/etc/portage/bashrc

post_src_unpack() {
    cd "${S}"
    if type epatch_user > /dev/null 2>&1 \
            && type epatch > /dev/null 2>&1; then
        epatch_user
    else
        . ${ROOT}etc/portage/env/epatch.sh
        epatch_user
        # To avoid issues when writing an ebuild
        unset epatch
        unset epatch_user
    fi
}