old-files.sh

#!/bin/bash
# name: old-files.sh
# author: Carlos Alexandro Becker (caarlos0@gmail.com)
#
# List the files not changed in a git repo in the last X time.
#
# Usage:
#  ./old-files.sh 1 year
#
set -eo pipefail
dir="$(mktemp -d)"

git log \
  --pretty="format:" \
  --since="$* ago" \
  --name-only | sort | uniq > "$dir/recently_changed"
git log \
  --pretty="format:" \
  --name-only | sort | uniq > "$dir/all"

for file in $(diff "$dir/recently_changed" "$dir/all" | cut -f2 -d' '); do
  [ -f "$file" ] && echo $file
done | sort | uniq