字符匹配
正則表達(dá)式的關(guān)鍵之處在于確定你要搜索匹配的東西，如果沒有這一概念，Res將毫無用處。
每一個(gè)表達(dá)式都包含需要查找的指令，如表A所示。
|
Table A: Character-matching regular expressions
|
|
操作
|
解釋
|
例子
|
結(jié)果
|
|
.
|
Match any one character
|
grep .ord sample.txt
|
Will match “ford”, “l(fā)ord”, “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 “l(fā)ord”, “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.
|
重復(fù)操作符
重復(fù)操作符，或數(shù)量詞，都描述了查找一個(gè)特定字符的次數(shù)。它們常被用于字符匹配語法以查找多行的字符，可參見表B。
|
Table B: Regular expression repetition operators
|
|
操作
|
解釋
|
例子
|
結(jié)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”
|
posted on 2006-10-25 16:58
創(chuàng)建更好的解決方案 閱讀(201)
評(píng)論(0) 編輯 收藏 引用