for

for a in ${arr[@]}  # must use ${arr[@]} don't use ${arr}
do
    echo $a
done

defind,空格分隔每个元素,小括号

arr=(1 2 3 'a' b 'c')

substring,index from 0

${arr[*]:1:3}
${arr[@]:1:3}
    2 3 a

get all

${arr[*]}
${arr[@]}
    1 2 3 a b c

get by index

${arr[1]}
    2

${arr[5]}
    c

length

${#arr[@]}
    6