How to add leading zeros for for-loop in shell?

Question

I have a basic number for loop which increments the variable num by 1 over each iteration...

for (( num=1; num<=5; num++ ))
do
 echo $num
done

Which outputs:

1
2
3
4
5

I'm trying to make it produce the output (add leading zero before $num):

01
02
03
04
05

Without doing:

echo 0$num

Answer 1

Use the following syntax:

$ for i in {01..05}; do echo "$i"; done
01
02
03
04
05

Disclaimer: Leading zeros only work in >=bash-4.

If you want to use printf, nothing prevents you from putting its result in a variable for further use:

$ foo=$(printf "%02d" 5)
$ echo "${foo}"
05