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<title>linux/bash/awk中RS,ORS,FS,OFS区别与联系</title>
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title="Permalink to linux/bash/awk中RS,ORS,FS,OFS区别与联系">
linux/bash/awk中RS,ORS,FS,OFS区别与联系
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<abbr class="published" title="2013-08-27T00:00:00">
<i class="icon-calendar"></i>二 27 八月 2013
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<p>学习awk时，一定要记得动手去实践，只有在实践中才能发现问题，以下就我在学习中和实践中的经验，总结一下RS,ORS,FS,OFS的区别和联系。</p>
<p>'''一，RS与ORS'''</p>
<p>1，RS是记录分隔符，默认的分隔符是\n，具体用法看下</p>
<ol>
<li>
<p>[root@krlcgcms01 mytest]# cat test1 /<em> //测试文件 </em>/</p>
</li>
<li>
<p>111 222</p>
</li>
<li>333 444</li>
<li>555 666</li>
</ol>
<p>2，RS默认分割符\n</p>
<ol>
<li>
<p>[root@krlcgcms01 mytest]# awk '{print $0}' test1 /<em> //awk 'BEGIN{RS="\n"}{print $0}' test1 这二个是一样的 </em>/</p>
</li>
<li>
<p>111 222</p>
</li>
<li>333 444</li>
<li>555 666</li>
</ol>
<p>其实你可以把'''上面test1文件里的内容理解为，111 222\n333 444\n555 6666，利用\n进行分割'''。看下一个例子</p>
<p>3，自定义RS分割符</p>
<ol>
<li>
<p>[zhangy@localhost test]$ echo "111 222|333 444|555 666"|awk 'BEGIN{RS="|"}{print $0,RT}'</p>
</li>
<li>
<p>111 222 |</p>
</li>
<li>333 444 |</li>
<li>555 666</li>
</ol>
<p>结合上面一个例子，就很容易理解RS的用法了。</p>
<p>4，RS也可能是正则表达式</p>
<ol>
<li>
<p>[zhangy@localhost test]$ echo "111 222a333 444b555 666"|awk 'BEGIN{RS="[a-z]+"}{print $1,RS,RT}'</p>
</li>
<li>
<p>111 [a-z]+ a</p>
</li>
<li>333 [a-z]+ b</li>
<li>555 [a-z]+</li>
</ol>
<p>从例3和例4，我们可以发现一点，'''当RT是利用RS匹配出来的内容。如果RS是某个固定的值时，RT就是RS的内容'''。</p>
<p>5，RS为空时</p>
<ol>
<li>
<p>[zhangy@localhost test]$ cat -n test2</p>
</li>
<li>
<p>1 111 222</p>
</li>
<li>2</li>
<li>3 333 444</li>
<li>4 333 444</li>
<li>5</li>
<li>6</li>
<li>7 555 666</li>
<li>[zhangy@localhost test]$ awk 'BEGIN{RS=""}{print $0}' test2</li>
<li>111 222</li>
<li>333 444</li>
<li>333 444</li>
<li>555 666</li>
<li>[zhangy@localhost test]$ awk 'BEGIN{RS="";}{print "<",$0,">"}' test2 /<em> //这个例子看着比较明显 </em>/</li>
<li>< 111 222 ></li>
<li>< 333 444 /<em> //这一行和下面一行，是一行 </em>/</li>
<li>333 444 ></li>
<li>< 555 666 ></li>
</ol>
<p>从这个例子，'''可以看出当RS为空时，awk会自动以多行来做为分割符'''。</p>
<p>6，ORS记录输出分符符，默认值是\n</p>
<p>'''把ORS理解成RS反过程，这样更容易记忆和理解'''，看下面的例子。</p>
<ol>
<li>
<p>[zhangy@localhost test]$ awk 'BEGIN{ORS="\n"}{print $0}' test1 /<em> //awk '{print $0}' test1二者是一样的 </em>/</p>
</li>
<li>
<p>111 222</p>
</li>
<li>333 444</li>
<li>555 666</li>
<li>[zhangy@localhost test]$ awk 'BEGIN{ORS="|"}{print $0}' test1</li>
<li>111 222|333 444|555 666|</li>
</ol>
<p>'''二，FS与OFS'''</p>
<p>1，FS指定列分割符</p>
<ol>
<li>
<p>[zhangy@localhost test]$ echo "111|222|333"|awk '{print $1}'</p>
</li>
<li>
<p>111|222|333</p>
</li>
<li>[zhangy@localhost test]$ echo "111|222|333"|awk 'BEGIN{FS="|"}{print $1}'</li>
<li>111</li>
</ol>
<p>2，FS也可以用正则</p>
<ol>
<li>
<p>[zhangy@localhost test]$ echo "111||222|333"|awk 'BEGIN{FS="[|]+"}{print $1}'</p>
</li>
<li>
<p>111</p>
</li>
</ol>
<p>3，FS为空的时候</p>
<ol>
<li>
<p>[zhangy@localhost test]$ echo "111|222|333"|awk 'BEGIN{FS=""}{NF++;print $0}'</p>
</li>
<li>
<p>1 1 1 | 2 2 2 | 3 3 3</p>
</li>
</ol>
<p>'''当FS为空的时候，awk会把一行中的每个字符，当成一列来处理'''。</p>
<p>4，RS被设定成非\n时，\n会成FS分割符中的一个</p>
<ol>
<li>
<p>[zhangy@localhost test]$ cat test1</p>
</li>
<li>
<p>111 222</p>
</li>
<li>333 444</li>
<li>555 666</li>
<li>[zhangy@localhost test]$ awk 'BEGIN{RS="444";}{print $2,$3}' test1</li>
<li>222 333</li>
<li>666</li>
</ol>
<p>'''222和333之间是有一个\n的，当RS设定成444后，222和333被认定成同一行的二列了，其实按常规思想是二行的一列才对'''。</p>
<p>5，OFS列输出分隔符</p>
<ol>
<li>
<p>[zhangy@localhost test]$ awk 'BEGIN{OFS="|";}{print $1,$2}' test1</p>
</li>
<li>
<p>111|222</p>
</li>
<li>333|444</li>
<li>555|666</li>
<li>[zhangy@localhost test]$ awk 'BEGIN{OFS="|";}{print $1 OFS $2}' test1</li>
<li>111|222</li>
<li>333|444</li>
<li>555|666</li>
</ol>
<p>'''test1只有二列，如果100列，都写出来太麻烦了吧。'''</p>
<ol>
<li>
<p>[zhangy@localhost test]$ awk 'BEGIN{OFS="|";}{print $0}' test1</p>
</li>
<li>
<p>111 222</p>
</li>
<li>333 444</li>
<li>555 666</li>
<li>[zhangy@localhost test]$ awk 'BEGIN{OFS="|";}{NF=NF;print $0}' test1</li>
<li>111|222</li>
<li>333|444</li>
<li>555|666</li>
</ol>
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