Create fixup for topmost non-fixup commit - this will allow to stack fixups

git-fixup.sh

# Git log:
#
# am3xn47 'fixup! Add file B'
# 302mx47 'Add file B'
# xn4273x 'Add file A'

NON_FIXUP_HEAD_COMMIT="$(
  git log --oneline 
  | grep --invert-match 'fixup' 
  | head -1 
  | awk '{print $1}' 
)"

echo "${NON_FIXUP_HEAD_COMMIT}"  # Outputs: 302mx47

git commit --fixup "${NON_FIXUP_HEAD_COMMIT}"

# Git log:
#
# pcm48c3 'fixup! Add file B'
# am3xn47 'fixup! Add file B'
# 302mx47 'Add file B'
# xn4273x 'Add file A'

git rebase --interactive --autosquash "${NON_FIXUP_HEAD_COMMIT}~1"

# Git log:
#
# e90e323 'Add file B'
# xn4273x 'Add file A'