Special characters in regular expressions in php

Character/
Meaning: For characters, it usually indicates the literal meaning, indicating that the subsequent characters are special characters, not explained.
For example:/B/matches the character 'B'. By adding a backslash (/B/) before B, the character becomes a special character, indicating
Match the dividing line of a word.
Or:
For a few characters, it is generally described as special. It is pointed out that the subsequent characters are not special, but should be interpreted literally.
For example, * is a special character that matches any character (including 0 characters). For example,/a */indicates that it matches 0 or multiple a characters. To match the literal *, add a backslash before a. For example,/a */matches 'A *'.

Character ^
Meaning: The matched characters must be at the frontend.
For example,/^ A/does not match 'A' in "an A,", but matches 'A' in the top of "An '.

Character $
Meaning: similar to ^, it matches the last character.
For example,/t $/does not match 'T' in "eater", but matches 'T' in "eat '.

Character *
Meaning: match the first character of * 0 or n times.
For example,/bo */matches 'boooo' in "A ghost booooed" or 'B' in "A bird warbled", but does not match "Agoat g
Any character in runted.

Character +
Meaning: match the character before the plus sign once or n times. It is equivalent to {1 ,}.
For example,/a +/matches all 'A' in "candy" and "caaaaaaandy '.

Character?
Meaning: match? The first character is 0 or 1 time.
Example:/e? Le? /Match 'El' in "angel" and 'le' in "angle '.

Character.
Meaning: (decimal point) match all single characters except line breaks.
For example,/. n/matches 'any' and 'on' in "nay, an apple is on the tree", but does not match 'nay '.


Character (x)
Meaning: Match 'X' and record the matched value.
For example,/(foo)/matches and records 'foo' in "foo bar '. Matching substrings can be returned by the element [1],..., [n] In the result array.
Return, or be returned by RegExp object attributes.

Character x │ y
Meaning: Match 'X' or 'y '.
For example,/green │ red/matches 'green' in "green apple" and 'red' in "red apple '.

Character {n}
Meaning: Here n is a positive integer. Match the previous n characters.
For example:/a {2}/does not match 'A' in "candy,", but matches all 'A' and "caaandy" in "caandy. "The first two 'A '.

Character {n ,}
Meaning: Here n is a positive integer. Match at least n FIRST characters.
For example,/a {2,} does not match 'A' in "candy", but matches all 'A' in "caandy" and "caaaaaaandy'

Character {n, m}
Meaning: both n and m are positive integers. Match at least n characters at most before m.
For example,/a {}/does not match any character in "cndy", but matches the first two characters in "candy," 'A', "caandy ,"
'A' and "caaaaaaandy" are the first three 'A'. Note: Even if "caaaaaaandy" has many 'A ', but only match the first three 'A', that is, "aaa ".

Character [xyz]
Meaning: A one-character list that matches any character in the list. You can use a hyphen to indicate a character range.
For example, [abcd] is the same as [a-c. They match 'B' in "brisket" and 'C' in "ache '.

Character [^ xyz]
Meaning: A character complement, that is, it matches everything except the listed characters. You can use a hyphen to indicate the one-character range.
For example, [^ abc] is equivalent to [^ a-c]. They first match 'R' in "brisket" and 'H' in "chop '.

Character
Meaning: match a space (do not confuse with B)

Character B
Meaning: match the boundary of a word, such as a space (not to be confused)
For example,/bnw/matches 'no' in "noonday",/wyb/matches 'ly 'in "possibly yesterday '.

Character B
Meaning: match the non-dividing line of a word
For example,/wBn/matches 'on' in "noonday",/yBw/matches 'Ye 'in "possibly yesterday '.

Character cX
Meaning: X is a control character. Matches the control character of a string.
For example,/cM/matches control-M in a string.

Character d
Meaning: matching a number is equivalent to [0-9].
For example,/d/or/[0-9]/matches '2' in "B2 is the suite number '.

Character D
Meaning: match any non-number, which is equivalent to [^ 0-9].
For example,/D/or/[^ 0-9]/matches 'B' in "B2 is the suite number '.

Character f
Meaning: match a form character

CHARACTER n
Meaning: match a linefeed.

Character r
Meaning: match a carriage return.

Character s
Meaning: match a single white space character, including space, tab, form feed, line feed, equivalent to [fnrtv].
For example,/sw */matches 'bar' in "foo bar '.

Character S
Meaning: match a single character except the white space character, which is equivalent to [^ fnrtv].
For example,/S/w * matches 'foo' in "foo bar '.

Character t
Meaning: match a tab

Character v
Meaning: match a top Tab

Character w
Meaning: match all numbers, letters, and underscores, equivalent to [A-Za-z0-9 _].
For example,/w/matches "apple," 'A', ". 28," '5' and "3D." '3 '.

Character W
Meaning: match other characters except numbers, letters, and underscores, equivalent to [^ A-Za-z0-9 _].
For example:/W/or/[^ $ A-Za-z0-9 _]/matches '%' in "50% '.

CHARACTER n
Meaning: Here n is a positive integer. Match the n value of the last substring of a regular expression (left parentheses ).

For example:/apple (,) sorange1/matches 'apple, orange, cherry, peach. ". Here is a more complete example.
Note: If the number in the left parentheses is smaller than the number specified by n, n removes the octal escape of a row as the description.

Ooctal and xhex
Meaning: ooctal here is an escape value of octal, and xhex is a hexadecimal escape value, allowing ASCII code to be embedded in a regular expression

Appendix: The following table provides a complete list of metacharacters and their behavior in the context of a regular expression:

Character Description
\
Mark the next character as a special character, a literal character, a back reference, or an octal escape character. For example, 'n' matches the character "n ". '\ N' matches a line break. The sequence '\' matches "" and "\ (" matches "(".
^
Matches the start position of the input string. If the Multiline attribute of the RegExp object is set, ^ matches the position after '\ n' or' \ R.
$
Matches the end position of the input string. If the Multiline attribute of the RegExp object is set, $ also matches the position before '\ n' or' \ R.
*
Matches the previous subexpression zero or multiple times. For example, zo * can match "z" and "zoo ". * Is equivalent to {0 ,}.
+ Match the previous subexpression once or multiple times. For example, 'Zo + 'can match "zo" and "zoo", but cannot match "z ". + Is equivalent to {1 ,}.
?
Match the previous subexpression zero or once. For example, "do (es )? "Can match" do "in" do "or" does ".? It is equivalent to {0, 1 }.
{N}
N is a non-negative integer. Match n times. For example, 'O {2} 'cannot match 'O' in "Bob", but can match two o in "food.
{N ,}
N is a non-negative integer. Match at least n times. For example, 'O {2,} 'cannot match 'O' in "Bob", but can match all o in "foooood. 'O {1,} 'is equivalent to 'o + '. 'O {0,} 'is equivalent to 'o *'.
{N, m}
Both m and n are non-negative integers, where n <= m. Match at least n times and at most m times. Liu, "o {1, 3}" will match the first three o in "fooooood. 'O {0, 1} 'is equivalent to 'o? '. Note that there must be no space between a comma and two numbers.
?
When this character is followed by any other delimiter (*, + ,?, The matching mode after {n}, {n ,}, {n, m}) is not greedy. The non-Greedy mode matches as few searched strings as possible, while the default greedy mode matches as many searched strings as possible. For example, for strings "oooo", 'O ++? 'Will match a single "o", and 'O +' will match all 'O '.
.
Matches any single character except "\ n. To match any character including '\ n', use a pattern like' [. \ n.
(Pattern)
Match pattern and obtain this match. The obtained match can be obtained from the generated Matches set. The SubMatches set is used in VBScript and {CONTENT}… is used in JScript }... Attribute. To match the parentheses, use '\ (' or '\)'.
(? : Pattern)
Matches pattern but does not get the matching result. That is to say, this is a non-get match and is not stored for future use. This is useful when you use the "or" character (|) to combine each part of a pattern. For example, 'industr (? : Y | ies) is a simpler expression than 'industry | industries.
(? = Pattern)
Forward pre-query: matches the search string at the beginning of any string that matches the pattern. This is a non-get match, that is, the match does not need to be obtained for future use. For example, 'windows (? = 95 | 98 | NT | 2000) 'can match "Windows" in "Windows 2000", but cannot match "Windows" in "Windows 3.1 ". Pre-query does not consume characters, that is, after a match occurs, the next matching search starts immediately after the last match, instead of starting after the pre-query characters.
(?! Pattern)
Negative pre-query: match the search string at the start of any string that does not match Negative lookahead matches the search string at any point where a string not matching pattern. This is a non-get match, that is, the match does not need to be obtained for future use. For example, 'windows (?! 95 | 98 | NT | 2000) 'can match "Windows" in "Windows 3.1", but cannot match "Windows" in "Windows 2000 ". Pre-query does not consume characters. That is to say, after a match occurs, the next matching search starts immediately after the last match, instead of starting after the pre-query characters.
X | y
Match x or y. For example, 'z | food' can match "z" or "food ". '(Z | f) ood' matches "zood" or "food ".
[Xyz]
Character Set combination. Match any character in it. For example, '[abc]' can match 'A' in "plain '.
[^ Xyz]
Negative value character set combination. Match any character not included. For example, '[^ abc]' can match 'p' in "plain '.
[A-z]
Character range. Matches any character in the specified range. For example, '[a-z]' can match any lowercase letter in the range of 'A' to 'Z.
[^ A-z]
Negative character range. Matches any character that is not within the specified range. For example, '[^ a-z]' can match any character that is not in the range of 'A' to 'Z.
\ B
Match A Word boundary, that is, the position between a word and a space. For example, 'er \ B 'can match 'er' in "never", but cannot match 'er 'in "verb '.
\ B
Match non-word boundary. 'Er \ B 'can match 'er' in "verb", but cannot match 'er 'in "never '.
\ Cx
Match the control characters specified by x. For example, \ cM matches a Control-M or carriage return character. The value of x must be either a A-Z or a-z. Otherwise, c is treated as an original 'C' character.
\ D
Match a numeric character. It is equivalent to [0-9].
\ D
Match a non-numeric character. It is equivalent to [^ 0-9].
\ F
Match a form feed. It is equivalent to \ x0c and \ cL.
\ N
Match A linefeed. It is equivalent to \ x0a and \ cJ.
\ R
Match a carriage return. It is equivalent to \ x0d and \ cM.
\ S
Matches any blank characters, including spaces, tabs, and page breaks. It is equivalent to [\ f \ n \ r \ t \ v].
\ S
Match any non-blank characters. It is equivalent to [^ \ f \ n \ r \ t \ v].
\ T
Match a tab. It is equivalent to \ x09 and \ cI.
\ V
Match a vertical tab. It is equivalent to \ x0b and \ cK.
\ W
Match any word characters that contain underscores. It is equivalent to '[A-Za-z0-9 _]'.
\ W
Match any non-word characters. It is equivalent to '[^ A-Za-z0-9 _]'.
\ Xn
Match n, where n is the hexadecimal escape value. The hexadecimal escape value must be determined by the length of two numbers. For example, '\ x41' matches "". '\ X041' is equivalent to '\ x04' & "1 ". The regular expression can use ASCII encoding ..
\ Num
Matches num, where num is a positive integer. References to the obtained matching. For example, '(.)' matches two consecutive identical characters.
\ N
Identifies an octal escape value or a backward reference. If at least n subexpressions are obtained before \ n, n is a backward reference. Otherwise, if n is an octal digit (0-7), n is an octal escape value.
\ Nm
Identifies an octal escape value or a backward reference. If there are at least is preceded by at least nm obtained subexpressions before \ nm, then nm is backward reference. If at least n records are obtained before \ nm, n is a backward reference followed by text m. If none of the preceding conditions are met, if n and m are Octal numbers (0-7), \ nm matches the octal escape value nm.
\ Nml
If n is an octal number (0-3) and m and l are Octal numbers (0-7), the octal escape value nml is matched.
\ Un
Match n, where n is a Unicode character represented by four hexadecimal numbers. For example, \ u00A9 matches the copyright symbol (?).