Shell script - regular expression

shell Script —— Regular expressions

One 、 Overview of regular expressions

1、 The concept of regular expression

It is usually used to judge , Used to check whether a string satisfies a certain format

Regular expressions are divided into basic regular expressions and extended regular expressions
It's not a tool program , It's a standard basis for string processing
Search with a single string 、 Match a series of strings that conform to a certain syntax rule
It consists of ordinary characters （a~z）, And special characters （ Also called “ Metacharacters ”） form
Ordinary characters include upper and lower case letters 、 Numbers 、 Punctuation and some other symbols
Metacharacters refer to special characters with special meaning in re regular expressions , It can be used to specify its leading characters （ The character before the metacharacter ） The occurrence pattern in the target object

2、 Supported by regular expressions Linux Text processing tools

#grep and awk Apply to extended regular expressions
grep -E
awk -r

3、 Common characters in basic regular expressions

Supported tools ：grep、egrep、sed、awk

4、 Extended regular expression metacharacter

5、 Regular Expression Matching E-mail Address

user name @

^([a-zA-Z0-9_-.+]+)@

subdomain

([a-zA-Z0-9_-.]+)

Top-level domain name

.([a-zA-Z]{2,5})$
a-zA-Z0-9_-.]+)

Top-level domain name

.([a-zA-Z]{2,5})$