Introduction to regular expression functions in PHP_PHP tutorial

Regular Expression

Regular expression system:
1. POSIX
2. Perl

The regex used in PHP is PCRE:
NOTE: PCRE (Perl Compatible Regular Expressions)

PCRE syntax:
1. Delimiter
Must appear in pairs, you can use anything except 0-9a-zA-Z Character
2. Atom
1. The visible and invisible characters that the regular expression needs to match are all atoms
2. A regular expression contains at least one atom
3. When it needs to match such as "(", "[", "^" and other semantic symbols need to be escaped with "" backslash

　 Atomic characters:
　 f matches the form feed character
n matches the newline character
r matches the carriage return character
t matches the tab character
v matches the vertical tab character

3. Metacharacters
Escape character
^ matches the beginning of the string
$ Matches the end of the string
Matches any single character except "n"

* Matches the previous subexpression 0 or more times
+ Matches the previous subexpression 1 time or multiple times
　? Match the previous subexpression 0 or 1 times

　{n} Match n times
　　{n,} Match n times or more than n times
　　{n, m} matches at least n times and at most m times, (n<=m)

　[] The square brackets represent the atom table, and the atom status in the middle is equal when matching. Characters
　[^] circumflex character, excludes characters contained in the following atom table.

　(pattern) Matches pattern and obtains this match.
　num refers to the obtained numth match. .


　(?:pattern) Match pattern but do not get this match

　(?=pattern) Positive pre-check, non-get matching, for example: windows(?= XP|7) can match windows in windows windows, cannot match windows in windows98
　(?<=pattern) Reverse positive pre-check, non-obtaining matching. For example: (?<=My|Postgre)SQL can match the SQL in MySQL, but cannot match the SQL in MSSQL
　 (?
　b matches word boundaries
　B matches characters other than word boundaries
　　🎜> d matches any number. Equivalent to [0-9]
D matches any non-digit character. Equivalent to [^0-9]

　s matches any whitespace character (including space, tab, form feed, etc.). Equivalent to [fnrtv]
S matches any non-whitespace character. Equivalent to [^fnrtv]
　
　w matches any number, letter, or underscore. Equivalent to [0-9a-zA-Z]
　W matches any character that is not a number, letter, or underscore. Equivalent to [^0-9a-zA-Z]

4. Mode modifier
i is not case sensitive
m If there is a carriage return or line feed in this mode, ^ and $ will Match the beginning and end of each line
s Let . match n
The carriage return is not ignored at the end. When there is a $ symbol at the end, if you add a carriage return after the matched string, $ can still match it successfully. But after adding D, the carriage return at the end no longer matches

NOTE: Regular expressions match from left to right


Related functions:
preg_filter — Perform a regular expression search and replace
preg_grep — Returns the array entries matching the pattern
preg_last_error — Returns the error code produced by the last PCRE regular expression
preg_match_all — Performs a global regular expression match
preg_match — Perform a regular expression match
Preg_quote — Escape regular expression characters
Preg_replace_callback — Perform a regular expression search and replace using a callback
Preg_replace — Perform a regular expression search and replace
preg_split — Split a string by a regular expression



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