A.P. Lawrence

Using System V interface scripts with CUPS printing

Author: TonyLawrence
Date: Tue Mar 15 12:00:16 2005
Subject: Using System V interface scripts with CUPS printing

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.

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 feeed 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.

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

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