8.7 Setting up LPR/LPD on FreeBSD

8.7.4.1 Types of Filters

Three types of filters can be defined in the /etc/printcap file. In this book all filter examples are for Input filters.

8.7.4.2 Printing Raw UNIX Text with a Filter

One of the first things that a new UNIX user will discover when plugging a standard LaserJet or impact printer into a UNIX system is the stairstep problem. The symptom is that the user dumps text to the printer, either through LPR or redirection (by catting it to the parallel device) and instead of receiving the expected Courier 10-point printout, gets a page with a single line of text, or two lines of text "stairstepped", text and nothing else.

The problem is rooted in how printers and UNIX handle textfiles internally. Printers by and large follow the "MS-DOS Textfile" convention of requiring a carriage return, then a linefeed, at the end of every text line. This is a holdover from the early days when printers were mechanical devices, and the print head needed to return and the platen to advance to start a new line. UNIX uses only the linefeed character to terminate a text line. So, simply dumping raw text out the parallel port works on MS-DOS, but not on UNIX.

If the printer is a PostScript printer, and doesn't support standard ASCII, then dumping UNIX text to it doesn't work. But then, neither would dumping MS-DOS text to it. (Raw text printing on PostScript printers is discussed later in this chapter.) Note also that if the printer is connected over the network to an HP JetDirect hardware print server, internal or external, the TEXT queue on the hardware print automatically adds the extra Carriage Return character to the end of a text line.

If the printer is the garden-variety HP LaserJet, DeskJet, or an impact printer, and under DOS the administrator is used to printing raw text from the command line for directory listings, there are two ways to fix stairstep. The first is to send a command to the printer to make it print in "unix textfile" mode, which makes the printer supply its own carriage return. This solution is ugly in a printer environment with UNIX and Windows machines attempting to share use of the same printer. Switching the printer to work with UNIX disrupts DOS/Windows raw text printouts.

The better solution is to use a simple filter that converts incoming text from UNIX style to DOS style. The following filter posted on questions@FreeBSD.org and the sample /etc/printcap entry can be used to do this:

#!/bin/sh
# /usr/local/libexec/crlfilter
#
# simple parlor trick to add CR to LF for printer
# Every line of standard input is printed with CRLF
# attached.
#

awk '{printf "%s\r\n", $0}' -

An alternative filter posted using sed could be written as:

#!/bin/sh
# /usr/local/libexec/crlfilter
#
# Add CR to LF for printer
# Every line of standard input is printed with CRLF
# attached.
#
# Note, the ^M is a *real* ^M (^V^M if your typing in vi)
#

sed 's/$/^M/' -

Here is an example of a filter that triggers the printers automatic LF-to-CR/LF converter (this option is only useful on HP LaserJets that support this command):

#!/bin/sh
# Simply copies stdin to stdout.  Ignores all filter
# arguments.
# Tells printer to treat LF as CR+LF.  Writes a form feed
# character after printing job.

printf "\033&k2G" && cat && printf "\f" && exit 0

exit 2

The printcap file used to trigger the filter is:

#/etc/printcap
# The trailer (tr) is used when the queue empties.  I found that the
# form feed (\f) was basically required for the HP to print properly.
# Banners also need to be shut off.
#

lp|local line printer:\
    :lp=/dev/lpt0:sd=/var/spool/output/lpd:lf=/var/log/lpd-errs:
    :if=/usr/local/libexec/crlfilter:sh:tr=\f:mx#0:
#

8.7.4.3 The pr filter

Although most filters are built by scripts or programs and are added to the UNIX machine by the administrator, there is one filter that is supplied with the FreeBSD operating system is very useful for raw text files: the pr filter. It is most commonly used when printing from the UNIX command shell. The pr filter paginates and applies headers and footers to ASCII text files. It is automatically invoked with the -p option used with the lpr program at the UNIX command prompt.

The pr filter is special - it runs in addition to any input filters specified for the print queue in /etc/printcap, if the user sets the option for a print job. This allows headers and pagination to be applied in addition to any special conversion, such as CR to CR/LF that a specified input filter may apply.

8.7.4.4 Printing PostScript Banner Pages with a Filter.

Unfortunately, the canned banner page supplied in the LPD program prints only on a text-compatible printer. If the attached printer understands only PostScript and the administrator wants to print banner pages, it is possible to install a filter into the /etc/printcap file to do this.

The following filter is taken from the FreeBSD Handbook. I've slightly changed its invocation for a couple of reasons. First, some PostScript printers have difficulty when two print files are sent within the same print job or they lack the trailing Control-D. Second is that the handbook invocation uses the LPRPS program, which requires a serial connection to the printer.

The following filter shows another trick: calling LPR from within a filter program to spin off another print job. Unfortunately, the problem with using this trick is that the banner page always gets printed after the job. This is because the incoming job spools first, and then FreeBSD runs the filter against it, so the banner page generated by the filter always spools behind the existing job.

There are two scripts, both should be put in the /usr/local/libexec directory, and the modes set to executable. The printcap also must be modified to create the nonbanner and banner versions of the print queue. Following the scripts is the /etc/printcap file showing how they are called. Notice that the sh parameter is turned on since the actual printed banner is being generated on the fly by the filter:

#!/bin/sh
# Filename /usr/local/libexec/psbanner
# parameter spacing comes from if= filter call template of:
# if -c -w -l -i -n login -h host
# parsing trickiness is to allow for the presence or absence of -c
# sleep is in there for ickiness of some PostScript printers

for dummy
do
  case "$1" in
    -n) alogname="$2" ;;
    -h) ahostname="$2" ;;
  esac
  shift
done

/usr/local/libexec/make-ps-header $alogname $ahostname "PostScript" | \
  lpr -P lpnobanner

sleep 10

cat && exit 0

Here is the make-ps-header listing.

#!/bin/sh
# Filename /usr/local/libexec/make-ps-header
#
# These are PostScript units (72 to the inch).  Modify for A4 or
# whatever size paper you are using:
#

page_width=612
page_height=792
border=72

#
# Save these, mostly for readability in the PostScript, below.
#

user=$1
host=$2
job=$3
date=`date`

#
# Send the PostScript code to stdout.
#

exec cat <<EOF
%!PS
%
% Make sure we do not interfere with user's job that will follow
%

%
% Make a thick, unpleasant border around the edge of the paper.
%

$border $border moveto
$page_width $border 2 mul sub 0 rlineto
0 $page_height $border 2 mul sub rlineto
currentscreen 3 -1 roll pop 100 3 1 roll setscreen
$border 2 mul $page_width sub 0 rlineto closepath
0.8 setgray 10 setlinewidth stroke 0 setgray

%
% Display user's login name, nice and large and prominent
%

/Helvetica-Bold findfont 64 scalefont setfont
$page_width ($user) stringwidth pop sub 2 div $page_height 200 sub moveto
($user) show

%
% Now show the boring particulars
%

/Helvetica findfont 14 scalefont setfont
/y 200 def
[ (Job:) (Host:) (Date:) ] {
200 y moveto show /y y 18 sub def
} forall
/Helvetica-Bold findfont 14 scalefont setfont
/y 200 def
[ ($job) ($host) ($date) ] {
270 y moveto show /y y 18 sub def
} forall

%
% That is it
%

showpage

Here is the /etc/printcap file.

#
lp|local line printer, PostScript, banner:\
  :lp=/dev/lpt0:sd=/var/spool/output/lpd:lf=/var/log/lpd-errs:\
  :if=/usr/local/libexec/psbanner:sh:mx#0:

lpnobanner|local line printer, PostScript, no banner:\
  :lp=/dev/lpt0:sd=/var/spool/output/lpd-noban:\
  :lf=/var/log/lpd-errs:sh:mx#0:
#