Shell prompt helper command

[ijanos]

I was using multirust ctl override-toolchain command to show the currently selected toolchain in my shell's prompt if the current directory contains a Cargo.toml file, similarly to showing the current git branch if the directory is a git repository. I've found issue #491 mentioning that ctl like commands are not likely to appear in rustup.

Would you consider this as a use case for a new rustup command or should I fall back to some other solution, like piping rustup's output through sed?

[kbknapp]

Although not a 1:1 solution, rustup show | tail -n 3 | head -n 1 shows something like:

$ rustup show | tail -n 3 | head -n 1
stable-x86_64-unknown-linux-gnu (default)

Which I'm sure could be cut down more if desired.

[ijanos]

Well, programming rust is fun, so I threw together a small helper program for this. I think a subcommand like rustup show override could still be useful for prompts and other scripting purposes, so I will leave the issue open but feel free to close it if you think this is out of scope for the rustup project.

[Diggsey]

Dupe of #491