---
epic: 11
story: 11.1
title: "Single Expression Evaluation"
status: draft
---

## Epic 11 — CLI Tool
**Goal:** Command-line tool for scripting and automation, same Rust engine.

### Story 11.1: Single Expression Evaluation

As a developer or power user,
I want to evaluate a single CalcPad expression from the command line,
So that I can quickly compute values without opening an editor.

**Acceptance Criteria:**

**Given** the user has `calcpad` installed
**When** they run `calcpad "5kg in lbs"`
**Then** the output is `11.023 lbs` (or equivalent precision) printed to stdout
**And** the process exits with code 0

**Given** the user passes an invalid expression
**When** they run `calcpad "5kg in ???"`
**Then** an error message is printed to stderr describing the issue
**And** the process exits with code 1

**Given** the user passes a plain arithmetic expression
**When** they run `calcpad "2 + 3 * 4"`
**Then** the output is `14` printed to stdout
**And** the process exits with code 0