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.)