Linux-grep command (description of regular expressions and options)

1. grep is a powerful text search tool that uses regular expressions to match.

Format is: Gerp option ' script ' file

2, Regular expression:

(1) of which characters: +,. , (), |,{}.

In datum mode: The meaning of ordinary characters, the need for escape \.

In extended mode: Take special meaning.

(2) Character class:

. : Matches any one by one characters.

[]: Matches any one by one characters within [].

[-]: any one by one characters in the match range.

[^-]: matches any one by one characters except this range.

[--]: matches any one by one characters in both ranges.

(3) Quantity qualifier:

。 : matches the character before it o/1 times.

+: Matches the preceding character 1/multiple times.

*: matches the preceding character 0/multiple times.

{n}: matches the preceding character N times.

{N,}: matches the preceding character at least n times.

{, n}: matches the characters before it up to N times. I can't use it on my computer.

{n,m}: matches the preceding character between n~m times.

(4) Position qualifier:

^: Matches the beginning of the line.

$: Matches the end of the line.

\<: Match the position where the word is opened.

\>: A position that matches the end of a word.

\b: Matches the start or end of a word.

\b: Matches the position of the beginning or end of a word (the middle position of the word).

3, grep options:

(1)-e: Supports extension of regular expressions. grep defaults to the baseline mode.

(2)-r: Recursive search file.

(3)-O: Outputs only the results that match.

(4)-V: Flip match, that is, the output does not match.

(5)-C: Output matching to a total of a few.

(6)-L: Output matching files.

(7)-I: Ignores case matching.

(8)-N: The line number is also output.