PHP regular expression summary, php regular expression summary_PHP tutorial

Summary of PHP regular expressions, summary of PHP regular expressions

1. Two commonly used regular functions in PHP

a.preg_match regular function, based on perl language

Syntax: preg_match(mode,string subject,array matches)

Description: mode parameter----regular module, that is, regular expression (grammar)
subject parameter----regular content
matches parameter---- regular result (obtained in the form of an array)

b.ereg regular function, based on POSIX (Unix, Script)

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

2. Elements included in regular expressions

a. Atoms (common characters: a-z A-Z 0-9, atom table, escape characters)
b. Metacharacters (characters with special functions, such as: #, *)
c. Pattern modifier (some system built-in characters i, m, S, U...)

3. "Atoms" in regular expressions

a.a-z A-Z _ 0-9 //The most common characters
b.(abc)(skd) //Unit symbol (a whole) enclosed in parentheses
c.[abcs][^abd] //Atom table enclosed in square brackets, ^ in the atom table represents exclusion or opposite content
d.Escape character
d contains all numbers [0-9]
D except all numbers [^0-9]
w contains all English characters [a-z A-Z 0-9]
W except all English characters [^a-z A-Z 0-9]
s carriage return, line feed, etc.
......

Note: Round brackets must be matched as a whole; square brackets can be matched as long as they are a subset (the content exists)

4. Regular expression metacharacters

* Match 0 times, 1 or more times of the previous content
. Matches 0 times of the content, 1 or more times, but does not include carriage returns and line feeds (referring to yourself, any content)
+ Match the previous content 1 or more times
? Matches 0 or 1 times of the previous content
| Select matching is similar to | in PHP (because this operator is a weak type, resulting in the most overall match in the front, similar to a word match)
^ Match the first content of the string
$ matches the content at the end of the string
b matches word boundaries, which can be spaces or special characters (with word delimiters, similar to spaces)
B matches content except with word boundaries (no word delimiters)
{m} matches the previous content repeated M times
{m,} matches the number of repetitions of the previous content greater than or equal to M times
{m,n} matches the number of repetitions of the previous content from M times to N times
( ) Merge the overall match and put it into the memory. You can use \1 \2... to obtain it in sequence (call the content put into the memory)

5. Order of operations

Still follows the operation rules from left to → right

Priority:
( ) Parentheses are the highest because they are processed in memory
*? + { } Repeat matching content followed by
^$b Boundary processing third
| Conditional processing fourth
Finally, the matching is calculated according to the order of operations

6. Mode modifier

Pattern modifier is a function that enhances and supplements regular expressions and is used outside of regular expressions. For example: /regular/U

Commonly used modifiers:
i Regular content is not case-sensitive when matching (default is case-sensitive)
m uses multi-line recognition matching when matching the first or last content
s will cancel the escape carriage return for single-line matching, such as when matching
x ignore whitespace in regex
A forces matching from scratch
D forces $ to match nothing at the end n
U prohibits greedy matching and only tracks the latest matching character and ends. Regular expressions commonly used in collection programs

7. Matching function

preg_match_all all matching functions
Syntax: preg_match_all ( string pattern, string subject, array matches [, int flags] )

Description: Sort the results so that $matches[0] is the number of all pattern matches
Purpose: intercept more detailed content, collect web pages, and analyze text

8. Replacement function

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

Description: Use regular expressions to replace relevant content, similar to the str_replace string replacement we learned before, but the function is stronger than it
Tips: 1. The replacement content can be a regular expression or an array regular expression
2. The replacement content can be solved by using the modifier e to replace the execution content
Purpose: Replace some more complex content, and can also be used for content conversion

9. Split function

preg_split regular cutting
Syntax: preg_split ( string pattern, string subject [, int limit [, int flags]] )
Note: Use regular expressions to cut related content, similar to the explode cutting function learned before, but explode can only cut in one way and has limitations.

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