国产av日韩一区二区三区精品,成人性爱视频在线观看,国产,欧美,日韩,一区,www.成色av久久成人,2222eeee成人天堂

Home Backend Development PHP Tutorial What does the character class '[^][]' do within a regular expression?

What does the character class '[^][]' do within a regular expression?

Nov 07, 2024 am 12:47 AM

What does the character class

Decoding the "[^][]" Character Class

Within the regex [(?:[^][]|(?R))*], the character class "[^][]" raises a peculiar question. Let's elucidate its meaning and dispel any ambiguity.

Meaning of "[^][]"

"[^][]" is a character class that matches any character except "[" and "]". This expression effectively excludes "[" and "]" from the set of matching characters.

Ambiguity Resolution

Some may argue that the sequence "[^]" is ambiguous, leading to a possible interpretation as an escape for "^" and a literal "]". However, PCRE, the regex engine utilized by preg_ functions, resolves this ambiguity. Since "[^]" is invalid in PCRE, the parsing interprets "]" as being enclosed within the character class, leaving the class to be closed by a subsequent "]".

Additional Contextual Rules

  • "[^]" can be written as "1" or "[^][]" without escaping the "[" or "]".
  • The inline "xx" modifier in PHP 7.3 eliminates the need for escaping even within character classes.
  • The first character in the character class determines the interpretation. "[^]]" matches any character followed by "]", while "2]" matches a non-"a" followed by "]".
  • In JavaScript, "[]" is defined as a token that never matches, while "[^]" matches any character.
  • The provided regex pattern [(?:[^][]|(?R))*] matches square brackets, allowing recursion for nested brackets.
  • A more efficient and reusable pattern for matching brackets is "([[^][](?:(?-1)[^][])* ])".

Conclusion

The character class "[^][]" simply excludes the characters "[" and "]" from matching. This interpretation is consistent across PCRE-compatible engines, including JavaScript (with some exceptions). By understanding these rules, programmers can effectively utilize this character class in their regex patterns.


  1. ?
  2. a ?

The above is the detailed content of What does the character class '[^][]' do within a regular expression?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undress AI Tool

Undress AI Tool

Undress images for free

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

How do I implement authentication and authorization in PHP? How do I implement authentication and authorization in PHP? Jun 20, 2025 am 01:03 AM

TosecurelyhandleauthenticationandauthorizationinPHP,followthesesteps:1.Alwayshashpasswordswithpassword_hash()andverifyusingpassword_verify(),usepreparedstatementstopreventSQLinjection,andstoreuserdatain$_SESSIONafterlogin.2.Implementrole-basedaccessc

How can you handle file uploads securely in PHP? How can you handle file uploads securely in PHP? Jun 19, 2025 am 01:05 AM

To safely handle file uploads in PHP, the core is to verify file types, rename files, and restrict permissions. 1. Use finfo_file() to check the real MIME type, and only specific types such as image/jpeg are allowed; 2. Use uniqid() to generate random file names and store them in non-Web root directory; 3. Limit file size through php.ini and HTML forms, and set directory permissions to 0755; 4. Use ClamAV to scan malware to enhance security. These steps effectively prevent security vulnerabilities and ensure that the file upload process is safe and reliable.

What are the differences between == (loose comparison) and === (strict comparison) in PHP? What are the differences between == (loose comparison) and === (strict comparison) in PHP? Jun 19, 2025 am 01:07 AM

In PHP, the main difference between == and == is the strictness of type checking. ==Type conversion will be performed before comparison, for example, 5=="5" returns true, and ===Request that the value and type are the same before true will be returned, for example, 5==="5" returns false. In usage scenarios, === is more secure and should be used first, and == is only used when type conversion is required.

How do I perform arithmetic operations in PHP ( , -, *, /, %)? How do I perform arithmetic operations in PHP ( , -, *, /, %)? Jun 19, 2025 pm 05:13 PM

The methods of using basic mathematical operations in PHP are as follows: 1. Addition signs support integers and floating-point numbers, and can also be used for variables. String numbers will be automatically converted but not recommended to dependencies; 2. Subtraction signs use - signs, variables are the same, and type conversion is also applicable; 3. Multiplication signs use * signs, which are suitable for numbers and similar strings; 4. Division uses / signs, which need to avoid dividing by zero, and note that the result may be floating-point numbers; 5. Taking the modulus signs can be used to judge odd and even numbers, and when processing negative numbers, the remainder signs are consistent with the dividend. The key to using these operators correctly is to ensure that the data types are clear and the boundary situation is handled well.

How can you interact with NoSQL databases (e.g., MongoDB, Redis) from PHP? How can you interact with NoSQL databases (e.g., MongoDB, Redis) from PHP? Jun 19, 2025 am 01:07 AM

Yes, PHP can interact with NoSQL databases like MongoDB and Redis through specific extensions or libraries. First, use the MongoDBPHP driver (installed through PECL or Composer) to create client instances and operate databases and collections, supporting insertion, query, aggregation and other operations; second, use the Predis library or phpredis extension to connect to Redis, perform key-value settings and acquisitions, and recommend phpredis for high-performance scenarios, while Predis is convenient for rapid deployment; both are suitable for production environments and are well-documented.

How do I stay up-to-date with the latest PHP developments and best practices? How do I stay up-to-date with the latest PHP developments and best practices? Jun 23, 2025 am 12:56 AM

TostaycurrentwithPHPdevelopmentsandbestpractices,followkeynewssourceslikePHP.netandPHPWeekly,engagewithcommunitiesonforumsandconferences,keeptoolingupdatedandgraduallyadoptnewfeatures,andreadorcontributetoopensourceprojects.First,followreliablesource

What is PHP, and why is it used for web development? What is PHP, and why is it used for web development? Jun 23, 2025 am 12:55 AM

PHPbecamepopularforwebdevelopmentduetoitseaseoflearning,seamlessintegrationwithHTML,widespreadhostingsupport,andalargeecosystemincludingframeworkslikeLaravelandCMSplatformslikeWordPress.Itexcelsinhandlingformsubmissions,managingusersessions,interacti

How to set PHP time zone? How to set PHP time zone? Jun 25, 2025 am 01:00 AM

TosettherighttimezoneinPHP,usedate_default_timezone_set()functionatthestartofyourscriptwithavalididentifiersuchas'America/New_York'.1.Usedate_default_timezone_set()beforeanydate/timefunctions.2.Alternatively,configurethephp.inifilebysettingdate.timez

See all articles