# R Cli App

> Build command-line apps in R using the Rapp package. Use when creating a CLI tool in R, adding argument parsing to an R script, turning an R script into a command-line app, shipping CLIs in an R package, or using Rapp (the alternative Rscript front-end). Also use for shebang scripts, exec/ directory in R packages, or subcommand-based R tools.

- **Type:** Skill
- **Install:** `agentstack add skill-posit-dev-skills-r-cli-app`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [posit-dev](https://agentstack.voostack.com/s/posit-dev)
- **Installs:** 0
- **Category:** [Agent Skills](https://agentstack.voostack.com/c/agent-skills)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [posit-dev](https://github.com/posit-dev)
- **Source:** https://github.com/posit-dev/skills/tree/main/r-lib/r-cli-app

## Install

```sh
agentstack add skill-posit-dev-skills-r-cli-app
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# Building CLI Apps with Rapp

Rapp (v0.3.0) is an R package that provides a drop-in replacement for `Rscript`
that automatically parses command-line arguments into R values. It turns simple
R scripts into polished CLI apps with argument parsing, help text, and subcommand
support — with zero boilerplate.

**R ≥ 4.1.0** | **CRAN:** `install.packages("Rapp")` | **GitHub:** `r-lib/Rapp`

After installing, put the `Rapp` launcher on PATH:

```r
Rapp::install_pkg_cli_apps("Rapp")
```

This places the `Rapp` executable in `~/.local/bin` (macOS/Linux) or
`%LOCALAPPDATA%\Programs\R\Rapp\bin` (Windows).

---

## Core Concept: Scripts Are the Spec

Rapp scans **top-level expressions** of an R script and converts specific
patterns into CLI constructs. This means:

1. The same script works identically via `source()` and as a CLI tool.
2. You write normal R code — Rapp infers the CLI from what you write.
3. Default values in your R code become the CLI defaults.

Only top-level assignments are recognized. Assignments inside functions,
loops, or conditionals are not parsed as CLI arguments.

---

## Pattern Recognition: R → CLI Mapping

This table is the heart of Rapp — each R pattern automatically maps to a
CLI surface:

| R Top-Level Expression | CLI Surface | Notes |
|---|---|---|
| `foo ` | String option |
| `foo ` | Integer option |
| `foo ` | Float option |
| `foo ` | Optional integer (NA = not set) |
| `foo ` | Optional string (NA = not set) |
| `foo     (string, default "world")
count      (integer, default 1)
threshold  (float, default 0.5)
seed       (optional, NA if omitted)
output     (optional, NA if omitted)
```

For optional arguments, test whether the user supplied them:

```r
seed   Number of coin flips [default: 1] [type: integer]
      --sep       [default: " "] [type: string]
      --wrap / --no-wrap  [default: true]
      --seed     [default: NA] [type: integer]
```

## Complete Example: Todo Manager (Subcommands)

```r
#!/usr/bin/env Rapp
#| name: todo
#| description: Manage a simple todo list.

#| description: Path to the todo list file.
#| short: s
store = 0L) tasks `, so only `base`
and the package are auto-loaded. Use `library()` for other dependencies.

---

## Quick Reference: Common Patterns

### NA vs NULL for optional arguments

- **NA** (`NA_integer_`, `NA_character_`) → optional **named option**.
  Test: `!is.na(x)`.
- **NULL** + `#| required: false` → optional **positional arg**.
  Test: `!is.null(x)`.

### stdin/stdout

```r
input_file <- NA_character_
con <- if (is.na(input_file)) file("stdin") else file(input_file, "r")
lines <- readLines(con)
writeLines(lines, stdout())
```

### Exit codes and stderr

```r
message("Error: something went wrong")   # writes to stderr
cat("Error:", msg, "\n", file = stderr()) # also stderr
quit(status = 1)                          # non-zero exit
```

### Error handling

```r
tryCatch({
  result <- do_work()
}, error = function(e) {
  cat("Error:", conditionMessage(e), "\n", file = stderr())
  quit(status = 1)
})
```

---

## Additional Reference

For less common topics — launcher customization (`#| launcher:` front matter),
detailed `Rapp::install_pkg_cli_apps()` API options, and more complete examples
(deduplication filter, variadic install-pkg, interactive fallback) — read
`references/advanced.md`.

## Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [posit-dev](https://github.com/posit-dev)
- **Source:** [posit-dev/skills](https://github.com/posit-dev/skills)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** no
- **Filesystem access:** no
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/skill-posit-dev-skills-r-cli-app
- Seller: https://agentstack.voostack.com/s/posit-dev
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.