git-unite.sh

#!/usr/bin/env bash

# Usage:
#
# git-unite "User Name" "new@email.com" \
#           "old1@email.com" \
#           "old2@email.com" \
#           ...

name="$1"
email="$2"

git config user.name "$name"
git config user.email "$email"

shift 2

for old_email in $*; do
echo "changing $old_email"
git filter-branch --force --env-filter '
if [ "$GIT_COMMITTER_EMAIL" = "$(echo $old_email)" ]
then
  export GIT_COMMITTER_NAME="$(echo $name)"
  export GIT_COMMITTER_EMAIL="$(echo $email)"
fi
if [ "$GIT_AUTHOR_EMAIL" = "$(echo $old_email)" ]
then
  export GIT_AUTHOR_NAME="$(echo $name)"
  export GIT_AUTHOR_EMAIL="$(echo $email)"
fi
' --tag-name-filter cat -- --branches --tags
done