EDIT: I don't know in advance at which "column" my digits are going to be and I'd like to have a one-liner. Apparently sed doesn't do arithmetic, so maybe a one-liner solution based on awk?

I've got a string: (notice the spacing)

eh oh    37

and I want it to become:

eh oh    36

(so I want to keep the spacing)

Using awk I don't find how to do it, so far I have:

echo "eh oh   37" | awk '$3>=0&&$3<=99 {$3--} {print}'

But this gives:

eh oh 36

(the spacing characters where lost, because the field separator is ' ')

Is there a way to ask awk something like "print the output using the exact same field separators as the input had"?

Then I tried yet something else, using awk's sub(..,..) method:

' sub(/[0-9][0-9]/, ...) {print}'

but no cigar yet: I don't know how to reference the regexp and do arithmetic on it in the second argument (which I left with '...' for now).

Then I tried with sed, but got stuck after this:

echo "eh oh   37" | sed -e 's/\([0-9][0-9]\)/.../' 

Can I do arithmetic from sed using a reference to the matching digits and have the output not modify the number of spacing characters?

Note that it's related to my question concerning Emacs and how to apply this to some (big) Emacs region (using a replace region with Emacs's shell-command-on-region) but it's not an identical question: this one is specifically about how to "keep spaces" when working with awk/sed/etc.