Grep/egrep Command collection in Linux

Syntax: grep [-cinvabc] ' word ' filename

-C: Print the number of lines that meet the requirements

-I: Ignore case

-N: Output with the same number of lines as required

-V: Print rows that do not meet the requirements

-A: followed by a number (with or without spaces), for example, –A2 to print the line that meets the requirements and the following two lines

-B: followed by a number, such as –B2, to print the line that meets the requirements and the above two lines

-C: followed by a number, such as –C2, to print the line that meets the requirements and two rows above and below

Examples:

Lines containing ' halt ' and two lines below this line are printed:

Grep-a2 ' Halt '/etc/passwd

The lines containing ' halt ' and the two lines above it are printed:

Grep-b2 ' Halt '/etc/passwd

The lines containing ' halt ' and the lines above and below the line are printed out:

Grep-c2 ' Halt '/etc/passwd

Filter out a line with a keyword and lose a travel number:

Grep-n ' Root '/etc/passwd

Filter lines that do not have a keyword, and enter the travel number:

Grep-nv ' Nologin '/etc/passwd

Filter out all rows that contain numbers:

grep ' [0-9] '/etc/inittab

Filter out all rows that do not contain numbers:

Grep-v ' [0-9] '/etc/inittab

Remove all lines that begin with ' # ':

Grep-v ' ^# '/etc/inittab

Remove all empty lines and lines that begin with ' # ':

Grep-v ' ^# '/etc/crontab |grep-v ' ^$ '

How to print a line that does not start with the English letter

grep ' ^[^a-za-z] ' test.txt

grep ' [^a-za-z] ' test.txt

Filter any character with repeating characters:

grep ' R.. O '/etc/passwd. Represents any one character

grep ' ooo* '/etc/passwd * represents 0 or more preceding characters

grep '. * '/etc/passwd |wc-l '. * ' denotes 0 or more arbitrary characters, and a blank line is included

Specify the number of occurrences of the character to filter:

grep ' o\{2\} '/etc/passwd

Filter one or more of the preceding characters:

Egrep ' o+ ' test.txt

Filter 0 or one of the preceding characters:

Egrep ' O? ' test.txt

Filter string 1 or String 2:

Egrep ' aaa|111|ooo ' test.txt

Applications in Egrep ():

Egrep ' R (oo) |                                                               (at) o ' test.txt () denotes a whole, for example (OO) + means 1 ' oo ' Or more ' oo '

Grep/egrep Command collection in Linux