字符匹配
正则表达式的关键之处在于确定你要搜索匹配的东西,如果没有这一概念,Res将毫无用处。每一个表达式都包含需要查找的指令,如表A所示。Table A: Character-matching regular expressions
操作
解释
例子
结果
.
Match any one character
grep .ord sample.txt
Will match “ford”, “lord”, “2ord”, etc. in the file sample.txt.
[ ]
Match any one character listed between the brackets
grep [cng]ord sample.txt
Will match only “cord”, “nord”, and “gord”
[^ ]
Match any one character not listed between the brackets
grep [^cn]ord sample.txt
Will match “lord”, “2ord”, etc. but not “cord” or “nord”
grep [a-zA-Z]ord sample.txt
Will match “aord”, “bord”, “Aord”, “Bord”, etc.
grep [^0-9]ord sample.txt
Will match “Aord”, “aord”, etc. but not “2ord”, etc.
重复操作符
重复操作符,或数量词,都描述了查找一个特定字符的次数。它们常被用于字符匹配语法以查找多行的字符,可参见表B。Table B: Regular expression repetition operators
操作
解释
例子
结果
?
Match any character one time, if it exists
egrep “?erd” sample.txt
Will match “berd”, “herd”, etc. and “erd”
*
Match declared element multiple times, if it exists
egrep “n.*rd” sample.txt
Will match “nerd”, “nrd”, “neard”, etc.
+
Match declared element one or more times
egrep “[n]+erd” sample.txt
Will match “nerd”, “nnerd”, etc., but not “erd”
{n}
Match declared element exactly n times
egrep “[a-z]{2}erd” sample.txt
Will match “cherd”, “blerd”, etc. but not “nerd”, “erd”, “buzzerd”, etc.
{n,}
Match declared element at least n times
egrep “.{2,}erd” sample.txt
Will match “cherd” and “buzzerd”, but not “nerd”
{n,N}
Match declared element at least n times, but not more than N times
egrep “n[e]{1,2}rd” sample.txt
Will match “nerd” and “neerd”
正则表达式的关键之处在于确定你要搜索匹配的东西,如果没有这一概念,Res将毫无用处。每一个表达式都包含需要查找的指令,如表A所示。Table A: Character-matching regular expressions
操作
解释
例子
结果
.
Match any one character
grep .ord sample.txt
Will match “ford”, “lord”, “2ord”, etc. in the file sample.txt.
[ ]
Match any one character listed between the brackets
grep [cng]ord sample.txt
Will match only “cord”, “nord”, and “gord”
[^ ]
Match any one character not listed between the brackets
grep [^cn]ord sample.txt
Will match “lord”, “2ord”, etc. but not “cord” or “nord”
grep [a-zA-Z]ord sample.txt
Will match “aord”, “bord”, “Aord”, “Bord”, etc.
grep [^0-9]ord sample.txt
Will match “Aord”, “aord”, etc. but not “2ord”, etc.
重复操作符
重复操作符,或数量词,都描述了查找一个特定字符的次数。它们常被用于字符匹配语法以查找多行的字符,可参见表B。Table B: Regular expression repetition operators
操作
解释
例子
结果
?
Match any character one time, if it exists
egrep “?erd” sample.txt
Will match “berd”, “herd”, etc. and “erd”
*
Match declared element multiple times, if it exists
egrep “n.*rd” sample.txt
Will match “nerd”, “nrd”, “neard”, etc.
+
Match declared element one or more times
egrep “[n]+erd” sample.txt
Will match “nerd”, “nnerd”, etc., but not “erd”
{n}
Match declared element exactly n times
egrep “[a-z]{2}erd” sample.txt
Will match “cherd”, “blerd”, etc. but not “nerd”, “erd”, “buzzerd”, etc.
{n,}
Match declared element at least n times
egrep “.{2,}erd” sample.txt
Will match “cherd” and “buzzerd”, but not “nerd”
{n,N}
Match declared element at least n times, but not more than N times
egrep “n[e]{1,2}rd” sample.txt
Will match “nerd” and “neerd”
解决方案 »
- 读取文件
- 大家帮我debug System.NullReferenceException~~~谢谢啦
- 烦...........................烦迷糊我了.
- 奇怪:byte = byte + byte 报类型转换错???
- Winform窗体分为左右两部分,然后对左部分进行隐藏和显示的问题
- 百货购物商城中关于商品的一个难题
- 如何将DOC转换成HTML,请教高手!
- C#中如何在windows应用程序里获取文件路径
- 奇怪,我以前一直可以调试的,现在不能调试了
- 字符串转换
- 请问.Net开发的应用程序可以在linux或是别的环境中运行吗?
- 如何做ASP.NET服务器控件,想自己做个PAGECONTROL服务器控件(大家讨论)
锚是指它所要匹配的格式,如图C所示。使用它能方便你查找通用字符的合并。例如,我用vi行编辑器命令:s来代表substitute,这一命令的基本语法是:s/pattern_to_match/pattern_to_substitute/
Table C: Regular expression anchors
操作
解释
例子
结果
^
Match at the beginning of a line
s/^/blah /
Inserts “blah “ at the beginning of the line
$
Match at the end of a line
s/$/ blah/
Inserts “ blah” at the end of the line
\<
Match at the beginning of a word
s/\</blah/
Inserts “blah” at the beginning of the word
egrep “\<blah” sample.txt
Matches “blahfield”, etc.
\>
Match at the end of a word
s/\>/blah/
Inserts “blah” at the end of the word
egrep “\>blah” sample.txt
Matches “soupblah”, etc.
\b
Match at the beginning or end of a word
egrep “\bblah” sample.txt
Matches “blahcake” and “countblah”
\B
Match in the middle of a word
egrep “\Bblah” sample.txt
Matches “sublahper”, etc.
间隔Res中的另一可便之处是间隔(或插入)符号。实际上,这一符号相当于一个OR语句并代表|符号。下面的语句返回文件sample.txt中的“nerd” 和 “merd”的句柄:egrep “(n|m)erd” sample.txt
间隔功能非常强大,特别是当你寻找文件不同拼写的时候,但你可以在下面的例子得到相同的结果:egrep “[nm]erd” sample.txt当你使用间隔功能与Res的高级特性连接在一起时,它的真正用处更能体现出来。
一些保留字符
Res的最后一个最重要特性是保留字符(也称特定字符)。例如,如果你想要查找“ne*rd”和“ni*rd”的字符,格式匹配语句“n[ei]*rd”与“neeeeerd” 和 “nieieierd”相符合,但并不是你要查找的字符。因为‘*’(星号)是个保留字符,你必须用一个反斜线符号来替代它,即:“n[ei]\*rd”。其它的保留字符包括:^ (carat)
. (period)
[ (left bracket}
$ (dollar sign)
( (left parenthesis)
) (right parenthesis)
| (pipe)
* (asterisk)
+ (plus symbol)
? (question )
{ (left curly bracket, or left brace)
\ backslash
一旦你把以上这些字符包括在你的字符搜索中,毫无疑问Res变得非常的难读。比如说以下的PHP中的eregi搜索引擎代码就很难读了。eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*$",$sendto)你可以看到,程序的意图很难把握。但如果你抛开保留字符,你常常会错误地理解代码的意思。总结
在本文中,我们揭开了正则表达式的神秘面纱,并列出了ERE标准的通用语法。如果你想阅览Open Group组织的规则的完整描述,你可以参见:Regular Expressions,欢迎你在其中的讨论区发表你的问题或观点。