Jenkins CI user that triggered build

Jenkinsfile

// This script should be placed inside your pipeline script
def getTriggeringUser() {
    def user = 'UNKNOWN' // Default value if user cannot be determined

    // Check each cause for the build to find a user cause
    currentBuild.rawBuild.getCauses().each { cause ->
        if (cause instanceof hudson.model.Cause$UserIdCause) {
            user = cause.getUserId()
        } else if (cause instanceof org.jenkinsci.plugins.workflow.support.steps.build.BuildUpstreamCause) {
            // If the build was triggered upstream, recursively check upstream builds
            def upstreamBuild = Jenkins.instance.getItemByFullName(cause.getUpstreamProject()).getBuildByNumber(cause.getUpstreamBuild())
            def upstreamUser = upstreamBuild.rawBuild.getCauses().find { it instanceof hudson.model.Cause$UserIdCause }
            if (upstreamUser) {
                user = upstreamUser.userId
            }
        }
    }

    return user
}