5.20 define option (-D)

This is the "name to add to definition list" option.

This option has some usage constraints. It:

• may appear an unlimited number of times.
• is a member of the define class of options.

The AutoGen define names are used for the following purposes:

1. Sections of the AutoGen definitions may be enabled or disabled by using C-style #ifdef and #ifndef directives.
2. When defining a value for a name, you may specify the index for a particular value. That index may be a literal value, a define option or a value #define-d in the definitions themselves.
3. The name of a file may be prefixed with $NAME/. The $NAME part of the name string will be replaced with the define-d value for NAME.
4. When AutoGen is finished loading the definitions, the defined values are exported to the environment with, putenv(3). These values can then be used in shell scripts with ${NAME} references and in templates with (getenv "NAME").
5. While processing a template, you may specify an index to retrieve a specific value. That index may also be a define-d value.