Using System V interface scripts with CUPS printing

CUPS is a powerful and flexible printing system, but sometimes all we need is the simplest things. For example, very often for application printing, all I want is a raw queue. I just want cups to pass my data untouched to some device. That's easy enough with cups:

 
lpadmin -p myprinter -E -v parallel:/dev/lp 
 

is all that is needed. The "-v" could also go to a network port or a serial port.

But what if I wanted to add an automatic form feed to the end of that, or do some other special processing? I'd have to get into cups ppd files, add a filter - a lot of work for something so simple. You might want to do that if your printer will handle both simple text that you need to mess with, but let's take the simple, text only case first.

It doesn't have to be. Cups can use System V interfaces scripts. We'll create a simple script that just adds a form feed:

 
#!/bin/bash 
shift;shift;shift;shift;shift 
cat $* 
echo -e "\f\c" 
 

Let's say we called that script "/tmp/myff". We add it to the raw printer like this:

 
lpadmin -p myprinter -E -i /tmp/myff -v parallel:/dev/lp 
 

YOU CAN ONLY USE SYS V INTERFACES SCRIPTS WITH RAW PRINTERS. No PPD files will be used, no other filters will be processed. This script will be the ONLY thing your data passes through.

The /tmp/myff will be copied to /etc/cups/interfaces. If you now send a job:

 
date | lp -d myprinter 
 

a form feed will be added.

By the way, that #!/bin/bash isn't optional here. Cups uses execve to run the script, so it needs a binary file or an interpreter line like that.

I threw away everything else here, but the variables passed to the script are the job number, the user, the source of the data (stdin), the number of copies, and finally the actual data file. So for the invocation above, the five variables I shifted away might have been

 
17 root (stdin) 1 /var/spool/cups/d00017-001 
 

Obviously, there's much more that you can do at this level - emailing, data transformation, whatever you need. However, for complicated tasks, the cups filtering system does have advantages, so this method should be reserved for the simple cases.

You CAN do both - that is, let Cups handle the stuff it wants to handle and have your script handle straight text. It's a bit more work, but the scripts themselves do not change,

To accomplish this, I created "/etc/cups/myfilters". Cups is security conscious (as it should be!) so make sure that directory has the same owner and group and perms as /etc/cups/ppd. Put your script in there, and again make ownership and perms match (-rwxr-xr-x 1 root _lp on my OS X machine).

You then need to modify the ppd file for the printer. In my case, that was "/etc/cups/ppd/hplaser" and I added a new "Filter" line:

*cupsFilter: "application/vnd.cups-raster 50 rastertohp"
*cupsFilter: "text/plain 0 /etc/cups/myfilters/TextToPrinter"
 

The first line was already there; I added the second.

Without that new line, text such as "date | lp -dhplaser" would have been handled by Cups. With this, text jobs go through my filter. This doesn't affect things like printing a web page from a browser or printing from TextEdit, but it will grab things like that command "date | lp -dhplaser".

You'll need to do a "killall -HUP cupsd" (OS X, Linux) or otherwise restart Cups when you initiate these changes; if you need to modify the filter later you can dispense with that and just go ahead and edit it.

In documentation for shell script filters you will see code like this:

[ -n "$6" ] && exec <"$6"
cat -
 

That's because filters can be chained together - the first filter gets passed the file to print in $6 and all others (except the last) are expected to read from stdin and write to stdout. The last filter is the "back-end" which writes to the actual printer hardware (or network port).

See Using Your Own Filters to Print with CUPS for a chaining example.

See also foomatic,magicfilter CUPS print to file - the hard way! What are printer interface scripts?
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16 comments

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Sun Oct 16 23:26:15 2005:   bruceg2005


When you add /tmp/myff, this is at the creation of the printer. Is it possible to add a filter to an existing printer?

- Bruce



Mon Oct 17 09:18:30 2005:   TonyLawrence


Not likle this, no. SysV filters are all or nothing. A "backend" filter is a little more complicated, but can be added to any printer (well, not a SysV style, but any ordinary cups printer).

But as I said in various places here, cups is complicated. Sometimes that's good, but it has a steep learning curve.



Mon Oct 17 13:51:39 2005:   bruceg2004


I purchased the ESP Print Pro version (by the writers of CUPS) - http://www.easysw.com - and they have some good bulletin boards for asking questions. I have already made some suggestions, which the author will incorporate into PrintPro 5.

The one thing I like about the "Pro" version of CUPS, other than the support system, is the graphical front end to 'lp', called 'glp'. This gives you more of a "Windows" type of print dialog for your jobs, which is greatly needed. Although KDE has a very nice interface, this is even more complete.

I will ask the support system what the easiest way to do what I am asking is, and post back here. The author is the one who answers the majority of support questions, which is nice. Usually, within 24 hours.

- Bruce




Mon Jul 2 17:35:21 2007:   TonyLawrence


I just had someone unable to do this - problem was the same as described at http://aplawrence.com/Bofcusm/1613.html

Don't use Windows to write your scripts!!!



Fri Aug 14 23:45:25 2009:   Marcelo


Hi there... I got the inverse problem you'd described in your example.

I receive print jobs from a mainframe via LPD. And it worked pretty well in my old Conectiva 8.0 (Brazilian Distro). But it crashes... then I'm trying Ubuntu 9.04 (yes I know it's pretty fresh).

The problem is that cups-lpd, the work-around for cups listen on port 515 an receive LPD jobs, adds a #$#$#$&% form feed at every job.

The epson FX-890, responsible to the hard work is printing a blank page at each job, thus wasting a lot of paper.

I'm scrutinizing the Internet to fix that, and I refuse to go back to Conectiva 8.0 - it's a honor matter :-) !

So I've found your page...

May I do a script to remove that form feed?
Any ideas?

Thanks in advance,

Marcelo



Sat Aug 15 02:18:05 2009:   TonyLawrence


That's in the printcap file.

Add ":sf:" to suppress formfeed.



Sat Aug 15 14:05:29 2009:   Marcelo


Yes I know "sf" do the magic, the problem is, at least in Ubuntu 9.04, that the /var/run/cups/printcap is written by cups itself, and any changes you make on it are lost. The /etc/printcap is of no use, all CUPS uses is the /etc/cups/ppd/myprinter.ppd.

Heeeeeeeeelp!



Sat Aug 15 14:12:05 2009:   Mabafu


Oooops...

Nevermind

https://bugs.launchpad.net/ubuntu/+source/cupsys/+bug/251458

Tks anyway for your attention!

[]s

Marcelo



Tue Dec 22 15:17:53 2009:   fsendinozaragozaes



We've migrated from an Unixware system to a Linux Box runing cups, we are using system v interfaces (through cups) to print to windows clients with a ftp server running.
Printing works just fine with normal files, but when printing a file with escape characters nothing happens. We've set cupsd to debug2 and when you issue an lp -dPRINTER we can see it start the job, but it doesn't call the inerface program and then cancels the job

Greetings
PD : old time reader, good work



Tue Dec 22 21:58:36 2009:   TonyLawrence


I suspect you aren't using the "raw" model (or pass "-o raw")



Wed Dec 23 02:13:53 2009:   TonyLawrence


Sorry - you said Sys V - I missed that.

Your script has to have a shebang line - does it?



Wed Dec 23 02:28:45 2009:   TonyLawrence


No - that can't be it either. Sorry - I'm tired. I'll look at it tomorrow.



Wed Dec 23 14:28:31 2009:   TonyLawrence


I'm awake now :-)

This really sounds to me like the Sysv interface isn't being seen and that you are not using a raw interface. Can you verify with "ls -lut" that the interface IS being hit when you print?



Wed Dec 23 15:46:17 2009:   TonyLawrence


The reason I say that is that if you don't use "raw" with normal cups, you can't send non-text through..

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