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<p>在Bash中，变量的默认类型都是字符串类型的，Shell编程中，使用变量无需事先声。<br><a id="more"></a></p>
<h3 id="变量的命名规范"><a href="#变量的命名规范" class="headerlink" title="变量的命名规范"></a>变量的命名规范</h3><p>变量名的命名须遵循如下规则：</p>
<ul>
<li>首个字符必须为字母（a-z，A-Z）</li>
<li>中间不能有空格，可以使用下划线(_)</li>
<li>不能使用标点符号</li>
<li>不能使用bash里的关键字（可用help命令查看保留关键字）</li>
</ul>
<h3 id="变量的分类"><a href="#变量的分类" class="headerlink" title="变量的分类"></a>变量的分类</h3><blockquote>
<ul>
<li>用户自定义变量：用户可以自己定义。</li>
</ul>
</blockquote>
<blockquote>
<ul>
<li>环境变量：这种变量中主要保存的是和系统操作环境相关的数据。变量可以自动一，但是对系统生效的环境变量名和变量作用是固定的。</li>
</ul>
</blockquote>
<blockquote>
<ul>
<li>位置参数变量：这种变量主要是用来向脚本当中传递参数或者数据的，变量名不能自定义，变量作用是固定的。</li>
</ul>
</blockquote>
<blockquote>
<ul>
<li>位置参数变量：是Bash中已经定义好的变量，变量名不能自定义，变量作用也是固定的。</li>
</ul>
</blockquote>
<h4 id="定义变量"><a href="#定义变量" class="headerlink" title="定义变量"></a>定义变量</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">变量名=变量值 (等号 =两边不能带空格)</span><br></pre></td></tr></table></figure>
<h4 id="变量调用"><a href="#变量调用" class="headerlink" title="变量调用"></a>变量调用</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">echo</span> $变量名</span><br></pre></td></tr></table></figure>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">如下示例:</span><br><span class="line"><span class="built_in">echo</span> <span class="variable">$x</span></span><br><span class="line"><span class="built_in">echo</span> <span class="variable">$name</span></span><br></pre></td></tr></table></figure>
<h4 id="变量叠加"><a href="#变量叠加" class="headerlink" title="变量叠加"></a>变量叠加</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">x=123</span><br><span class="line">x=<span class="string">"<span class="variable">$x</span>"</span>456</span><br><span class="line">x=<span class="variable">${x}</span>789</span><br></pre></td></tr></table></figure>
<p>最终使用<code>echo $x</code>将输出<code>123456789</code></p>
<h4 id="变量查看"><a href="#变量查看" class="headerlink" title="变量查看"></a>变量查看</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">set</span></span><br><span class="line"> 选项:</span><br><span class="line"> -u 如果设定此选项，调用未声明变量时会报错（默认无任何提示）</span><br></pre></td></tr></table></figure>
<h4 id="变量的删除"><a href="#变量的删除" class="headerlink" title="变量的删除"></a>变量的删除</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">unset</span> 变量名 （注意，此处不能加$符号）</span><br></pre></td></tr></table></figure>
<h3 id="环境变量"><a href="#环境变量" class="headerlink" title="环境变量"></a>环境变量</h3><p>环境变量和用户自定义变量的区别:</p>
<blockquote>
<ul>
<li>用户自定义变量只在当前的shell中生效，环境变量在当前shell和这个shell的所有子shell中生效。</li>
</ul>
</blockquote>
<blockquote>
<ul>
<li>环境变量是全局变量，用户自定义变量是局部变量。</li>
</ul>
</blockquote>
<blockquote>
<ul>
<li>对系统生效的环境变量名和变量作用是固定的。</li>
</ul>
</blockquote>
<h4 id="设置环境变量"><a href="#设置环境变量" class="headerlink" title="设置环境变量"></a>设置环境变量</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">export</span> 变量名=变量值</span><br><span class="line"></span><br><span class="line">变量名=变量值</span><br><span class="line"><span class="built_in">export</span> 变量名</span><br></pre></td></tr></table></figure>
<h4 id="查看环境变量"><a href="#查看环境变量" class="headerlink" title="查看环境变量"></a>查看环境变量</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">set</span> <span class="comment">#查看所有变量</span></span><br><span class="line">env <span class="comment">#查看环境变量</span></span><br></pre></td></tr></table></figure>
<h4 id="常用环境变量"><a href="#常用环境变量" class="headerlink" title="常用环境变量"></a>常用环境变量</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">HOSTNAME：主机名</span><br><span class="line">SHELL：当前的shell</span><br><span class="line">TREM：终端环境</span><br><span class="line">HISTSIZE：历史命令条数</span><br><span class="line">SSH_CLIENT：当前操作环境是用ssh链接的，这里记录客户端的ip</span><br><span class="line">SSH_TTY：ssh连接的终端是pts/1</span><br><span class="line">USER:当前登录的用户</span><br></pre></td></tr></table></figure>
<h4 id="PATH变量"><a href="#PATH变量" class="headerlink" title="PATH变量"></a>PATH变量</h4><blockquote>
<p><code>PATH</code>变量：系统查找命令的路径。</p>
</blockquote>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line"><span class="built_in">echo</span> <span class="variable">$PATH</span> <span class="comment">#查看PATH变量的值</span></span><br><span class="line">PATH=<span class="string">"<span class="variable">$PATH</span>"</span>:/root/sh <span class="comment">#增加PATH变量的值</span></span><br></pre></td></tr></table></figure>
<h4 id="PS1变量"><a href="#PS1变量" class="headerlink" title="PS1变量"></a>PS1变量</h4><blockquote>
<p><code>PS1</code>变量：命令提示符设置</p>
</blockquote>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">- \d 显示日期，格式为”星期 月 日“</span><br><span class="line">- \H 显示完整的主机名<span class="string">"localhost.localdomain"</span></span><br><span class="line">- \t 显示24小时制时间，格式为<span class="string">"HH:MM:SS"</span></span><br><span class="line">- \A 显示24小时制时间，格式为<span class="string">"HH:MM"</span></span><br><span class="line">- \u 显示当前用户名</span><br><span class="line">- \w 显示当前所在目录的完整名称</span><br><span class="line">- \W 显示当前所在目录的最后一个目录</span><br><span class="line">- \$ 提示符、如果是root用户会显示提示符为<span class="string">"#"</span>,如果是普通用户会显示提示符为<span class="string">"$"</span></span><br></pre></td></tr></table></figure>
<h4 id="当前语系查询"><a href="#当前语系查询" class="headerlink" title="当前语系查询"></a>当前语系查询</h4><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># locale #查询当前语系</span></span><br><span class="line"> -LANG 定义系统主要语系（当前生效语系）</span><br><span class="line"> -LC:ALL 定义整体语系的变量（下次启动可能会生效）</span><br><span class="line"></span><br><span class="line"><span class="built_in">echo</span> <span class="variable">$LANG</span> <span class="comment">#查看系统当前语系</span></span><br><span class="line"></span><br><span class="line">locale -a | more <span class="comment">#查看linux支持的所有语系</span></span><br><span class="line"></span><br><span class="line">cat /et/sysconfig/i18n <span class="comment">#查询系统的默认语系（开机生效读取的语系环境）</span></span><br></pre></td></tr></table></figure>
<h4 id="Linux中文支持"><a href="#Linux中文支持" class="headerlink" title="Linux中文支持"></a>Linux中文支持</h4><blockquote>
<p>前提条件：正确安装中文字体和中文语系。</p>
<ul>
<li>如果有图形界面，可以正确支持中文显示。</li>
<li>如果使用第三方远程工具，只要语系设定正确，可以支持中文显示。</li>
<li>如果使用纯字符界面，必须使用第三方插件（zhcon等）</li>
</ul>
</blockquote>
<h3 id="位置参数变量"><a href="#位置参数变量" class="headerlink" title="位置参数变量"></a>位置参数变量</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="variable">$n</span> n为数字，<span class="variable">$0</span>代表命令本身，<span class="variable">$1</span>~<span class="variable">$9</span>代表第一到第九个参数，十以上的参数需要用到大括号包含，如<span class="variable">${10}</span>。</span><br><span class="line">$* 这个变量代表命令行中所有的参数，$*把所有的参数看作是一个整体。</span><br><span class="line"><span class="variable">$@</span> 这个变量也代表命令行中所有的参数，不过<span class="variable">$@</span>把每个参数区分呢对待。</span><br><span class="line"><span class="variable">$#</span> 这个变量代表命令行中所有参数的个数</span><br></pre></td></tr></table></figure>
<blockquote>
<p>$n 使用示例<code>sum.sh</code></p>
</blockquote>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#!/bin/bash</span></span><br><span class="line">num=<span class="variable">$1</span></span><br><span class="line">num2=<span class="variable">$2</span></span><br><span class="line">sum=$((<span class="variable">$num1</span>+num2))</span><br></pre></td></tr></table></figure>
<p>执行上述<code>sum.sh</code>脚本:</p>
<pre><code>./sum.sh 100 200
</code></pre><p>输出为300</p>
<blockquote>
<p>$* $@ $# 使用示例 <code>sum1.sh</code></p>
</blockquote>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#!/bin/bash</span></span><br><span class="line"><span class="built_in">echo</span> <span class="string">"\$* 参数是: $*"</span></span><br><span class="line"><span class="built_in">echo</span> <span class="string">"\@* 参数是: <span class="variable">$@</span>"</span></span><br><span class="line"><span class="built_in">echo</span> <span class="string">"\#* 参数个数是: <span class="variable">$#</span>"</span></span><br></pre></td></tr></table></figure>
<blockquote>
<p>$* $@ 使用示例 <code>sum2.sh</code></p>
</blockquote>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">#!/bin/bash</span></span><br><span class="line"><span class="keyword">for</span> i <span class="keyword">in</span> <span class="string">"$*"</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#!/bin/bash</span></span><br><span class="line"><span class="keyword">for</span> i <span class="keyword">in</span> <span class="string">"$*"</span></span><br><span class="line"> $*中的所有参数看成是一个整体，所以这个<span class="keyword">for</span>循环只会循环一次。</span><br><span class="line"> <span class="keyword">do</span></span><br><span class="line"> <span class="built_in">echo</span> <span class="string">" The parameter is : <span class="variable">$i</span>"</span></span><br><span class="line"> <span class="keyword">done</span></span><br><span class="line"><span class="keyword">for</span> y <span class="keyword">in</span> <span class="string">"<span class="variable">$@</span>"</span></span><br><span class="line"> <span class="variable">$@</span>中的每个参数都看很是独立的，所有<span class="string">"<span class="variable">$@</span>"</span>中有几个参数，就会循环几次</span><br><span class="line"> <span class="keyword">do</span></span><br><span class="line"> <span class="built_in">echo</span> <span class="string">"Parameter : <span class="variable">$y</span> "</span></span><br><span class="line"> <span class="keyword">done</span></span><br></pre></td></tr></table></figure>
<h3 id="预定义变量"><a href="#预定义变量" class="headerlink" title="预定义变量"></a>预定义变量</h3><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line">$? 最后一次执行的命令的返回状态。如果这个变量的值为0，证明上一个命令正确执行；如果这个变量的值非0（具体是哪个数，由命令自己决定），则证明上一个命令执行不正确了。</span><br><span class="line">$$ 当前进程的进程号（PID）</span><br><span class="line">$! 后台运行的最后一个进程的进程号（PID）</span><br></pre></td></tr></table></figure>
<p>使用示例：<br><figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line">ls</span><br><span class="line"><span class="built_in">echo</span> $? <span class="comment">#将在终端打印结果为0</span></span><br><span class="line"></span><br><span class="line">ls QERTYUTIYKNB</span><br><span class="line"><span class="built_in">echo</span> $? <span class="comment">#将在终端打印结果为2（非0）</span></span><br></pre></td></tr></table></figure></p>
<blockquote>
<p>其实，逻辑运算符<code>&&</code>(逻辑与运算）和<code>||</code>（逻辑或运算）就是通过判断前一个命令的返回值来判断命令是否正确执行。</p>
</blockquote>
<figure class="highlight bash"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">ls && <span class="built_in">echo</span> yes</span><br><span class="line">ls || <span class="built_in">echo</span> no</span><br></pre></td></tr></table></figure>
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<div class="post-toc-content"><ol class="nav"><li class="nav-item nav-level-3"><a class="nav-link" href="#变量的命名规范"><span class="nav-number">1.</span> <span class="nav-text">变量的命名规范</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#变量的分类"><span class="nav-number">2.</span> <span class="nav-text">变量的分类</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#定义变量"><span class="nav-number">2.1.</span> <span class="nav-text">定义变量</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#变量调用"><span class="nav-number">2.2.</span> <span class="nav-text">变量调用</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#变量叠加"><span class="nav-number">2.3.</span> <span class="nav-text">变量叠加</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#变量查看"><span class="nav-number">2.4.</span> <span class="nav-text">变量查看</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#变量的删除"><span class="nav-number">2.5.</span> <span class="nav-text">变量的删除</span></a></li></ol></li><li class="nav-item nav-level-3"><a class="nav-link" href="#环境变量"><span class="nav-number">3.</span> <span class="nav-text">环境变量</span></a><ol class="nav-child"><li class="nav-item nav-level-4"><a class="nav-link" href="#设置环境变量"><span class="nav-number">3.1.</span> <span class="nav-text">设置环境变量</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#查看环境变量"><span class="nav-number">3.2.</span> <span class="nav-text">查看环境变量</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#常用环境变量"><span class="nav-number">3.3.</span> <span class="nav-text">常用环境变量</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#PATH变量"><span class="nav-number">3.4.</span> <span class="nav-text">PATH变量</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#PS1变量"><span class="nav-number">3.5.</span> <span class="nav-text">PS1变量</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#当前语系查询"><span class="nav-number">3.6.</span> <span class="nav-text">当前语系查询</span></a></li><li class="nav-item nav-level-4"><a class="nav-link" href="#Linux中文支持"><span class="nav-number">3.7.</span> <span class="nav-text">Linux中文支持</span></a></li></ol></li><li class="nav-item nav-level-3"><a class="nav-link" href="#位置参数变量"><span class="nav-number">4.</span> <span class="nav-text">位置参数变量</span></a></li><li class="nav-item nav-level-3"><a class="nav-link" href="#预定义变量"><span class="nav-number">5.</span> <span class="nav-text">预定义变量</span></a></li></ol></div>
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