Parse arguments in Rust with clap crate

01-parse-arguments-with-clap.rs

use clap::Parser;

#[derive(Parser,Default,Debug)]
#[clap(author="Nasqueron project", version, about="Import FANTOIR database into PostgreSQL")]
struct Arguments {
    /// Create table if it doesn't exist
    #[arg(short = 'c')]
    create_table: bool,

    /// Truncate table if it already exists, allowing the overwrite mode.
    /// If not specified, the script will fail if table exists.
    #[arg(short = 't')]
    overwrite_table: bool,

    /// The FANTOIR file to import
    fantoir_file: String,

    /// The name of the table to populate
    fantoir_table: String,
}

fn main() {
    let args = Arguments::parse(); // Will exit if argument is missing or --help --version provided.

    let database_url = ...;

    import(&args.fantoir_file, &database_url, &args.fantoir_table);
}

fn import(file: &str, database_url: &str, table: &str) {
    // ...
}

02-alternative.rs

// Same struct Arguments
// But pass all the struct to the main helper function, and show how to read it.

fn main() {
    let args = Arguments::parse(); // Will exit if argument is missing or --help --version provided.

    let database_url = ...;

    import(&args, &database_url);
}

fn import(args: &Arguments, database_url: &str) {
    let fd = File::open(&args.fantoir_file).expect("Can't open file.");
    // ...

    if args.create_table {
        // ...
    }

    // ...
}

The code is extracted from fantoir2db utility I'm currently writing.

Arguments are the current real ones. Output of ./fantoir2db --help is :

Import FANTOIR database into PostgreSQL

Usage: fantoir2db [OPTIONS] <FANTOIR_FILE> <FANTOIR_TABLE>

Arguments:
  <FANTOIR_FILE>   The FANTOIR file to import
  <FANTOIR_TABLE>  The name of the table to populate

Options:
  -c             Create table if it doesn't exist
  -t             Truncate table if it already exists, allowing the overwrite mode. If not specified, the script will fail if table exists
  -h, --help     Print help information
  -V, --version  Print version information

To simplify the gist and focus on arguments parsing, the code has been written as synchronous, whereas fantoir2db uses async code for I/O and database access, but that's not in the scope of this example.

Another simplification is the use of &str for filename argument, where we can allow more generic types for a path.