How To Build CLI App In Rust Using Clap - Part 2

How To Build CLI App In Rust Using Clap - Part 2

Generate Command

Shreyas K S's photo
Shreyas K S
·Sep 28, 2022·

3 min read

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Previously, we ran our first iteration of the cli application by setting up the project and adding commands. In this post, we will cover our first command, generate, that generates a secret containing the key and the IV (initial-value) to the output file given as a flag for this command.

Implementing Generate Command Logic

Create a new file and start adding logic to generate a key and an IV (initial-value). Install a new dependency for generating random values by running the below command.

cargo add rand

Screenshot 2022-09-28 at 2.42.30 PM.png

Import newly added dependency to file. And import in

Let us add logic to the file:

Here, we are using a crate called serde for serialization and deserialization. Add serde dependencies to Cargo.toml file.

serde_json = "1.0.85"
serde = "1.0.85"
serde_derive = "1.0.85"

More on serde

Define a struct Secret with two members key and initial-value both are of type String.

Now implement a function new for Secret struct. This function is used to generate a Secret by encoding the key and initial-value to base64.

Using rand crate a key and an initial value are generated from random values. Both key and initial-value are of length 16. Then the secret is written to the output file path which is received as user input.

use super::*;

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Secret {
    key: String,
    inital_value: String,

impl Secret {
    pub fn new(out_path: String) {
        let mut key = [0u8; 16];
        thread_rng().fill_bytes(&mut key[..]);

        let mut inital_value = [0u8; 16];
        thread_rng().fill_bytes(&mut inital_value[..]);

        let secret = Secret {
            key: base64::encode(key),
            inital_value: base64::encode(inital_value),

        let secret = to_vec(&secret).unwrap();
        let mut file = File::create(out_path).unwrap();

        println!("Secret Generated Successfully")

Fixing up file to generate the secret Keystore.

use clap::{Parser, Subcommand};
use generate::Secret;
use rand::*;
mod commands;
use commands::Cryptifer;
mod generate;
use serde_derive::{Deserialize, Serialize};
use serde_json::to_vec;
use std::fs::File;
use std::io::Write;

fn main() {
    let cryptifer = Cryptifer::parse();

    match cryptifer.command {
        commands::Commands::Generate { output_path } => {
        commands::Commands::Encrypt {
            file_path: _,
            key_path: _,
        } => todo!(),
        commands::Commands::Decrypt {
            encrypted_file: _,
            key_path: _,
        } => todo!(),

Running Your First Command

cargo run generate -o Keystore.secret

Screenshot 2022-09-28 at 6.24.20 PM.png

That generates the secret file with the key and Initial-value. Screenshot 2022-09-28 at 6.27.30 PM.png

Wrapping Things Up

In this post, we achieved our milestone by completing the first command of our CLI application. This command generates key and initial-value from the random values. Then we encoded those values into base64 and stored them in a file. If you run into any issues with any part of this tutorial, please leave a comment so that I can update the content to be more clear. If you like this post, please follow me on Hashnode and subscribe to my newsletter for future updates.

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