Bash 中的逻辑和（&） | Linux 中国

有人可能会认为两篇文章中的 & 意思差不多，但实际上并不是。虽然 第一篇文章讨论了如何在命令末尾使用 & 来将命令转到后台运行[1]，在之后剖析了流程管理，第二篇文章将 & 看作引用文件描述符的方法[2]，这些文章让我们知道了，与 < 和 > 结合使用后，你可以将输入或输出引导到别的地方。

但我们还没接触过作为 AND 操作符使用的 &。所以，让我们来看看。

& 是一个按位运算符

如果你十分熟悉二进制数操作，你肯定听说过 AND 和 OR 。这些是按位操作，对二进制数的各个位进行操作。在 Bash 中，使用 & 作为 AND 运算符，使用 | 作为 OR 运算符：

AND：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span></code></section></li>
</ol>

OR：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">|</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">|</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">|</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">|</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span></code></section></li>
</ol>

你可以通过对任何两个数字进行 AND 运算并使用 echo 输出结果：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">2</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">3</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">00000010</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> AND </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">00000011</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">00000010</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">2</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">120</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">97</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">01111000</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> AND </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">01100001</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">01100000</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">96</span></code></section></li>
</ol>

OR（|）也是如此：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">2</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">|</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">3</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">00000010</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> OR </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">00000011</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">00000011</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">3</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">120</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">|</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">97</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">01111000</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> OR </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">01100001</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">01111001</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">121</span></code></section></li>
</ol>

说明：

提示： 如果你想看看十进制数字在二进制下会是什么样子，你可以使用 bc ，这是一个大多数 Linux 发行版都预装了的命令行计算器。比如：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;"><li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">bc </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"><<<</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="str" style="overflow-wrap: break-word;color: rgb(101, 176, 66);">"obase=2; 97"</span></code></section></li></ol>

这个操作将会把 97 转换成十二进制（obase 中的 o 代表 “output” ，也即，“输出”）。

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;"><li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">bc </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"><<<</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="str" style="overflow-wrap: break-word;color: rgb(101, 176, 66);">"ibase=2; 11001011"</span></code></section></li></ol>

这个操作将会把 11001011 转换成十进制（ibase 中的 i 代表 “input”，也即，“输入”）。

&& 是一个逻辑运算符

虽然它使用与其按位表达相同的逻辑原理，但 Bash 的 && 运算符只能呈现两个结果：1（“真值”）和0（“假值”）。对于 Bash 来说，任何不是 0 的数字都是 “真值”，任何等于 0 的数字都是 “假值”。什么也是 “假值”同时也不是数字呢：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">4</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">5</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">两个非零数字，两个为</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">true</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">true</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">1</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">5</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">有一个为零，一个为</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">false</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">false</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">((</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> b </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">5</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">))</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="com" style="overflow-wrap: break-word;color: rgb(174, 174, 174);font-style: italic;">#</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">其中一个不是数字，一个为</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">false</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">=</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">false</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">0</span></code></section></li>
</ol>

与 && 类似， OR 对应着 || ，用法正如你想的那样。

以上这些都很简单……直到它用在命令的退出状态时。

&& 是命令退出状态的逻辑运算符

正如我们在之前的文章中看到的[2]，当命令运行时，它会输出错误消息。更重要的是，对于今天的讨论，它在结束时也会输出一个数字。此数字称为“返回码”，如果为 0，则表示该命令在执行期间未遇到任何问题。如果是任何其他数字，即使命令完成，也意味着某些地方出错了。

所以 0 意味着是好的，任何其他数字都说明有问题发生，并且，在返回码的上下文中，0 意味着“真”，其他任何数字都意味着“假”。对！这 与你所熟知的逻辑操作完全相反 ，但是你能用这个做什么？ 不同的背景，不同的规则。这种用处很快就会显现出来。

让我们继续！

返回码 临时 储存在 特殊变量[5] ? 中 —— 是的，我知道：这又是一个令人迷惑的选择。但不管怎样，别忘了我们在讨论变量的文章中说过[4]，那时我们说你要用 $ 符号来读取变量中的值，在这里也一样。所以，如果你想知道一个命令是否顺利运行，你需要在命令结束后，在运行别的命令之前马上用 $? 来读取 ? 变量的值。

试试下面的命令：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">find</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">etc </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">-</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">iname </span><span class="str" style="overflow-wrap: break-word;color: rgb(101, 176, 66);">"*.service"</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">find</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">:</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="str" style="overflow-wrap: break-word;color: rgb(101, 176, 66);">'/etc/audisp/plugins.d'</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">:</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="typ" style="overflow-wrap: break-word;color: rgb(137, 189, 255);">Permission</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> denied</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">etc</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">systemd</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">system</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">dbus</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">-</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">org</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">freedesktop</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">nm</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">-</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">dispatcher</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">service</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">etc</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">systemd</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">system</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">dbus</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">-</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">org</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">freedesktop</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="typ" style="overflow-wrap: break-word;color: rgb(137, 189, 255);">ModemManager1</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">service</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">[......]</span></code></section></li>
</ol>

正如你在上一篇文章中看到的一样[2]，普通用户权限在 /etc 下运行 find 通常将抛出错误，因为它试图读取你没有权限访问的子目录。

所以，如果你在执行 find 后立马执行……

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;"><li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">echo</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> $</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">?</span></code></section></li></ol>

……，它将打印 1，表明存在错误。

（注意：当你在一行中运行两遍 echo $? ，你将得到一个 0 。这是因为 $? 将包含第一个 echo $? 的返回码，而这条命令按理说一定会执行成功。所以学习如何使用 $? 的第一课就是： 单独执行 $? 或者将它保存在别的安全的地方 —— 比如保存在一个变量里，不然你会很快丢失它。）

一个直接使用 ? 变量的用法是将它并入一串链式命令列表，这样 Bash 运行这串命令时若有任何操作失败，后面命令将终止。例如，你可能熟悉构建和编译应用程序源代码的过程。你可以像这样手动一个接一个地运行它们：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;">
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ configure</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">make</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">make</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> install</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
<li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span></code></section></li>
</ol>

你也可以把这三行合并成一行……

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;"><li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ configure</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">;</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">make</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">;</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">make</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> install</span></code></section></li></ol>

…… 但你要希望上天保佑。

为什么这样说呢？因为你这样做是有缺点的，比方说 configure 执行失败了， Bash 将仍会尝试执行 make 和 sudo make install——就算没东西可 make ，实际上，是没东西会安装。

聪明一点的做法是：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;"><li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">$ configure </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">make</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">make</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> install</span></code></section></li></ol>

这将从每个命令中获取退出码，并将其用作链式 && 操作的操作数。

但是，没什么好抱怨的，Bash 知道如果 configure 返回非零结果，整个过程都会失败。如果发生这种情况，不必运行 make 来检查它的退出代码，因为无论如何都会失败的。因此，它放弃运行 make，只是将非零结果传递给下一步操作。并且，由于 configure && make 传递了错误，Bash 也不必运行make install。这意味着，在一长串命令中，你可以使用 && 连接它们，并且一旦失败，你可以节省时间，因为其他命令会立即被取消运行。

你可以类似地使用 ||，OR 逻辑操作符，这样就算只有一部分命令成功执行，Bash 也能运行接下来链接在一起的命令。

鉴于所有这些（以及我们之前介绍过的内容），你现在应该更清楚地了解我们在 这篇文章开头[1]出现的命令行：

<ol class="linenums list-paddingleft-2" style="margin-left: 2em;margin-right: 2em;"><li><section style="overflow-wrap: break-word;width: 1200px;max-width: 1200px !important;"><code style="overflow-wrap: break-word;background: none;color: rgb(33, 150, 243);line-height: 1.2em;padding-left: 10px !important;border-radius: 0px !important;margin-top: 1em !important;margin-bottom: 1em !important;border-width: initial !important;border-style: none !important;border-color: initial !important;"><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">mkdir</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> test_dir </span><span class="lit" style="overflow-wrap: break-word;color: rgb(51, 135, 204);">2</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">></span><span class="str" style="overflow-wrap: break-word;color: rgb(101, 176, 66);">/dev/</span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">null</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">||</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">touch</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> backup</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">dir</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">images</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">txt </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&&</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">find</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">-</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">iname </span><span class="str" style="overflow-wrap: break-word;color: rgb(101, 176, 66);">"*jpg"</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">></span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);"> backup</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="kwd" style="overflow-wrap: break-word;color: rgb(226, 137, 100);">dir</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">/</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">images</span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">.</span><span class="pln" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">txt </span><span class="pun" style="overflow-wrap: break-word;color: rgb(184, 255, 184);">&</span></code></section></li></ol>

因此，假设你从具有读写权限的目录运行上述内容，它做了什么以及如何做到这一点？它如何避免不合时宜且可能导致执行中断的错误？下周，除了给你这些答案的结果，我们将讨论圆括号，不要错过了哟！

via: https://www.linux.com/blog/learn/2019/2/logical-ampersand-bash

作者：Paul Brown[7] 选题：lujun9972 译者：zero-MK 校对：wxy

本文由 LCTT 原创编译，Linux中国 荣誉推出