document distributed with 4.2BSD

SCCS-vsn: usr.sbin/lpr/SMM.doc/5.t 5.1

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+.\" Copyright (c) 1983 Regents of the University of California.
+.\" All rights reserved.  The Berkeley software License Agreement
+.\" specifies the terms and conditions for redistribution.
+.\"
+.\"    @(#)5.t 5.1 (Berkeley) %G%
+.\"
+.NH 1
+Output filter specifications
+.PP
+The filters supplied with 4.2BSD
+handle printing and accounting for most common
+line printers, the Benson-Varian, the wide (36") and
+narrow (11") Versatec printer/plotters. For other devices or accounting
+methods, it may be necessary to create a new filter.
+.PP
+Filters are spawned by \fIlpd\fP
+with their standard input the data to be printed, and standard output
+the printer.  The standard error is attached to the
+.B lf
+file for logging errors.  A filter must return a 0 exit
+code if there were no errors, 1 if the job should be reprinted,
+and 2 if the job should be thrown away.
+When \fIlprm\fP
+sends a kill signal to the \fIlpd\fP process controlling
+printing, it sends a SIGINT signal 
+to all filters and descendents of filters.
+This signal can be trapped by filters which need
+to perform cleanup operations such as
+deleting temporary files.
+.PP
+Arguments passed to a filter depend on its type.
+The
+.B of
+filter is called with the following arguments.
+.DS
+\fIofiler\fP \fB\-w\fPwidth \fB\-l\fPlength
+.DE
+The \fIwidth\fP and \fIlength\fP values come from the
+.B pw
+and
+.B pl
+entries in the printcap database.
+The
+.B if
+filter is passed the following parameters.
+.DS
+\fIfilter\fP [\|\fB\-c\fP\|] \fB\-w\fPwidth \fB\-l\fPlength \fB\-i\fPindent \fB\-n\fP login \fB\-h\fP host accounting_file
+.DE
+The
+.B \-c
+flag is optional, and only supplied when control characters
+are to be passed uninterpreted to the printer (when the
+.B \-l
+option of
+.I lpr
+is used to print the file).
+The
+.B \-w
+and
+.B \-l
+parameters are the same as for the
+.B of
+filter.
+The
+.B \-n
+and
+.B \-h
+parameters specify the login name and host name of the job owner.
+The last argument is the name of the accounting file from
+.IR printcap .
+.PP
+All other filters are called with the following arguments:
+.DS
+\fIfilter\fP \fB\-x\fPwidth \fB\-y\fPlength \fB\-n\fP login \fB\-h\fP host accounting_file
+.DE
+The
+.B \-x
+and
+.B \-y
+options specify the horizontal and vertical page
+size in pixels (from the
+.B px
+and
+.B py
+entries in the printcap file).
+The rest of the arguments are the same as for the
+.B if
+filter.