[SOLVED] Random numbers in scripts

business_kid · 02-23-2021, 11:26 AM

Code:

bash-5.1$ min=0; max=15; number =$(expr $min + $RANDOM % $max); echo $number
number: illegal number: =6

I'm no expert in scripts, they're definitely ugly and obtuse to my mind, but why is every number illegal? I simply want a pseudo random generator between two known figures.

astrogeek · 02-23-2021, 11:32 AM

Quote:

Originally Posted by business_kid

Code:

bash-5.1$ min=0; max=15; number =$(expr $min + $RANDOM % $max); echo $number
number: illegal number: =6

I'm no expert in scripts, they're definitely ugly and obtuse to my mind, but why is every number illegal? I simply want a pseudo random generator between two known figures.

Because of the space here:

Code:

...number =$(expr...

No space is allowed between the var name and the equal sign.

It is not the number that is illegal, it is the assignment syntax.

michaelk · 02-23-2021, 11:34 AM

Code:

 min=0; max=15; number =$(expr $min + $RANDOM % $max); echo $number

You have a space between number and =

To slow...

business_kid · 02-24-2021, 04:25 AM

Thanks. This worked

Code:

number=$(expr $min + $RANDOM % $max)

shruggy · 02-24-2021, 05:36 AM

Pretty much every POSIX-compatible shell has arithmetic expansion nowadays. No need for expr here.

Code:

number=$((min + RANDOM % max))

business_kid · 02-24-2021, 06:54 AM

Yeah, that works too. Thanks shruggy.

FYI, the random function in bash is poor. I set this at 0-15, and ran it for a few minutes. I didn't count, but about 5 numbers repeated, 5 came occasionally, and 5 never showed. It's interesting nevertheless

shruggy · 02-24-2021, 08:08 AM

Perhaps /dev/urandom would give better results?

Code:

echo $((0+$(hexdump -n1 -e'"%u"' /dev/urandom)%15))

business_kid · 02-24-2021, 12:08 PM

Thx shruggy. It is better, but still not great. I thought havegd provided a good random seed. But I am writing something and will simply find another illustration. I'll have to wipe a paragraph. The problem of logically producing complete randomness has no perfect answers - yet.

shruggy · 02-24-2021, 02:28 PM

Another possibility is shuf

Code:

number=$(shuf -i0-15 -n1)

An obligatory xkcd reference: https://xkcd.com/221