Gri: `get env' command

Gri Commands 1: Introduction 2: Simple example 3: Fancy example 4: Running Gri 5: Programming Gri 6: General Issues 7: X-Y Plots 8: Contour Plots 9: Image Plots 10: Examples 11: Handling Data 12: Gri Commands 13: Gri Extras 14: Evolution of Gri 15: Installing Gri 16: Gri Bugs 17: System Tools 18: Acknowledgments 19: License 20: Newsgroup 21: Concept Index | ## 12.14: The ``get env`' Command
    `get env \result \environment_variable'
Get the value of an "environment variable" from the unix operating system, and store the result in the indicated synonym. This makes most sense on unix systems (hence the name, patterned after the unix command ``getenv`'). This command can be useful in making gri programs resistant to changes in data-file locations. Suppose, for example, there is a file called ``data`', normally in a local directory called ``Bravo`'. The line ``open Bravo/data`' will fail if the Bravo directory is moved. But if the name of the datafile is stored in an unix environment variable, ``DIR_BRAVO`' say, then the gri program will work no matter where the Bravo data are moved, so long as an appropriate environment variable is modified when the data are moved. Example:
    get env \dir DIR_BRAVO
    if {rpn "\dir" "" ==}
        show "Cannot determine location of the Bravo data,"
        show "which should be stored in the environment"
        show "variable DIR_BRAVO.  You should"
        show "do something like"
        show "export DIR_BRAVO='/data/Bravo/'"
        show "in your ~/.environment file"
        quit

        quit
    end if
    open \dir/data
    ...