$ set comspec
ComSpec=C:\WINDOWS\system32\cmd.exe

$ echo %comspec%
C:\WINDOWS\system32\cmd.exe

$ echo %COMSPEC%
C:\WINDOWS\system32\cmd.exe

$ perl -le "print 'comspec : ', $ENV{comspec}"
comspec : C:\WINDOWS\system32\cmd.exe

$ perl -le "print 'COMSPEC : ', $ENV{COMSPEC}"
COMSPEC : C:\WINDOWS\system32\cmd.exe

##</code><code>##

$ set | grep -i ^shell
shell   /bin/tcsh

$ echo $shell
/bin/tcsh

$ echo $SHELL 

$ perl -le 'print "shell : ", $ENV{shell}'
shell : 

$ perl -le 'print "SHELL : ", $ENV{SHELL}'
SHELL : /bin/bash

##</code><code>##

$ set var
var=%OS%

$ perl -MWin32 -e "print $ENV{var} .= ' evaled' , '  => ', Win32::ExpandEnvironmentStrings($ENV{var})"
%OS% evaled  => Windows_NT evaled


##</code><code>##

$ set var=Foo

$ set var
var=Foo

$ set var=Bar & perl -MWin32 -e "print Win32::ExpandEnvironmentStrings('%var%')"
Foo

$ set var
var=Bar

$ set var=Baz & perl -MWin32 -e "print Win32::ExpandEnvironmentStrings('!var!')"
Baz

$ set var
var=Baz