [ $COMP_CWORD -eq 4 ]; then
        local tables=$(nft list tables | awk '{print $3 }' | tr -d ' ')
        if [[ "$families" =~ "$prev" ]]; then
            local tables=$(nft list tables "${prev}" | awk '{print $3 }' | tr -d ' ')
            COMPREPLY=( $(compgen -W "${tables}" -- $cur) )
        fi

        if [ "${COMP_WORDS[1]}" != "add" ] && [[ "$tables" =~ "$prev" ]]; then
            COMPREPLY=( $(compgen -W "${sets}" -- $cur) )
        fi

        if [ "${COMP_WORDS[1]}" == "add" ] && [ "${COMP_WORDS[2]}" == "element" ] && [[ "$tables" =~ "$prev" ]]; then
            COMPREPLY=( $(compgen -W "${sets}" -- $cur) )
        fi
    fi

    return 0;
}

complete -F _nft nft

Un truc un peu pédago qui parle de nftables

via blue, le remplaçant d'iptables codé par redhat, les syntaxes sont orientées "block" pour éviter les séquences imho, ça m'a l'air bien puissant