5.8 Environment keys

The [DEFAULT] section may contain a special <keys_variable> option/setting pair that can be used to specify an environment variable name to be used to provide a default list of section keys to use to obtain options. <keys_variable> found in sections other than [DEFAULT] are ignored.

For example, setting the keys environment variable from the command line:

Linux: $ export keys=RACK0,DEV1
DOS:   C:\> set keys=RACK0,DEV1

Makes:

# system.ini
[DEFAULT]
<keys_variable> = keys
desc = 'default description'
[RACK0]
desc = 'main rack'
path[DEV0] = 192.168.0.0
path[DEV1] = 192.168.0.1

Equivalent to:

# system.ini
[DEFAULT]
path = 192.168.0.1
desc = 'main rack'
[RACK0]
desc = 'main rack'
path[DEV0] = 192.168.0.0
path[DEV1] = 192.168.0.1