How to autocomplete a shell command starting with (an alias involving) sudo

Question

Assume one has the following alias in your .bashrc:

alias docker='sudo docker'

then try to autocomplete docker run -v /tmp/test:/foo … in a bash terminal, starting from docker run -v /tmp| → due to the presence of sudo in the alias, one gets the following distracting behavior:

$ docker run -v /tmpTAB
$ docker run -v /tmp[sudo] password for user: 

and at that point, it is almost impossible to further edit the command line, apart from doing Ctrl+C and restarting.

Are there solutions to overcome that behavior? namely, keep the sudo implied in the alias, but avoid the password prompt when we are just expecting some regular autocompletion.

A solution that is independent of the alias feature would be nice (given the issue presented here also arises when typing any $ sudo command … directly).

Answer 1

If you're looking to avoid a password prompt on sudo, try the -n option.

The man page for sudo reads:

-n, --non-interactive

Avoid prompting the user for input of any kind. If a password is required for the command to run, sudo will display an error message and exit.

Answer 2

Relying on @ApolloXI's advice regarding sudo -n and doing more experimentations, I was able to overcome the drawback I was mentioning in my previous comment.

To sum up, when autocompleting docker … commands, the following code is loaded:

• From /etc/bash.bashrc: . /usr/share/bash-completion/bash_completion;
• From /usr/share/bash-completion/bash_completion:
  • __load_completion docker,
  • then . /usr/share/bash-completion/completions/docker;
• From /usr/share/bash-completion/completions/docker:
  • docker version -f '{{.Client.Experimental}} {{.Server.Experimental}} {{.Server.Os}}, etc.
  • which re-runs the docker command (or the alias, if it exists).

So a working solution would just amount to replace my alias with a bash function, detecting whether it is called from the bash-completion feature. This can be done by reading the BASH_SOURCE array.

As a result, we could adopt the following solution:

docker() {
    if [[ "${BASH_SOURCE[*]}" =~ "bash-completion" ]]; then
        sudo -n docker "$@"
    else
        sudo docker "$@"
    fi
}

or if we want to be able to easily disable the wrapper, write instead:

__docker() {
    if [[ "${BASH_SOURCE[*]}" =~ "bash-completion" ]]; then
        docker "$@"
    else
        sudo docker "$@"
    fi
}

alias docker=__docker

Then, the sudo -n prefix is not necessary anymore, and it is possible to run for example:

$ \docker run --help