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Command Section
filter(7)                         Apple Inc.                         filter(7)

NAME
       filter - cups file conversion filter interface

SYNOPSIS
       filter job user title num-copies options [ filename ]

       #include <cups/cups.h>

       ssize_t cupsBackChannelRead(char *buffer, size_t bytes,
                                   double timeout);

       cups_sc_status_t cupsSideChannelDoRequest(cups_sc_command_t command,
                                                 char *data, int *datalen,
                                                 double timeout);

       #include <cups/ppd.h>

       const char *cupsGetOption(const char *name, int num_options,
                        cups_option_t *options);

       int cupsMarkOptions(ppd_file_t *ppd, int num_options,
                           cups_option_t *options);

       int cupsParseOptions(const char *arg, int num_options,
                            cups_option_t **options);

       ppd_choice_t *ppdFindMarkedChoice(ppd_file_t *ppd, const char *keyword);

       void ppdMarkDefaults(ppd_file_t *ppd);

       ppd_file_t *ppdOpenFile(const char *filename);

DESCRIPTION
       The CUPS filter interface provides a standard method for adding support
       for new document types or printers to CUPS.  Each filter is capable of
       converting from one or more input formats to another format that can
       either be printed directly or piped into another filter to get it to a
       printable format.

       Filters MUST be capable of reading from a filename on the command-line
       or from the standard input, copying the standard input to a temporary
       file as required by the file format.  All output MUST be sent to the
       standard output.  Filters MUST NOT attempt to communicate directly with
       the printer, other processes, or other services.

       The command name (argv[0]) is set to the name of the destination
       printer but is also available in the PRINTER environment variable.

OPTIONS
       Options are passed in argv[5] and are encoded from the corresponding
       IPP attributes used when the job was submitted. Use the
       cupsParseOptions() function to load the options into a cups_option_t
       array and the cupsGetOption() function to get the value of a specific
       attribute.  Be careful to look for common aliases of IPP attributes
       such as "landscape" for the IPP "orientation-requested" attribute.

       Options passed on the command-line typically do not include the default
       choices the printer's PPD file. Use the ppdMarkDefaults() and
       cupsMarkOptions() functions in the CUPS library to apply the options to
       the PPD defaults and map any IPP attributes to the corresponding PPD
       options.  Use ppdFindMarkedChoice() to get the user-selected choice for
       a PPD option. For example, a filter might use the following code to
       determine the current value of the Duplex PPD option:

           ppd_file_t *ppd = ppdOpenFile(getenv("PPD"));
           cups_option_t *options = NULL;
           int num_options = cupsParseOptions(argv[5], 0, &options);

           ppdMarkDefaults(ppd);
           cupsMarkOptions(ppd, num_options, options);

           ppd_choice_t *choice = ppdFindMarkedChoice(ppd, "Duplex");

       Raster filters should use option choices set through the raster page
       header, as those reflect the options in effect for a given page.
       Options specified on the command-line determine the default values for
       the entire job, which can be overridden on a per-page basis.

LOG MESSAGES
       Messages sent to the standard error are generally stored in the
       printer's "printer-state-message" attribute and the current ErrorLog
       file.  Each line begins with a standard prefix:

       ALERT: message
            Sets the "printer-state-message" attribute and adds the specified
            message to the current ErrorLog using the "alert" log level.

       ATTR: attribute=value [ ... attribute=value]
            Sets the named job or printer attribute(s). The following job
            attributes can be set: "job-media-progress". The following printer
            attributes can be set: "auth-info-required", "marker-colors",
            "marker-high-levels", "marker-levels", "marker-low-levels",
            "marker-message", "marker-names", "marker-types", "printer-alert",
            and "printer-alert-description".

       CRIT: message
            Sets the "printer-state-message" attribute and adds the specified
            message to the current ErrorLog using the "critical" log level.

       DEBUG: message
            Adds the specified message to the current ErrorLog using the
            "debug" log level.  DEBUG messages are never stored in the
            "printer-state-message" attribute.

       DEBUG2: message
            Adds the specified message to the current ErrorLog using the
            "debug2" log level.  DEBUG2 messages are never stored in the
            "printer-state-message" attribute.

       EMERG: message
            Sets the "printer-state-message" attribute and adds the specified
            message to the current ErrorLog using the "emergency" log level.

       ERROR: message
            Sets the "printer-state-message" attribute and adds the specified
            message to the current ErrorLog using the "error" log level.

       INFO: message
            Sets the "printer-state-message" attribute. If the current
            LogLevel is set to "debug2", also adds the specified message to
            the current ErrorLog using the "info" log level.

       NOTICE: message
            Sets the "printer-state-message" attribute and adds the specified
            message to the current ErrorLog using the "notice" log level.

       PAGE: page-number #-copies

       PAGE: total #-pages
            Adds an entry to the current PageLog. The first form adds #-copies
            to the "job-media-sheets-completed" attribute. The second form
            sets the "job-media-sheets-completed" attribute to #-pages.

       PPD: Keyword=Value [ ... KeywordN=Value ]
            Sets the named keywords in the printer's PPD file. This is
            typically used to update default option keywords such as
            DefaultPageSize and the various installable options in the PPD
            file.

       STATE: printer-state-reason [ ... printer-state-reason ]

       STATE: + printer-state-reason [ ... printer-state-reason ]

       STATE: - printer-state-reason [ ... printer-state-reason ]
            Sets, adds, or removes "printer-state-reason" keywords for the
            current queue. Typically this is used to indicate media, ink, and
            toner conditions on a printer.

       WARNING: message
            Sets the "printer-state-message" attribute and adds the specified
            message to the current ErrorLog using the "warning" log level.

ENVIRONMENT VARIABLES
       The following environment variables are defined by the CUPS server when
       executing the filter:

       CHARSET
            The default text character set, typically "utf-8".

       CLASS
            When a job is submitted to a printer class, contains the name of
            the destination printer class. Otherwise this environment variable
            will not be set.

       CONTENT_TYPE
            The MIME media type associated with the submitted job file, for
            example "application/postscript".

       CUPS_CACHEDIR
            The directory where semi-persistent cache files can be found and
            stored.

       CUPS_DATADIR
            The directory where data files can be found.

       CUPS_FILETYPE
            The type of file being printed: "job-sheet" for a banner page and
            "document" for a regular print file.

       CUPS_MAX_MESSAGE
            The maximum size of a message sent to stderr, including any
            leading prefix and the trailing newline.

       CUPS_SERVERROOT
            The root directory of the server.

       FINAL_CONTENT_TYPE
            The MIME media type associated with the output destined for the
            printer, for example "application/vnd.cups-postscript".

       LANG The default language locale (typically C or en).

       PATH The standard execution path for external programs that may be run
            by the filter.

       PPD  The full pathname of the PostScript Printer Description (PPD) file
            for this printer.

       PRINTER
            The name of the printer.

       RIP_CACHE
            The recommended amount of memory to use for Raster Image
            Processors (RIPs).

       SOFTWARE
            The name and version number of the server (typically
            CUPS/major.minor).

       TZ   The timezone of the server.

       USER The user executing the filter, typically "lp" or "root"; consult
            the cups-files.conf file for the current setting.

CONFORMING TO
       While the filter interface is compatible with System V interface
       scripts, CUPS does not support System V interface scripts.

NOTES
       CUPS filters are not meant to be run directly by the user.  Aside from
       the legacy System V interface issues (argv[0] is the printer name),
       CUPS filters also expect specific environment variables and file
       descriptors, and typically run in a user session that (on macOS) has
       additional restrictions that affect how it runs.  Unless you are a
       developer and know what you are doing, please do not run filters
       directly.  Instead, use the cupsfilter(8) program to use the
       appropriate filters to do the conversions you need.

SEE ALSO
       backend(7), cups(1), cups-files.conf(5), cupsd(8), cupsfilter(8),
       CUPS Online Help (http://localhost:631/help)

COPYRIGHT
       Copyright (C) 2007-2017 by Apple Inc.

19 October 2015                      CUPS                            filter(7)
Command Section