LINUX中详解AWK内建变量FS,NF,NR,RT,RS,ORS,OFS
<p>看了网上好多关于AWK内建变量的文章，这里加上个人的理解和记忆，可以让大家掌握这些变量的基本用法。</p>
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FS 指定字段un列分隔符（Font Space）</p>
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<code class="xhtml plain">[~/AWK_learning]$ echo "111|222|333" | awk '{print $1}'</code>
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<code class="xhtml plain">111|222|333</code>
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<code class="xhtml plain">[~/AWK_learning]$ echo "111|222|333" | awk 'BEGIN{FS="|"}{print $1}'</code>
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<code class="xhtml plain">111</code>
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OFS 指定输出字段列分隔符（Output Font space）</p>
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<code class="xhtml plain">[~/AWK_learning]$ echo "111 222 333" |awk 'BEGIN{OFS="|";}{print $1,$2,$3}'</code>
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<code class="xhtml plain">111|222|333</code>
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RS指定行分隔符 默认分隔符为\n（Row Space）</p>
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<code class="xhtml plain">[~/AWK_learning]$ echo "111 222|333 444|555 666" | awk 'BEGIN{RS="|"}{print $0}'</code>
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<code class="xhtml plain">111 222</code>
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<code class="xhtml plain">333 444</code>
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<code class="xhtml plain">555 666</code>
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ORS指定输出行分隔符</p>
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<code class="xhtml plain">[~/AWK_learning]$ awk 'BEGIN{ORS="|";}{print $0;}' test.txt</code>
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<code class="xhtml plain">111 222|333 444|555 666</code>
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RT 代指分隔符</p>
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<code class="xhtml plain">[~/AWK_learning]$ echo "111 222|333 444|555 666" | awk 'BEGIN{RS="|"}{print $0,RT}'</code>
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<code class="xhtml plain">111 222 |</code>
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<code class="xhtml plain">333 444 |</code>
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<code class="xhtml plain">555 666 |</code>
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<p>
NF 每行字段总数(Number of Font)</p>
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<code class="xhtml plain">[~/AWK_learning]$ cat test.txt</code>
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<code class="xhtml plain">111 222</code>
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<code class="xhtml plain">333 444</code>
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<code class="xhtml plain">555 666</code>
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<code class="xhtml plain">[~/AWK_learning]$ awk '{print NF}' test.txt</code>
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<code class="xhtml plain">2</code>
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<code class="xhtml plain">2</code>
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<code class="xhtml plain">2</code>
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<code class="xhtml plain">[~/AWK_learning]$ awk '{print $NF}' test.txt</code>
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<code class="xhtml plain">222</code>
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<code class="xhtml plain">444</code>
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<code class="xhtml plain">666</code>
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NR 当前行数(Number of Row)</p>
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<code class="xhtml plain">[~/AWK_learning]$ cat test.txt</code>
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<code class="xhtml plain">111 222</code>
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<code class="xhtml plain">333 444</code>
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<code class="xhtml plain">555 666 777</code>
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<code class="xhtml plain">[~/AWK_learning]$ awk '{print NR}' test.txt</code>
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<code class="xhtml plain">1</code>
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<code class="xhtml plain">2</code>
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<code class="xhtml plain">3</code>
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<code class="xhtml plain">[~/AWK_learning]$ awk '{print $NR}' test.txt</code>
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<code class="xhtml plain">111</code>
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<code class="xhtml plain">777</code>
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<p>
下面我们在来看下，在内建变量执行中的相关问题：</p>
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NR表示从awk开始执行后，按照记录分隔符读取的数据次数，默认的记录分隔符为换行符，因此默认的就是读取的数据行数，NR可以理解为Number of Record的缩写。</p>
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在awk处理多个输入文件的时候，在处理完第一个文件后，NR并不会从1开始，而是继续累加，因此就出现了FNR，每当处理一个新文件的时候，FNR就从1开始计数，FNR可以理解为File Number of Record。</p>
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NF表示目前的记录被分割的字段的数目，NF可以理解为Number of Field。</p>
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下面以示例程序来进行说明，首先准备两个输入文件class1和class2，记录了两个班级的成绩信息，内容分别如下所示：</p>
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<code class="xhtml plain">CodingAnts@ubuntu:~/awk$ cat class1</code>
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<code class="xhtml plain">zhaoyun 85 87</code>
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<code class="xhtml plain">guanyu 87 88</code>
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<code class="xhtml plain">liubei 90 86</code>
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<code class="xhtml plain">CodingAnts@ubuntu:~/awk$ cat class2</code>
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<code class="xhtml plain">caocao 92 87 90</code>
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<code class="xhtml plain">guojia 99 96 92</code>
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<p>
现在要查看两个班级的所有成绩信息，并在每条信息前加上行号，则可以使用下面的awk指令；</p>
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<code class="xhtml plain">CodingAnts@ubuntu:~/awk$ awk '{print NR,$0}' class1 class2</code>
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<code class="xhtml plain">1 zhaoyun 85 87</code>
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<code class="xhtml plain">2 guanyu 87 88</code>
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<code class="xhtml plain">3 liubei 90 86</code>
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<code class="xhtml plain">4 caocao 92 87 90</code>
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<code class="xhtml plain">5 guojia 99 96 92</code>
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<p>
这里的行号就是通过NR来实现的，awk每读取一条记录，NR的值便加一。如果要求每个班级的行号从头开始变化，则需要使用FNR来实现，如下：</p>
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<code class="xhtml plain">CodingAnts@ubuntu:~/awk$ awk '{print FNR,$0}' class1 class2</code>
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<code class="xhtml plain">1 zhaoyun 85 87</code>
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<code class="xhtml plain">2 guanyu 87 88</code>
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<code class="xhtml plain">3 liubei 90 86</code>
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<code class="xhtml plain">1 caocao 92 87 90</code>
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<code class="xhtml plain">2 guojia 99 96 92</code>
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原文链接：http://blog.csdn.net/cengineering/article/details/78529292</p>
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