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Regular expressions usually contain alphabetic text (Literaltext) and metacharacters (metacharacter)

Alphabetical text refers to plain text such as "abcde" that matches any string that contains "abcde" in the string.

Metacharacters are more flexible in using general expressions to match all strings that conform to the rules of this expression.

C # regular expression syntax 1. Match a single character

[]-- Select a character match

Types supported in the middle: word characters ([ae]), non-word characters ([!,; @ # $*]), letter range ([Amurz]), numeric range ([0])

Eg. Regular expressions can match strings

[ae] ffectaffect,effect

(in this case, "[ae]" is a metacharacter and "ffect" is alphabetic text)

Note: 1. To match a hyphen in a character class, list the hyphen as * characters.

two。 You can include multiple character classes in a single regular expression.

Eg. [01] [0-9]: [0-5] [0-9] [ap] m can be used to match all times such as 12:59pm format

^-excludes certain characters (this is expressed in [] and can also indicate the beginning of a string)

Eg. Regular expressions can match strings and do not match strings.

M [^ a] tmet,mit,m&t. Mat

C # regular expression syntax II. Matching special characters

Special characters that can be used:

\ tMutual-match the configuration table character

\ rmusic-matches the hard return character

\ FML-match the feed character

\ nMurray-match newline character

Describes the metacharacters that represent the character class:

.-- matches any character except\ n (or any character in single-line mode)

\ w Mel-matches any word character (any letter or number)

\ Wmurf-matches any non-word character (any character except letters and numbers)

\ sMel-matches any white space characters (including spaces, line feeds, tabs, etc.)

\ Smurf-matches any non-white space character (except for spaces, newlines, tabs, etc.)

\ dMel-matches any numeric character (0,9 digits)

\ Dmurf-matches any non-numeric character (any character except 0,9)

Represents the character position in the string:

^-matches the beginning of a string (or the beginning of a line down in multiline mode).

$- matches the end of a string, either a character before the end of the string "\ n", or the end of a line in multiline mode.

\ Amure-matches the beginning of the string (ignores multiline mode)

\ Zmurf-matches the end of the string or the * * one character before the end of the string "\ n" (ignores multiline mode).

\ zMel-matches the end of the string.

\ Gmurf-matches the location where the current search starts.

\ bmusic-matches the boundary of the word.

\ Bmure-matches the non-boundary of the word.

Note:

1. The period character (.) is particularly useful. You can use it to represent any character.

Eg. Regular expressions can match strings

01.17.8401Grampact 17Compact 84JEI 01-17-84pr 011784pr 01.17.84

two。 You can use\ b to match the boundaries of words

Eg. Regular expressions can match strings and do not match strings.

\ blet\ bletletter,hamlet

3.\ An and\ z are useful in ensuring that a string contains an expression rather than anything else.

Eg. To determine whether the Text control contains the word "sophia" without any extra characters, line breaks, or whitespace.

\ Asophia\ z

4. Period character (.) Has a special meaning. To express the meaning of the alphabetic character itself, precede it with a backslash:\.

C # regular expression syntax III. Character sequence selected for matching

|-- choose one of two to play the Standard PvP match

Eg. Regular expressions can match strings

Col (o | ou) rcolor,colour

Note:\ b (bill | ted) and\ bbill | ted are different.

The latter can also match "malted" because\ b metacharacters only apply to "bill".

C # regular expression grammar IV. Quantifier matching

*-match 0 or more times

+-match one or more times

?-match 0 times or 1 time

{n}-- match exactly n times

{n,}-- match at least n times

{nrecom}-match at least n times, but not more than m times

Eg. Regular expressions can match strings

Brothers?brother,brothers

Eg. Regular expressions can match strings

\ bp\ d {3helmin5}\ b begins with p and ends with three or five digits

Note: you can also use a quantifier with () to apply the quantifier to the entire letter sequence.

Eg. Regular expressions can match strings

(The)? Schoolisbeautiful.schoolisbeautiful,Theschoolisbeautiful.

C # regular expression syntax 5. Identify regular expressions and greed

Some quantifiers are greedy (greedy). They will match as many characters as possible.

For example, the quantifier * matches 0 or more characters. Suppose you want to match any HTML tag in the string. You might use the following regular expression:

Existing string Aquantifiercanbegreedy

As a result, it matches all the quantifiercanbegreedy.

To solve this problem, we need to use a special non-greedy character "?" with quantifiers. So the expression changes as follows:

In this way, we can match, and.

? Can force quantifiers to match as few characters as possible? It can also be used in the following quantifiers:

*?-non-greedy quantifier *

+?-non-greedy quantifier +

Non-greedy quantifier?

{n}?-- non-greedy quantifier {n}

{n,}?-- non-greedy quantifier {n,}

{nmagnetic m}?-- the non-greedy quantifier {nmagnetic m}

VI. Capture and reverse reference

A capturegroup is like a variable in a regular expression. The capture group can capture the character pattern in the regular expression and refer to the changed pattern by the number or name after the regular expression.

()-- used to capture the string in it

\ number-referenced by number

Eg.

Regular expressions can match strings

(\ W) (\ w)\ 2\ 1abba

Note: 1. Backreferences are very effective for matching html tags such as tags in similar formats.

two。 By default, characters contained in parentheses are captured as long as parentheses are used. You can use the n option to disable this default behavior (described in more detail in Article 7), or add? In parentheses Eg. (?: sophia) or (? n:sophia) does not capture sophia at this time.

(?)\ KMUE-quote by name

Eg.

Regular expressions can match strings

(? \ W) abc\ kxabcx

Note: the format of using capture group in replacement mode is slightly different. Use $1, $2, etc., to reference capture by numeric value, and use names such as ${sophia} to reference capture group by name.

Setting options for regular expressions

Eg.

Stringstr= "sophia"

RegExobjRegEx=newRegEx ("(. *)")

Response.Write (objRegEx.Replace (str, "$2"))

IMurt-the matching performed is case-insensitive (the property in .net is IgnoreCase)

Mmure-specifies the multiline mode (the property in .net is Multiline)

NMurt-captures only groups that are named or numbered (the attribute in .net is ExplicitCapture)

Cmure-compiles regular expressions, which results in faster execution but slower startup (the property in .net is Compiled)

Smurf-specifies the single-line mode (the property in .net is SingleLine)

XMY-eliminates non-escaped white space characters and comments (property in .net is IgnorePatternWhitespace)

Rmure-search from right to left (the property in .net is RightToLeft)

-indicates disabled.

Eg. (? im-r:sophia) allows case-insensitive matching of sophia, using multiline mode, but disables right-to-left matching.

Note: 1.m affects how the starting metacharacter (^) and the ending metacharacter ($) are parsed. By default, ^ and $only match the beginning of the entire string, even if the string contains multiple lines of text. If m is enabled, they can match the beginning and end of each line of text.

2.s affects how the period metacharacter (.) is parsed. Usually a period can match all characters except newline characters. However, in single-line mode, the period can also match a newline character.

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