The Linux printing system---the lp system---is a port of the source
code written by the Regents of the University of California for the Berkeley
Software Distribution version of the UNIX operating system.

By far, the most simplistic way to print in the Linux operating system is
to send the file to be printed directly to the printing device. One way
to do this is to use the cat command. As the root user,
one could do something like

# cat thesis.txt > /dev/lp

In this case, /dev/lp is a symbolic link to the actual printing
device---be it a dot-matrix, laser printer, typesetter, or plotter. (See
ln(1) for more information on symbolic links.)

For the purpose of security, only the root user and users in the
same group as the print daemon are able to write directly to the printer.
This is why commands such as lpr, lprm, and lpq
have to be used to access the printer.

Because of this, users have to use lpr to print a file. The
lpr command takes care of all the initial work needed to print
the file, and then it hands control over to another program, lpd,
the line printing daemon. The line printing daemon then tells the printer
how to print the file.

When lpr is executed, it first copies the specified file to a
certain directory (the spool directory) where the file remains until
lpd prints it. Once lpd is told that there is a file to
print, it will spawn a copy of itself (what we programmers call forking).
This copy will print our file while the original copy waits for more
requests. This allows for multiple jobs to be queued at once.

The syntax of lpr(1) is a very familiar one,

$ lpr [ options ] [ filename ... ]

If filename is not specified, lpr expects input to come
from standard input (usually the keyboard, or another program's output).
This enables the user to redirect a command's output to the print spooler.
As such,

$ cat thesis.txt | lpr

or,

$ pr -l60 thesis.txt | lpr

The lpr command accepts several command-line arguments that allow a
user to control how it works. Some of the most widely used arguments are:
-Pprinter specifies the printer to use, -h suppresses printing of
the burst page, -s creates a symbolic link instead of copying the file
to the spool directory (useful for large files), and -#num
specifies the number of copies to print. An example interaction with
lpr might be something like

$ lpr -#2 -sP dj thesis.txt

This command will create a symbolic link to the file thesis.txt in
the spool directory for the printer named dj, where it would be
processed by lpd. It would then print a second copy of
thesis.txt.

Another useful feature of any printing system is the ability to cancel a job
that has been previously queued. To do this, use lprm.

$ lprm -

The above command cancels all of the print jobs that are owned by the user
who issued the command. A single print job can be canceled by first getting
the job number as reported by lpq and then giving that number to
lprm. For example,

The lpc(8) program is used to control the printers that lpd serves.
you can enable or disable a printer or its queues, rearrange entries within
a queue, and get a status report on the printers and their queues.
Lpc is mostly used in a setup where there are multiple printers hanging off
one machine.

$ lpc

The above will start the lpc program. By default, this enters you into
an interactive mode, and you can begin issuing commands. The other option
is to issue an lpc command on the command line.

$ lpc status all

A list of the available commands are in the lpd man page, but here
are a few of the major commands you'll want to know about. Any commands
marked with option can either be a printer name (lp, print, etc) or
the keyword all, which means all printers.

Just a quick note here on RedHat's amazing printtool program. It seems
to do everything that a magicfilter would do. RedHat already installs many
of the programs to do the filtering. Here's how I have my printer set up
under RH 4.0 with an HP LJ 4L connected to my parallel port (should be
the same for other versions of RH as well).

Become root and fire up printtool (if you su'ed, you remembered to
SETENV DISPLAY :0.0 and xhost +, right?)