Randomly choose 10, 100, 1000 or 10000

rng · 04-09-2013, 09:16 PM

I am trying to choose randomly 10, 100, 1000 or 10000. I am using following code which does not work:

Code:

DIGITS=$[ ( $RANDOM % 4 )  + 1 ]
echo "Choice= $[ ( 10 ^ $DIGITS ) ]"

Where is the error? Thanks for your help.

pan64 · 04-10-2013, 12:30 AM

which language is it?

chrism01 · 04-10-2013, 12:41 AM

Wrong type of brackets and exponential operator; try this

Code:

digits=$((RANDOM%4 +1))
echo $digits
echo $((10 ** digits))

http://tldp.org/LDP/abs/html/ops.html

eklavya · 04-10-2013, 12:51 AM

@chrism01
EXCELLENT !!!

I was doing something like this because OP didn't mention script language.

Code:

number=$(python -c 'import random; print(random.randint(1, 4))')
echo $((10 ** $number))

But your solution is accurate because OP asked

Code:

Where is the error?

rng · 04-10-2013, 03:20 AM

Many thanks for your replies. It is linux bash script. Just changing the operator from '^' to '**' works well.

How should you choose between using '[ ]' and '( )' (and '{ }')

sundialsvcs · 04-10-2013, 07:55 AM

For simplicity and clarity, I'd define a constant array with these four values in it, then choose a random index (0..3) to pick from that array.

Now, it's obvious what the choices will be, and they no longer have to be a power-of-ten. They could be anything.

chrism01 · 04-10-2013, 08:02 AM

Re bracket types:

1. use [[ .. ]] for string comparisons (optionally also numeric comparisons)
http://tldp.org/LDP/abs/html/testcon...ml#DBLBRACKETS

2. use (( )) for doing arithmetic and doing numeric comparisons

3. use {} for varnames embedded in strings eg var v2 is embedded in strings below

Code:

v1=asd${v2}df

v1=asdf${v2}

v1=${v2}asd

Enables the parser to pick out the var from the surrounding chars

Have a read of
http://rute.2038bug.com/index.html.gz
http://tldp.org/LDP/Bash-Beginners-G...tml/index.html
http://www.tldp.org/LDP/abs/html/
http://mywiki.wooledge.org/

rng · 04-10-2013, 11:42 AM

Thanks for clarifying. Apparently there is no need to combine brackets like '[( code )]'

chrism01 · 04-10-2013, 09:27 PM

Forgot ( )
4. $(cmd) used usually to assign cmd results to a var eg
v1=$(cmd)

Combined sets of different bracket types are used in certain situations eg arrays http://tldp.org/LDP/abs/html/arrays.html, regexes http://stackoverflow.com/questions/1...-regex-in-bash etc.