How to test a couple of Environment variables and fail builld

In one workflow, the first thing I want to do is check the TAG of the release that triggered the build and the name of the branch.
The naming convention we have means that the TAG used should be in the name of the branch, I just want a quick check to make sure this is the case.
I was thinking of something like this.
I create a Do anything with script step, that looks a bit like this…
run_if: |-
{{ “BITRISE_GIT_BRANCH” does not contain “BITRISE_GIT_TAG”}}{ exit 123

I need to know if/how I can test with “not contains” and how do I exit with an error?

Cheers.

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