I would be very useful to have the jenkins login id exposed as an environment variable to shells executed as a build step. Basically added to this set:

The following variables are available to shell scripts

BUILD_NUMBER
The current build number, such as "153"
BUILD_ID
The current build id, such as "2005-08-22_23-59-59" (YYYY-MM-DD_hh-mm-ss)
JOB_NAME
Name of the project of this build, such as "foo" or "foo/bar"
BUILD_TAG
String of "jenkins-${JOB_NAME}-${BUILD_NUMBER}". Convenient to put into a resource file, a jar file, etc for easier identification.
EXECUTOR_NUMBER
The unique number that identifies the current executor (among executors of the same machine) that's carrying out this build. This is the number you see in the "build executor status", except that the number starts from 0, not 1.
NODE_NAME
Name of the slave if the build is on a slave, or "master" if run on master
NODE_LABELS
Whitespace-separated list of labels that the node is assigned.
WORKSPACE
The absolute path of the directory assigned to the build as a workspace.
JENKINS_HOME
The absolute path of the directory assigned on the master node for Jenkins to store data.
JENKINS_URL
Full URL of Jenkins, like http://server:port/jenkins/
BUILD_URL
Full URL of this build, like http://server:port/jenkins/job/foo/15/
JOB_URL
Full URL of this job, like http://server:port/jenkins/job/foo/