I am trying to get the current workspace of my Jenkins build using a Groovy pipeline script:
node('master') {
    // PULL IN ENVIRONMENT VARIABLES
    // Jenkins makes these variables available for each job it runs
    def buildNumber = env.BUILD_NUMBER
    def workspace = env.WORKSPACE
    def buildUrl = env.BUILD_URL
    // PRINT ENVIRONMENT TO JOB
    echo "workspace directory is ${workspace}"
    echo "build URL is ${env.BUILD_URL}"
}
It returns:
[Pipeline] Allocate node : Start
Running on master in /Users/Shared/Jenkins/Home/jobs/test/workspace
[Pipeline] node {
[Pipeline] echo
workspace directory is null
[Pipeline] echo
build URL is http://localhost:8080/job/test/5/
[Pipeline] } //node
[Pipeline] Allocate node : End
[Pipeline] End of Pipeline
Finished: SUCCESS