why double brackets for array loop?

Shell Programming and Scripting
1

Dear All,

Recently got some sample from internet search for array handle in shell script, and I can not understand why we need to put double brackets when extracting array values by this way :

for ((i=0; i<${#admins[@]}; i++)); do
echo "${admins[$i]}"
done

if modify from double to single bracket in for loop, I got this error:

syntax error near unexpected token `('
`for (i=0; i<${#admins[@]}; i++); do'

can someone advise why ?? Thanks in advance.
Rgds,
kevin

2

maybe some special character it cannot understand ( without ((. You must pad it

sometime back I had similar problem using square brackets, a forumer here advised to use [[ instead of [ and it solved the problem

3

Hi.

Because

for (( ...

is the syntax for that statement.

The meaning of single and double parentheses is different. See man ksh or man bash ... cheers, drl