Powershell sub-expression syntax used by TFS/Azure Devops

Question

TFS/Azure DevOps allows you to reference custom variables and built in build/release variables using the following syntax:

$(variable_name)

For example, if I wanted to grab the build definition name, I would grab the value from the following sub-expression:

$(Build.DefinitionName)

But, as far as I can tell, the above syntax is not a valid powershell sub-expression.

If "Build.DefinitionName" was a variable, it would need to look like:

$($Build.DefinitionName)

If it were a collection/hashtable, it would use curly braces:

${Build.DefinitionName}

If it were an object with a static property, it would be:

${Build::DefinitionName}

So what the heck is "Build" in the above example? Is TFS/VSTS/Azure DevOps doing some magic string replacement here or something?

Answer 1

It's not a Powershell language element, it's a simple TFS/VSTS placeholder syntax, just like SQLCMD uses: https://learn.microsoft.com/en-us/sql/relational-databases/scripting/sqlcmd-use-with-scripting-variables?view=sql-server-2017

TFS/VSTS inserts the values for these placeholders before invoking your Powershell tasks.

Answer 2

Build/release variables are made available to processes running in the scope of a build/release in the form of environment variables.

As an example, the build definition name is available the same way you'd access any other environment variable in PowerShell: $env:BUILD_DEFINITIONNAME. Note that periods are replaced with underscores.

The exception is secrets. Anything defined as a secret will have to be explicitly passed in to the consuming script, as they are not populated as environment variables.