Linux Text Search tool grep

Linux Text Search tool grep

grep function: Search for text based on patterns and display lines of text that conform to the pattern

Pattern: The matching condition of the wildcards regular of the expression with the text character

1 wildcard characters:

*: Any character of any length

?: any single character

[]: matches any single character within the specified range

[^]: contrary to []

2 Regular Expressions:

Metacharacters

.: Matches any single character

*: Number of matches (working in greedy mode, as long as possible),

Match any of its preceding characters

. *: Any character of any length

\?: Match its preceding character 1 or 0 times

\{m,n\}: Matches the preceding character at least m times, up to N times

\{1,\}: Match its preceding characters at least 1 times

Location anchoring:

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

$: Anchor line end, any content in front of this character must appear at the end of the row

^$: Blank Line

\< or \b: Any character following it must appear as the header of the word

\> or \b: Any character preceding it must appear as the tail of the word

Group

\ (string\): string as a set of characters, a whole, for a back reference

Back to reference

\1: Refers to the first opening parenthesis and all the contents of the corresponding closing parenthesis

\2

\3

grep Basic usage:

grep [OPTIONS] PATTERN [FILE ...]

OPTIONS

-I: Ignore case

--color: descriptor color of the searched word

-V: Show rows that are not matched by the pattern

-O: Displays only the string that is matched to

-A #: Indicates the line to which grep matches and the # line after it

-B #: Indicates the line to which grep matches and the previous # line

-C #: Indicates the line to which grep matches and the # lines before and after

-e: Match extended regular expression

Extended Regular Expression Egrep

Number of Matches

+: Match the characters in front of it at least 1 times

Group

(): In parentheses as a whole

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Linux Text Search tool grep