get-jenkins-creds.groovy

import jenkins.*
import jenkins.model.* 
import hudson.*
import hudson.model.*
import org.apache.commons.io.IOUtils
def jenkinsCredentials = com.cloudbees.plugins.credentials.CredentialsProvider.lookupCredentials(
        com.cloudbees.plugins.credentials.Credentials.class,
        Jenkins.instance,
        null,
        null
);


for (creds in jenkinsCredentials) {
  if(creds.id == "some-uuid-like-d0c63045-3999-43d1-80b4-17b361412500"){
    // For SecretFile
    println(IOUtils.toString(creds.getContent(), "UTF-8"))
    // For Username / Password
    // println(creds.username)
    // println(creds.password)
  }
}