# Creating a new local package

This page provides instructions on how to create a new local package to share code between applications in a Caplin Trader workspace.

## Requirements

Packages for Caplin Trader 5 applications are created within the context of a Caplin Trader development workspace. For more information on creating a development workspace, see [Creating a new workspace](creating-a-new-workspace.md).

## Creating a new local package

You create a local package by using Caplin CLI’s `create-package` command:

```
$ caplin-cli create-package <package-name>
```

To create a new local package called my-package, for example, follow the steps below:

1. From the root directory of your CT5 development workspace, run the command below to create a local package called my-package:

   ```
   $ caplin-cli create-package my-package
   ```

   Your new local package has the following structure:

   ```plantuml
   @startsalt
   scale 1.25
   {
   {T
    + <color:goldenrod><&folder></color> ct-workspace
    ++ <color:goldenrod><&folder></color> packages
    +++ <color:goldenrod><&folder></color> my-package
    ++++ <color:goldenrod><&folder></color> _test-ut
    +++++ <color:cornflowerblue><&file></color> my-package-test.js
    ++++ <color:cornflowerblue><&file></color> my-package.js
    ++++ <color:cornflowerblue><&file></color> package.json
   }
   }
   @endsalt
   ```
2. Change directory to `<workspace>/packages/my-package`, and run the command below to download the new package’s dependencies:

   ```
   $ yarn install
   ```

## Installing a local package in an application

You install local packages to an application by passing a local path to the `yarn add` command.

To install the package `my-package` created in the previous section, follow the steps below, run the command below from the root directory of your Caplin Trader application:

```
$ yarn add file:../../packages/my-package
```

## Updating a local package in an application

Each time you update the source code for your local package under your workspace’s `packages` directory, you will need to update your application’s copy of the local package.

Run the command below from your application’s root directory to update its copy of the local package:

```
$ yarn upgrade <package-name>
```

If your local package is in active development, running `yarn upgrade` each time you change your package’s code can quickly become tedious. To save time, you can use the `yarn link` command to symlink your application’s copy of the package to the local package.

Follow the steps below:

1. In the local package’s directory, run `yarn link`:

   ```console
   $ cd ~/dev/ct5-workspace/package/my-package
   $ yarn link
   yarn link v1.10.1
   success Registered "my-package".
   info You can now run `yarn link "my-package"` in the projects where you want to use this package and it will be used instead.
   Done in 0.04s.
   ```
2. Run the command below from the root directory of your application:

   ```console
   $ cd ~/dev/ct5-workspace/apps/my-app
   $ yarn link my-package
   yarn link v1.10.1
   warning package.json: No license field
   success Using linked package for "my-package".
   Done in 0.04s.
   ```

For more information, including how to unlink a package, follow the links below:

* [yarn link](https://classic.yarnpkg.com/en/docs/cli/link)
* [yarn unlink](https://classic.yarnpkg.com/en/docs/cli/unlink)