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What is a regular expression? His usage? What are his characteristics? (with detailed explanation)

#1: A brief introduction to regular expressions:

  • Regular expressions describe the string arrangement pattern A custom syntax rule

  • Don't use regular expressions if the task can be accomplished using string processing functions

  • There are some Complex operations can only be completed with regular expressions

  • Regular expression is also called a pattern expression

  • Regular expression The formula is to compare, split, match, search, and replace the input string information by constructing a pattern with specific rules.

2. What is Regular expression

Example:

 */<img \s+src=\" . *?\" V/ alt="What is a regular expression? His usage? What are his characteristics? (with detailed explanation)" >/" 它就是正则表达式

A bunch of messy characters piled together, mysterious symbols, with strange meanings.

3. Learn what regular expressions can do

  • #Verify whether the username length is legal.

  • Verify email rules

  • Verify mobile phone number

  • Verify URL

  • BBS Editor

  • ##QQ Chat Expression

  • ##News Collector, (Thief Program)
4: Look at several characteristics of regular expressions

    Regular expression is also a string
  • A string composed of characters with special meaning
  • has certain writing rules and is also a pattern
  • is regarded as A derogatory term for the language, because it uses some special characters to write a string according to the rules to form a pattern-regular expression
  • If the regular expression does not match the function When used together, it is just an ordinary string. Only if the regular expression is amplified and used in a function can the role of the regular expression be brought into play
5 . PHP provides two sets of regular expression function libraries

    posix extended regular expression ereg
  • perl compatible regular expression preg
  • It is recommended to use per1 compatible regular expression function library
6. When learning regular expressions, there are two aspects to learn .

    How to write regular expression patterns
  • Learn the powerful processing functions of regular expressions
7. The syntax of regular expressions

    Regular delimiters
  • In regular expressions Atoms
  • Metacharacters (atom modifiers) of regular expressions
  • Pattern modifiers of regular expressions
  • Recommended learning: "
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