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FD）是一个非负整数，用于标识打开的文件、输入/输出设备或其他资源。标准输入、标准输出和标准错误是最常用的文件描述符，其对应的值为 0、1 和 2，具体含义和使用说明如下："/><meta property="og:image" content="https://cloudcache.tencentcs.com/open_proj/proj_qcloud_v2/gateway/shareicons/cloud.png"/><meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1, viewport-fit=cover"/><link rel="dns-prefetch" href="//qccommunity.qcloudimg.com"/><link rel="dns-prefetch" href="//ask.qcloudimg.com"/><link rel="dns-prefetch" href="//cloudcache.tencentcs.com"/><link rel="canonical" href="https://cloud.tencent.com/developer/article/2465765"/><meta name="next-head-count" content="20"/><link rel="stylesheet" href="https://imgcache.qq.com/open_proj/proj_qcloud_v2/gateway/portal/css/base.css"/><link rel="stylesheet" href="https://cloudcache.tencentcs.cn/qcloud/ui/cloud-community/build/base/base-202411191502.css"/><style type="text/css"> .rno-markdown p * { white-space: pre-wrap; word-break: break-all; } .tea-overlay { z-index: 99999!important; } </style><link 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class="cdc-m-header-article__title-logo"></div></div><div class="cdc-m-header-article__extra"><div class="cdc-m-header-article__extra-icon"><i class="extra-search"></i></div><div class="cdc-m-header-article__extra-operate"><div class="cdc-m-header-article__extra-icon"><i class="extra-man"></i></div></div></div></div></div></div><div class="cdc-global__main"><div class="cdc-article__body"><div class="cdc-layout"><div class="cdc-layout__main"><div class="cdc-crumb mod-crumb"><div class="cdc-crumb__inner"><a class="cdc-crumb__item" href="/developer">社区首页</a><span class="cdc-crumb__split"> ></span><a class="cdc-crumb__item" href="/developer/column">专栏</a><span class="cdc-crumb__split"> ></span><span class="cdc-crumb__item current">文件描述符fd和0 & 1 & 2的含义（stdin..）</span></div></div><div class="mod-article-content"><div class="mod-header2"><div class="mod-header2__top"><div class="mod-header2__title"><h1 class="title-text">文件描述符fd和0 & 1 & 2的含义（stdin..）</h1></div></div><div class="mod-article-source header"><div class="mod-article-source__main"><div class="mod-article-source__avatar"><img src="https://developer.qcloudimg.com/avatar/26311.png" alt="作者头像"/></div><div class="mod-article-source__detail"><div class="mod-article-source__name"><span>ljw695</span></div></div><button class="cdc-btn mod-article-source__operate cdc-btn--primary"><span><i></i>关注</span></button></div></div><div class="mod-header2__bottom"><div class="mod-header2__detail"><div class="mod-header2__date"><span class="date-text">发布于 2024-11-15 08:31:52</span></div><div class="mod-header2__infos"><div class="cdc-icon__list"><span class="cdc-svg-icon-con"><span class="cdc-svg-icon" style="width:16px;height:16px"><svg width="16" height="16" viewBox="0 0 16 16" fill="currentcolor" xmlns="http://www.w3.org/2000/svg"><g id="icon-view" transform="translate(0.000000, 3.000000)" fill="currentcolor" fill-rule="nonzero"><path d="M15.885,4.68036 C14.9951,3.57569 11.7987,-0.004272 7.99883,-0.004272 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xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" clip-rule="evenodd" d="M8 13.414L5.58594 11H2V3H14V11H10.4141L8 13.414ZM5.17175 12L8 14.8282L10.8282 12H15V2H1V12H5.17175ZM4 6C3.44775 6 3 6.44769 3 7C3 7.55231 3.44775 8 4 8C4.55225 8 5 7.55231 5 7C5 6.44769 4.55225 6 4 6ZM7 7C7 6.44769 7.44775 6 8 6C8.55225 6 9 6.44769 9 7C9 7.55231 8.55225 8 8 8C7.44775 8 7 7.55231 7 7ZM12 6C11.4478 6 11 6.44769 11 7C11 7.55231 11.4478 8 12 8C12.5522 8 13 7.55231 13 7C13 6.44769 12.5522 6 12 6Z"></path></svg></span><span class="cdc-svg-icon-text">0</span></span></div></div><div class="mod-header2__date is-mobile"><span class="date-text">发布于 2024-11-15 08:31:52</span></div></div><div class="mod-header2__operates"><div class="mod-header2__operate"><span class="cdc-svg-icon-con is-operate"><span class="cdc-svg-icon" style="width:16px;height:16px"><svg width="16" height="16" viewBox="0 0 16 16" fill="currentcolor" xmlns="http://www.w3.org/2000/svg"><path fill-rule="evenodd" clip-rule="evenodd" d="M9.21101 2.54545C8.80733 1.81818 7.79814 1.81818 7.39446 2.54545L1.94481 12.3636C1.54113 13.0909 2.04573 14 2.85308 14H13.7524C14.5597 14 15.0643 13.0909 14.6607 12.3636L9.21101 2.54545ZM2.85308 12.9091L8.30273 3.09091L13.7524 12.9091H2.85308ZM8.00037 6H9.00037V10H8.00037V6ZM8.00037 11H9.00037V12H8.00037V11Z" fill="currentcolor"></path></svg></span><span class="cdc-svg-icon-text">举报</span></span></div></div></div><div class="mod-header2__special"><div class="cdc-special-guide"><span><i class="cdc-special-guide-icon"></i>文章被收录于专栏：</span><a class="cdc-special-guide-name">ljw</a></div></div></div><div class="mod-content"><div class="mod-content__markdown"><div><div class="rno-markdown new-version rno-"><p>重定向的实质</p><figure class=""><div class="rno-markdown-img-url" style="text-align:center"><div class="rno-markdown-img-url-inner" style="width:100%"><div style="width:100%"><img src="https://developer.qcloudimg.com/http-save/yehe-11276311/d59c92d55316e9990d723371aea0cb60.png" alt="" style="width:100%"/></div></div></div></figure><p>1和2的区别</p><figure class=""><div class="rno-markdown-img-url" style="text-align:center"><div class="rno-markdown-img-url-inner" style="width:100%"><div style="width:100%"><img src="https://developer.qcloudimg.com/http-save/yehe-11276311/c5ea139d7d79fa2c18d189372f4c9014.png" alt="" style="width:100%"/></div></div></div></figure><figure class=""><div class="rno-markdown-img-url" style="text-align:center"><div class="rno-markdown-img-url-inner" style="width:100%"><div style="width:100%"><img src="https://developer.qcloudimg.com/http-save/yehe-11276311/033cc2100ef7e724bfa18fa28e3f530c.png" alt="" style="width:100%"/></div></div></div></figure><p>在 Linux 系统中，文件描述符（File Descriptor, FD）是一个非负整数，用于标识打开的文件、输入/输出设备或其他资源。标准输入、标准输出和标准错误是最常用的文件描述符，其对应的值为 0、1 和 2，具体含义和使用说明如下：</p><h5 id="d8bm0" name="%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E7%9A%84%E5%90%AB%E4%B9%89">文件描述符的含义</h5><ol class="ol-level-0"><li> <strong>标准输入</strong>（stdin） <ul class="ul-level-1"><li><strong>描述符：</strong> <code>0</code></li><li><strong>用途：</strong> 接收输入数据，通常是来自键盘的用户输入。</li><li><strong>使用场景：</strong> 例如，当你在命令行中运行程序时，可以通过键盘输入数据，这些数据会被程序读取。</li></ul></li><li> <strong>标准输出</strong>（stdout） <ul class="ul-level-1"><li><strong>描述符：</strong> <code>1</code></li><li><strong>用途：</strong> 用于输出数据，通常是显示在终端上的信息。</li><li><strong>使用场景：</strong> 例如，<code>echo "Hello, World!"</code> 会将字符串输出到标准输出，即命令行界面。</li></ul></li><li> <strong>标准错误</strong>（stderr） <ul class="ul-level-1"><li><strong>描述符：</strong> <code>2</code></li><li><strong>用途：</strong> 用于输出错误信息，通常也会显示在终端上，但可以与标准输出分开重定向。</li><li><strong>使用场景：</strong> 例如，运行一个不存在的命令会产生错误信息，这些信息会输出到标准错误。</li></ul></li></ol><h5 id="1hhon" name="%E4%BD%BF%E7%94%A8%E7%A4%BA%E4%BE%8B">使用示例</h5><p>以下是一些文件描述符的常见使用示例：</p><h6 id="8ko4j" name="1.-%E5%9F%BA%E6%9C%AC%E8%BE%93%E5%87%BA">1. 基本输出</h6><div class="rno-markdown-code"><div class="rno-markdown-code-toolbar"><div class="rno-markdown-code-toolbar-info"><div class="rno-markdown-code-toolbar-item is-type"><span class="is-m-hidden">代码语言：</span>javascript</div></div><div class="rno-markdown-code-toolbar-opt"><div class="rno-markdown-code-toolbar-copy"><i class="icon-copy"></i><span class="is-m-hidden">复制</span></div></div></div><div class="developer-code-block"><pre class="prism-token token line-numbers language-javascript"><code class="language-javascript" style="margin-left:0">bash</code></pre></div></div><div class="rno-markdown-code"><div class="rno-markdown-code-toolbar"><div class="rno-markdown-code-toolbar-info"><div class="rno-markdown-code-toolbar-item is-type"><span class="is-m-hidden">代码语言：</span>javascript</div></div><div class="rno-markdown-code-toolbar-opt"><div class="rno-markdown-code-toolbar-copy"><i class="icon-copy"></i><span class="is-m-hidden">复制</span></div></div></div><div class="developer-code-block"><pre class="prism-token token line-numbers language-javascript"><code class="language-javascript" style="margin-left:0"># 将字符串输出到标准输出 echo "This is standard output"</code></pre></div></div><h6 id="3873i" name="2.-%E9%94%99%E8%AF%AF%E8%BE%93%E5%87%BA">2. 错误输出</h6><p>bash</p><div class="rno-markdown-code"><div class="rno-markdown-code-toolbar"><div class="rno-markdown-code-toolbar-info"><div class="rno-markdown-code-toolbar-item is-type"><span class="is-m-hidden">代码语言：</span>javascript</div></div><div class="rno-markdown-code-toolbar-opt"><div class="rno-markdown-code-toolbar-copy"><i class="icon-copy"></i><span class="is-m-hidden">复制</span></div></div></div><div class="developer-code-block"><pre class="prism-token token line-numbers language-javascript"><code class="language-javascript" style="margin-left:0"># 使用不正确的命令产生错误信息 some_nonexistent_command</code></pre></div></div><h6 id="7v3v2" name="3.-%E9%87%8D%E5%AE%9A%E5%90%91%E6%A0%87%E5%87%86%E8%BE%93%E5%87%BA">3. 重定向标准输出</h6><p>将标准输出重定向到文件：</p><p>bash</p><div class="rno-markdown-code"><div class="rno-markdown-code-toolbar"><div class="rno-markdown-code-toolbar-info"><div class="rno-markdown-code-toolbar-item is-type"><span class="is-m-hidden">代码语言：</span>javascript</div></div><div class="rno-markdown-code-toolbar-opt"><div class="rno-markdown-code-toolbar-copy"><i class="icon-copy"></i><span class="is-m-hidden">复制</span></div></div></div><div class="developer-code-block"><pre class="prism-token token line-numbers language-javascript"><code class="language-javascript" style="margin-left:0"># 将输出重定向到文件 output.txt echo "This will be saved to a file" > output.txt</code></pre></div></div><h6 id="1t38c" name="4.-%E9%87%8D%E5%AE%9A%E5%90%91%E6%A0%87%E5%87%86%E9%94%99%E8%AF%AF">4. 重定向标准错误</h6><p>将标准错误重定向到文件：</p><p>bash</p><div class="rno-markdown-code"><div class="rno-markdown-code-toolbar"><div class="rno-markdown-code-toolbar-info"><div class="rno-markdown-code-toolbar-item is-type"><span class="is-m-hidden">代码语言：</span>javascript</div></div><div class="rno-markdown-code-toolbar-opt"><div class="rno-markdown-code-toolbar-copy"><i class="icon-copy"></i><span class="is-m-hidden">复制</span></div></div></div><div class="developer-code-block"><pre class="prism-token token line-numbers language-javascript"><code class="language-javascript" style="margin-left:0"># 将输出重定向到文件 output.txt echo "This will be saved to a file" > output.txt</code></pre></div></div><h6 id="7cj4u" name="5.-%E5%90%8C%E6%97%B6%E9%87%8D%E5%AE%9A%E5%90%91%E6%A0%87%E5%87%86%E8%BE%93%E5%87%BA%E5%92%8C%E6%A0%87%E5%87%86%E9%94%99%E8%AF%AF">5. 同时重定向标准输出和标准错误</h6><p>将标准输出和标准错误同时重定向到同一个文件：</p><p>bash</p><div class="rno-markdown-code"><div class="rno-markdown-code-toolbar"><div class="rno-markdown-code-toolbar-info"><div class="rno-markdown-code-toolbar-item is-type"><span class="is-m-hidden">代码语言：</span>javascript</div></div><div class="rno-markdown-code-toolbar-opt"><div class="rno-markdown-code-toolbar-copy"><i class="icon-copy"></i><span class="is-m-hidden">复制</span></div></div></div><div class="developer-code-block"><pre class="prism-token token line-numbers language-javascript"><code class="language-javascript" style="margin-left:0"># 将标准输出和标准错误都重定向到 same_output_and_error.txt echo "This will go to the file" > same_output_and_error.txt 2>&1</code></pre></div></div><h5 id="f9c85" name="%E7%9B%B8%E5%85%B3%E7%B3%BB%E7%BB%9F%E8%B0%83%E7%94%A8">相关系统调用</h5><p>在编程中，你还可以使用系统调用来操作文件描述符，以下是一些常用的：</p><ul class="ul-level-0"><li><code>open()</code>: 打开文件并返回文件描述符。</li><li><code>read()</code>: 从文件描述符中读取数据。</li><li><code>write()</code>: 向文件描述符写入数据。</li><li><code>close()</code>: 关闭文件描述符。</li></ul><h5 id="efa80" name="%E5%B0%8F%E7%BB%93">小结</h5><p>文件描述符 <code>0</code>、<code>1</code> 和 <code>2</code> 用于表示标准输入、标准输出和标准错误，它们在 Linux 等类 Unix 系统中是处理输入输出的基础。通过合理地使用它们，可以方便地进行 I/O 操作和错误处理。</p><h3 id="fgcg1" name="%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E6%80%BB%E7%BB%93">文件描述符总结</h3><p>Linux中的文件描述符总结如下：</p><p>定义与用途：</p><p>文件描述符是内核为了高效管理已被打开的文件所创建的索引，是一个非负整数。它用于代指被打开的文件，所有通过I/O操作的系统调用都通过文件描述符进行。</p><p>分配规则：</p><p>当进程启动时，默认会打开三个文件描述符：标准输入（stdin，文件描述符为0）、标准输出（stdout，文件描述符为1）、标准错误（stderr，文件描述符为2）。之后打开的文件，文件描述符会从3开始依次递增，为连续的整数。</p><p>限制：</p><p>系统级限制：限制所有用户打开文件描述符的总和，可以通过sysctl命令或查看proc文件系统来查询和修改。用户级限制：限制每个用户登录后执行的程序占用的文件描述符总数，可以通过ulimit命令查询和修改。</p><p>重定向：</p><p>文件描述符支持重定向操作，包括输出重定向、输入重定向和追加重定向。重定向允许用户将标准输入、输出或错误重定向到文件或其他设备。</p><p>与文件对象的关系：</p><p>用户在访问文件时，系统会将文件相关信息从磁盘中加载到内存，并在内核中创建文件对象。文件描述符用于快速定位到这些文件对象，每个文件描述符都对应一个打开文件的文件对象。</p><p>缓冲区：</p><p>每个被打开的文件都各自拥有一个缓冲区。使用write系统调用写入数据时，数据首先被拷贝到目标文件的缓冲区中，再由操作系统决定何时将数据刷新到外设中。</p><p>一切皆文件：</p><p>在Linux下，一切皆文件，包括硬件设备、网络连接等，都可以通过文件描述符进行访问和操作。</p><p>综上所述，文件描述符是Linux内核中用于管理打开文件的一种机制，它提供了高效的文件访问方式，并支持重定向等高级功能。</p><h3 id="3r56b" name="%E4%B8%AD%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E7%9A%84%E5%85%B7%E4%BD%93%E4%BD%9C%E7%94%A8%E6%98%AF%E4%BB%80%E4%B9%88">中文件描述符的具体作用是什么</h3><p>Linux中文件描述符的具体作用主要体现在以下几个方面：</p><p>唯一标识打开的文件或资源：文件描述符是一个非负整数，由操作系统内核分配，用于唯一标识一个已经打开的文件或输入输出资源（如管道、网络连接等）。这使得进程能够准确地访问和操作特定的文件或资源。</p><p>支持多种I/O操作：文件描述符是进程与外部世界之间的桥梁。通过文件描述符，进程可以进行文件的读写操作、网络通信、进程间通信等。例如，使用read、write等系统调用进行文件内容的读取和写入，或者使用socket进行网络通信。</p><p>实现重定向：文件描述符支持重定向操作，允许用户将标准输入、标准输出或标准错误重定向到文件或其他设备。这种灵活性使得程序能够更灵活地处理输入输出数据。</p><p>管理打开的文件：每个进程都有一个文件描述符表，用于记录该进程打开的所有资源。文件描述符表对文件描述符进行管理，确保每个文件描述符都对应一个有效的打开文件或资源。同时，文件描述符的数量也是有限的，这有助于操作系统有效地管理资源。</p><p>综上所述，Linux中的文件描述符是一种高效、灵活的资源管理机制，它使得进程能够方便地访问和操作各种文件和资源。</p><h3 id="gulf" name="%E5%A6%82%E4%BD%95%E7%90%86%E8%A7%A3%E2%80%9C%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E2%80%9D">如何理解“文件描述符”</h3><p>文件描述符是：</p><p>一个非负整数，由操作系统内核分配。用于标识和访问已经打开的文件或I/O资源（如管道、网络连接）。通过文件描述符，进程可执行文件的读写操作、网络通信等。文件描述符支持重定向，允许灵活处理输入输出数据。</p></div></div></div><div class="mod-content__source"><div 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15.9989 17.928 17.0553 18.1201L20 18.6555V5.2669L17.29 5.02054C16.2699 4.9278 15.246 5.1506 14.3566 5.65879L13 6.43401V18.528Z"></path></svg></span></span><span class="cdc-suspend-pill__item-text">推荐</span></button></div></div></div></div></div><script> if (!String.prototype.replaceAll) { String.prototype.replaceAll = function (str, newStr) { // If a regex pattern if (Object.prototype.toString.call(str).toLowerCase() === '[object regexp]') { return this.replace(str, newStr); } // If a string return this.replace(new RegExp(str, 'g'), newStr); }; } </script><script src="https://developer.qcloudimg.com/static/jquery.min.js"></script><script src="https://cloud.tencent.com/qccomponent/login/api.js"></script><script src="https://cloudcache.tencent-cloud.com/qcloud/main/scripts/release/common/vendors/react/react.16.8.6.min.js"></script><script src="https://web.sdk.qcloud.com/player/tcplayer/release/v4.5.1/libs/TXLivePlayer-1.2.0.min.js" defer=""></script><script 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type="application/json">{"props":{"isMobile":false,"isSupportWebp":false,"currentDomain":"cloud.tencent.com","baseUrl":"https://cloud.tencent.com","reqId":"u7kZj6jcQpTeb1nI3ve9O","query":{"articleId":"2465765"},"platform":"other","env":"production","__N_SSP":true,"pageProps":{"fallback":{"#url:\"/api/article/detail\",params:#articleId:2465765,,":{"articleData":{"articleId":2465765,"codeLineNum":11,"readingTime":453,"wordsNum":2076},"articleInfo":{"articleId":2465765,"channel":2,"commentNum":0,"content":{"blocks":[{"key":"21s4q","text":"重定向的实质","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"5trr8","text":"\ud83d","type":"atomic","depth":0,"inlineStyleRanges":[],"entityRanges":[{"offset":0,"length":1,"key":0}],"data":{}},{"key":"149f3","text":"1和2的区别","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"16faa","text":"\ud83d","type":"atomic","depth":0,"inlineStyleRanges":[],"entityRanges":[{"offset":0,"length":1,"key":1}],"data":{}},{"key":"78l3k","text":"\ud83d","type":"atomic","depth":0,"inlineStyleRanges":[],"entityRanges":[{"offset":0,"length":1,"key":2}],"data":{}},{"key":"48gn0","text":"在 Linux 系统中，文件描述符（File Descriptor, FD）是一个非负整数，用于标识打开的文件、输入/输出设备或其他资源。标准输入、标准输出和标准错误是最常用的文件描述符，其对应的值为 0、1 和 2，具体含义和使用说明如下：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"d8bm0","text":"文件描述符的含义","type":"header-four","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E7%9A%84%E5%90%AB%E4%B9%89"}},{"key":"4so","text":" 标准输入（stdin）\n ","type":"ordered-list-item","depth":0,"inlineStyleRanges":[{"offset":1,"length":4,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"1jcnl","text":"描述符： 0","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":4,"style":"BOLD"},{"offset":5,"length":1,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"euetj","text":"用途：接收输入数据，通常是来自键盘的用户输入。","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":3,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"5q3f","text":"使用场景：例如，当你在命令行中运行程序时，可以通过键盘输入数据，这些数据会被程序读取。","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":5,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"5rgjf","text":" 标准输出（stdout）\n ","type":"ordered-list-item","depth":0,"inlineStyleRanges":[{"offset":1,"length":4,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"5n40p","text":"描述符： 1","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":4,"style":"BOLD"},{"offset":5,"length":1,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"tskc","text":"用途：用于输出数据，通常是显示在终端上的信息。","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":3,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"2531o","text":"使用场景：例如，echo \"Hello, World!\" 会将字符串输出到标准输出，即命令行界面。","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":5,"style":"BOLD"},{"offset":9,"length":20,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"1ph","text":" 标准错误（stderr）\n ","type":"ordered-list-item","depth":0,"inlineStyleRanges":[{"offset":1,"length":4,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"av5li","text":"描述符： 2","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":4,"style":"BOLD"},{"offset":5,"length":1,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"6d517","text":"用途：用于输出错误信息，通常也会显示在终端上，但可以与标准输出分开重定向。","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":3,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"32irp","text":"使用场景：例如，运行一个不存在的命令会产生错误信息，这些信息会输出到标准错误。","type":"unordered-list-item","depth":1,"inlineStyleRanges":[{"offset":0,"length":5,"style":"BOLD"}],"entityRanges":[],"data":{}},{"key":"1hhon","text":"使用示例","type":"header-four","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E4%BD%BF%E7%94%A8%E7%A4%BA%E4%BE%8B"}},{"key":"amnrn","text":"以下是一些文件描述符的常见使用示例：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"8ko4j","text":"1. 基本输出","type":"header-five","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"1.-%E5%9F%BA%E6%9C%AC%E8%BE%93%E5%87%BA"}},{"key":"3ltvv","text":"bash","type":"code-block","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"syntax":"javascript"}},{"key":"dofu","text":"# 将字符串输出到标准输出\necho \"This is standard output\"","type":"code-block","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"syntax":"javascript"}},{"key":"3873i","text":"2. 错误输出","type":"header-five","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"2.-%E9%94%99%E8%AF%AF%E8%BE%93%E5%87%BA"}},{"key":"9mrcq","text":"bash","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"87scl","text":"# 使用不正确的命令产生错误信息\nsome_nonexistent_command","type":"code-block","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"syntax":"javascript"}},{"key":"7v3v2","text":"3. 重定向标准输出","type":"header-five","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"3.-%E9%87%8D%E5%AE%9A%E5%90%91%E6%A0%87%E5%87%86%E8%BE%93%E5%87%BA"}},{"key":"gmn6","text":"将标准输出重定向到文件：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"9jr0d","text":"bash","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"5c1ms","text":"# 将输出重定向到文件 output.txt\necho \"This will be saved to a file\" \u003e output.txt","type":"code-block","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"syntax":"javascript"}},{"key":"1t38c","text":"4. 重定向标准错误","type":"header-five","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"4.-%E9%87%8D%E5%AE%9A%E5%90%91%E6%A0%87%E5%87%86%E9%94%99%E8%AF%AF"}},{"key":"7c81s","text":"将标准错误重定向到文件：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"5j0dq","text":"bash","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"6dlrh","text":"# 将输出重定向到文件 output.txt\necho \"This will be saved to a file\" \u003e output.txt","type":"code-block","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"syntax":"javascript"}},{"key":"7cj4u","text":"5. 同时重定向标准输出和标准错误","type":"header-five","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"5.-%E5%90%8C%E6%97%B6%E9%87%8D%E5%AE%9A%E5%90%91%E6%A0%87%E5%87%86%E8%BE%93%E5%87%BA%E5%92%8C%E6%A0%87%E5%87%86%E9%94%99%E8%AF%AF"}},{"key":"8el71","text":"将标准输出和标准错误同时重定向到同一个文件：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"98t4u","text":"bash","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"558vc","text":"# 将标准输出和标准错误都重定向到 same_output_and_error.txt\necho \"This will go to the file\" \u003e same_output_and_error.txt 2\u003e\u00261","type":"code-block","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"syntax":"javascript"}},{"key":"f9c85","text":"相关系统调用","type":"header-four","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E7%9B%B8%E5%85%B3%E7%B3%BB%E7%BB%9F%E8%B0%83%E7%94%A8"}},{"key":"5tiv","text":"在编程中，你还可以使用系统调用来操作文件描述符，以下是一些常用的：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"4mqi1","text":"open(): 打开文件并返回文件描述符。","type":"unordered-list-item","depth":0,"inlineStyleRanges":[{"offset":0,"length":6,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"8jv62","text":"read(): 从文件描述符中读取数据。","type":"unordered-list-item","depth":0,"inlineStyleRanges":[{"offset":0,"length":6,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"dj22s","text":"write(): 向文件描述符写入数据。","type":"unordered-list-item","depth":0,"inlineStyleRanges":[{"offset":0,"length":7,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"e0drj","text":"close(): 关闭文件描述符。","type":"unordered-list-item","depth":0,"inlineStyleRanges":[{"offset":0,"length":7,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"efa80","text":"小结","type":"header-four","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E5%B0%8F%E7%BB%93"}},{"key":"e0rvo","text":"文件描述符 0、1 和 2 用于表示标准输入、标准输出和标准错误，它们在 Linux 等类 Unix 系统中是处理输入输出的基础。通过合理地使用它们，可以方便地进行 I/O 操作和错误处理。","type":"unstyled","depth":0,"inlineStyleRanges":[{"offset":6,"length":1,"style":"CODE"},{"offset":8,"length":1,"style":"CODE"},{"offset":12,"length":1,"style":"CODE"}],"entityRanges":[],"data":{}},{"key":"fgcg1","text":"文件描述符总结","type":"header-two","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E6%80%BB%E7%BB%93"}},{"key":"50p67","text":"Linux中的文件描述符总结如下：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"cebm9","text":"定义与用途：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"5r11p","text":"文件描述符是内核为了高效管理已被打开的文件所创建的索引，是一个非负整数。\n 它用于代指被打开的文件，所有通过I/O操作的系统调用都通过文件描述符进行。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"1hqt2","text":"分配规则：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"fe1m","text":"当进程启动时，默认会打开三个文件描述符：标准输入（stdin，文件描述符为0）、标准输出（stdout，文件描述符为1）、标准错误（stderr，文件描述符为2）。\n 之后打开的文件，文件描述符会从3开始依次递增，为连续的整数。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"9hr1c","text":"限制：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"3pg9e","text":"系统级限制：限制所有用户打开文件描述符的总和，可以通过sysctl命令或查看proc文件系统来查询和修改。\n 用户级限制：限制每个用户登录后执行的程序占用的文件描述符总数，可以通过ulimit命令查询和修改。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"c9po7","text":"重定向：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"3vop7","text":"文件描述符支持重定向操作，包括输出重定向、输入重定向和追加重定向。\n 重定向允许用户将标准输入、输出或错误重定向到文件或其他设备。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"bqo2c","text":"与文件对象的关系：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"40dec","text":"用户在访问文件时，系统会将文件相关信息从磁盘中加载到内存，并在内核中创建文件对象。\n 文件描述符用于快速定位到这些文件对象，每个文件描述符都对应一个打开文件的文件对象。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"2huaq","text":"缓冲区：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"1k40n","text":"每个被打开的文件都各自拥有一个缓冲区。\n 使用write系统调用写入数据时，数据首先被拷贝到目标文件的缓冲区中，再由操作系统决定何时将数据刷新到外设中。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"b2r0j","text":"一切皆文件：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"5l41k","text":"在Linux下，一切皆文件，包括硬件设备、网络连接等，都可以通过文件描述符进行访问和操作。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"82eig","text":"综上所述，文件描述符是Linux内核中用于管理打开文件的一种机制，它提供了高效的文件访问方式，并支持重定向等高级功能。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"3r56b","text":"中文件描述符的具体作用是什么","type":"header-two","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E4%B8%AD%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E7%9A%84%E5%85%B7%E4%BD%93%E4%BD%9C%E7%94%A8%E6%98%AF%E4%BB%80%E4%B9%88"}},{"key":"102iu","text":"Linux中文件描述符的具体作用主要体现在以下几个方面：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"7rfdn","text":"唯一标识打开的文件或资源：文件描述符是一个非负整数，由操作系统内核分配，用于唯一标识一个已经打开的文件或输入输出资源（如管道、网络连接等）。这使得进程能够准确地访问和操作特定的文件或资源。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"9glf1","text":"支持多种I/O操作：文件描述符是进程与外部世界之间的桥梁。通过文件描述符，进程可以进行文件的读写操作、网络通信、进程间通信等。例如，使用read、write等系统调用进行文件内容的读取和写入，或者使用socket进行网络通信。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"4csu6","text":"实现重定向：文件描述符支持重定向操作，允许用户将标准输入、标准输出或标准错误重定向到文件或其他设备。这种灵活性使得程序能够更灵活地处理输入输出数据。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"je12","text":"管理打开的文件：每个进程都有一个文件描述符表，用于记录该进程打开的所有资源。文件描述符表对文件描述符进行管理，确保每个文件描述符都对应一个有效的打开文件或资源。同时，文件描述符的数量也是有限的，这有助于操作系统有效地管理资源。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"7s810","text":"综上所述，Linux中的文件描述符是一种高效、灵活的资源管理机制，它使得进程能够方便地访问和操作各种文件和资源。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"gulf","text":"如何理解“文件描述符”","type":"header-two","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{"text":"%E5%A6%82%E4%BD%95%E7%90%86%E8%A7%A3%E2%80%9C%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6%E2%80%9D"}},{"key":"a8ail","text":"文件描述符是：","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}},{"key":"94vu8","text":"一个非负整数，由操作系统内核分配。\n 用于标识和访问已经打开的文件或I/O资源（如管道、网络连接）。\n 通过文件描述符，进程可执行文件的读写操作、网络通信等。\n 文件描述符支持重定向，允许灵活处理输入输出数据。","type":"unstyled","depth":0,"inlineStyleRanges":[],"entityRanges":[],"data":{}}],"entityMap":{"0":{"type":"IMAGE","mutability":"IMMUTABLE","data":{"imageUrl":"https://developer.qcloudimg.com/http-save/yehe-11276311/d59c92d55316e9990d723371aea0cb60.png","imageAlt":"","name":"","blockWidth":736,"blockHeight":417}},"1":{"type":"IMAGE","mutability":"IMMUTABLE","data":{"imageUrl":"https://developer.qcloudimg.com/http-save/yehe-11276311/c5ea139d7d79fa2c18d189372f4c9014.png","imageAlt":"","name":"","blockWidth":720,"blockHeight":348}},"2":{"type":"IMAGE","mutability":"IMMUTABLE","data":{"imageUrl":"https://developer.qcloudimg.com/http-save/yehe-11276311/033cc2100ef7e724bfa18fa28e3f530c.png","imageAlt":"","name":"","blockWidth":1431,"blockHeight":1768}}}},"createTime":1731630712,"ext":{"closeTextLink":0,"comment_ban":0,"description":"","focusRead":0},"favNum":0,"isOriginal":0,"likeNum":1,"pic":"https://developer.qcloudimg.com/http-save/yehe-11276311/d59c92d55316e9990d723371aea0cb60.png","plain":"重定向的实质\n1和2的区别\n在 Linux 系统中，文件描述符（File Descriptor, FD）是一个非负整数，用于标识打开的文件、输入/输出设备或其他资源。标准输入、标准输出和标准错误是最常用的文件描述符，其对应的值为 0、1 和 2，具体含义和使用说明如下：\n文件描述符的含义\n 标准输入（stdin）\n \n描述符： 0\n用途：接收输入数据，通常是来自键盘的用户输入。\n使用场景：例如，当你在命令行中运行程序时，可以通过键盘输入数据，这些数据会被程序读取。\n 标准输出（stdout）\n \n描述符： 1\n用途：用于输出数据，通常是显示在终端上的信息。\n使用场景：例如，echo \"Hello, World!\" 会将字符串输出到标准输出，即命令行界面。\n 标准错误（stderr）\n \n描述符： 2\n用途：用于输出错误信息，通常也会显示在终端上，但可以与标准输出分开重定向。\n使用场景：例如，运行一个不存在的命令会产生错误信息，这些信息会输出到标准错误。\n使用示例\n以下是一些文件描述符的常见使用示例：\n1. 基本输出\nbash\n# 将字符串输出到标准输出\necho \"This is standard output\"\n2. 错误输出\nbash\n# 使用不正确的命令产生错误信息\nsome_nonexistent_command\n3. 重定向标准输出\n将标准输出重定向到文件：\nbash\n# 将输出重定向到文件 output.txt\necho \"This will be saved to a file\" \u003e output.txt\n4. 重定向标准错误\n将标准错误重定向到文件：\nbash\n# 将输出重定向到文件 output.txt\necho \"This will be saved to a file\" \u003e output.txt\n5. 同时重定向标准输出和标准错误\n将标准输出和标准错误同时重定向到同一个文件：\nbash\n# 将标准输出和标准错误都重定向到 same_output_and_error.txt\necho \"This will go to the file\" \u003e same_output_and_error.txt 2\u003e\u00261\n相关系统调用\n在编程中，你还可以使用系统调用来操作文件描述符，以下是一些常用的：\nopen(): 打开文件并返回文件描述符。\nread(): 从文件描述符中读取数据。\nwrite(): 向文件描述符写入数据。\nclose(): 关闭文件描述符。\n小结\n文件描述符 0、1 和 2 用于表示标准输入、标准输出和标准错误，它们在 Linux 等类 Unix 系统中是处理输入输出的基础。通过合理地使用它们，可以方便地进行 I/O 操作和错误处理。\n文件描述符总结\nLinux中的文件描述符总结如下：\n定义与用途：\n文件描述符是内核为了高效管理已被打开的文件所创建的索引，是一个非负整数。\n 它用于代指被打开的文件，所有通过I/O操作的系统调用都通过文件描述符进行。\n分配规则：\n当进程启动时，默认会打开三个文件描述符：标准输入（stdin，文件描述符为0）、标准输出（stdout，文件描述符为1）、标准错误（stderr，文件描述符为2）。\n 之后打开的文件，文件描述符会从3开始依次递增，为连续的整数。\n限制：\n系统级限制：限制所有用户打开文件描述符的总和，可以通过sysctl命令或查看proc文件系统来查询和修改。\n 用户级限制：限制每个用户登录后执行的程序占用的文件描述符总数，可以通过ulimit命令查询和修改。\n重定向：\n文件描述符支持重定向操作，包括输出重定向、输入重定向和追加重定向。\n 重定向允许用户将标准输入、输出或错误重定向到文件或其他设备。\n与文件对象的关系：\n用户在访问文件时，系统会将文件相关信息从磁盘中加载到内存，并在内核中创建文件对象。\n 文件描述符用于快速定位到这些文件对象，每个文件描述符都对应一个打开文件的文件对象。\n缓冲区：\n每个被打开的文件都各自拥有一个缓冲区。\n 使用write系统调用写入数据时，数据首先被拷贝到目标文件的缓冲区中，再由操作系统决定何时将数据刷新到外设中。\n一切皆文件：\n在Linux下，一切皆文件，包括硬件设备、网络连接等，都可以通过文件描述符进行访问和操作。\n综上所述，文件描述符是Linux内核中用于管理打开文件的一种机制，它提供了高效的文件访问方式，并支持重定向等高级功能。\n中文件描述符的具体作用是什么\nLinux中文件描述符的具体作用主要体现在以下几个方面：\n唯一标识打开的文件或资源：文件描述符是一个非负整数，由操作系统内核分配，用于唯一标识一个已经打开的文件或输入输出资源（如管道、网络连接等）。这使得进程能够准确地访问和操作特定的文件或资源。\n支持多种I/O操作：文件描述符是进程与外部世界之间的桥梁。通过文件描述符，进程可以进行文件的读写操作、网络通信、进程间通信等。例如，使用read、write等系统调用进行文件内容的读取和写入，或者使用socket进行网络通信。\n实现重定向：文件描述符支持重定向操作，允许用户将标准输入、标准输出或标准错误重定向到文件或其他设备。这种灵活性使得程序能够更灵活地处理输入输出数据。\n管理打开的文件：每个进程都有一个文件描述符表，用于记录该进程打开的所有资源。文件描述符表对文件描述符进行管理，确保每个文件描述符都对应一个有效的打开文件或资源。同时，文件描述符的数量也是有限的，这有助于操作系统有效地管理资源。\n综上所述，Linux中的文件描述符是一种高效、灵活的资源管理机制，它使得进程能够方便地访问和操作各种文件和资源。\n如何理解“文件描述符”\n文件描述符是：\n一个非负整数，由操作系统内核分配。\n 用于标识和访问已经打开的文件或I/O资源（如管道、网络连接）。\n 通过文件描述符，进程可执行文件的读写操作、网络通信等。\n 文件描述符支持重定向，允许灵活处理输入输出数据。","showReadNum":79,"sourceDetail":null,"sourceType":99,"status":2,"summary":"在 Linux 系统中，文件描述符（File Descriptor, FD）是一个非负整数，用于标识打开的文件、输入/输出设备或其他资源。标准输入、标准输出和标准错误是最常用的文件描述符，其对应的值为 0、1 和 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