Summary of regular expressions in PHP

Source: Internet
Author: User
Tags ereg explode mixed modifier regular expression

two common regular functions in 1.PHP

A.preg_match regular functions, based on the Perl language

Syntax: Preg_match (mode,string Subject,array matches)

Description: Mode parameter----regular module, i.e. regular expression (syntax)

Subject parameters----Regular content

Matches parameter----Regular result (get the form of an array)

B.ereg regular functions, POSIX based (Unix, Script)

Syntax: Ereg (mode, string subject, array regs)

  2. Elements included in regular expressions

A. Atom (ordinary character: A-Z-A-Z 0-9, Atomic table, escape character)

B. metacharacters (characters with special features, such as: #, *)

C. Pattern modifier (System built-in partial characters I, M, S, U ...)

  3. "Atoms" in regular expressions

A.a-z-A-Z _ 0-9//most common characters

B. (ABC) (SKD)//cell notation enclosed in parentheses (a whole)

C.[ABCS][^ABD]///with square brackets containing atomic tables, ^ in atomic tables excluding or opposing content

D. Escape characters

D contains all the numbers [0-9]

D except for all numbers [^0-9]

W contains all English characters [A-Z-Z 0-9]

W except for all English characters [^a-z-Z 0-9]

s return, line change, etc.

......

Note: Parentheses must be a whole to match; Square brackets can be matched as long as they are subsets (content exists)

  4. Regular expression meta-characters

* 0 times 1 or more occurrences of the previous content

. Matches 0 times of content 1 or more times, but does not include carriage return line wrapping (refer to yourself, any content)

+ 1 or more times to match the previous content

? Match 0 or 1 times before the previous content

| Select match similar to PHP | (because this operation conforms to a weak type leading to the most overall match, similar to a word match)

^ Match String header content

$ Match String Tail content

b matches the word boundary, the boundary can be a space or a special match (with Word delimiters, similar spaces)

B matches unexpected content except word boundary (no word delimiter)

{m} matches the previous content with a repeat number of M times

{m,} repeat times greater than or m times to match previous content

{M,n} matches the repeat number of the previous content m times to N times

() Merge the overall match, and put in memory, you can use 1 2 ... Get (call into in-memory content) sequentially

  5. Order of operation

Still follow the rules of operation from left to right

Priority level:

() parentheses are highest because they are memory processed

* ? + {} Repeat match content second

^ $ b Border processing third

| Conditional Treatment IV

Finally, the match is calculated in order of operation

  6. Pattern modifier

A pattern modifier is a feature that is enhanced and supplemented for regular expressions and is used outside of the regular for example:/Regular/U

Common modifiers:

I regular content is not case-sensitive when matching (default is distinguished)

M uses multiple line recognition matching when matching first content or tail content

s the escape carriage return cancellation is for a single line matching such as. Match the time

x ignores whitespace in the regular

A force to start A match from scratch

D force $ match tail without any content n

U prohibits greedy matches from tracking only to a recent match and ends, regular expressions commonly used on the acquisition program

  7. Matching function

Preg_match_all All matching functions

Syntax: Preg_match_all (string pattern, string subject, array matches [, int flags])

Description: Sorts results to match the number of $matches [0] to all patterns

Uses: Intercepts the more detailed content, collects the webpage, analyzes the text

  8. Replacement function

Preg_replace Regular substitution function

Syntax: preg_replace (mixed pattern, mixed replacement, mixed subject [, int limit])

Description: Replace the relevant content with a regular expression, similar to the previously learned str_replace string substitution, but the function is stronger than it

Tip: 1, the replacement content can be a regular or can be an array of regular

2, replacement content can be replaced by the modifier e to address the implementation of the content

Use: Replace some of the more complex content, can also be used for the conversion of content

  9. Split function

Preg_split Regular Cutting

Syntax: Preg_split (string pattern, string subject [, int limit [, int flags]])

Note: Through regular expressions to cut related content, similar to the previous learned explode cutting function, but explode can only be cut in one way has limitations.

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