Shell script random number generating

Question

var=$RANDOM creates random numbers but how can i specify a range like between 0 and 12 for instance?

Solution 1

If you already have your random number, you can say

var=$RANDOM
var=$[ $var % 13 ]

to get numbers from 0..12.

Edit: If you want to produce numbers from $x to $y, you can easily modify this:

var=$[ $x + $var % ($y + 1 - $x) ]

Solution 2

Between 0 and 12 (included):

echo $((RANDOM % 13))

---

Edit: Note that this method is not strictly correct. Because 32768 is not a multiple of 13, the odds for 0 to 8 to be generated are slightly higher (0.04%) than the remaining numbers (9 to 12).

Here is shell function that should give a balanced output:

randomNumber()
{
  top=32768-$((32768%($1+1)))
  while true; do
    r=$RANDOM
    [ r -lt $top ] && break
  done
  echo $((r%$1))
}

Of course, something better should be designed if the higher value of the range exceed 32767.

Solution 3

An alternative using shuf available on linux (or coreutils to be exact):

var=$(shuf -i0-12 -n1)

Solution 4

Here you go

echo $(( $RANDOM % 12 ))

I hope this helps.

Solution 5

This document has some examples of using this like RANGE and FLOOR that might be helpful: http://tldp.org/LDP/abs/html/randomvar.html

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Comments

[Hai Vu]

Correction: $(( $RANDOM % 13 ))

[shellter]

yes, agreed, thanks. I was so excited to get to answer an easy one first, I didn't test closely enough! Thanks for the 2 up-votes (whoever you are) ;-)

[jlliagre]

Note the inner $ is optional as non numeric strings found there cannot be but variable names.

[Edward Falk]

Meh. Then your script isn't portable.

[Edward Falk]

Mac OS X has jot too. But not Linux, so this isn't portable.