Get Real Branch Name in Jenkins during PRs

getBranchName.groovy

def getBranchName() {
    def branchName = env.BRANCH_NAME
    // if it is a PR, then we need to find back the name of the real branch from the commit.
    if (branchName.contains("PR-")) {
        repoUrl = sh(returnStdout: true, script: "echo ${env.CHANGE_URL} | sed 's/pull.*//'").trim()
        // simulate a git fetch
        // but stays on the current branch
        git branch: branchName, credentialsId: 'github_username_password', url: repoUrl
        // store the current commit
        gitCommit = sh(returnStdout: true, script: 'git rev-parse HEAD').trim()
        // find all the remote branches that have the git commit
        // but it is not the a PR
        // we tail -1 in case of several remote branches have the same commit.
        // we don't really care about the name of the branch associated with the commit anyway
        branchName = sh(
                returnStdout: true,
                script: "git branch -a --contains ${gitCommit} | grep -v PR- | sed 's/^.*\\///' | tail -1"
        ).trim()
    }
    branchName
}