Auto-deriving environment variables

Environment variables tend to be called after the corresponding struct's field, as in example above. The field is secret_value and the env var is "SECRET_VALUE"; the name is the same, except casing is different.

It's pretty tedious and error-prone to type the same name twice, so you can ask structopt to do that for you.

# use structopt::StructOpt;

#[derive(StructOpt)]
struct Foo {
  #[structopt(long = "secret", env)]
  secret_value: String
}

It works just like #[structopt(short/long)]: if env is not set to some concrete value the value will be derived from the field's name. This is controlled by #[structopt(rename_all_env)].

rename_all_env works exactly as rename_all (including overriding) except default casing is SCREAMING_SNAKE_CASE instead of kebab-case.

StructOpt book

Auto-deriving environment variables