Question

From what I’ve read at tldp.org, the double parenthesis construct (( ... )) allows you to reference bash variables without the $ prefix. However, when attempting to reference the argument count variable $#, the script refuses to work with a

bash: ((: i < # : syntax error: operand expected (error token is "# ")

oddly enough, when the hash is prefixed, the script works fine.

For your reference, here’s the working code:

fun(){
    i=0
    while (( i < $# )); do
            echo $1;
            shift
    done
}

My question is: How do I know when it is correct to include the prefix and when it is not?

Answer 1

You can forgo the $ as long as it’s not a SPECIAL PARAMETER. Also, if you are doing PARAMETER EXPANSION inside (( )) you also need the $