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A comprehensive guide on expanding GitHub Actions `run` strings and linting shell scripts using Actionlint and ShellCheck for improved workflow reliability.
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Expanding GitHub Actions Steps run Strings

GitHub Actions is a powerful tool that allows you to automate, test, and deploy your code directly from GitHub. However, when it comes to writing shell scripts within these workflows, issues can arise with syntax—notably, the GitHub Actions-specific variable syntax ${{ ... }} can complicate things, especially when you attempt to lint your scripts using tools like ShellCheck. In this post, we will explore how to effectively expand these run strings while ensuring your shell scripts are properly linted.

The Problem: Incompatible Syntax

When you have shell code wrapped inside GitHub Actions workflow files (usually located at .github/workflows/*.yml), you might encounter complications in the syntax used. Here's a common example:

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The ${{ ... }} syntax is specific to GitHub Actions, creating a challenge if you want to lint your scripts using traditional tools such as ShellCheck.

The Solution: Using Actionlint and ShellCheck

Actionlint is an excellent tool designed to help troubleshoot GitHub Actions workflows. It not only runs ShellCheck on your run steps but also intelligently manages the GitHub Actions-specific variable syntax. Here’s how to set it up and use it in your workflow.

Step 1: Install Actionlint and ShellCheck

First, you need to have Actionlint and ShellCheck installed in your development environment. This can typically be done using package managers specific to your operating system.

For Ubuntu:

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For macOS:

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Step 2: Lint Your Workflow Files

Once you have both tools installed, the next step is to run Actionlint against your GitHub Actions workflow files to check for any issues. Use the following command:

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Step 3: Detect and Fix Variable Syntax

Actionlint will parse the work files and replace GitHub Actions-specific syntax like ${{ ... }} with underscores, making it compliant for ShellCheck to lint. Here’s what to watch out for during this step:

Ensure that variable names and values are clearly defined and that there are no errors in how they are referenced.

Avoid using ${{ env.VARIABLE_NAME }} for values directly. Instead, prefer setting values in the environment of the step and use $VARIABLE_NAME. This method is often safer and avoids potential pitfalls with shell execution.

Example Fix

Instead of writing:

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You can redefine it as:

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Conclusion

By following these steps using Actionlint and ShellCheck, you can effectively lint your GitHub Actions workflow files, making sure your shell scripts are reliable and free of syntax errors. Remember that it’s often better to use environment variable syntax for better clarity and safety.

Implement these practices in your workflows, and you’ll find that your GitHub Actions not only run more smoothly but are also much easier to manage and debug. Happy coding!