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

### 9.3.1: ``assert`'

    `assert .condition. ["message"]

The condition may be a variable, a synonym, or an RPN expression. If this condition is true (i.e. evaluates to a non-zero number), do nothing. If the condition is false, the program will terminate with an error condition (in unix, it will terminate with a non-zero exit code).

Before termination, a message will be printed, the form of which depends on the optional ``"message"`' string.

If no ``"message"`' string is given, the the printed message will indicate the name of the command-file and the line at which the assert command was encountered.

If a ``"message"`' string is given, and if it ends in a newline (``"\\n"`'), then this string is printed.

If a ``"message"`' string is given, and if it does not end in ``"\\n"`', then the string is printed along with an indication of the location in the command-file.

(Perl users will recognize this as being patterned on the ``"die"`' command.)