正则表达式

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
格式说明：
---------------
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”

第三部分：
----------------
锚
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/\Inserts “blah” at the beginning of the word

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