Linux grep and Regular Expressions (notes)

grep print lines matching a pattern printing line matching mode

grep This command is used to query and match a string in a text file

Example grep ' root '/etc/passwd This command is used to match the line that contains the root string in the passwd file

[[email protected] ~]# grep ' root '/etc/passwd
Root:x:0:0:root:/root:/bin/bash
Operator:x:11:0:operator:/root:/sbin/nologin

Parameters

-I ignores case (that is, the case will be matched to match the string)

--color This parameter is to highlight the matching string (user-friendly)

-V Reverse match, meaning that the string displayed is not matched to the row

-O displays only the matched string

Regular Expressions REGEXP (REGular expression)

Metacharacters

. The decimal point is used to denote a single character

Number of characters

* An asterisk matches any number of previous characters

. * These two symbols combine to represent any length of any character

？ A question mark indicates that a previous character is matched one or 0 times

Linux grep and Regular Expressions (notes)