Changes a user's Git name and email address in a repo's commit history.

update_git_author.sh

#!/bin/sh

git filter-branch -f --commit-filter '
  if [ "$GIT_COMMITTER_NAME" = "<old name>" ];
  then
    GIT_COMMITTER_NAME="<new name>";
    GIT_AUTHOR_NAME="<new name>";
    GIT_COMMITTER_EMAIL="<new email>";
    GIT_AUTHOR_EMAIL="<new email>";
    git commit-tree "$@";
  else
    git commit-tree "$@";
  fi' HEAD