Detailed explanation of using regular operators

This time I will bring you a detailed explanation of the use of regular operators. What are the precautions when using regular operators? The following is a practical case, let's take a look.

The examples in this article describe the operators and descriptions in regular expressions. Share it with everyone for your reference, the details are as follows:

1. Ordinary characters

include all printing and non-printing characters that are not explicitly designated as metacharacters, such as Uppercase and lowercase letters, numbers, punctuation marks, etc.

2. Metacharacters

Metacharacters are characters that have special meanings in regular expressions. Because metacharacters have special meaning in regular expressions, these characters cannot be used to represent themselves and must be escaped by prefixing them with a backslash. The resulting escape sequence will match that character itself rather than Its special metacharacter meaning. For example, [ represents the beginning of a character set. If you want to match [ in a regular expression, you need to quote it like this: \[ to represent [ itself.

##{} to mark the beginning and end of a qualifier expression. To match { or }, use \{ or \. }.

^	matches the input character at the beginning of the string, unless used in a square bracket expression, in which case it means not Accept this character set. To match the ^ character itself, use \^.
$	Matches the end of the input string. If multiline matching is set, $ also matches '\n' or '\r'. To match the $ character itself, use \$.
()	Marks the beginning and end of a subexpression. Subexpressions can be obtained for later use. To match these characters, use [Math Processing Error].
?	Matches the preceding subexpression zero or one time, or specifies a non-greedy qualifier. To match the ? character, use \?.
*	Matches the preceding subexpression zero or more times. To match * characters, use \*.
+	Matches the preceding subexpression one or more times. To match the + character, use \+.
.	Matches any single character except the newline character \n. To match ., use \.
[]	Marks the beginning and end of a character set. To match [or], use [Math Processing Error].
\	Mark the next character as a special character , or a literal character, or a backward reference, or an octal escape character. For example, 'n' matches the character 'n'. '\n' matches a newline character. The sequence '\\' matches "\", while '\(' matches "(".
|	Specifies a choice between two items. To To match |, use \|.

##3. Non-printing characters

##\cxMatch the control character specified by x. For example, \cM matches a Control-M or carriage return character. The value of x must be one of A-Z or a-z. Otherwise, c is treated as a literal 'c' character. matches a form feed. Equivalent to \x0c and \cL. Matches a newline character. Equivalent to \x0a and \cJ. Matches a carriage return character. cM. #\t matches a tab character. Equivalent to \x09 and \cI. v matches a vertical tab character. Equivalent to \x0b and \cK. 4. Predefined characters . \d

	#\f
	#\r
Any character (may or may not match the end character \r\n)

Numbers, equivalent to [0-9]

\DNon-digits, equivalent to [^0-9]White space character, equivalent to [ \t\n\x0B\f\r]Non-whitespace characters, equivalent to [^\s] word characters, equivalent to [a-zA-Z_0 -9]##\W non-word characters, equivalent to [^\w]\bThe front or back boundary of a word\B represents a non-word boundary

5. POSIX characters

	\s
	\S
	\w

##[:alpha:] Any letter is equivalent to [a-zA-Z][:blank:]Space or tab character, equivalent to [\t][:cntrl:]ASCII control characters (ASCII 0 to 31, plus ASCII127) [:digit:]Any number, equivalent to [0- 9]##[:graph:][:lower :][:print:][:punct:] [:space:][:upper :][:xdigit:]

[:alnum:]	Any letter or number is equivalent to [a -zA-Z0-9]
Any printable character, but not including spaces
Any lowercase letter, equivalent to [a-z]
Any printable character
Any character that does not belong to [:alnum:] and [:cntrl:]
Any white space character, including spaces, is equivalent to [^\f\n\r\t\v]
Any uppercase letter is equivalent to [A-Z]
Any hexadecimal digit, Equivalent to [a-fA-F0-9]

6. Qualifier

*+?{n}{n,}{n,m}This is just to classify some operators used in regular expressions according to their different functions. It may not be accurate, just to illustrate the operators in regular expressions. .

Matches the preceding subexpression zero or more times. For example, zo* matches "z" and "zoo". * Equivalent to {0,}.
Matches the preceding subexpression one or more times. For example, 'zo+' matches "zo" and "zoo", but not "z". + is equivalent to {1,}.
Matches the preceding subexpression zero or one time. For example, "do(es)?" matches "do" or "do" in "does". ? Equivalent to {0,1}.
n is a non-negative integer. Match a certain number of n times. For example, 'o{2}' does not match the 'o' in "Bob", but it does match both o's in "food".
n is a non-negative integer. Match at least n times. For example, 'o{2,}' does not match the 'o' in "Bob", but it matches all o's in "foooood". 'o{1,}' is equivalent to 'o+'. 'o{0,}' is equivalent to 'o*'.
m and n are both non-negative integers, where n <= m. Match at least n times and at most m times. For example, "o{1,3}" will match the first three o's in "fooooood". 'o{0,1}' is equivalent to 'o?'. Please note that there cannot be a space between the comma and the two numbers.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

Recommended reading:

Detailed analysis of matching single characters using regular expressions

Detailed explanation of the use of regular metacharacters

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