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 | ## 9.1: Overview of Gri Commands The Gri commands may be divided roughly into a few categories, as indicated in the following list. Working with files: Commands are ``open`', ``close`', ``skip`', ``read`', and ``rewind`'. Controlling parameters of the drawn material: Various ``set`' commands control values of parameters, like size of plot, linewidth, font, etc. Drawing things: Various ``draw`' commands let you draw data, axes, etc. Interacting with the user: The ``query`' command gets instructions from the user. The ``show`' command displays messages to user. Controlling program flow: The ``if`' statement controls optional execution of commands (see If Statements). The ``while`' statement allows loops. Moving around in directories: The ``pwd`', ``cd`' and ``ls`' commands do the usual unix things. Using the operating system The ``system`' command passes instructions to the operating system; the output may be saved into a synonym by using ``\syn = system ...`'. The ``get env`' command determines the value of any unix environment variables the system has defined. For more discussion (see Operating System). Statistical operations: Some very limited capabilities exist; for example, ``regress`' does linear regression. Mathematical operations: Simple mathematical manipulation of column, grid, and image data is provided. Also, wherever Gri expects a number, it will accept a reverse-polish expression; for example, ``set x size 10`' could also be written ``set x size {rpn 20 2 /}`'. For details (see Mathematics).