Linux_grep and regular expressions

linux-basic-grep and regular expressions

Text Lookup command:

Grep,egrep,fgerp

grep: Searches text based on patterns and displays lines of text that conform to the pattern

Pattern: The matching criteria for the combination of meta-characters of the expression wildcards regular the text character

grep [option] PATTERN [FILE ...]

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To find the contents of a file that contains the root string

Parameters for grep

-I: Indicates ignoring case

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The case of the H letter is ignored in the

--color: The matching option is highlighted with highlighting

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-V: Reverse lookup, rows that are matched to are not displayed, rows that do not match are displayed

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-O: Displays only the strings that are matched, one row for each string

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-W: Absolute match

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@@@@@@@@@@@

The following are the definitions in the wildcard characters:

*: Any character of any length

？ : Any single character

[]: Within the specified range

[^]: outside the specified range

These definitions have been changed in the meta-character, note the distinction between

@@@@@@@@@@@

Regular Expressions: Regular expression

Metacharacters

.: Any single character

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Represents any two single characters between R and T, and all r/ft on the way are matched.

[]: matches any single character within the specified range

[^]: matches any single character outside the specified range

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The above character sets correspond to each other: numeric lowercase letters, uppercase punctuation, whitespace characters, all letters, all numbers and characters, these references need to be used in addition [], two []

Number of characters

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*: Match the characters in front of it Fuzhin Italian Times

For example, a*b means that there is an arbitrary number of a in front of B ( instead of A and B can have any character, A and B can have any character is a wildcard representation, not a meta-character representation ), that is, can match the preceding 0 a, 1 a,ab , the first 2 A,aab, and so on, so in addition to the number one and the last three, the other can be matched to.

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All red is the matching success.

. *: denotes arbitrary length of any character, greedy mode, as long as possible to match

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The a.*b means a begins, B ends, and any character in the middle

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Unable to match to SSADDB

It can be understood that the second and subsequent values in front are dead, must exist, and that the first character in front can be any number, which can be 0.

\?: Match its preceding character 1 or 0 times

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AaB cannot be fully matched

\{m,n\}: Matches its preceding character at least m times, more than n times

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\{1,\}: Indicates at least once, up to No limit

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Indicates that a minimum of 1 to 3 characters can occur between A and B

Location anchoring:

^: Anchor the beginning of the line, any content after this character must appear at the beginning of the line

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$: Anchor Line end. Any content preceding this character must appear at the end of the line

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^$: Blank Line

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^#$: Represents a row that matches a line that starts with #, with empty contents in the middle

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Represents the content that matches a number ending with a white space character

\< or \b: Anchor word, any character following it must appear as the first word

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\> or \b: anchors the ending, any character in front of which must appear as the tail of the word

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Not counted as part of the tail of the word

\<root\>: Exact Match root word

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Group:

\(\)

\ (ab\) *: This means AB can appear 0 or any time, back reference

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This article is from the "It_landscape" blog, make sure to keep this source http://huangyisan.blog.51cto.com/6925110/1690105

Linux_grep and regular expressions