Line printers are very rare now, but all printers can deal with line printer output (no font support, no italics or bold - just text). Most printers (HP OfficeJet, Cannon InkJet) speak HP specific printer languages (not Postscript - sometimes PCL). Most of the larger LaserJets speak PostScript.
Most folks use print filters to turn PostScript output into the language specific to your printer.
A good place to start would be CUPS -- http://www.cups.org/
There's lots of documentation to read there.