Linux Text Processing tool 2-grep

grep Text Search Tool:

grep [options] pattern [file ...] --Pattern Mode: string, Regular expression

Matches the target text row by line , based on the user-specified pattern, and prints the line to which it matches .
Pattern Pattern: Filter conditions written by regular expression characters and text characters.

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#===============================

grep command Options

--color=auto: Coloring the text to match to a display

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-V: Shows rows that are not matched by pattern--take counter

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-I: Ignore character case

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-N: Show matching line numbers

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-C: Count the number of matching rows

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-O: Show only the matched string/display the searched string

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-Q: Silent mode, does not output any information-grep root/etc/passwd &>/dev/null

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-A #: After, # lines-Root after three lines

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-B #: Before, Front # line

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Small action: View the IP address that the company runs/occupies?

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-c #:context, front and back # lines

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-E: Implementing a logical or relationship between multiple options

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Grep–e ' Cat '-e ' dog ' file

-and the relationship

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-W: Matches entire word

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-E: Use ere-f: Equivalent to Fgrep, does not support regular expressions

#=====================================

Meta-character classification: character matching, number of matches, position anchoring, grouping

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Basic regular Expression meta-characters

1) Character matching:
. Match any single character

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[] matches any single character within the specified range

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[^] matches any single character outside the specified range

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[: Alnum:] Letters and numbers

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[: Alpha:] represents any English uppercase and lowercase characters, i.e. A-Z, A-Z

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[: Lower:] lowercase letter [: Upper:] Uppercase

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[: Blank:] white space characters (spaces and tabs)

[: Space:] Horizontal and vertical white space characters (more than [: blank:] contains a wide range)
[: Cntrl:] non-printable control characters (backspace, delete, alarm ...) ）
[:d igit:] decimal digits [: xdigit:] hexadecimal digits
[: Graph:] printable non-whitespace characters
[:p rint:] printable characters
[:p UNCT:] Punctuation

#===================================

What is the version number for version 6.9 and version 7.4? What if the version is 17?

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#======================================

Number of matches: used after the number of characters to be specified, to specify the number of occurrences of the preceding character
* match the preceding characters any time, including 0 greedy modes: match as long as possible

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. * Any character of any length --remember: Any character starting with r any length

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A * Access file name as a wildcard | "A *" ' A * ' is caused by a regular.

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Summary: grep * anaconda-ks.cfg default as a wildcard search for what? A * and anaconda-ks.cfg

is a start, if it is b* other will search anaconda-ks.cfg text, insurance, or add

"" ' Of course it doesn't matter if you use/root/anaconda-ks.cfg. | Add the quotes.

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Match the preceding characters 0 or 1 times------ -----the wireless loop matches multiple times

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\+ matches the characters in front of it at least 1 times

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\{n\} matches the preceding character n times

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\{m,n\} matches the preceding character at least m times, up to N times | Match multiple times

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\{,n\} matches the preceding character up to n times |0-5 0-5 .... Multiple matches

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\{n,\} matches the preceding character at least n times

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#===============================================

Position anchoring: positioning where it appears
^ Beginning of the line anchor, for the leftmost mode

$ line End anchor for the right side of the pattern
^pattern$ for pattern matching entire row
^$ Empty Line
^[[:space:]]*$ Blank Line
\< or \b The first anchor for the left side of the word pattern
\> or \b ending anchor; for the right side of the word pattern
\<pattern\> Match Whole Word

This article from "Linux-mylog" blog, declined reprint!

Linux Text Processing tool 2-grep