Special characters in PHP regular expressions_PHP tutorial

Character/
Meaning: For characters, it usually means literal meaning, indicating that the following characters are special characters without explanation.
For example: /b/ matches the character 'b'. By adding a backslash in front of b, that is, /b/, the character becomes a special character, indicating the dividing line of matching a word.
or:
For several characters, it is usually stated that they are special, indicating that the following characters are not special and should be interpreted literally.
For example: * is a special character, matching any number of characters (including 0 characters); for example: /a*/ means matching 0 or more a. To match a literal *, precede a with a backslash; for example: /a*/ matches 'a*'.

Character^
Meaning: Indicates that the matching character must be at the front.
For example: /^A/ does not match the 'A' in "an A," but matches the first 'A' in "An A.".

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

Character*
Meaning: Match the character before * 0 or n times.
For example: /bo*/ matches the 'boooo' in "A ghost booooed" or the 'b' in "A bird warbled", but does not match any characters in "Agoat g
runted".

Character+
Meaning: Match the character before the + sign 1 or n times. Equivalent to {1,}.
For example: /a+/ matches the 'a' in "candy" and all the 'a's in "caaaaaaandy."

characters?
Meaning: Match the character before ? 0 or 1 times.
For example: /e?le?/ matches the 'el' in "angel" and the 'le' in "angle.".

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

Character (x)
Meaning: Match 'x' and record the matching value.
For example: /(foo)/ matches and records 'foo' in "foo bar." The matching substring can be returned by the elements [1], ...,[n] in the result array, or by the properties, ..., of the RegExp object.

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

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

Characters { n, } Meaning: n here is a positive integer. Matches at least n previous characters.
For example: /a{ 2, } does not match the 'a' in "candy", but matches all the 'a's in "caandy" and all the 'a's in "caaaaaaandy."

Character {n,m} Meaning: n and m here are both positive integers. Matches at least n and at most m previous characters.
For example: /a{ 1,3 }/ does not match any character in "cndy", but matches the 'a' in "candy," and the first two
'a' in "caandy," And the first three 'a's in "caaaaaaandy", note: even if there are many 'a's in "caaaaaaandy", only the first three 'a's, that is, "aaa" are matched.

Character [xyz]
Meaning: A list of characters, matching any character in the list. You can specify a range of characters using the hyphen -. For example: [abcd] is the same as [a-c]. They match the 'b' in "brisket" and the 'c' in "ache".

Character[^xyz]
Meaning: One-character complement, that is, it matches everything except the listed characters. You can use hyphens to indicate a range of characters. For example: [^abc] and [^a-c] are equivalent, they first match the 'r' in "brisket" and the 'h' in "chop.".

Characters
Meaning: Match a space (not to be confused with b)

Character b
Meaning: Match a word A dividing line, such as a space (not to be confused with) For example: /bnw/ matches the 'no' in "noonday", /wyb/ matches the 'ly' in "possibly yesterday."

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

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

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

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

Character f Meaning: Match a form character

Character n Meaning: Match a newline character

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