The Linux base command grep

grep :

Searches for text based on pattern (mode) and displays lines of text that conform to the pattern, without modifying the original file.

Usage: grep [options] ' pattern '/file #也可以利用管道进行匹配

-I ignore ignoring case

--colour the matched string with a color.

-V reverse lookup, showing rows that do not match pattern

-O displays only strings that are matched by the pattern

Regular Expressions REGular expressionWork in greedy mode and try to match as much as possible. Meta characters:

. : Matches any single character

[]: matches any single character within the range

[:d Igit:] number [: lower:] lowercase letter [: Upper:] Uppercase [:p UNCT:] punctuation [: space:] space [: Alpha:] All characters [: Alnum:] All letters and numbers

Usage: [[:d Igit:]]

[^]: matches any single character outside the range

number of matching characters:

*: matches the preceding character any time (including 0 times)

. *: Any character of any length

\？ : matches the preceding character 1 or 0 times, generally add \

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

\{1,\}: Matches the preceding character 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

^$: Blank Line

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

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

Grouping

\ (\) usage difference: ab* \ (ab\) *

Can back reference: he love his lover

She like her liker

He like his lover

\1: Represents the invocation of the first opening parenthesis and all the contents of the corresponding closing parenthesis.

\2: ...

The Linux base command grep