Including output of environment variable in command line?

[Doug Lawlor]

Hello list, I used to know how to do this but can't think of it at the 
moment.  How does one go about including the output of an environment 
variable in a command line?  I thought it was something like the following 
command line example.
  'program --directory $HOME$/test' where $HOME$ is the variable I want to 
insert.  When I try this the program complains it can not find the directory.

Any help on this would be appreciated.

Doug