In a recently downloaded version of mac tcl/tk 8.3.3 the documentation indicates that the env(PWD) contains the initial working directory. In fact env(HOME) contains the initial working directory and env(PWD) does not exist.
It seems likely that the documentation is out of date at
file://localhost/Cartan/Applications/Tcl%2FTk/Tcl%2FTk HTML Manual/TclCmd/tclvars.htm
-- Mike Gage