UNIX 支持各种目录导航工具。

UNIX supports a wide variety of directory-navigation tools.

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使用pushd和popd管理目录导航。

Manage directory navigation with pushd and popd.

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现在，我们有了一些不显眼的基础元素，我们可以向前迈进，并添加各种面向客户的特性：目录导航、购物车、以及结算过程等等。

Now that we have the fundamental elements out of the way, we can forge ahead and add all of the customer-facing features: navigation by category, a shopping cart, and a checkout process.

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