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，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。
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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 |
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