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

## 10.2: Online Help

Type ``help`' to get a list of available commands and other topics of interest. Here's how Gri responds

    Type `help' followed by a command-name:
     assert      cd            close         convert
     create      debug         delete        differentiate
     draw        expecting     filter        flip
     get         help          if            ignore
     input       insert        interpolate   list
     ls          mask          move          new
     open        pwd           query         quit
     read        regress       reorder       rescale
     resize      return        rewind        set
     show        skip          sleep         smooth
     source      sprintf       state         superuser
     system      write
    Or type `help -' followed by a topic from this list:
     example     extending     files         math
     strings     synonyms      variables     manual

Some commands have more words than shown. You can type these additional words to narrow the help down; otherwise Gri will give you help on all commands that begin with the indicated words. For example, try ``help set`' and ``help set x`'. When you ask for help on a multi-word command, Gri tells you about all commands which begin with the words you've typed. Thus,

    help
    help draw
    help draw zero
    help draw zero line

narrow in on the command ``draw zero line`'. The response to the most complete request is

    `draw zero line [horizontally|vertically]'
      draw zero line
        Draw line y=0 if it is within axes
      draw zero line horizontally
        Draw line y=0 if it is within axes
      draw zero line vertically
        Draw line x=0 if it is within axes

The part enclosed in angled quotes is the syntactical description of the command. (NOTE: The square brackets indicate an optional word (in this case) or words. The vertical bar indicates that either the item on the left or the item on the right may appear; it is a logical OR operator. The only other special characters in syntax descriptions are the braces ``{}`', which are used to enclose multiple words which act as one unit; they are used to clarify the choices presented to the OR operator.) Following the syntactical description are examples. Each example is indented 2 spaces, and a description of it (which always starts with an upper-case character and ends with a period, to indicate that it is an English description) follows that, indented by an additional 2 spaces.