github modify username and email in old commits

#!/bin/bash

git filter-branch --env-filter '

an="$GIT_AUTHOR_NAME"
am="$GIT_AUTHOR_EMAIL"
cn="$GIT_COMMITTER_NAME"
cm="$GIT_COMMITTER_EMAIL"

if [ "$GIT_COMMITTER_EMAIL" = "old email" ]
then
    cn="new name"
    cm="new eamil"
fi
if [ "$GIT_AUTHOR_EMAIL" = "old email" ]
then
    an="new name"
    am="new email"
fi

export GIT_AUTHOR_NAME="$an"
export GIT_AUTHOR_EMAIL="$am"
export GIT_COMMITTER_NAME="$cn"
export GIT_COMMITTER_EMAIL="$cm"
'