Our example array:

arr=(a b c d e f)

Using a for..in loop:

for i in "${arr[@]}"; do
    echo "$i"
done

Using C-style for loop:

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

Using while loop:

i=0
while [ $i -lt ${#arr[@]} ]; do
    echo "${arr[$i]}"
    i=$((i + 1))
done

Using while loop with numerical conditional:

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

Using an until loop:

i=0
until [ $i -ge ${#arr[@]} ]; do
    echo "${arr[$i]}"
    i=$((i + 1))
done

Using an until loop with numerical conditional:

i=0
until (( $i >= ${#arr[@]} )); do
    echo "${arr[$i]}"
    ((i++))
done