java regular expression introduction to regular expression functions in PHP

Regular Expression (Regular Expression)
Regular expression system:
　1.POSIX
　2.Perl
The regex used in PHP is PCRE:
　NOTE: PCRE (Perl Compatible Regular Expressions, Perl Compatible Regular Expressions)
PCRE syntax:
　1. Delimiters
　　Must appear in pairs, you can use any character except 0-9a-zA-Z
　2. Atom
　1. The visible and invisible characters that the regular expression needs to match are all atoms
　2. A regular expression The expression contains at least one atom
　　3. When you need to match semantic symbols such as "(", "[", "^" and other semantic symbols, you need to use "" backslash to escape
　　 Atomic character:
　　 f matches the form feed character
　　n matches newline character
　　r matches carriage return character
　　t matches tab character
　　v matches vertical tab character
　3. Metacharacter
　　Escape character
　　^ matches the beginning of the string
　　$ matches the end of the string
　. match Any single character except "n"
　　 * Matches the previous subexpression 0 or more times
　　 + Matches the previous subexpression 1 or more times
　　? Matches the previous subexpression 0 or 1 times
　　　{ n} matches n times
　　{n,} matches n times or more
　　{n,m} matches at least n times and at most m times, (n<=m)
　[] The square brackets represent the atom table, the atoms in the middle The status is equal. When matching, match any character in the table
　　[^] and exclude the characters contained in the following atomic table.
　　(pattern) matches pattern and obtains this match. The numth matching reference.
　　(?:pattern) matches pattern but does not obtain this match
　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　ute quo=pattern) 　　　　　　　　　　　　　　　　　　　　　　　　utebilt (?=pattern) 　　　　　　　　　　　　　　　　　　　　　　　　　lainvicous (?=pattern)  Matches pattern but does not get this match Windows in Windows
　　(?<=pattern) Reverse affirmative search, non-obtaining matching. For example: (?<=My|Postgre)SQL can match SQL in MySQL, but cannot match 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 character other than a number. 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. Pattern modifier
　 i is not case-sensitive
　 m If there is a carriage return or line feed in this pattern, ^ and $ will match the beginning and end of each line.
　 s allows . to match n
　If you add a carriage return after the string, $ can still match it successfully. But after adding D, the carriage return at the end no longer matches
NOTE: Regular expressions are matched from left to right
Related functions:
preg_filter — perform a regular expression search and replace
preg_grep — return the matching pattern Array entries
　 preg_last_error — Returns the error code generated by the last PCRE regular expression
　 preg_match_all — Performs a global regular expression match
Preg_replace — Perform a regular expression search and replace using a callback
Preg_split — Split a string by a regular expression
The above has introduced the regular expression function in java regular expression in PHP, including the content of java regular expression. I hope it will be helpful to friends who are interested in PHP tutorials.