You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: main.rs
    path of file: ./repos/tock/tools/sha256sum/src
    
    the code of the file until where you have to start completion: //! Example copied from https://github.com/RustCrypto/hashes/blob/master/sha2/examples/sha256sum.rs
//!
//! Please refer to the license at: https://github.com/RustCrypto/hashes#licen
    
fn main() {
    let args = env::args();
    // Process files listed in command line arguments one by one
    // If no files provided process input from stdin
    if args.len() > 1 {
        for path in args.skip(1) {
            if let Ok(mut file) = fs::File::open(&path) {
                process::<Sha256, _>(&mut file, &path);
            }
        }
    } else {
        process::<Sha256, _>(&mut io::stdin(), "-");
    }
}