LPRng-HOWTO: 15 Oct 2001 (For LPRng-3.7.9)
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# 16.4. OF Filter

The `:of` filter is used to process banners and job separators. The `:of` filter is responsible for performing appropriate processing of this information and sending to the printer for action.

While the various file filters are invoked on a once per print file basis, the `:of` filter is invoked on a once per print job basis.

This filter is the first one to be started, and should perform whatever specialized device initialization is needed. It should also do whatever accounting procedure is desired for start of job accounting.

The `:of` filter will be given any banner printing or job separation information for a job. As part of its operation, it can detect a specific string, corresponding to a banner print request, and generate a banner. (See the Job Processing Steps and Printcap Options for details.)

During operation, the lpd server will send the special stop sequence of `\031\001` to the `:of` filter. The filter must then suspend itself using a `kill -STOP` operation. The lpd server will detect that the `:of` filter has suspended itself and then will perform other printing operations.

After the other printing operations have been completed, the `:of` will then be sent a `kill -CONT` signal.

This sequence will continue until all information has been printed, and then the `:of` filter's STDIN will be closed. The filter will then perform whatever cleanup operations are needed, update accounting or other information, and exit.

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