This build step exports various build job and hudson parameters into a property file named hudsonBuild.properties in the project workspace. This file contains the following informations:

build.jobName	Name of running job.
build.number	Number of running job.
build.user.name	User that triggered this job.
build.user.fullName	Full name of user that triggered this job.
build.user.emailAddress	Email address of user that triggered this job. If no user with email address was found, the admin email address stands here.
build.admin.emailAddress	This is the current administrator email address. See main hudson configure sheet: E-mail Notification, entry System Admin E-mail Address.
build.id	Build id.
build.summary	Build summary like Executor #3 for master : executing MyJob #28.
build.cvsBranch	CVS branch, if configured.
build.hudson.version	Running hudson version.