We have a shell script driven build, that uses the value of GIT_BRANCH to figure out what branch we are building. This works fine for a simple configuration with one branch configured.

Recently, I added a 'Merge before build' step to the configuration, so a specific topic branch is merged into master before building. This results in GIT_BRANCH being unset. I was expecting it to be set to the branch, that is being merged into (e.g. master), since that is still the branch that should be tracked for changes.

How can I pass branch information into a shell script when using 'Merge before build'?