Unix random number generate in given range

Shell Programming and Scripting
1

Hi All,

I have extracted some report from database for few activities done.

Now I have a requirement to add some random time(In range of 10-35) in front of each activity.

Can be generated random numbers in any bash/sh shell within a given number range, let's say in between 10-30.

Could you please help me.

2

Have a look at

 $RANDOM

Manipulate it a bit to get numbers b/w 10 and 30

3

Panyam, thanks for revert, but how do I manipulate it ? any suggestion ?

4 
 
echo "10+$RANDOM%10*(2)+2 " | bc 
 
will generate random numbers in 12~30 range, if that suffice.
1 Like
5

Thanks Panyam for your useful & quick help, this is what I wanted to do. :slight_smile:

6

You can use also builtin calculation, tested using ksh and bash

echo $(( 10+RANDOM%21 ))
# or more generic
min=10
max=30
((diff=max-min+1))
echo $(( min + RANDOM%diff ))
1 Like
7

Hi.

shuf -i 10-30 -n 1

produces, in 3 separate runs:

26
% shuf -i 10-30 -n 1
15
% shuf -i 10-30 -n 1
25

The shuf utility is part of GNU coreutils, Coreutils - GNU core utilities which you could download, configure, compile, etc., if your system does not have coreutils installed or available via your package manager -- easier for Linux than for one of the Unix systems, Solaris, *BSD, etc.

Many features, see on-line man page is at: shuf(1): make random permutations - Linux man page

Best wishes ... cheers, drl

8

For the heck of it, using sh and /dev/random, or when shell does not have $RANDOM

#!/bin/sh

if [ -z "$1" ]; then a=0; b=65536; else b=$((1+$1)); fi
[ -z "$2" ] || { a="$1"; b=$((1+$2-a));}
echo $((a+$(od -An -dN2 /dev/random)%b))

exit 0

Usage: this_script.sh outputs a value between 0 and 65535

this_script.sh MAX outputs a value between 0 and MAX

this_script.sh MIN MAX outputs a value between MIN and MAX

9

Hi.

Another handy utility, jot produces, for 3 runs:

% jot -r 1 10 30
29
% jot -r 1 10 30
10
% jot -r 1 10 30
12

I first ran across jot in UNIX PowerTools, Second Edition - O'Reilly Media , but the version on Debian 5 (lenny) has been extended beyond that. There is a source tar file at http://ftp.de.debian.org/debian/pool/main/a/athena-jot/athena-jot_9.0.orig.tar.gz -- I unpacked, configured, and compiled the source successfully:

% ./jot -r 1 100 500
346

Like shuf, jot has more features, see Man Page for jot (FreeBSD Section 1) - The UNIX and Linux Forums

Best wishes ... cheers, drl

10

Hey...Thanks to all for providing such useful info.

11

Hi.

There is a characteristic of /dev/random that could become an issue. There may be a limit to how many bits one can pull from /dev/random because it may block. The alternate /dev/urandom is not blocked and is probably as good as /dev/random for many purposes.

For example, I can only get 200-300 numbers from the posted script before /dev/random blocks (Debian 5 -- lenny -- GNU/Linux).

See /dev/random - Wikipedia, the free encyclopedia for details on this and other aspects ... cheers, drl