Command-line and config file, both use-cases become possible with structopt?

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Issue by SamuelMarks
Wednesday Jun 05, 2019 at 04:46 GMT
Originally opened as TeXitoi/structopt#197

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A few common use-cases:

• Accept input from config file
• Accept input from environment variables
• Accept input from command-line

Then, overriding config file attributes with environment variable or command line.

I'm not sure exactly how to represent this in Rust, but something like:

#[derive(StructOpt, Debug)]
#[structopt(name = "example", about = "An example of StructOpt usage.")]
struct Opt {
    /// The config file
    #[structopt(short = "c", long = "config", help = "Config file")]
    config_file: Option<Config>,

    #[structopt(flatten, required_unless = "config_file")
    options: Option<Config>,
}

#[derive(StructOpt, Debug)]
struct Config {
    /// A flag, true if used in the command line.
    #[structopt(short = "d", long = "debug", help = "Activate debug mode")]
    debug: bool,

    /// An argument of type float, with a default value.
    #[structopt(short = "s", long = "speed", help = "Set speed", default_value = "42")]
    speed: f64,

    /// Needed parameter, the first on the command line.
    #[structopt(help = "Input file")]
    input: String,

    /// An optional parameter, will be `None` if not present on the
    /// command line.
    #[structopt(help = "Output file, stdout if not present")]
    output: Option<String>,

    /// An optional parameter with optional value, will be `None` if
    /// not present on the command line, will be `Some(None)` if no
    /// argument is provided (i.e. `--log`) and will be
    /// `Some(Some(String))` if argument is provided (e.g. `--log
    /// log.txt`).
    #[structopt(
        long = "log",
        help = "Log file, stdout if no file, no logging if not present"
    )]
    log: Option<Option<String>>,

    /// An optional list of values, will be `None` if not present on
    /// the command line, will be `Some(vec![])` if no argument is
    /// provided (i.e. `--optv`) and will be `Some(Some(String))` if
    /// argument list is provided (e.g. `--optv a b c`).
    #[structopt(long = "optv")]
    optv: Option<Vec<String>>,
}

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Comment by TeXitoi
Wednesday Jun 05, 2019 at 09:15 GMT

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See also #72

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Comment by TeXitoi
Wednesday Jun 05, 2019 at 09:41 GMT

---

Note that clap support environment variable. You can use that:

#[derive(StructOpt, Debug)]
struct Opt {
    #[structopt(short, long, env = "FILE", default_value = "foo")]
    file: String,
}

if -f or --file is given on the command line, it is used, else if the environment variable FILE is setted, it is used, else the default value "foo" is used.

[epage]

I'm closing this in favor of #3113 to track config layering