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Posted on 6/18/2019 9:38:16 PM
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This post was last edited by Kongcicada on 2019-6-18 21:39
preface
When doing some data matching, rule qualification, and crawler analysis data in the project, we will use regular expressions. The following is a summary of the basic knowledge of regularity, all of which are study notes from the early years.
Text
#Regular expression basics
. Represents any single character other than \n
[ ] Character filtering
[^] Equivalent to non
| means or
() Change the priority of the operation.
* qualifier, which indicates that the previous expression occurs 0 or more times.
+ qualifier, indicating that the preceding expression must appear 1 or more times. It must appear at least once.
? qualifiers, indicating that the preceding expression must appear 0 or 1 times.
{n} qualifier, which qualifies the expression that precedes it must occur n times.
{n,} qualifier, which qualifies the preceding expression to occur at least n times.
{n,m} qualifier, which qualifies the preceding expression to occur at least n times and at most m times.
^ $ is the beginning and end of the string
\d is equivalent to [0-9]
\D is equivalent to [^0-9]
\s represents all those whitespace characters that are invisible
\S is all characters except \s.
\w Indicates [0-9a-zA-Z_]
\w is all the other characters except \w.
\b indicates the boundary of the word. (Assert, judge only, mismatch.) ）
=================================================
. Represents any single character other than \n
a.b
a,b
=========================================
[ ] Character filtering
a[0-9]b
a[a-z]b
a[0-9a-zA-Z]b
a1b
axb
aAb
a[^0-9]b means that only any single character other than 0123456789 can appear between a and b.
a[^0-9a-z]b
=====================================================
| means or
z|food due to| has a very low priority, so this expression can match z or food this expression does not match zood
(z|f)ood means zood or food
===========================================
() Change the priority of the operation.
Extraction group.
=======================================
* qualifier, which indicates that the previous expression occurs 0 or more times.
zoo* means zo zoo zoooooooooo
(zoo)* indicates zoozoo.......
a.*b stands for AB AADDDDB AFJDSKLF%$#@dsklfjdsklfjdsklfjb
================================================
+ qualifier, indicating that the preceding expression must appear 1 or more times. It must appear at least once.
a.+b
a9dfjsakl3824urnj324239feb
==================================================
? qualifiers, indicating that the preceding expression must appear 0 or 1 times.
a.? b
ab
axb
? Another function is to "end the greed mode". Regular expressions default to greed mode.
======================================================================
a[0-9]+b
a0b
a00b
a09b
a99999999999999999999b
========================== other qualifiers =====================
{n} qualifier, which qualifies the expression that precedes it must occur n times.
a[0-9]{10}b
a1234567899b
======================
{n,} qualifier, which qualifies the preceding expression to occur at least n times.
1[a-z]{3,}2
1axffdsafdsafdasfdsafdsafdsafdsfdsafsdfdsfdsfdsa2
========================================
{n,m} qualifier, which qualifies the preceding expression to occur at least n times and at most m times.
a[0-9]{3,7}b
a0000000b
===========================================
^ indicates the beginning of the string
$ indicates the end of the string.
^ and $ represent the two features of the string. One indicates the beginning feature and the other represents the end
^abc.*xyz$ ^abc122345xyz$
^abcdefg$ ^abcdefg
fdsfdsfxyz xyz$
===========================================
a[0-9]b
a\db
\dEquivalent to [0-9]
digital
\D [^0-9]
\s represents all those whitespace, invisible characters
a\s*b
ab
a
b
\S is all characters except \s.
=================================================
\w [0-9a-zA-Z_]
word means word character.
\w is all the other characters except \w.
\b indicates the boundary of the word. (Assert, judge only, mismatch.) ）
============================================
.
The following methods can indicate that any single character appears between abs.
a[\s\S]b
a[\d\D]b
a[\w\W]b
#Actual combat
1: Create a new console application
2: Paste the following code, you can test module by module
Epilogue
Regular expression online test The hyperlink login is visible.
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