Read-only and Write-only environment variables

You can use REXX to create environment variables that the CMD.EXE either 
can not read or not write. 

To create read-only environment variables use names with an imbedded equal 
sign, for example =MYREXXVAR. 

The CMD.EXE can only read (but not change) environment variables that 
contain equal signs in the name. It is not possible to modify or delete 
those variables from the command line or from within a plain batch 
program. 

---------- * ----------

To create write-only environment variables use the names 0, 1, to 9. 

The CMD.EXE can only write (or delete) these environment variables but not 
read them. If you code something like 

 
  ECHO %1
  SET myvar=%2

%1 or %2 always reference the parameter of the batch program. And if you 
use them on the command line they are either empty or contain their name 
as value.