Generating a POSIX random number? Post: 302977366

Sponsored Content

Top Forums Shell Programming and Scripting Generating a POSIX random number? Post 302977366 by Don Cragun on Saturday 16th of July 2016 09:20:44 PM

07-16-2016

Registered User

/dev/urandom is not specified by POSIX. So, besides being ugly, it doesn't really conform to POSIX.

The shell variable RANDOM is not specified by POSIX either, but if you're using ksh or bash, the following code is a LOT faster and simpler:

Code:

#!/bin/sh
while true
do
	byteone=$((RANDOM % 255))
	bytetwo=$((RANDOM % 255))
	echo "$byteone $bytetwo"
	sleep 1
done

Note that on many systems, /bin/sh is not a POSIX-conforming shell. And, as you have seen in many of my earlier posts, /bin/awk or /usr/bin/awk might not be a POSIX-conforming awk utility. But as long as /bin/sh is a shell that recognizes Bourne shell syntax, the following usually works on any POSIX-conforming system:

Code:

#!/bin/sh
PATH=`getconf PATH`
export PATH
sh <<-"EOF"
	awk '
	BEGIN {	srand()
		while(1)
			printf("%d %d\n", 256 * rand(), 256 * rand())
	}' | while read byteone bytetwo
	do	echo "$byteone $bytetwo"
		sleep 1
	done
EOF

There is other implementation-defined initialization code that is needed on some systems to really set up a POSIX-conforming environment, but the above should work for the minimal features used by this script.

This User Gave Thanks to Don Cragun For This Post:

Don Cragun

View Public Profile for Don Cragun

Find all posts by Don Cragun

9 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

Generating random number within a specific range (0.5-1.5)

Hello, need a way to generate numbers within 0.5-1.5 range Has to be totally random: 0.6 1.1 0.8 1.5 0.6 and so on.... How to?

2. Shell Programming and Scripting

Generating random numbers

Hi, I am having trouble with generating random numbers. can this be done with awk? So I have a file that looks like this: 23 30 24 40 26 34 So column1 is start and column2 is end. I want to generate 3 random #'s between start and stop: So the output will look like this: ...

3. Programming

generating 16 digit random number in C

Hi, How can we generate 16 digit random nos in C.

4. Programming

C Help; generating a random number.

Im new to C, and Im having a hard time getting a random number. In bash, I would do something similar to the following to get a random number; #!/bin/bash seed1=$RANDOM seed2=$RANDOM seed3=$RANDOM SEED=`expr $seed1 * $seed2 / $seed3` echo ${SEED%.*} Now, in online examples...

5. Programming

Generating Random Number in Child Process using Fork

Hello All, I am stuck up in a program where the rand functions ends up giving all the same integers. Tried sleep, but the numbers turned out to be same... Can anyone help me out how to fix this issue ? I have called the srand once in the program, but I feel like when I call fork the child process...

6. Shell Programming and Scripting

Generating Random Number in certain range

Hi there I am trying to generate a random number between 40 and 70 using the shell here is my code so far and it keeps going above 70. all help much appreciated! comp=$(( RANDOM%70+40 )) echo $comp

7. Shell Programming and Scripting

Random number generating script?

Having a hard time with this. Very new to scripting and linux. Spent all sunday trying to do this. Appreciate some help and maybe help breaking down what the syntax does. Create a Bash program. It should have the following properties • Creates a secret number between 1 and 100 i. The...

8. Shell Programming and Scripting

Generating a Random String of 'n' length

Hi, How can I generate a string of random characters (alpha+numeric) of a particular length ? For e.g. for n=5, output = 'kasjf' n=10, output = 'hedbcd902k' Also, please let me know if random (valid) dates could also be generated. Thanks

9. OS X (Apple)

Generate a random number in a fully POSIX compliant shell, 'dash'...

Hi all... Apologies for any typos, etc... This took a while but it didn't beat me... Although there are many methods of generating random numbers in a POSIX shell this uses integer maths and a simple C source to create an executable to get epoch to microseconds accuracy if it is needed. I take...

LEARN ABOUT LINUX

bzexe

BZEXE(1)						      General Commands Manual							  BZEXE(1)

NAME

       bzexe - compress executable files in place

SYNOPSIS

       bzexe [ name ...  ]

DESCRIPTION

       The  bzexe  utility  allows you to compress executables in place and have them automatically uncompress and execute when you run them (at a
       penalty in performance).  For example if you execute ``bzexe /bin/cat'' it will create the following two files:
	   -r-xr-xr-x  1 root  bin   9644 Feb 11 11:16 /bin/cat
	   -r-xr-xr-x  1 bin   bin  24576 Nov 23 13:21 /bin/cat~
       /bin/cat~ is the original file and /bin/cat is the self-uncompressing executable file.  You can remove /bin/cat~ once  you  are	sure  that
       /bin/cat works properly.

       This utility is most useful on systems with very small disks.

OPTIONS

       -d     Decompress the given executables instead of compressing them.

SEE ALSO

       bzip2(1), znew(1), zmore(1), zcmp(1), zforce(1)

CAVEATS

       The  compressed	executable  is a shell script. This may create some security holes. In particular, the compressed executable relies on the
       PATH environment variable to find gzip and some other utilities (tail, chmod, ln, sleep).

BUGS

       bzexe attempts to retain the original file attributes on the compressed executable, but you may have to fix them manually  in  some  cases,
       using chmod or chown.

																	  BZEXE(1)