# R quickstart

> How do I write R scripts in Windmill? Create, test and deploy R scripts with CRAN package dependency management.

In this quick start guide, we will write our first script in [R](https://www.r-project.org/).

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Scripts are the basic building blocks in Windmill. They can be [run and scheduled](../../../triggers/index.mdx) as standalone, chained together to create [Flows](../../../flows/1_flow_editor.mdx) or displayed with a personalized User Interface as [Apps](../../7_apps_quickstart/index.mdx).

Scripts consist of 2 parts:

- [Code](#code): for R scripts, they must have a `main` function defined as `main <- function(...)`.
- [Settings](#settings): settings & metadata about the Script such as its path, summary, description, [jsonschema](../../../core_concepts/13_json_schema_and_parsing/index.mdx) of its inputs (inferred from its signature).

When stored in a code repository, these 2 parts are stored separately at `<path>.r` and `<path>.script.yaml`

Windmill automatically manages [dependencies](/docs/getting_started/scripts_quickstart/r#dependencies-management) for you.
When you use packages in your R script through `library()` or `require()` calls,
Windmill parses these dependencies upon saving the script and automatically resolves versions from CRAN,
ensuring that the same version of the script is always executed with the same versions of its dependencies.

This is a simple example of a script built in R with Windmill:

```r
library(httr)
library(jsonlite)

main <- function(url = "https://httpbin.org/get", message = "Hello from Windmill!") {
  response <- GET(url, query = list(message = message))

  list(
    status = status_code(response),
    body = content(response, as = "parsed"),
    message = "Request completed successfully"
  )
}
```

In this quick start guide, we'll create a script that greets the operator running it.

From the Home page, click **New** and select **Script**. This will take you to the first step of script creation: Metadata.

## Settings

![R Settings](./r-settings.png "R Settings")

As part of the [settings](../../../script_editor/settings.mdx) menu, each script has metadata associated with it, enabling it to be defined and configured in depth.

- **Path** is the Script's unique identifier that consists of the
  [script's owner](../../../core_concepts/16_roles_and_permissions/index.mdx), and the script's name.
  The owner can be either a user, or a group ([folder](../../../core_concepts/8_groups_and_folders/index.mdx#folders)).
- **Summary** (optional) is a short, human-readable summary of the Script. It
  will be displayed as a title across Windmill. If omitted, the UI will use the `path` by
  default.
- **Language** of the script.
- **Description** is where you can give instructions through the [auto-generated UI](../../../core_concepts/6_auto_generated_uis/index.mdx)
  to users on how to run your Script. It supports markdown.
- **Script kind**: Action (by default), [Trigger](../../../flows/10_flow_trigger.mdx), [Approval](../../../flows/11_flow_approval.mdx) or [Error handler](../../../flows/7_flow_error_handler.md). This acts as a tag to filter appropriate scripts from the [flow editor](../../6_flows_quickstart/index.mdx).

This menu also has additional settings on [Runtime](../../../script_editor/settings.mdx#runtime), [Generated UI](#generated-ui) and [Triggers](../../../script_editor/settings.mdx#triggers).

Now click on the code editor on the left side, and let's build our Hello World!

## Code

Windmill provides an online editor to work on your Scripts. The left-side is
the editor itself. The right-side [previews the UI](../../../core_concepts/6_auto_generated_uis/index.mdx) that Windmill will
generate from the Script's signature - this will be visible to the users of the
Script. You can preview that UI, provide input values, and [test your script](#instant-preview--testing) there.

![R Editor](./r-editor.png "R Editor")

As we picked `R` for this example, Windmill provided some R
boilerplate. Let's take a look:

```r
library(crayon)
library(dplyr)
library(zoo)
library(jsonlite)

main <- function(
  x,
  name = "default",
  age = 25,
  data = list(1, 2, 3),
  flag = TRUE
) {
  # Use Windmill helpers:
  # var <- get_variable("f/my_var")
  # res <- get_resource("f/my_resource")

  df <- tibble(name = name, age = age, x = x)
  result <- df %>% mutate(greeting = paste("Hello", name))

  return(toJSON(result, auto_unbox = TRUE))
}
```

In Windmill, R scripts must have a `main` function defined as `main <- function(...)` that will be the script's
entrypoint. There are a few important things to note about the `main` function:

- The main arguments are used for generating
  1.  the [input spec](../../../core_concepts/13_json_schema_and_parsing/index.mdx) of the Script
  2.  the [frontend](../../../core_concepts/6_auto_generated_uis/index.mdx) that you see when running the Script as a standalone app.
- Default values are used to infer argument types and generate the UI form. String defaults create string inputs, numeric defaults create number inputs, list/vector defaults create appropriate JSON inputs, etc.
- You can customize the UI in later steps (but not change the input type!).

Back to our Hello World. We can clean up the boilerplate, change the
main to take in the user's name. Let's also return the `name`, maybe we can use
this later if we use this Script within a [flow](../../../flows/1_flow_editor.mdx) or [app](../../../full_code_apps/index.mdx) and need to pass its result on.

```r
main <- function(name = "World") {
  print(paste("Hello", name, "! Greetings from R!"))
  name
}
```

## Accessing variables and resources

R scripts can access Windmill [variables](../../../core_concepts/2_variables_and_secrets/index.mdx) and [resources](../../../core_concepts/3_resources_and_types/index.mdx) using built-in helper functions:

```r
library(httr)
library(jsonlite)

main <- function() {
  # Get a variable
  secret <- get_variable("f/examples/secret")

  # Get a resource (returns a list/object)
  db_config <- get_resource("f/examples/postgres")

  # Access context variables from environment
  user <- Sys.getenv("WM_USERNAME")
  workspace <- Sys.getenv("WM_WORKSPACE")

  list(
    secret = secret,
    db_host = db_config$host,
    user = user,
    workspace = workspace
  )
}
```

## Instant preview & testing

Look at the UI preview on the right: it was updated to match the input
signature. Run a test (`Ctrl` + `Enter`) to verify everything works.

You can change how the UI behaves by changing the main signature. For example,
if you remove the default for the `name` argument, the UI will consider this field
as required.

```r
main <- function(name)
```

Now let's go to the last step: the "Generated UI" settings.

## Generated UI

From the Settings menu, the "Generated UI" tab lets you customize the script's arguments.

The UI is generated from the Script's main function signature, but you can add additional constraints here. For example, we could use the `Customize property`: add a regex by clicking on `Pattern` to make sure users are providing a name with only alphanumeric characters: `^[A-Za-z0-9]+$`. Let's still allow numbers in case you are some tech billionaire's kid.

![Generated UI](../14_ruby_quickstart/customize-ui.png "Generated UI")

## Run!

We're done! Now let's look at what users of the script will do. Click on the [Deploy](../../../core_concepts/0_draft_and_deploy/index.mdx) button
to load the script. You'll see the user input form we defined earlier.

Note that Scripts are [versioned](../../../core_concepts/34_versioning/index.mdx#script-versioning) in Windmill, and
each script version is uniquely identified by a hash.

Fill in the input field, then hit "Run". You should see a run view, as well as
your logs. All script runs are also available in the [Runs](../../../core_concepts/5_monitor_past_and_future_runs/index.mdx) menu on
the left.

You can also choose to [run the script from the CLI](../../../advanced/3_cli/index.mdx) with the pre-made Command-line interface call.

## Dependencies management

R dependencies are automatically detected from `library()` and `require()` calls in your script. Windmill resolves package versions from CRAN:

```r
library(httr)
library(jsonlite)
library(dplyr)
library(ggplot2)

main <- function(data_url = "https://example.com/data.csv") {
  # Use httr for HTTP requests
  response <- GET(data_url)

  # Parse JSON responses
  data <- fromJSON(content(response, as = "text"))

  # Use dplyr for data manipulation
  result <- data %>%
    filter(!is.na(value)) %>%
    summarise(mean_value = mean(value))

  result
}
```

Windmill will automatically:
- Parse your `library()` and `require()` calls when you save the script
- Resolve versions from CRAN (with 3-day TTL caching for lockfiles)
- Install packages to a shared cache directory
- Cache dependencies for faster execution

### Verbose mode

By default, renv output is suppressed during package installation. To enable verbose output for debugging, add a `#verbose` annotation at the top of your script:

```r
#verbose

library(httr)
library(jsonlite)

main <- function() {
  # Your code here
}
```

## Caching

Every R package dependency is cached on disk by default. Furthermore if you use the [Distributed cache storage](../../../core_concepts/38_object_storage_in_windmill/index.mdx#instance-object-storage-distributed-cache-for-python-rust-go), it will be available to every other worker, allowing fast startup for every worker.

## What's next?

This script is a minimal working example, but there's a few more steps that can be useful in a real-world use case:

- Pass [variables and secrets](../../../core_concepts/2_variables_and_secrets/index.mdx)
  to a script.
- Connect to [resources](../../../core_concepts/3_resources_and_types/index.mdx).
- [Trigger that script](../../../triggers/index.mdx) in many ways.
- Compose scripts in [Flows](../../../flows/1_flow_editor.mdx), [low-code apps](../../../apps/0_app_editor/index.mdx) or [full-code apps](../../../full_code_apps/index.mdx).
- You can [share your scripts](../../../misc/1_share_on_hub/index.md) with the community on [Windmill Hub](https://hub.windmill.dev). Once
  submitted, they will be verified by moderators before becoming available to
  everyone right within Windmill.

Scripts are immutable and there is a hash for each deployment of a given script. Scripts are never overwritten and referring to a script by path is referring to the latest deployed hash at that path.

For each script, a UI is autogenerated from the jsonschema inferred from the script signature, and can be customized further as standalone or embedded into rich UIs using the [App builder](../../7_apps_quickstart/index.mdx).

In addition to the UI, sync and async [webhooks](../../../core_concepts/4_webhooks/index.mdx) are generated for each deployment.