Using a CI class from a unix command line

[eluser]Unknown[/eluser]
Wondering if it is possible to run a CI class from unix command line? As of now, the class extends Controller because the class is part of a much larger program. If you try 'php myfile.php' at the unix command line, it produces the following error:

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Fatal error: Class myfile: Cannot inherit from undefined class controller in ci/system/application/controllers/myfile.php on line
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Is it possible to use just one class of a much larger program and execute it from the unix command line?