# Cromwell

Cromwell is the original execution engine for WDL and can be run in either server or local command line mode. A majority of Cromwell users today run their workflows in Terra, using Docker and workflows in the WDL format, however, Cromwell supports various other backends and workflows.

Below will outline how to run the `02_download_collection_files` workflow in the WDL format locally using Cromwell and Docker.

## Prerequisites

* Java 8 or higher
* [Docker](https://docs.docker.com/desktop/)
* Optional: cURL and git

## Setup Instructions

You'll need to download:

* [cromwell.jar](https://github.com/broadinstitute/cromwell/releases/download/74/cromwell-74.jar)
* [02\_download\_collection\_files.wdl](https://raw.githubusercontent.com/DNAstack/dnastack-client-library-worked-examples/master/examples/wdl/02_download_collection_files.wdl)

## Getting the Example Workflow

Download the worked examples repository using either method:

### Clone with Git

```shell
git clone https://github.com/DNAstack/dnastack-client-library-worked-examples.git
```

**Or** [Download](https://github.com/DNAstack/dnastack-client-library-worked-examples/archive/refs/heads/master.zip) **and unzip** the repository manually.

2. [Download](https://github.com/DNAstack/dnastack-client-library-worked-examples/archive/refs/heads/master.zip) and Unzip

It is assumed that all commands will be run from the root directory of this repository on your local machine. From the directory where you’ve downloaded the examples repository.

```shell
cd dnastack-client-library-worked-examples/
```

### Installing Cromwell

Download the latest Cromwell version:

#### **Using cURL**

```shell
curl -o cromwell.jar -L https://github.com/broadinstitute/cromwell/releases/download/64/cromwell-64.jar
```

**Or** download manually from the [releases page](https://github.com/broadinstitute/cromwell/releases) and rename to `cromwell.jar`.

## Running the workflow

To run the workflow:

```shell
java -jar cromwell.jar run ./examples/wdl/02_download_collection_files.wdl
```

Output files can be found in the directory

`cromwell-executions/download_first_ten_files/<workflow id>/call-download_files/execution/out/` where `<workflow id>` corresponds to ID given by cromwell.

{% hint style="info" %}
All commands should be run from the repository's root directory on your local machine.
{% endhint %}


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