Use boolean variable as lowercase string in Azure Devops YML pipeline script

Question

I have the following variable in my pipeline script:

variables:
  is_main: $[eq(variables['Build.SourceBranch'], 'refs/heads/main')]

And I want to use it like this:

- script: npm run build -- --source-map=$(is_main)

Unfortunately that leads to an error because "True" is not allowed:

> ng build "--source-map=True"

Cannot parse arguments. See below for the reasons.
    Argument --source-map could not be parsed using value "True".Valid type(s) is: boolean
##[error]Bash exited with code '1'.
Finishing: Angular build

I need to lowercase the boolean, and I want to do so in the script step to keep the variable in the pipeline as a true boolean (as opposed to a string) until the last possible moment. I've tried several options. To summarize:

Option 1 $(is_main) leads to:

Argument --source-map could not be parsed using value "True".Valid type(s) is: boolean

Option 2 $[lower($(is_main))] leads to:

lower(True): syntax error in expression (error token is "(True)")

Option 3 $[lower(variables('is_main'))] leads to:

 lower(variables('is_main')): syntax error in expression (error token is "(variables('is_main'))")

Option 4 $[lower(variables['is_main'])] leads to:

 lower(variables['is_main']): syntax error in expression (error token is "(variables['is_main'])")

Option 5 ${{ lower(variables.is_main) }} (which should not work as far as I could tell from documenation, because it is not used for runtime evaluation, but hey....) leads to:

eq(variables['build.sourcebranch'], 'refs/heads/main'): syntax error in expression (error token is "(variables['build.sourcebranch'], 'refs/heads/main')")

I've read through the "Expressions" documentation on Azure Pipelines MSDN pages and my above attempts are based on it already.

What is the proper way to convert a boolean variable in an Azure Devops pipeline to a lowercase string to be used inside a script step?

---

Footnote:

For now I use this workaround:

variables:
  is_main: $[eq(variables['Build.SourceBranch'], 'refs/heads/main')]
  generate_source_maps: $[lower(variables['is_main'])] # script step requires lowercase boolean

And use it like this:

- script: npm run build -- --source-map=$(generate_source_maps)

Quite suboptimal because generate_source_maps is a string whereas the name suggests it's a boolean, and the conversion to lowercase happens very far from the place in the yml where it is relevant and obvious that this is needed. But it works.

Answer 1

My team and I encountered a similar problem just now [A], and convertToJson worked for us as a way to convert a Pipeline boolean value to lowercase string literal.

Since your initial value is a non-static variable, I don't think you can inline this expression into your script line though [B] - you probably still need an extra variable.

Perhaps this would work for you?

variables:
  is_main: $[eq(variables['Build.SourceBranch'], 'refs/heads/main')]
  is_main_str: $[convertToJson(variables['is_main'])]

- script: npm run build -- --source-map=$(is_main_str)

[A]: Specifically, we wanted to pass a Pipeline parameter value of type boolean to an ARM template parameter via overrideParameters on an AzureResourceManagerTemplateDeployment@3 task.

[B]: According to the docs, Compile time expressions can be used anywhere; runtime expressions can be used in variables and conditions., and only runtime expressions can access non-static variables. Looks like the $() macro syntax cannot evaluate an expression.