For a programming project, I’m supposed to demonstrate different ways that randomization can be utilized within a Linux shell script. Can you help get me started, please?
Randomization and random numbers are both quite fascinating and rather obscure topics from a mathematical perspective. Turns out that it’s pretty dang hard to truly produce random numbers, though you wouldn’t think so. Heck, just think of a deck of playing cards: How many times do you need to shuffle it to truly randomize the cards? [actually, that’s a function of how many cards are in the deck and the answer is seven for a standard deck of 52 cards. Seven good shuffles and your deck will be optimally randomized, as explained in painful mathematical detail in this article. Now you know.]
I also generally have a practice of not helping students out with homework, but I let your question “age” for a few weeks so either you’ve figured it out and turned in your assignment or you’re now running late. 🙂
In any case, like all operating systems, Linux has a fair amount of code within the system to aid in generating sequences of random numbers. They’re important for all sorts of reasons, but you can access them easily enough. The standard way from the command line is the rand command, but let’s do that Linux thing and see what comes up with a search:
$ man -k random | grep '(1' apg (1) - generates several random passwords openssl-rand (1ssl) - generate pseudo-random bytes rand (1ssl) - generate pseudo-random bytes shuf (1) - generate random permutations $
You can see that there are four user level commands (section 1 of the man pages, which is why I used that as the grep pattern). Of these rand is the most important and easiest to work with:
$ rand 5709 $ rand 5654
Turns out you can accomplish exactly the same with the special Bash shell variable RANDOM too:
$ echo $RANDOM 23918 $ echo $RANDOM 25248 $ echo $RANDOM 15456
This isn’t present in every shell, however, so using the rand function is more portable. Want to choose between two possible outcomes, or have a 50% chance that you’ll pick a given option? Here’s some basic code:
if [ $(( $(rand) % 2 )) -eq 1 ] # 50% chance then echo it happened else echo it did not happen fi
How about a 25% chance? Just change the conditional expression to $(rand) % 4 and look for a single value. 10% chance? $(rand) % 10 and look for a single value. It really is that easy.
It’s interesting is to tap one of the other randomized command line utilities while we’re talking about random and randomization. For example, the random password generator apg is handy:
$ apg =Ovitweb4 (EQUAL_SIGN-Ov-it-web-FOUR) Loyk~On2owtyo (Loyk-TILDE-On-TWO-owt-yo) ^okDyufJuksh4 (CIRCUMFLEX-ok-Dyuf-Juksh-FOUR) fi!froxVium0 (fi-EXCLAMATION_POINT-frox-Vi-um-ZERO) omm:Ledeben1 (omm-COLON-Led-eb-en-ONE) =oz3DretAparv (EQUAL_SIGN-oz-THREE-Dret-Ap-arv)
I have no idea why the default is to offer a pronounceable version of each password, but you can disable that with the -a 1 flag, like so:
$ apg -a 1
bk,1Q6g7
}k^j?&mS{
:Eu]:'5A~
E$/HikQAV
gJg/&t["#I
TdBNLH}/X>
Finally, the shuf command is potentially useful in a script too as you can feed it lines of text and it’ll “shuffle” them and then output the contents as a randomized sequence of lines. For example:
$ cat cards ace of spades two of spades three of spades four of spades five of spades six of spades $ shuf cards two of spades three of spades six of spades ace of spades four of spades five of spades $ shuf cards ace of spades three of spades two of spades five of spades four of spades six of spades
There’s lots more you can do with random numbers in the Linux shell, but that’ll definitely get you started. And if you haven’t yet started, well, good luck with your assignment.
Pro Tip: I’ve been writing about Linux scripting for years. I even wrote a book about it! Please check out my Linux help library for lots more tutorials!
