Linux Regular Expressions (awk, sed, grep)

Regular expressions: Regular expressions are a set of rules and methods that are defined for processing a large number of strings.

Regular expressions are widely used in almost all languages (e.g. Java, C, C + +, PHP, Python, etc.)

==================== Basic Regular =====================

^ Match with what to start with, ^w matches content starting with W

$ match with what ends, $w matches content ending with W

^$ Matching Blank lines

. Represents and can only represent any one character

\ escape character, such as \. Represents only.

* Repeat 0 or more of the preceding characters

. * Match All characters

Regular ==================== of ===================== strengthening

[ABC] matches any character in a character set

[^ABC] matches the content of any character that does not contain ^, the ^ in parentheses is the inverse
---------------need to use Egrep or sed-r if you do not use these two command brackets need to be escaped-----------

A{N,M} match repeats N to M times

A{n,} match repeats at least n times

A{n} match repeats n times

A{,M} match repeats up to M times
===================== Extended Regular =====================

+ denotes repeating "one or more" preceding characters

？ Represents repeating "0 or one" preceding characters

| means filtering multiple strings at the same time

() group filtering, referencing backward

Linux Regular Expressions (awk, sed, grep)