I can not access my system environment variables from the Tcl plugin. For example, I create the following plugin code to display my environment:

puts "Environment (as seen from Tcl)"
foreach {var val} [array get ::env] {
  puts "$var=$val"
}

Running the Job, the output looks like this:

Environment (as seen from Tcl)
java.vm.version=23.25-b01
javax.net.ssl.trustStorePassword=changeit
java.vendor.url=http://java.oracle.com/
sun.jnu.encoding=Cp1252
hudson.lifecycle=hudson.lifecycle.WindowsServiceLifecycle
java.vm.info=mixed mode
java.awt.headless=true
user.dir=C:\Jenkins
sun.cpu.isalist=pentium_pro+mmx pentium_pro pentium+mmx pentium i486 i386 i86
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
sun.os.patch.level=Service Pack 1
javax.net.ssl.trustStore=C:\Jenkins\keystore
java.io.tmpdir=C:\Windows\TEMP\
....

I don't see my Windows environment variables (say, PATH or USERNAME) with the exception of CLASSPATH, TCL_CLASSPATH, USER and HOME, nor do I see any of the environment variables I have defined in the environment definition of my Jenkins job. Instead, I find on ::env a lot of settings which look to me like the contents of a Java property file.

Funnily, some settings from the environment are present, though under a different name. For example, the content of the environment name USERNAME is now found under ::env(user.name).