Shell - syntax error in expression (error token is "0 ")

Question

What is wrong with this code?

if  (( `date +%U` % 2 -eq 0 ))
then
   VOLUME= "A"
else
    VOLUME="B"
fi

I´m getting "syntax error in expression (error token is "0 ")" eror.

Answer 1

You need to use command substitution using $(...) syntax.

You can use this command:

(( $(date +%U) % 2 == 0 )) && VOLUME="A" || VOLUME="B"

Answer 2

Your problem is the use of -eq operator in the context of an arithmetic test (the double parenthesis).

You need Command Substitution $(…):

if (( $(date +%U) % 2 == 0 )); then VOLUME= "A" else VOLUME="B"; fi

N.B.: Why is $(…) preferred over `…` (backticks)?