A package uses Ballerina library packages as dependencies. The sections below include information about working with library packages.

Create a library package

Execute the command below to create a new library package named hello.

$ bal new --template lib hello

This creates the files below.

$ cd hello
$ tree .
    .
    ├── Ballerina.toml
    ├── Module.md
    ├── Package.md
    ├── hello.bal
    ├── resources
    └── tests
        └── lib_test.bal

2 directories, 5 files

• The Ballerina.toml file identifies the directory as a Ballerina package. You can edit the Ballerina.toml file to change the organization, name, and the version of the package.
• The Package.md is required when you publish a package to a repository. You can edit the content to add a meaningful description about the package.
• The hello.bal file, resources/ directory tests/ directory, and the Module.md file belong to the default module of the package.

For more information on these files, see Package layout.

To generate the Ballerina archive, execute the command below.

$ bal pack

You view the output below.

Compiling source
	user/hello:0.1.0

Creating bala
	target/bala/user-hello-any-0.1.0.bala

Publish a library package to Ballerina Central

You can publish a Ballerina archive to the Ballerina Central. Before you publish, ensure the package works as intended because a publish is permanent. Once published to Ballerina Central, you cannot overwrite the version or remove the package. However, the number of package versions you can push to Ballerina Central is not restricted.

Tip: As a precaution, use the local repository first to test out the functionality of the library package before publishing it to Ballerina Central.

Prepare for publishing

1. Create an account on Ballerina Central. To register, visit the home page and log in via a Google or GitHub account.

2. Navigate to the Dashboard and acquire an access token.

3. Download and place the Settings.toml file in your home repository (<USER_HOME>/.ballerina/). If you already have a Settings.toml file configured in your home repository, follow the other option and copy the access token into the Settings.toml. If you are connected to the internet via an HTTP proxy, add the following section to Settings.toml and change accordingly.

[proxy]
host = "localhost"
port = "3128"
username = ""
password = ""

Define the organization

When you push a package to Ballerina Central, the organizations are validated against the value of the org field defined in the Ballerina.toml file. Therefore, when you have more than one organization in Ballerina Central, pick the organization name that you intend to push the package into, set that as the org in the Ballerina.toml file inside the package directory, and rebuild the package. If you do not have any organizations created, you can visit the organizations page to create one.

Also, organization names starting with ballerina (e.g., ballerina, ballerinax, ballerinai, etc.) are reserved for system use, and you cannot publish any packages starting with the ballerina prefix to Ballerina Central. Therefore, if you have used a name pattern matching this, update the Ballerina.toml and rebuild the package.

You can also choose who will have access to the package you are publishing by setting the package visibility in the Ballerina.toml file. If you set the visibility as private, it will only be visible and accessible to the members within the organization you are pushing the package into. Private packages will be visible on Ballerina Central only if you are logged in. Likewise, if you or a member of your organization wants to pull a private package, the Settings.toml file needs to be set up according to the previous section (if not set up already).

Publish the package

Now, that you are ready to publish, execute the command below to publish the package to Ballerina Central.

$ bal push

Publish a new version of a package

If you require adding new features/improvements/fixes to a library package which you have already published to Ballerina central, you are allowed to publish them under a new version, based on the Semantic Versioning Specification. However, it's the library developer's responsibility to be cautious when deciding on the new package versions (especially when there are potential breaking/backward-incompatible API changes), as otherwise, it may result in library versions that are compatible only by the version but not by the implementation.

Tip: As a precaution, use the Ballerina semver validator CLI tool (experimental) to check if your new API changes conform to the version that you are trying to publish to Ballerina central.

By default, running the bal semver command on the root directory of the package will compare the local changes with the "closest compatible" published version available in Ballerina Central. (Use bal semver --help for the CLI help text which outlines all the available command options)

Note: Semver validator CLI support is only available from Swan Lake Update 2 onwards.

Use the packages in Ballerina Central

After publishing your first package, you can create a second package and use the already published package in it. Any package published in Ballerina Central is public and can be used in other packages. For more information, see Import a module.