Ignore sudo in bash script if using root

This question is not duplicate of Ignore sudo in bash script

I am making a docker image based on Ubuntu 14.04 docker image. As you know, root is default user in docker. When I ran a bash script to install a software, got

sudo: error in /etc/sudo.conf, line 0 while loading plugin `sudoers_policy'
sudo: /usr/lib/sudo/sudoers.so must be owned by uid 0
sudo: fatal error, unable to load plugins

I have tried chown root /usr/lib/sudo/sudoers.so,but it is not working.

This behavior is weird :

ls    (everyone can do this)
sudo ls   (you can't do this even if you are root)

Because I am building a docker image, I don't want to install uncorrelated packages to make sudo support root. But there are bunch of sudo in some bash scripts,so simply replacing sudo to empty may not a good choice.

So I'm wondering if is there any way to only ignore sudo when you are root

In your scripts, towards the beginning, define sudo to be a function that calls the actual sudo if needed:

sudo ()
{
    [[ $EUID = 0 ]] || set -- command sudo "$@"
    "$@"
}

command sudo foo bar tells bash to use the actual sudo command instead of functions or aliases. $EUID is the effective user ID, which might be different from $UID.

Disclaimer: Does not work with pipes

An alternative to the answer by @muru is to use an alias and a check if the user is root. This avoids running the commands in function and the side effects that that might have. A solution that should work on all shells (tested on Alpine Linux):

if [ $(id -u) -eq 0 ]; then
  alias sudo=eval
fi

On more modern shells, the following can also be used:

if (( $EUID == 0 )); then
  alias sudo=eval
fi