Bash - non-numeral arguments to [] operator(array)

Question

I have a small script below; however, I don't quite understand the for loop and if statement. First, let's take a look at script:

listFieldNumbers ()
 { for ii in ${!field_number[@]}; 
do 
if [ $ii -lt $(( ${#field_number[*]}-1 )) ];
 then echo -n "$(( ${field_number[$ii]} + 1 )),"; 
else echo "$(( ${field_number[$ii]} + 1))"; 
fi; 
done; }

I don't understand what do following statements mean:

1. field_number[@]
2. {#field_number[*]}

Answer 1

field_number is an array
${!field_number[@]} gives you the list of indices of the array
${#field_number[*]} is the number of elements in the array.

I'd recommend you look for a bash tutorial about arrays. They are a bit tricky to work with.

Answer 2

1. reference all the element in the field_number array
2. it's ${#field_number[*]}, the number of field_number elements

Just read this tutorial: http://www.thegeekstuff.com/2010/06/bash-array-tutorial/