In windows you can use LPR
In Linux you can do lpr or 'data.txt > /dev/lpt1/'
How do I do it on a Mac?
lpr works great on the Mac.
If you type "lpr foo.txt" on my MacBook Pro, it gets sent to my default printer. Make sure that you have a printer setup.
Update: I asked a few of the Mac guys in the office about this and they indicated that in the past, some low-end "Win-Printers" with Mac drivers were unable to actually process plain text coming from LPR. We've since removed all of these printers from our inventory, so I'm unable to verify.
Another handy option is to use netcat to send a raw postscript file directly to a networked printer. This is occasionally useful in wierd circumstances, like if you don't have or don't want to install printer drivers. I find it particularly useful on Linux boxes since you never know quite how they are set up.
Most Mac and Linux apps will print to a postcript file, and then you can run:
nc 255.255.255.255 9100 < file.ps
to send the postscript file directly to a printer on the network. (Replace the 255s with the actual printer IP address.)
Not something you'll use every day, but if you do a lot of consulting/troubleshooting on the road with your laptop it may come in handy.