Shell Programming and Scripting

Appreciated. And sorry. I'm not a Mac person. Did you try it with the seed call?

1) There is no need to apologise, you gave a good method and I found its foibles.
2) We have both learnt something from this thread, me moreso than you.
3) Yes I did try it with 'srand()' and now I think understand why 'while(1)' is used. See EDIT: in post #7.
4) It shouldn't matter about the platform if the code is fully 'sh' compliant.

Boy oh boy, keeping everything POSIX compliant is difficult; especially as I like to do animations and hit the hardware, (bang the metal <wink>).

All I want now is the answer to edited section in my post #3.

In most implementations of awk, random number sequences start are seeded with a constant value (not with the current time) unless you call srand() before calling rand() the first time. (So, as you saw when invoking awk once a second to just produce two random numbers without calling srand() you frequently end up with with the same pair of random numbers every time you call awk. Furthermore, calling srand() with no operand supplies the number of Seconds since the Epoch as an integer number of seconds as the seed value in all but one implementation of awk that I know of. So, if awk is invoked to generate two random numbers calling srand() but without sleeping between invocations of awk you may get the same pair of random numbers a few times until the time in seconds changes.

While it is true that the while(1) loop in the following awk script is an infinite loop, it will only go through that loop a few hundred times before the pipe to the shell fills up (putting awk to sleep for a while). And, yes, byteone and bytetwo are only defined in the while do loop, it was my assumption that whatever you want to do with those variables will be placed in that loop replacing the echo command.

Code:

	awk '
	BEGIN {	srand()
		while(1)
			printf("%d %d\n", 256 * rand(), 256 * rand())
	}' | while read byteone bytetwo
	do	echo "$byteone $bytetwo"
		sleep 1
	done

But, obviously, if a known number of pairs of random numbers are wanted, the while(1) can be changed to a while(cnt++<num) loop, or the shell's while read loop can break or exit when it is done instead of using sleep or just continuing to process the next pair of random numbers.

Hi Don...

Thanks for the info, it is all logged down in the old grey matter for future use.

As for while(1) I assumed that it was filling up a buffer of some kind but never guessed that it was the pipe, | , that it was filling up.
Clever idea that one. (I love lateral thinking.)

I assumed also - like in Python - that while(1) is the equivalent of while(True): . Both (1) and (True) are valid in Python even in Python's latest guise.
Python has not deprecated the (1) which goes back to the start of the Python project.

LBNL, I got the idea of my original ugly code from the WWW from many sources and no-one considered that '/dev/urandom' was NOT in the POSIX specifications. Even the WWW can give answers that are effectively false, so......

......I now consider this thread _solved_ and thanks again Don, you saved the day.

Hello wisecracker,

In Python3.4 you could try following and let me know if this helps you.

Code:

cat random_numbers.py
import random
print("%s" % '[1, 100]:')
for i in range(3):
    print("%d" % random.randint(1, 100))
print("%s" % '\n[-5, 5]:')
for i in range(3):
    print("%d" % random.randint(-5, 5))

Following will be output on same.

Code:

python3 random_numbers.py
[1, 100]:
88
94
55
[-5, 5]:
1
3
3

Thanks,
R. Singh

Hi RavinderSingh13...

I can't use Python in any guise as I have no idea if it is part of ALL *NIX installations.
Similarly Perl, but I have no knowledge of Perl programming anyhow.

It had to be purely POSIX 'sh' compliant and it became much more difficult than I had imagined. As Don so succinctly put it WRT my Post #1:-
There is also the fact that, is Python subject to POSIX compliance?

Again, I have no idea, so rather than use it I avoided it...

In fact I have all but abandoned Python in preference to shell scripting now.

And finally, all my Python code that I have uploaded to the WWW usually works form Python 1.4.0, (Classic AMIGA 1200(HD)), to Python 3.4.3, my latest on various current platforms without modification. This is also seriously difficult to do!

However thanks for your input...