Bash Scripting: Printer Test Script

Print Script Tutorial Lecture
TheCAT
11/19/2014

Objective: Send a printer test page to a group of networked printers. Ideally, the test page has a date and user name. Additionally it should be in color and span the depth and breadth of the page. This script can then be used in conjunction with lab checks to ensure that the printers in the labs are in good working order and so that an individual that encounters the page can understand its purpose.

Minimum Command Requirements:

man

lp or lpr

chmod

Optional Commands:

date

cat

convert

lpoptions

& many more possible

Possible Syntax:

for, do, done

if then else fi

case esac

exit

shift

Tools:

nano/vim/emacs

a .jpg or two

Side note: A print script can range from 5 lines to 150 or more. You can use any language and there are no hard and fast rules beyond the objectives – which are more of a guideline.

First let's look at what lp and lpr do.

user@machine$ man lp

user@machine$ man lpr

While I personally think that lp is a little more versatile offering a lot of options I actually used lpr for my script – no real rhyme or reason there so consider either one a viable alternative.

So you can see that you are ultimately going to have to provide some data to the command like the name of the printer and the file to print.

But what to do when there is more than one printer?

Well, we could just run the command multiple times, each time updating the name of the printer to reflect the next printer on our list of printers. In fact that is exactly what we are going to do, but we aren't going to do it by hand, we are going to put it in a script.

One method for doing something a lot of times is to put it in a for-loop. In this case each iteration of the loop corresponds to printing the same file to a new printer.

You now have the foundation for the entire script; the rest is just refining the bits of what we discussed so far. And for that we will work individually... more on this at the very end. Other questions to ask yourself

* What are the printers?

       - do these live in the script?

       - do they live in a separate file?

* What file to use?

       - do I create my own image?

       - Text or picture?

* How to get the date on it?

* How to get a name on it?

* Do I test all the printers at once?

But before we start coding (and after we finish solving the problem) let's start with something we will need at the top of any script: the magic cookie. No not that chocolate yummy thing. This is a line at the top of our file that reads as follows:

#! /bin/bash

This tells kernel to run the script in a bash shell. So when you run a command from the command line, there is a fork command that creates and entirely new shell which is an exact copy of the shell currently running. We want to make certain that when the script is run, that the new shell is also a bash shell. This falls under the execve command that follows (but we now we are way out of scope)...

Lastly let's discuss chmod. Change file mode allows us to set permissions for a file. On our systems when you create a new file the permissions default to: -rw------- meaning only we can read and write to it, but cannot execute. For a text file this isn't terrible, but since we are building a script we will want to make it executable. Additionally there is the consideration of whether we want other people to run our script. Do you want to let other cats run it? Or anyone at all? For now let's assume that we want to make it so that only we can run it. When we are done, we will want to:

chmod 700 my_script 

Now let's get to work and start thinking about how to set up what we need based on the previous bullet point questions....


For Loop Syntax

for item in apple banana cherry; do
    echo $item
done


for number in {1..9}; do
    echo $number
done

for f in `ls`; do 

    echo $f

done