First, create the named pipe:
# mkfifo /home/fifo-printers/inv
Next, create the printer "inv" specifying /home/fifo-printers/inv as the device. This will queue the print jobs properly to the named pipe.
redhat-printer-config created this entry in /etc/cups/printers.conf:
Info Created by redhat-config-printer 0.6.x Location Invoice Printer DeviceURI file:/home/fifo-printers/inv State Idle Accepting Yes JobSheets none none QuotaPeriod 0 PageLimit 0 KLimit 0
Changing the Device URI from "file" to "serial" will be required:
# /etc/init.d/cups restart
Finally, catch the output and send it to the port (this is the pass-through printer port device from a Digi Portserver TS4):
# while : ; do cat < /home/fifo-printers/inv >> /dev/prb00; done &
This should be added into a script that runs at boot-up to be sure the named pipe is still there and to start a process running in the background to catch those print jobs and direct them along to the desired serial port.