Classic Shell Scripting

Printing

Compared to computers, printers are slow devices, and because they are commonly shared, it is generally undesirable for users to send jobs directly to them. Instead, most operating systems provide commands to send requests to a print daemon ^[2] that queues jobs for printing, and handles printer and queue management. Print commands can be handled quickly because printing is done in the background when the needed resources are available.

Printing support in Unix evolved into two camps with differing commands but equivalent functionality, as summarized in Table 4-2. Commercial Unix systems and GNU/Linux usually support both camps, whereas BSD systems offer only the Berkeley style. POSIX specifies only the lp command.

Table 4-2. Printing commands

Berkeley	System V	Purpose
lpr	lp	Send files to print queue
lprm	cancel	Remove files from print queue
lpq	lpstat	Report queue status

Here is an example of their use, first with the Berkeley style:

$ lpr -Plcb102 sample.ps                 
            Send PostScript file to print queue lcb102

$ lpq -Plcb102                           
            Ask for print queue status
lcb102 is ready and printing
Rank    Owner   Job     File(s)     Total Size
active  jones   81352   sample.ps   122888346 bytes

$ lprm -Plcb102 81352                    
            Stop the presses! Kill that huge job

and then with the System V style:

$ lp -d lcb102 sample.ps                 
            Send PostScript file to print queue lcb102
request id is lcb102-81355 (1 file(s))

$ lpstat -t lcb102                       
            Ask for print queue status
printer lcb102 now printing lcb102-81355

$ cancel lcb102-81355                    
            Whoops! ...