Code Review Request: My First Rust Project - "cosmic-ctl"

[dire torrent]

Looks good!
I think the only real complaint I have is that the main function is really long. I'd say at least split the subcommands into their own functions, like you did with the first three.

Then for further niceties, I think a custom Error type may be nice. I'm personally not a huge fan of having println scattered everywhere. I prefer having a custom Error/Result type and then do all the strings in a display implementation. But here you could definitely argue for preference either way.

[pulsar prairie]

main.rs needs to be split up.
I'd suggest creating commands.rs, and config.rs.

I'd also suggest encapsulating the commands into their own distinct structs, and implementing a common actionable trait for each - i.e. each command has an associated action. You can put this trait in an action.rs.

// ---------------------------------- //
// action.rs
// ---------------------------------- //

trait Action {
    // The error type to be returned on failure.
    type Err;

    // Perform the action.
    fn action(&self) -> Result<(), Self::Err>;
}

// ---------------------------------- //
// command/mod.rs
// ---------------------------------- //

enum Command {
    Read(ReadCommand),
    // etc...
}

impl Action for Command {
    // Use string errors for now.
    type Err = String;

    fn action(&self) -> Result<(), Self::Err> {
        match self {
            Self::Read(read_command) => read_command.action(),
            // etc...
        }
    }
}

// ---------------------------------- //
// command/read.rs
// ---------------------------------- //

struct ReadCommand {
    // version: u64,
    // component: String,
    // entry: String,
}

impl Action for ReadCommand {
    // Use string errors for now.
    type Err = String;

    fn action(&self) -> Result<(), Self::Err> {
        println!("Action Read");
        // etc...
        Ok(())
    }
}

// ---------------------------------- //
// main.rs
// ---------------------------------- //

fn main() {
    let command = Command::Read(ReadCommand{ /* ... */ });
    command.action();
}

Then, all your functions at the bottom (like read_configuration) can go in the file with it's command and impl action, or some common actions file.