I'm probably about where the OP was when this started, looking for something simple that would let me use git difftool with vimdiff to review changes to files in my repo starting from a specific commit. I wasn't too happy with answers I was finding, so I threw this git incremental reporter (gitincrep) script together and it's been useful to me:
#!/usr/bin/env bash
STARTWITH="${1:-}"
shift 1
DFILES=( "$@" )
RunDiff()
{
GIT1=$1
GIT2=$2
shift 2
if [ "$(git diff $GIT1 $GIT2 "$@")" ]
then
git log ${GIT1}..${GIT2}
git difftool --tool=vimdiff $GIT1 $GIT2 "$@"
fi
}
OLDVERS=""
RUNDIFF=""
for NEWVERS in $(git log --format=format:%h --reverse)
do
if [ "$RUNDIFF" ]
then
RunDiff $OLDVERS $NEWVERS "${DFILES[@]}"
elif [ "$OLDVERS" ]
then
if [ "$NEWVERS" = "${STARTWITH:=${NEWVERS}}" ]
then
RUNDIFF=true
RunDiff $OLDVERS $NEWVERS "${DFILES[@]}"
fi
fi
OLDVERS=$NEWVERS
done
Called with no args, this will start from the beginning of the repo history, otherwise it will start with whatever abbreviated commit hash you provide and proceed to the present - you can ctrl-C at any time to exit. Any args after the first will limit the difference reports to include only the files listed among those args (which I think is what the OP wanted, and I'd recommend for all but tiny projects). If you're checking changes to specific files and want to start from the beginning, you'll need to provide an empty string for arg1. If you're not a vim user, you can replace vimdiff with your favorite diff tool.
Behavior is to output the commit comments when relevant changes are found and start offering vimdiff runs for each changed file (that's git difftool behavior, but it works here).
This approach is probably pretty naive, but looking through a lot of the solutions here and at a related post, many involved installing new tools on a system where I don't have admin access, with interfaces that had their own learning curve. The above script did what I wanted without dealing with any of that. I'll look into the many excellent suggestions here when I need something more sophisticated - but I think this is directly responsive to the OP.