linux中xargs命令的各种使用技巧
<p><span><strong>前言</strong></span></p>
<p>
xargs命令是把接收到的数据重新格式化，再将其作为参数提供给其他命令，下面介绍xargs命令的各种使用技巧，一起来看看吧。</p>
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<span><strong>一、将多行输入转换成单行输入：</strong></span></p>
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<code class="bash plain"></code><code class="bash comments"># echo -e "1 2 3 4 5 \n6 7 8 \n9 10 11 12" >example.txt</code>
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<code class="bash plain"></code><code class="bash comments"># cat example.txt </code>
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<code class="bash plain">1 2 3 4 5 </code>
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<code class="bash plain">6 7 8 </code>
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<code class="bash plain">9 10 11 12</code>
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<code class="bash plain"></code><code class="bash comments"># cat example.txt |xargs </code>
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<code class="bash plain">1 2 3 4 5 6 7 8 9 10 11 12</code>
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将单行输入转换成多行输出：</p>
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<code class="bash plain"></code><code class="bash comments"># cat example.txt | xargs -n 3</code>
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<code class="bash plain">1 2 3</code>
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<code class="bash plain">4 5 6</code>
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<code class="bash plain">7 8 9</code>
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<code class="bash plain">10 11 12</code>
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自定义定界符进行转换（默认的定界符是空格）：</p>
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<code class="bash plain"></code><code class="bash comments"># echo "Hello:Hello:Hello:Hello" | xargs -d : -n 2</code>
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<code class="bash plain">Hello Hello</code>
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<code class="bash plain">Hello Hello</code>
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<span><strong>二、在脚本中运用：</strong></span></p>
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<code class="bash plain"></code><code class="bash comments"># cat echo.sh </code>
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<code class="bash preprocessor bold">#!/bin/bash</code>
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<code class="bash functions">echo</code> <code class="bash plain">$* </code><code class="bash string">'^-^'</code>
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当参数传递给<code>echo.sh</code>后，它会将这些参数打印出来，并且以"^-^"作为结尾：</p>
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<code class="bash plain"></code><code class="bash comments"># echo -e "Tom\nHarry\nJerry\nLucy" > args.txt</code>
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<code class="bash plain"></code><code class="bash comments"># cat args.txt | xargs bash echo.sh </code>
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<code class="bash plain">Tom Harry Jerry Lucy ^-^</code>
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<code class="bash plain"></code><code class="bash comments"># cat args.txt | xargs -n 2 bash echo.sh </code>
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<code class="bash plain">Tom Harry ^-^</code>
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<code class="bash plain">Jerry Lucy ^-^</code>
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在上面的例子中，我们把参数源都放入args.txt文件，但是除了这些参数，我们还需要一些固定不变的参数，比如：</p>
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<code class="bash plain"></code><code class="bash comments"># bash echo.sh Welcome Tom </code>
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<code class="bash plain">Welcome Tom ^-^</code>
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在上述命令执行过程中，Tom是变量，其余部分为常量，我们可以从"args.txt"中提取参数，并按照下面的方式提供给命令：</p>
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<code class="bash plain"></code><code class="bash comments"># bash echo.sh Welcome Tom </code>
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<code class="bash plain"></code><code class="bash comments"># bash echo.sh Welcome Herry</code>
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<code class="bash plain"></code><code class="bash comments"># bash echo.sh Welcome Jerry</code>
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<code class="bash plain"></code><code class="bash comments"># bash echo.sh Welcome Lucy</code>
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<p>
<strong>这时我们需要使用xargs中-I命令：</strong></p>
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<code class="bash plain"></code><code class="bash comments"># cat args.txt | xargs -I {} bash echo.sh Welcome {} </code>
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<code class="bash plain">Welcome Tom ^-^</code>
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<code class="bash plain">Welcome Harry ^-^</code>
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<code class="bash plain">Welcome Jerry ^-^</code>
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<code class="bash plain">Welcome Lucy ^-^</code>
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-I {} 指定替换字符串，对于每一个命令参数，字符串{}都会被从stdin读取到的参数替换掉，</p>
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使用-I的时候，命令以循环的方式执行，如果有4个参数，那么命令就会连同{}一起被执行4次，在每一次执行中{}都会被替换为相应的参数。</p>
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<span><strong>三、结合find使用</strong></span></p>
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xargs和find是一对非常好的组合，但是，我们通常是以一种错误的方式运用它们的，比如：</p>
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<code class="bash plain"></code><code class="bash comments"># find . -type f -name "*.txt" -print | xargs rm -f</code>
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这样做是有危险的，有时会删除不必删除的文件，如果文件名里包含有空格符(' '),则xargs很可能认为它们是定界符（例如，file text.txt会被xargs误认为file和text.txt）。</p>
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如果我们想把find的输出作为xargs的输入，就必须将-print0与find结合使用以字符null（'\0'）来分隔输出，用find找出所有.txt的文件，然后用xargs将这些文件删除：</p>
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<code class="bash plain"></code><code class="bash comments"># find . -type f -name "*.txt" -print0 | xargs -0 rm -f</code>
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这样就可以删除所有的.txt文件了，<code>xargs -0</code> 将\0作为输入定界符。</p>
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<span><strong>四、运用while语句和子shell</strong></span></p>
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<code class="bash plain"></code><code class="bash comments"># cat files.txt | (while read arg ;do cat $arg;done)</code>
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这条命令等同于：</p>
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<code class="bash plain"></code><code class="bash comments"># cat files.txt | xargs -I {} cat {}</code>
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<p>
在while循环中，可以将<code>cat $arg</code>替换成任意数量的命令，这样我们就可以对同一个参数执行多条命令，也可以不借助管道，将输出传递给其他命令，这个技巧适应于多种问题场景。子shell操作符内部的多个命令可作为一个整体来运行。</p>
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<span><strong>总结</strong></span></p>
<p>
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助，如果有疑问大家可以留言交流，谢谢大家对的支持。</p>
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原文链接：http://www.cnblogs.com/01-single/p/6882652.html</p>
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