Gri: `get env' command

Chapters: 1: Introduction 2: Simple example 3: Invocation 4: Finer Control 5: X-Y Plots 6: Contour Plots 7: Image Plots 8: Examples 9: Gri Commands 10: Programming 11: Environment 12: Emacs Mode 13: History 14: Installation 15: Gri Bugs 16: Test Suite 17: Gri in Press 18: Acknowledgments 19: License Indices: Concepts Commands Variables | ### 9.3.13: ``get env`'
    `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
    end if
    open \dir/data
    ...