append_path_once() {
    [ -d "$1" ] || return 1
    case ":$PATH:" in
        *":$1:"*) :;;  # Do nothing
        *) PATH="$PATH:$1";;
    esac
}

prepend_path_once() {
    [ -d "$1" ] || return 1
    case ":$PATH:" in
        *":$1:"*) :;;  # Do nothing
        *) PATH="$1:$PATH";;
    esac
}

prepend_path_once "$HOME/bin"
append_path_once "$HOME/local/bin"

export PATH