gdf

#! /bin/sh

# --- diff relative to HEAD

#     gdf       - list files changed between prior commit and HEAD (HEAD~1 HEAD~0)
#     gdf n     - list files changed between HEAD~n and HEAD (HEAD~n HEAD~0)
#     gdf n m   - list files changed between HEAD~n and HEAD~m
#     gdf n m o - diff 'o'th file between HEAD~n and HEAD~m

D1=${1-1}
D2=${2-0}
if [ -z "$3" ]; then
  echo "Files changed from HEAD~${D1} to HEAD~${D2}:"
  git diff HEAD~${D1} HEAD~${D2} --name-status | awk '{print NR ". " $0}'
else
  FN=$(git diff HEAD~${D1} HEAD~${D2} --name-status | awk -v line=$3 'NR==line{print;exit}')
  if [ -z "$FN" ]; then
    echo "File '$3' is not one of the choices."
  else
    TYPE=$(echo $FN | awk '{print $1}')
    NAME=$(echo $FN | awk '{print $2}')
    if [ "A" = "$TYPE" ]; then
      echo "New file; no diff available: $NAME"
    else
      git diff HEAD~${D1}:${NAME} HEAD~${D2}:${NAME}
    fi
  fi
fi