1 What is regex 2 Types of regex 3 Define BRE Patterns 4 Special Characters 5 Anchor Characters 6 The dot Character 7 Character Classes 8 Negating Character Classes 9 Using Ranges 10 Special Character Classes 11 The Asterisk 12 Extended Regular Expressions 12.1 The question mark 12.2 The Plus Sign 12.3 Curly Braces 12.4 Pipe Symbol 13 Grouping Expressions 14 Practical examples 14.1 Counting Directory Files 14.2 Validating E-mail Address

2. Regex Tutorial For Linux
In order to successfully work with the Linux sed editor and the awk command in your shell
scripts, you have to understand regular expressions or in short regex. Since there are many
engines for regex, we will use the shell regex and see the bash power in working with regex.
First, we need to understand what regex is, then we will see how to use it.
Table of Contents [hide]
1 What is regex
2 Types of regex
3 Define BRE Patterns
4 Special Characters
5 Anchor Characters
6 The dot Character
7 Character Classes
8 Negating Character Classes
9 Using Ranges
10 Special Character Classes
11 The Asterisk

3. 12 Extended Regular Expressions
12.1 The question mark
12.2 The Plus Sign
12.3 Curly Braces
12.4 Pipe Symbol
13 Grouping Expressions
14 Practical examples
14.1 Counting Directory Files
14.2 Validating E-mail Address
What is regex
For some people, when they see the regular expressions for the first time they said what are
these ASCII pukes !!
Well, A regular expression or regex, in general, is a pattern of text you define that a Linux
program like sed or awk uses it to filter text.
We saw some of those patterns when introducing basic Linux commands and saw how the ls
command uses wildcard characters to filter output.

4. Complete article
https://likegeeks.com/regex-tutorial-linux/