When you use the Smart Label or Advanced Search, under Inventory | Devices to filter which managed devices comply with it and zero devices return.For example:
To confirm it works. Check through, Inventory › Devices › Device Detail.
The Smart Label or Advanced Search features are capable of using these options: matches REGEX, or contains. However, it may depend how the data is returned.
Note: When searching for the results of the custom inventory rule's ShellCommandTextReturn output, it does not return results when using =, <, >, is NULL, begins with, or ends with to filter.
Shown below is an example of a successful custom inventory rule. The example .cfg file was supposed to get devices with different records than 45d.
After saving the custom inventory rule, you can verify it worked by viewing the rule under the Custom Inventory Field of an inventoried device and the record will not show any values containing 45d.