This is a script performing git status -> git diff -> git add.

gitdiffadd

#!/bin/bash

for f in $(git status | gawk 'BEGIN{staged=0}{if(staged){if(/modified:/){print gensub(/.*modified:[ \\t]*(.*)/,"\\1","g",$0)}}if(/^Changes not staged for commit:$/){staged=1}}')
do
  clear
  git status

  echo "Target file: ${f}"

  # git diff
  while
    echo "See diff? (y/n/q)"
    read ans
  do
    case ${ans} in
      y)
        git diff ${f}
        break;;
      n)
        break;;
      q)
        exit 0;;
      *)
    esac
  done

  # git add
  while
    echo "Stage ${f}? (y/n/q)"
    read ans
  do
    case ${ans} in
      y)
        git add ${f}
        break;;
      n)
        break;;
      q)
        exit 0;;
      *)
    esac
  done
done

exit 0