Question

Well I learning Shell Script this one thing is annoying me
I cant find what actually ${ } suppose to do

I google around to found out that ${ } is used for substitution

but what I not able to understand is here

If ${ } is suppose to do a substitution then

distro=("redhat" "debian" "gentoo")

echo ${distro[0]}
echo ${distro[2]}

echo ${#distro[@]} 

How come it running the above code when there isnt any substitution .

I’m wrong on this

Answer 1

man bash, search for ${ with /\${, press n a couple of time and voila..

Any element of an array may be referenced using ${name[subscript]}.

and

${#name[subscript]} expands to the length of ${name[subscript]}. If
subscript is * or @, the expansion is the number of elements in the
array.

Checking the previous paragraphs you will also find this:

Arrays are assigned to using compound assignments of the form name=(value1
… valuen), where each value is of the form [subscript]=string. Indexed
array assignments do not require the bracket and subscript.