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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | LOG MESSAGES | ENVIRONMENT VARIABLES | CONFORMING TO | NOTES | SEE ALSO | COPYRIGHT | COLOPHON |
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filter(7) OpenPrinting filter(7)
filter - cups file conversion filter interface
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);
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 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.
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.
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.
While the filter interface is compatible with System V interface
scripts, CUPS does not support System V interface scripts.
CUPS printer drivers and backends are deprecated and will no
longer be supported in a future feature release of CUPS. Printers
that do not support IPP can be supported using applications such
as ippeveprinter(1).
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.
backend(7), cups(1), cups-files.conf(5), cupsd(8), cupsfilter(8),
CUPS Online Help (http://localhost:631/help)
Copyright © 2020-2024 by OpenPrinting.
This page is part of the CUPS (a standards-based, open source
printing system) project. Information about the project can be
found at ⟨https://github.com/openprinting/cups⟩. If you have a
bug report for this manual page, see
⟨https://github.com/OpenPrinting/cups/issues⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/openprinting/cups⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-07.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
2021-02-28 CUPS filter(7)
Pages that refer to this page: backend(7), notifier(7), cupsd(8), cupsd-helper(8), cupsfilter(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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