Linux.CommanlineTool.grep

grep

grep [options] PATTERN [FILE...]
grep [options] [-e PATTERN | -f FILE] [FILE...]

 

1. grep的Regular Expression

Ref[1]

A): 匹配单字符

reg ex中基本的构建块是匹配单个字符的reg ex。大多数字符(包括数字和字母)都是匹配自己的reg ex。

B): 元字符

任何有特殊含义的元字符(metacharacter)都是被前导的反斜线(backslash, 即: )开始标识。

C): bracket expression

bracket expression是由[]包围的字符列表。这类表达式匹配列表中的任何一个字符(注意是 只匹配一个字符)。

如果^是字符列表中的第一个字符，则该表达式匹配任意一个不在列表中的字符。

例如：[0123456789] 匹配任意一个单一数字; [a-z] 匹配任意一个小写字母。

要匹配字符']', 则需要将']'放在字符列表的第一个位置。例如: []a-z]

类似的要匹配'^'需要将'^'放在字符列表中非第一的位置。例如: [a^]

类似的要匹配'-'需要将'-'放在字符列表中的最后的位置。 例如: [a-]

D): 命名的字符类别 (named classes of characters)

[:alnum:]  [:alpha:] [:cntrl:] [:digit:] [:graph:] [:lower:] [:print:] [:punct:] [:space:] [:upper:] [:xdigit:]

E): '.' 圆点匹配任意一个单一字符。 w 和 [[:alnum:]] 同义, W 和 [^[:alnum:]] 同义。

F): ^ 和 $ 分别匹配一行的开始和结尾的空字符串。例如:

$ grep ^line1 data 

匹配文件data中以"line1"开头的行。

G): < > 

The symbols < and > respectively match the empty string at the beginning and end of a word.

H):  B

The symbol  matches the empty string at the edge of a word, and B matches the empty string

provided it's not at the edge of a word.

I): 重复操作符 (repetition operator)

repetition operator

?	The preceding item is optional and matched at most once.
*	The preceding item will be matched zero or more times.
+	The preceding item will be matched one or more times.
{n}	The preceding item is matched exactly n times.
{n,}	The preceding item is matched n or more times.
{n,m}	The preceding item is matched at least n times, but not more than m times.

J): 匹配元字符 *

?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions ?, +, {, |, (, and )

K): reg ex的操作: concatenation, join

Two regular expressions may be concatenated; the resulting regular expression matches any string formed

by concatenating two substrings that respectively match the concatenated subexpressions.

Two regular expressions may be joined by the infix operator |; the resulting regular expression matches

any string matching either subex- pression.

Repetition takes precedence over concatenation, which in turn takes precedence over alternation.

A whole subexpression may be enclosed in parentheses to override these precedence rules.

The backreference , where n is a single digit, matches the substring previously matched by the nth parenthesized

subexpression of the regu- lar expression.

例如: $ grep "line1|line2" data

匹配包含"line1"或者"line2"的行。

2. grep的Example

[Todo]: Ref[2] 

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Reference

1. grep

http://unixhelp.ed.ac.uk/CGI/man-cgi?grep

2. Advanced Regular Expressions in Grep Command with 10 Examples – Part II

http://www.thegeekstuff.com/2011/01/advanced-regular-expressions-in-grep-command-with-10-examples-%E2%80%93-part-ii/