How to zero pad a sequence of integers in bash so that all have the same width?

I need to loop some values,

for i in $(seq $first $last)
do
    does something here
done

For $first and $last, i need it to be of fixed length 5. So if the input is 1, i need to add zeros in front such that it becomes 00001. It loops till 99999 for example, but the length has to be 5.

E.g.: 00002, 00042, 00212, 012312 and so forth.

Any idea on how i can do that?

Solution 1:

In your specific case though it's probably easiest to use the -f flag to seq to get it to format the numbers as it outputs the list. For example:

for i in $(seq -f "%05g" 10 15)
do
  echo $i
done

will produce the following output:

00010
00011
00012
00013
00014
00015

More generally, bash has printf as a built-in so you can pad output with zeroes as follows:

$ i=99
$ printf "%05d\n" $i
00099

You can use the -v flag to store the output in another variable:

$ i=99
$ printf -v j "%05d" $i
$ echo $j
00099

Notice that printf supports a slightly different format to seq so you need to use %05d instead of %05g.

Solution 2:

Easier still you can just do

for i in {00001..99999}; do
  echo $i
done

Solution 3:

If the end of sequence has maximal length of padding (for example, if you want 5 digits and command is "seq 1 10000"), than you can use "-w" flag for seq - it adds padding itself.

seq -w 1 10

produce

01
02
03
04
05
06
07
08
09
10