Regular Expressions in Php

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A brief introduction to regular expressions Expressions and their functions

Ø Understanding regular expressions

n Regular expression is a custom language rule that describes the string arrangement pattern

n If you can use string processing functions to complete the task, do not use regular expressions

n There are some complex operations, only Regular expressions can be used

n Regular expressions are also called a pattern expression

n Regular expressions are defined by having specific rules mode, perform operations such as comparison, segmentation, search, and replacement with the input string information.

Ø Characteristics of regular expressions

n Regular expression is also a string

n It consists of A string composed of strings with special meanings

n has certain writing rules and is also a pattern

n is regarded as a kind of programming Language: It uses some special characters to write a string according to the rules to form a pattern

Note: If the regular expression is not used with a function, it is a string. Only if the regular expression is used in a function can the real role of the regular expression be brought into play.

Ø PHP provides two sets of regular expression function libraries

PosixExtended regular expressions Functions starting with ereg_

perlCompatible with regular expressions## Functions starting with #preg_

It is recommended to use prel Compatible regular expression function library

The syntax of regular expression

Ø

Regular delimiter

Ø

Regular expression Atoms in

Ø

Metacharacters in regular expressions

Ø

Pattern modifiers for regular expressions

Regular delimiters

Regular delimiters are symbols used to declare the boundaries of regular expressions.

Commonly used boundary characters for regular expressions are /, in fact, any non-numeric letters and backslashes \ ## Any character other than # can be used as a regular expression boundary character.

Note: A complete regular expression has two boundary characters

n

One is a quotation mark boundary character of string type

''n

One is the boundary character of the regular expression

//(Generally use /)n

The whole is

'//'

The atoms of the regular expression

The smallest unit that makes up the regular expression That’s atoms

Regular numbers and letters are atoms, and most invisible characters are also atoms.

For example: \n\r\t...These translation characters are elements

Ø regular atoms

\d represents a number between 0-9

\D represents any character except 0-9

\s means matching any whitespace character including \n\r\t..

\S means except whitespace characters or translation Any character other than

\w represents any character among uppercase and lowercase characters, numbers and underscores

\W represents any character except uppercase and lowercase alphanumeric characters and underscores

Regular Metacharacters (atom modifiers) in expressions

Ø [] Atomic list

means selecting an atom in the specified character

For example :[5-9] means 5 6 7 8 9 The consecutive characters are allowed to be abbreviated as : [Start character -End character]

Ø [^] Exclusion list

For example: [^4 ] means except 4# Any character other than ## can

Ø

Use metacharacters (atom modifiers) to simulate atoms

\d [0 -9]                                                                                                                                          #          \S[^\n\r\t]

##\w[a-zA-Z0-9]                                                      

\W[^a-zA-Z0-9]Ø Atomic number modifier

? means that the previous atom appears 0 times or

1 times

## Indicates that the previous atom appears 1 or multiple times

*

Indicates that the previous atom appears 0 or multiple times

Ø Atomic number modification list

n {m,n} Indicates that the previous atom appears at least m times, Appears at most n times

n {m,} means that the preceding atom is at least Appears m times

n {m} Represents the previous atom onlyCan appear m times

Ø Atomic quantity modification list Simulation quantity modifier

? {0,1}

{1,}

* {0,}

Ø String boundary modifier

^ Represents content starting with the specified character

$ represents content ending with the specified character

Note:

^ $一 The first and the last indicate whether the content between the two is consistent with the precise modification

u If you want to use ^ and $ can match the beginning and end of each line, you need to use the simulation modifier m

##Ø | Select modifier

n

or similar to and

Ø () Mode unit

n

Change priority

n

To treat multiple atoms as one atom, you can use Atomic number modifier

n

Temporarily store the content in the matched brackets in memory

n

If you use() Just to simulate an atom using the atomic number modifier, you can use ?: at the beginning of the brackets to access the function of the existing content and improve efficiency

n

The contents of the brackets can be back-referenced with the help of functions

Ø

Metacharacters

. (dot) matches any character except \n

Regular expression emulation modifier

Ø i Ignore case

Ø x Ignore whitespace in regular expressions

Ø s Use .(metacharacter) to match \n

Ø S Accelerated Matching

Ø U Mode ChangeGreedy Mode

Change the greedy mode. The program defaults to the greedy mode, matching until the farthest end. We can use *? in the regular expression Use non-greedy mode when matching any characters

Note: If the program is in greedy mode at this time, after using U, Then the program changes to non-greedy mode. If the program is in non-greedy mode at this time, after using U, the program will become greedy mode

Regular expression function

Ø preg_grep() Returns the array unit that matches the pattern

@param1: Regular expression

@param2: Array to match

@param3: Optional parameter defaults to false. Set to true means to return the array element that is the opposite of the pattern match

Return value: Return the pattern match The array unit

Ø preg_match() Perform a regular matchIs it suitable for querying?

@param1：Regular expression

@param2： String to match

@param3：Optional parameter, return content matching the regular expression

Return value: Returns 1 on success, 0 on failure 1 represents the number of matches

Ø preg_match_all() Perform regular matching How many queries are suitable

@param1：Regular expression

@param2：String to match

@param3：Optional parameter, return content matching the regular expression

Return value: Returns the number of matches. If there is no matching band, return 0

Ø preg_split() Separate strings with regular expression

@param1: Regular expression

@param2：String to be separated

@param3：Return the separated array

Ø preg_replace() Perform regular expression replacement

@param1： To find the regular expression

@param2: What to replace

@param3 : Where to perform the replacement operation (array or string)

Return value: Return the replaced array or string

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