I've got this script in sh (macOS 10.6) to look through an array of files:

files="*.jpg"
for f in $files
    do
        echo $f | grep -oEi '[0-9]+_([a-z]+)_[0-9a-z]*'
        name=$?
        echo $name
    done

So far $name merely holds 0, 1 or 2, depending on if grep found that the filename matched the matter provided. What I'd like is to capture what's inside the parens ([a-z]+) and store that to a variable.

I'd like to use grep only, if possible. If not, please no Python or Perl, etc. sed or something like it – I would like to attack this from the *nix purist angle.