There are a number of environment variables available during the build of a binary. One of them is the CARGO_PKG_VERSION variable that contains the version number as written in the Cargo.toml file.

Using the env! macro we can extract the value during the build phase of the compilation and we can include it on our code either as a constant using the const keyword or we can make it a regular variable either explicitely making it a static variable or letting Rust figure out the type.

The difference will be the location where the value is stored.

{% include file="examples/embed-version-number/src/main.rs" %}

Cargo.toml with the version number

{% include file="examples/embed-version-number/Cargo.toml" %}

Note

I'd go with the const.

If you only need to have a --version flag you can tell Clap to create a --version flag.