#!/bin/bash
(( $# != 4 )) && { echo "$0 <repo> <oldmail> <newauthor> <newmail>" >&1 ; exit 1 ; }

_repo="$1"
_oldmail="$2"
_newauthor="$3"
_newmail="$4"

cd "$_repo" || exit $?

git filter-branch --force --commit-filter '
    if [ "$GIT_AUTHOR_EMAIL" = "'"$_oldmail"'" ];
    then
        export GIT_AUTHOR_NAME="'"$_newauthor"'";
        export GIT_AUTHOR_EMAIL="'"$_newmail"'";
        git commit-tree -S "$@"
    elif [ "$GIT_COMMITTER_EMAIL" = "'"$_oldmail"'" ];
    then
        export GIT_COMMITTER_NAME="'"$_newauthor"'";
        export GIT_COMMITTER_EMAIL="'"$_newmail"'";
        git commit-tree -S "$@"
    fi' \
    --tag-name-filter cat \
    -- --branches --tags