Adjust timestamps of git author date and committer data.

adjust.sh

#!/bin/sh
export FILTER_BRANCH_SQUELCH_WARNING=1

timediff=$(( $(date -d "2019/11/30 18:28:46" +%s) - $(date -d "Wed Nov 27 08:16:58 2019" +%s) ))
for commit_hash in $(git log --pretty=oneline --author=$1 | cut -d" " -f1); do
  git log -n1 $commit_hash --pretty=fuller

  author_fixed=$(date -d @"$(( $(date -d "$(git log $commit_hash -n1 --pretty=fuller | grep AuthorDate | cut -d: -f2- | rev | cut -d" " -f2- | rev)" +%s) + $timediff ))" +%s)
  commit_fixed=$(date -d @"$(( $(date -d "$(git log $commit_hash -n1 --pretty=fuller | grep CommitDate | cut -d: -f2- | rev | cut -d" " -f2- | rev)" +%s) + $timediff ))" +%s)
  echo "author: " $(date -d @"$author_fixed")
  echo "commit: " $(date -d @"$commit_fixed")

  git filter-branch -f --env-filter "
    if [ \$GIT_COMMIT = $commit_hash ]
      then
        export GIT_AUTHOR_DATE=\"$author_fixed\"
        export GIT_COMMITTER_DATE=\"$commit_fixed\"
      fi
  "
done