grep
1 grep [options] PATTERN [FILE...] 2 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 \B
The symbol \b 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)
| ? |
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 \n, 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]
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/