Git advanced notes

Dates

Show commit logs with author and commit date

git log --pretty=fuller

Keep original commit dates when rebasing

Use

git rebase --committer-date-is-author-date

Check that the commit date matches the author date:
```
git log --pretty=fuller
```

Tags

Lightweight vs. annotated tags

Lightweight tags simply point to a commit. They don’t have their own hash, date, or message.

Annotated tags point to a commit, but they have their own hash, date, and message.

GitHub typically creates lightweight tags.

Convert annotated tags to lightweight tags

Can an annotated tag be replaced with a lightweight tag?

Update tags after a rebase

ⓘ If you find that many of the tag timestamps are the same after running this command, see Keep original commit dates when rebasing

This script will attempt to update the references for tags after a rebase has changed the hashes of the commits the tags are referencing:

for tag in $(git for-each-ref --format="%(refname:short)" "refs/tags/*"); do
  objecttype=$(git for-each-ref --format="%(objecttype)" "refs/tags/${tag}")
  if [ "$objecttype" == "tag" ]; then
    originalcommithash=$(git for-each-ref --format="%(*objectname)" "refs/tags/${tag}")
    tagdate=$(git for-each-ref --format="%(creatordate)" "refs/tags/${tag}")
    tagmessage=$(git for-each-ref --format="%(subject)" "refs/tags/${tag}")

  elif [ "$objecttype" == "commit" ]; then
    originalcommithash=$(git for-each-ref --format="%(objectname)" "refs/tags/${tag}")
  fi

  originalcommitmessage="$(git log --format=%B -n 1 ${originalcommithash})"
  matchedcommithashes=()

  for commithash in $(git log --format=%H); do
    commitmessage="$(git log --format=%B -n 1 ${commithash})"
    if [ "$commitmessage" == "$originalcommitmessage" ]; then
      matchedcommithashes+=("$commithash")
    fi
  done

  if [ ${#matchedcommithashes[@]} -ne 1 ]; then
    echo "WARNING: No exact commit match for tag ${tag}: ${matchedcommithashes[@]}"
    echo "    NOT updating tag"
  else
    # Update annotated tags
    if [ "$objecttype" == "tag" ]; then
      #echo "GIT_COMMITTER_DATE=\"$tagdate\" git tag -f -a \"$tag\" \"${matchedcommithashes[0]}\" -m \"$tagmessage\""
      GIT_COMMITTER_DATE="$tagdate" git tag -f -a "$tag" "${matchedcommithashes[0]}" -m "$tagmessage"
    # Update lightweight tags
    elif [ "$objecttype" == "commit" ]; then
      #echo "git tag -f ${tag} ${matchedcommithashes[0]}"
      git tag -f ${tag} ${matchedcommithashes[0]}
    fi
  fi
done

If you wish, you can use this to see the tags and the commit hashes they point to with this command:

git for-each-ref --sort -v:refname --format '%(objectname) %(objecttype) %(refname)
%(*objectname) %(*objecttype) %(*refname)' refs/tags

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