Install the groovy plugin:
In order to install the groovy plugin in your jenkins server, first we download the the required (groovy) plugin from the plugin repository https://updates.jenkins-ci.org/download/plugins/groovy/.
The plugin extensions are hpi. Once the plugin is downloaded from the plugin repository, go to Manage Jenkins page and Manage Plugins page. Now goto Advanced tab, then chose the plugin file you have downloaded and click upload. This will install the groovy plugin on your jenkins server.
Write groovy code in the groovy script console.
Refer the https://www.cloudbees.com/jenkins/juc-2015/presentations/JUC-2015-USEast-Groovy-With-Jenkins-McCollum.pdf
groovy Script vs System Groovy Script
The plain "Groovy Script" is run in a forked JVM, on the slave where the build is run. It's the basically the same as running the "groovy" command and pass in the script.
The system groovy script, OTOH, runs inside the Jenkins master's JVM. Thus it will have access to all the internal objects of Jenkins, so you can use this to alter the state of Jenkins
Where to store the script?
● Can put it in source and pull it from source
● Or you can put the script directly into the command box that is provided
