9.1: Overview of Gri Commands

• 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).