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.
The command name (argv[0]) is set to the name of the destination printer but is also available in the PRINTER environment variable.
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.
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
Sets the printer-state-message attribute and adds the specified
message to the current ErrorLog using the "debug" log level.
DEBUG2: message
Sets the printer-state-message attribute and adds the specified
message to the current ErrorLog using the "debug2" log level.
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 to 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.
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 type associated with the file (e.g.
application/postscript).
CUPS_CACHEDIR
The directory where semi-persistent cache files can be found.
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.
DEVICE_URI
The device-uri associated with the printer.
FINAL_CONTENT_TYPE
The MIME type associated with the printer (e.g.
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/1.2).
TZ
The timezone of the server.
USER
The user executing the filter, typically "lp" or "root"; consult the
cupsd.conf(5) file for the current setting.