Regular Expressions for Linux Learning

The regular expression string represents different types of expressions with different degrees of rigor: Basic Regular Expressions and extended regular expressions,

Next let's take a look at the basic regular expression:

Frequently Used symbols

 

[; Alnum:] represents 0-9 A-Z A-Z

[: Alpha:] represents a-Z A-Z

[: Lower:] indicates a-z

[: Upper:] indicates a A-Z

[: Digit:] indicates 0-9

 

Before learning regular expressions, it is necessary to understand the use of grep.

 

Grep [-A] [-B] [-- color = auto] 'query string 'filename'

A can be followed by a number, which means after. In addition to listing this row, N industries will be listed later.

B can be followed by a number, which is the meaning of before. In addition to listing and modifying rows, the preceding n industries are listed.

 

 

 

 

 

 

 

Now, let's give an exercise regular expression in English:

"Open Source" is a good mechanic to develop programs.
Apple is my favorite food.
Football game is not use feet only.
This dress doesn' t fit me.
However, this dress is about $3183 dollars. ^ m
GNU is free air not free beer. ^ m
Her hair is very beauty. ^ m
I can't finish the test. ^ m
Oh! The soup taste good. ^ m
Motorcycle is cheap than car.
This window is clear.
The symbol '*' is represented as start.
Oh! My God!
The GD software is a library for drafting programs. ^ m
You are the best is mean you are the No. 1.
The world I like dog.
Google is the best tools for search keyword.
Goooooogle yes!
Go! Go! Let's go.
# I am vbird

(Download from laruence's private dish)

 

There are 22 rows in this file, and the bottom line is blank. Now let's start with a case study.

 

Case 1: Search for rows containing

Case 2

Search for rows that do not contain

 

Case 3: rows containing the 'or''

 

Case 4: Search for rows containing test and taste,

Careful analysis requirements: Both test and taste contain t s and T

 

 

Case 5: locate the rows that are not g in front of OO

 

Case 6: Search for rows containing numbers

 

Case 7: Search for rows starting with lowercase letters

Case 8: the end of the trip is the decimal point.

 

Case 10 search for blank lines

 

 

In the expression

. Represents any character

* Indicates that the previous character has been repeated for 0 or multiple times.

Then. * indicates that any character is repeated for any number of times, including 0

 

Explain the last knowledge point to limit the continuous character range {}

Case 11: Search for rows with 2-5 consecutive 0 rows

 

Basic Regular Expression characters

 

 

^ Word: string to be queried at the beginning of a row

Wrod $ string to be checked at the end of the row

* Repeat 0 to Infinitely multiple first characters

[LIST] Find the desired characters from the character set and

[^ List] returns a string range from the characters in the set.

\ {M, N \} consecutive m to N previous characters