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.