一、grep 命令
grep �help查看grep命令发现可选参数太多。这里挑几个常用的来举例说明。
示例文件如下：
[root@localhosttest]#moregrep.txt xy yxay xxxy yaxy yyxxyyxx yyaaxxyyaa xaaay axay xaya rootxyxyxyxyxyxyx xyxyxyxyxyxyx xyxyxyxyxyx xyxXYXYXYXyxyx xyxyxyxyxyxyxxy xyxyxixixixinsnsnsnxixiyxyx XYXYXxy XaaaaY XYXYXYXYXYX XsdfsfasfY XXYYYAAAA XXXAAAAYYY
[root@localhost test]# grep -c ‘xy’grep.txt
12
-i ：忽略大小差异
[root@localhost test]# grep -ci ‘xy’grep.txt
14 #发现忽略大小写多了2行。
-n ：显示行号
[root@localhosttest]#grep-n'xyxy'grep.txt 10:rootxyxyxyxyxyxyx 11:xyxyxyxyxyxyx 12:xyxyxyxyxyx 14:xyxyxyxyxyxyxxy 15:xyxyxixixixinsnsnsnxixiyxyx
-A+n（n代表数字） ：After的意思，显示匹配字符后n行数据
-B+n（n代表数字） ：Before的意思，显示匹配字符前n行数据
[root@localhosttest]#grep-nA2'xixi'grep.txt 15:xyxyxixixixinsnsnsnxixiyxyx 16-XYXYXxy 17-XaaaaY
[root@localhosttest]#grep-nB2'xixi'grep.txt 13-xyxXYXYXYXyxyx 14-xyxyxyxyxyxyxxy 15:xyxyxixixixinsnsnsnxixiyxyx
-v ：显示没有匹配的行。
[root@localhosttest]#grep-nv'x'grep.txt 17:XaaaaY 18:XYXYXYXYXYX 19:XsdfsfasfY 20:XXYYYAAAA 21:XXXAAAAYYY
注意：一般为了显示明显，一般会使用―color=auto。一般系统会通过别名的方式自带此参数，如果没有可以自己添加个别名就可以了：alias grep='grep --color=auto'。还有对于要查找的字符应用‘’（单引号）引起来，一般不建议用双引号，容易被程序误解。
二、基本正则表达式
申明：C：表示单个字符（char），S：表示字符串（String）
^S :表示搜索以S开头的行。
[root@localhosttest]#grep-n'^xy'grep.txt#查找以xy开头的行 1:xy 11:xyxyxyxyxyxyx 12:xyxyxyxyxyx 13:xyxXYXYXYXyxyx 14:xyxyxyxyxyxyxxy 15:xyxyxixixixinsnsnsnxixiyxyx [root@localhosttest]#grep-n'^xyx'grep.txt#查找以xyx开头的行 11:xyxyxyxyxyxyx 12:xyxyxyxyxyx 13:xyxXYXYXYXyxyx 14:xyxyxyxyxyxyxxy 15:xyxyxixixixinsnsnsnxixiyxyx
[root@localhost test]# grep -n 'xy^'grep.txt #注意^是放在最前面的。
S$ :搜索以S结束的行，与^对应
[root@localhosttest]#grep-n'xyx$'grep.txt#查找以xyx结束的行 10:rootxyxyxyxyxyxyx 11:xyxyxyxyxyxyx 12:xyxyxyxyxyx 13:xyxXYXYXYXyxyx 15:xyxyxixixixinsnsnsnxixiyxyx
[root@localhost test]# grep -n '$xy'grep.txt #同样$需要放在后面，放在字符串前面是不对的
. :点号，匹配任意一个字符，注意只是一个字符
[root@localhosttest]#grep-n'a..x'grep.txt#查找行中有a..x的 6:yyaaxxyyaa
\ :斜杠，转义字符
[root@localhosttest]#grep-n"\""grep.txt#通过转义 25:"xy" [root@localhosttest]#grep-n'"'grep.txt#可以看到通过单引号引用时不需要转义字符 25:"xy"
[] :匹配[]内的字符中任意一个
[root@localhosttest]#grep-n[higk]grep.txt 15:xyxyxixixixinsnsnsnxixiyxyx 22:x,y,z,e,f,g,h
[c1-c2]:匹配字符范围中的一个字符 [root@localhosttest]#grep-ni[h-k]grep.txt 15:xyxyxixixixinsnsnsnxixiyxyx 22:x,h
[^S] ：匹配字符串内字符以外的字符
[root@localhosttest]#grep-ni[^aefjkxyz\'\"]grep.txt 10:rootxyxyxyxyxyxyx 15:xyxyxixixixinsnsnsnxixiyxyx 19:XsdfsfasfY 22:x,h
c\{n1,n2\} :前面的字符重复n1，n2次。注意是重复出现
[root@localhosttest]#grep-ni'xa\{3,5\}'grep.txt#重复a3-5次，这里-i忽略大小
7:xaaay
17:XaaaaY
21:XXXAAAAYYY
[root@localhosttest]#grep-ni'xy\{3,5\}'grep.txt#同样重复y3-5次
20:XXYYYAAAA
\<S ：匹配文中单词是以S开头的
[root@localhosttest]#grep-n'\<yx'grep.txt 2:yxay S\>：匹配文中单词是以S结尾的 [root@localhosttest]#grep-n'xyxyx\>'grep.txt 10:rootxyxyxyxyxyxyx 11:xyxyxyxyxyxyx 12:xyxyxyxyxyx
C* ：匹配前面的单个字符重复0到多次。即包不包含C字符无所谓
[root@localhosttest]#grep-n'axy*'grep.txt#是否包含y无所谓 4:yaxy 6:yyaaxxyyaa 8:axay
三、扩展正则表达式
egrep :grep命令的扩展命令。与grep�E作用一样。
C+ ：重复前面单个字符1到多次。即需包含前面这个字符
[root@localhosttest]#egrep-n'ay+'grep.txt#带有a开始，并且紧跟后面包含至少一个y 2:yxay 7:xaaay 8:axay 9:xaya
C? ：匹配0次或1次前面的字符C
[root@localhosttest]#egrep-n'ax?'grep.txt#以带有a开头后跟不跟x无所谓 2:yxay 4:yaxy 6:yyaaxxyyaa 7:xaaay 8:axay 9:xaya 17:XaaaaY 19:XsdfsfasfY
[root@localhosttest]#egrep-n'ax+'grep.txt#带有a开头后紧跟x或者多个x如6 4:yaxy 6:yyaaxxyyaa 8:axay
S|S ：匹配前面的字符串或后面字符串
[root@localhosttest]#egrep-n'aaxx|aaaa'grep.txt 6:yyaaxxyyaa 17:XaaaaY
(S) :匹配括号字符串S
[root@localhosttest]#egrep-n'(axx)|(xixi)'grep.txt 6:yyaaxxyyaa 15:xyxyxixixixinsnsnsnxixiyxyx
