Rust CLI Project Structure

Command-line application with clap, proper error handling, and cross-platform builds.

#rust #cli #command-line #clap

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Project Directory

mycli/

Cargo.toml

Package manifest

Cargo.lock

LICENSE

README.md

.gitignore

rust-toolchain.toml

Pin Rust version

src/

main.rs

Entry point, CLI parsing

lib.rs

Library code for testing

cli.rs

Clap argument definitions

error.rs

Custom error types

commands/

Subcommand implementations

mod.rs

init.rs

mycli init

run.rs

mycli run

config/

mod.rs

settings.rs

Config file parsing

tests/

Integration tests

cli_tests.rs

End-to-end CLI tests

Why This Structure?

Rust CLIs are fast, reliable, and compile to single binaries. This structure uses clap with derive macros for declarative argument parsing. The lib.rs pattern allows testing business logic separately from the CLI layer.

Key Directories

src/main.rs-Entry point, minimal—delegates to lib
src/cli.rs-Clap structs with derive macros
src/commands/-One module per subcommand
src/error.rs-thiserror-based error types

Clap Derive Pattern

// src/cli.rs
use clap::{Parser, Subcommand};

#[derive(Parser)]
#[command(name = "mycli", version, about)]
pub struct Cli {
    #[command(subcommand)]
    pub command: Commands,

    #[arg(short, long, global = true)]
    pub verbose: bool,
}

#[derive(Subcommand)]
pub enum Commands {
    Init { name: String },
    Run { config: Option },
}

Getting Started

cargo new mycli
cargo add clap --features derive
cargo add anyhow thiserror
Define CLI in src/cli.rs
cargo build --release

When To Use This

Building fast, single-binary CLI tools
Commands with subcommands
Need cross-platform distribution
Want compile-time argument validation
Performance-critical CLI applications

Trade-offs

Compile times-Rust compilation is slower than Go/Python
Learning curve-Ownership and lifetimes take time
Binary size-Default builds are larger (strip + LTO helps)

Naming Conventions

Modules-snake_case (commands/init.rs)
Types-PascalCase (Cli, Commands, Config)
Functions-snake_case (run_command, parse_config)

Testing Strategy

Unit tests-In-module #[cfg(test)] blocks
Integration tests-tests/ directory for CLI invocation
assert_cmd-Crate for testing CLI output