nice faux pas 
I take it you mean Nuke not Shake ![]()
you can use python to get all environment variables:
import os
for (key, value) in os.environ.iteritems():
print '%s = %s' % (key, value)
to get an environment variable's value inside an expression do something like :
[getenv USER]
the shot length won't be an environment variable unless you make it one. You could create it in the init.py on start up like this:
import os
os.environ['FRAME_RANGE'] = '1,20'
