How to differentiate build triggers in Jenkins Pipeline

I'm hoping to add a conditional stage to my Jenkinsfile that runs depending on how the build was triggered. Currently we are set up such that builds are either triggered by:

1. changes to our git repo that are picked up on branch indexing
2. a user manually triggering the build using the 'build now' button in the UI.

Is there any way to run different pipeline steps depending on which of these actions triggered the build?

The following code should works to determine if a user has started the pipeline or a timer/other trigger:

def isStartedByUser = currentBuild.rawBuild.getCause(hudson.model.Cause$UserIdCause) != null

The ability to get causes for a workflow run was released in version 2.22 (2018 Nov 02) to the Pipeline Supporting APIs Plugin. The feature was requested in JENKINS-41272.

A couple methods were added to the currentBuild global variable with that release:

getBuildCauses

• Returns a JSON array of build causes for the current build

EXPERIMENTAL - MAY CHANGE getBuildCauses(String causeClass)

• Takes a string representing the fully qualified Cause class and returns a JSON array of build causes filtered by that type for the current build, or an empty JSON array if no causes of the specified type apply to the current build

And an example from me submitting:

echo "${currentBuild.buildCauses}" // same as currentBuild.getBuildCauses()
echo "${currentBuild.getBuildCauses('hudson.model.Cause$UserCause')}"
echo "${currentBuild.getBuildCauses('hudson.triggers.TimerTrigger$TimerTriggerCause')}"

And the output:

[Pipeline] echo
[[_class:hudson.model.Cause$UserIdCause, shortDescription:Started by user anonymous, userId:null, userName:anonymous], [_class:org.jenkinsci.plugins.workflow.cps.replay.ReplayCause, shortDescription:Replayed #12]]
[Pipeline] echo
[]
[Pipeline] echo
[]
[Pipeline] End of Pipeline
Finished: SUCCESS

NOTE

There appears to be an issue with the currentBuild.getBuildCauses(type) when the type is a type of Cause contributed by a plugin. For example, currentBuild.getBuildCauses('org.jenkinsci.plugins.workflow.cps.replay.ReplayCause') fails with a java.lang.ClassNotFoundException. This was reported in JENKINS-54673 for the 2.22 version of the Pipeline: Supporting APIs (workflow-support) plugin. It is reportedly fixed in the 2.24 version.

In Jenkins Pipeline without currentBuild.rawBuild access the build causes could be retrieved in the following way:

// started by commit
currentBuild.getBuildCauses('jenkins.branch.BranchEventCause')
// started by timer
currentBuild.getBuildCauses('hudson.triggers.TimerTrigger$TimerTriggerCause')
// started by user
currentBuild.getBuildCauses('hudson.model.Cause$UserIdCause')

You can get a boolean value with:

isTriggeredByTimer = !currentBuild.getBuildCauses('hudson.triggers.TimerTrigger$TimerTriggerCause').isEmpty()

Or, as getBuildCauses() returns an array, the array's size will work correctly with Groovy truthy semantics:

if (currentBuild.getBuildCauses('hudson.triggers.TimerTrigger$TimerTriggerCause')) {

I think that the answers here are incomplete and do not provide an actual ready to use answer. Here's my code to get it working:

import com.cloudbees.groovy.cps.NonCPS

@NonCPS
def isStartedByTimer() {
    def buildCauses = currentBuild.rawBuild.getCauses()
    echo buildCauses

    boolean isStartedByTimer = false
    for (buildCause in buildCauses) {
        if ("${buildCause}".contains("hudson.triggers.TimerTrigger\$TimerTriggerCause")) {
            isStartedByTimer = true
        }
    }

    echo isStartedByTimer
    return isStartedByTimer
}

// [...]
// Other pipeline stuff

script {
    isStartedByTimer()
}

When started by user:

00:00:01.353 [hudson.model.Cause$UserIdCause@fa5cb22a]
[Pipeline] echo
00:00:01.358 false

When started by timer:

00:00:01.585 [hudson.triggers.TimerTrigger$TimerTriggerCause@5]
[Pipeline] echo
00:00:01.590 true

Note: the NonCPS decorator is needed because otherwise the next non-script step will throw.