SCO Unix/System V Printing FAQ
This article is from a FAQ concerning SCO operating
systems. While some of the information may be applicable to any OS,
or any Unix or Linux OS, it may be specific to SCO Xenix, Open
Desktop or Openserver.
There is lots of Linux, Mac OS X and general Unix info elsewhere on
this site: Search this site is the best
way to find anything.
First, are you really sure you need to do this? Only very lame
software can't handle a spooled printer. However, if you must:
The basic concept is to create a named pipe. For example, you
might do this:
mknod /dev/myfakenetprint p
That creates a "device" that your application can print to. Use
"chmod" as necessary to give it whatever permissions you need (666
if everyone needs to use it).
Now you need something that runs all the time in background.
It's a shell script (see New to Unix
if you don't know how to make a shell script) and it needs to start
automatically whenever the machine is rebooted (see Automating Program Startup). This
script assumes that your network printer already exists in the
cat /dev/myfakenetprint | lp -dmyrealnetprinter
Some folks have found that this works better in some places:
You could also use hpnpf or netcat (see Network Printing ) directly:
cat /dev/myfakenetprint | netcat -h printername -p 3001
netcat -h printername -p 3001
These work because the "cat" will hang until something (your
application) writes data to the named pipe. The "lp" won't complete
until cat is done reading, which will be when your application
closes its writing. Although it might look like this ties up your
cpu, it doesn't- the cat sleeps while it hangs, and so does lp or
netcat: there's nothing going on until you write data to the named
pipe. If switching from a serial environment, you may find How can I assign a user process
to a specific pseudo tty? useful also.
On a very busy system, it's possible for the writing process to
send new data to the pipe before your reader process has sent it to
the print server. You could implement a cooperative locking system
to prevent that, but a small sleep at the end of the interface script
will probably work.
You can use this same concept to implement "printers" that send email,
queue faxes or do anything else you need done.
See Race conditions also.
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