For more on creating a custom subcommand, see [the cargo
book](https://doc.rust-lang.org/cargo/reference/external-tools.html#custom-subcommands).
The crate [`clap-cargo`](https://github.com/crate-ci/clap-cargo) can help in
mimicking cargo's interface.
The help looks like:
```console
$ cargo-example --help
Usage: cargo <COMMAND>
Commands:
example A simple to use, efficient, and full-featured Command Line Argument Parser
help Print this message or the help of the given subcommand(s)
Options:
-h, --help Print help information
$ cargo-example example --help
A simple to use, efficient, and full-featured Command Line Argument Parser
Usage: cargo example [OPTIONS]
Options:
--manifest-path <PATH>
-h, --help Print help information
-V, --version Print version information
```
Then to directly invoke the command, run:
```console
$ cargo-example example
None
$ cargo-example example --manifest-path Cargo.toml
Some("Cargo.toml")
```