logcount (B6 — Rust CLI Greenfield)

A small command-line tool that reads a log file and counts how many lines are INFO, WARN, and ERROR. Built in Rust with cargo.

✅ Verification status: verified 2026-06-17 with Rust 1.96.0 (Homebrew). cargo test → 7 passed; cargo run -- sample.log → INFO: 2 / WARN: 1 / ERROR: 1; missing file → exit 1; no args → exit 2. Full run log: B6_verification.md.

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Project Structure

B6/
├── src/
│   ├── main.rs      # CLI layer: argv parsing, output, exit codes
│   ├── parser.rs    # Parsing layer: text/file -> LogCounts
│   ├── models.rs    # Business logic: LogLevel + LogCounts (+ Display)
│   └── lib.rs       # Exposes modules so tests/ can use them
├── tests/
│   └── cli.rs       # Integration tests (cargo test)
├── sample.log       # Example input
├── Cargo.toml
└── README.md

Layering: CLI (main.rs) → Parsing (parser.rs) → Business logic (models.rs).

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Installation

Requires the Rust toolchain. Install via rustup:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
# then restart your shell, or: source "$HOME/.cargo/env"

Build

cd B6
cargo build --release      # binary at target/release/logcount

Run

cargo run -- sample.log
# or, after build:
./target/release/logcount sample.log

Test

cargo test

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Example Input (sample.log)

INFO Application started
WARN Cache miss
INFO Request received
ERROR Database unavailable

Example Output

INFO: 2
WARN: 1
ERROR: 1

Missing file

cargo run -- missing.log

Error:
File not found: missing.log

Exits with a non-zero status code (1) and does not panic.

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How counting works

Each line is classified by its first whitespace-separated token. If that token is INFO, WARN, or ERROR, the corresponding counter increments; any other line (blank lines, DEBUG, free text) is ignored.