Explain this BASH expression

Question

I want to get random number within specific range:

random_number=$(( RANDOM % $RANGE ))

this gives me an error

 ")syntax error: invalid arithmetic operator (error token is "

I assume I can't use $RANGE in this expression, but why? How can I rewrite this?

You should probably see this : http://stackoverflow.com/questions/673016/bash-how-to-do-a-variable-expansion-within-an-arithmetic-expression — zakinster, Apr 29 '13 at 12:00
Try this: http://stackoverflow.com/questions/2556190/random-number-from-a-range-in-a-bash-script — girardengo, Apr 29 '13 at 12:20

score 3 · Accepted Answer · edited May 23 '17 at 12:12

3

Isn't it this:

random_number = $(( $RANDOM % $RANGE ))

$ before RANDOM

If that doesn't work this post:

Suggests:

shuf -i 2000-65000 -n 1

UPDATE
A way to rewrite this is as follows:

 random_number = $(( $RANDOM % some_numeric_value ))

edited May 23 '17 at 12:12

Community

answered Apr 29 '13 at 12:00

Woot4Moo

1

Actually you can omit the `$` within an arithmetic expression. – zakinster Apr 29 '13 at 12:02
@minerals I updated with an approach, where you just feed the upper limit you want to mod against, instead of relying on `$Range` let me know if this works for you. Is there a bash fiddle or something equivalent so I can better test? – Woot4Moo Apr 29 '13 at 12:03

zakinster · Answer 2 · 2013-04-29T12:21:33.500

2

It looks like your variable RANGE may be polluted by a carriage return or something else.

If you're on Windows, there may be an \r from a misconfiguration of the EOL, you could try this :

random_number = $(( RANDOM % $(tr -d '\r' <<< "$RANGE") ))

edited Apr 29 '13 at 12:21

answered Apr 29 '13 at 12:02

zakinster

interesting, I'm getting RANGE from `cat list.txt | wc -l`, don't think wc -l adds carriage return – minerals Apr 29 '13 at 12:04
@minerals what is your OS ? – zakinster Apr 29 '13 at 12:06
So it will add `\r\n` at the end of the line, bash won't trim the `\r`. – zakinster Apr 29 '13 at 12:07
it is! yes, '\r' in the end of $RANGE, confused \r for \n, my bad:) Thanks – minerals Apr 29 '13 at 12:20

2 Answers2