Expansion of environment variables

If value of given parameter contains the following string :

      ${ANY_VAR_NAME}

PIL expands it to the value of ANY_VAR_NAME environment variable. Any number of environment variables can be specified. Also the same variable can be specified many times. As an example, for a user joe with home directory in /home/joe :

      ${HOME}/pfiles/${HOME}

is expanded to

      /home/joe/pfiles/home/joe