How can I access the last built revision according to jenkins?

You can directly access the Jenkins BUILD_NUMBER as system environment variable.

task getBuildNumber << {
    ext.env = System.getenv()
    ext.buildNumber = env.BUILD_NUMBER?.toInteger()
    println "Build Number: $buildNumber"
}

Turns out, the Git plugin DOES export the last build revision as an environment variable. So instead of using the accepted answer:

curl -sf "$BUILD_URL/api/xml?xpath=//lastBuiltRevision/SHA1/text()"

you can just use this instead:

GIT_PREVIOUS_COMMIT

One failproof way to see exactly what's available to your build script is to choose Add Build Step > Execute Shell then simply add the following:

export

view your console (for the build) and you should see lots of great environment variables available to you. The git-related variables that were available to me (using the git plugin) were:

GIT_AUTHOR_EMAIL
GIT_AUTHOR_NAME
GIT_BRANCH
GIT_COMMIT
GIT_COMMITTER_EMAIL
GIT_COMMITTER_NAME
GIT_PREVIOUS_COMMIT
GIT_URL

Lastly, to see a less comprehensive list of available environment variables, you can also just go to this url: http://[your-jenkins-domain-and-port]/env-vars.html

The current build-number is provided as the Jenkins-variable BUILD_NUMBER

• In Unix it is set for you as ${BUILD_NUMBER}
• In Windows it is available as %BUILD_NUMBER%

The complete list of variables is available on your Jenkins server, at:
http://[your-jenkins-server]/env-vars.html