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I'm reading the code of Substrate Node Template, trying to get a deeper understanding of the implementation of it. However, I stuck when I tried to find out how the node deals with command line arguments, such as --dev.

From what I have learned from the codes, I believe that the SubstrateCli::from_iter function is responsible for parsing command line arguments, and the program crashes at the let matches = app.try_get_matches_from(iter).unwrap_or_else(|e| e.exit()); statement if I enter a incorrect cli argument(--devx, for instance). But how does the program know that --devx is incorrect while --dev is the correct one?

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I think this is a built-in feature of clap instead of Substrate.

https://github.com/clap-rs/clap

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  • And specifically, Substrate uses clap's derive macros (formerly known as structopt) Commented Jan 9 at 5:28
  • Could you please tell me if --dev is a built-in feature of clap? Also, is there a way for the node to determine if the user has provided this flag in the CLI? Commented Jan 10 at 6:05
  • First question clap is a cli framework, --dev is a custom flag that they use this framework to build. Second question github.com/substrate-developer-hub/substrate-node-template/blob/….
    – AurevoirXavier
    Commented Jan 10 at 6:26

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