GitHub Actions Day 16: Conditionals with Shared Data

This is day 16 of my GitHub Actions Advent Calendar. If you want to see the whole list of tips as they're published, see the index.

Yesterday we looked at how we can set custom data in one of our workflow steps that we could use in subsequent steps. We did that by adding data to the env context, which is a property bag that you can read and write.

But you don't have to limit yourself to using the env context only in your steps. You can also use the env context within your workflow itself, setting up conditionals based on data that you set in earlier steps.

For example, you might have a workflow that you want to run every day, and you want to make a minor modification to how this workflow runs on Mondays. You can use a schedule trigger to run a workflow every day. And you could duplicate that workflow and add in the special changes that you want to run only on Mondays. But, ugh, maintaining two similar but only slightly different workflows is a serious pain.

Instead, you can look at the day of the week and set up an environment variable based on that -- here, I'll use bash syntax to run the date command to print the abbreviated day-of-week, and put that inside my echo statement that will set up the DAY_OF_WEEK variable in our env context. Then I'll use that env.DAY_OF_WEEK as a conditional for a subsequent step.

With this configuration, I'll run the workflow every day at 05:00 UTC. On a Monday, like today, the Monday-only step will be run.

But for the rest of the week, that step will be skipped.

This is another great example of how GitHub Actions gives you simple primitives that you can combine together to create powerful workflows.