Linux Command Text Search tool grep, Egrep, Fgrep

Linux Command Text Search tool grep, Egrep, Fgrep

grep, the global search regular Expression_r (RE) and print out, is a powerful text search tool that uses regular expressions to search for text and print matching lines.

The grep family includes grep, Egrep, and Fgrep:egrep are the extensions of grep; Fgrep finds one or more rows in a file that matches the given string or phrase, does not support regular expressions

Syntax: grep [OPTIONS] PATTERN [FILE ...]

Common parameter Options

--color=auto: Highlighting the matched string

-C: Output only the number of matching rows

-I: Case insensitive

-O: Show only strings that can be matched to a pattern

-V: Show all rows that do not match

-e: Allow use of extended pattern matching

Meta-character set pattern matching, common basic meta characters have the following:

.: Match one character

*: matches any character

[]: Matches a character within a specified range

[^]: matches a character that is not within the specified range

[[: Upper:]]:[a-z]

[[: Lower:]]:[a-z]

[[:d igit:]]:[0-9]

[[: Alnum:]]:[0-9a-za-z]

[[: Space:]]: space or TAB key

[[: Alpha:]]:[a-za-z]

\(.. \): Tag matching characters

^: Anchoring the beginning of the line

$: Anchor Line End

\<: Anchor Word first

\>: Anchor ending

X\{m\}: Repeat character x,m times

X\{m,\}: Repeat character x, at least m times

x\{m,n\}: Repeat character x, at least m times, no more than n times

\ (\): Grouping

Back to reference

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

[2]

[3]

Example: Display a line of any single character or any character following the AB string in the Abc.log file in the/tmp/log/directory

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Displays the line of the letter X after AB in the Abc.log file in the/tmp/log/directory, and is case-insensitive

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Displays the line of any letter in the Abc.log file at the beginning of the/tmp/log/directory, and is case-insensitive

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Show lines ending in bash in the/etc/passwd file

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Displays the two-digit or three-digit number in the/etc/passwd file

The first of these methods

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The second method: note that the red border in the figure

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Displays lines that end with ' LISTEN ' followed by 0, one, or more whitespace characters in the ' Netstat-tan ' command result

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Add user bash, Testbash, basher, and Nologin user (Nologin the user's shell is/sbin/nologin), and then find the row in the/etc/passwd file that has the same user name as its shell name

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Displays the default shell and UID for root, CentOS, or User1 users on the current system (please create these users beforehand, if not present)

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Find a word in the/etc/rc.d/init.d/functions file (the middle of the word can be underlined) followed by a set of parentheses on the line

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Egrep command execution effect is similar to GREP-E, the syntax and parameters used can refer to the grep instruction above, the difference between grep is the method of interpreting the string, the following meta-character set

Syntax: Egrep [OPTIONS] PATTERN [FILE ...]

Common parameter Options

--color=auto: Highlighting the matched string

-C: Output only the number of matching rows

-I: Case insensitive

-O: Show only strings that can be matched to a pattern

-V: Show all rows that do not match

-e: Allow use of extended pattern matching

Common basic meta characters have the following:

.: Match one character

*: matches any character

[]: Matches a character within a specified range

[^]: matches a character that is not within the specified range

[[: Upper:]]:[a-z]

[[: Lower:]]:[a-z]

[[:d igit:]]:[0-9]

[[: Alnum:]]:[0-9a-za-z]

[[: Space:]]: space or TAB key

[[: Alpha:]]:[a-za-z]

\(.. \): Tag matching characters

^: Anchoring the beginning of the line

$: Anchor Line End

\<: Anchor Word first

\>: Anchor ending

X{M}: Repeat character x,m times

X{m,}: Repeat character x, at least m times

X{m,n}: Repeat character x, at least m times, no more than n times

(): Group

Back to reference

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

[2]

[3]

Note: Some characters are slightly different

Example: Compare to the examples listed above

Displays the two-digit or three-digit number in the/etc/passwd file

The first of these methods

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The second method of

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Displays lines that end with ' LISTEN ' followed by 0, one, or more whitespace characters in the ' Netstat-tan ' command result

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Add user bash, Testbash, basher, and Nologin user (Nologin the user's shell is/sbin/nologin), and then find the row in the/etc/passwd file that has the same user name as its shell name

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Displays the default shell and UID for root, CentOS, or User1 users on the current system (please create these users beforehand, if not present)

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Find a word in the/etc/rc.d/init.d/functions file (the middle of the word can be underlined) followed by a set of parentheses on the line

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Use echo to output a path, then egrep to find its path base name, and further use Egrep to remove its directory name

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Find the number between 1-255 in the ifconfig command execution result

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FGREP command: Retrieves a fixed string, which does not recognize a regular expression, is a quick search command.

Syntax: fgrep [option]pattern [FILE] ...

Common parameter options refer to grep or egrep

Example: Searching for lines with XY characters under/tmp/log/abc.log, including case

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This article is from the "10,000-hour Law" blog, be sure to keep this source http://daisywei.blog.51cto.com/7837970/1689526

Linux Command Text Search tool grep, Egrep, Fgrep