nonprinting characters, special characters, qualifier instance usages (regular expression character set 2)

non-printable characters

Character meaning

\CX matches the control character indicated by X. For example, \cm matches a control-m or carriage return. The value of x must be one of a-Z or a-Z. Otherwise, c is treated as a literal ' C ' character.

\f matches a page break. Equivalent to \x0c and \CL.

\ n matches a line break. Equivalent to \x0a and \CJ.

\ r matches a carriage return character. Equivalent to \x0d and \cm.

\s matches any whitespace character, including spaces, tabs, page breaks, and so on. equivalent to [\f\n\r\t\v].

\s matches any non-whitespace character. equivalent to [^ \f\n\r\t\v].

\ t matches a tab character. Equivalent to \x09 and \ci.

\v matches a vertical tab. Equivalent to \x0b and \ck.

Special characters

The so-called special character, is some special meaning of the character, such as the above said "*.txt" in the *, simply means that the meaning of any string. If you are looking for a file with * in the file name, you need to escape the *, which is preceded by a \. LS \*.txt. The regular expression has the following special characters.

Special Character description

$ matches the end position of the input string. If the Multiline property of the RegExp object is set, then $ also matches ' \ n ' or ' \ R '. To match the $ character itself, use \$.

() to mark the start and end positions of a sub-expression. Sub-expressions can be obtained for later use. To match these characters, use \ (and \).

* matches the preceding subexpression 0 or more times. To match the * character, use \*.

+ matches the preceding subexpression one or more times. to match the + character, use \+.

. Matches any single character except for the newline character \ n. To match, please use \.

[Marks the beginning of a bracket expression. to match [, please use \[.

? Matches the preceding subexpression 0 or one time, or indicates a non-greedy qualifier. to match? characters, use \?.

\ marks the next character as either a special character, or a literal character, or a backward reference, or octal escape character. For example, ' n ' matches the character ' n '. ' \ n ' matches line breaks. The sequence ' \ \ ' matches ' \ ', while ' \ (' then Match ' (".

^ matches the starting position of the input string, unless used in a square bracket expression, at which point it indicates that the character set is not accepted. To match the ^ character itself, use \^.

{The beginning of the tag qualifier expression.} To match {, use \{.

| Indicates a choice between the two items. to match |, please use \|.

The method of constructing a regular expression is the same as the method for creating a mathematical expression. That is, using a variety of meta-characters and operators to combine small expressions together to create larger expressions. A component of a regular expression can be a single character, a character set, a range of characters, a selection between characters, or any combination of all of these components.

Qualifier

Qualifiers are used to specify how many times a given component of a regular expression must appear to satisfy a match. There are 6 types of * or + or? or {n} or {n,} or {n,m}.

The *, +, and? Qualifiers are greedy because they match as many words as possible, but only after they are added with one? You can implement a non-greedy or minimal match.

The qualifiers for a regular expression are:

Character description

* matches the preceding subexpression 0 or more times. For example, zo* can match "z" and "Zoo". * Equivalent to {0,}.

+ matches the preceding subexpression one or more times. For example, ' zo+ ' can match "Zo" and "Zoo", but not "Z". + equivalent to {1,}.

? Matches the preceding subexpression 0 or one time. For example, "Do (es)?" can match "do" in "do" or "does".? Equivalent to {0,1}.

{n} n is a non-negative integer. Matches the determined 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} m and n are non-negative integers, where n <= m. Matches at least n times and matches up to M times. For example, "o{1,3}" will match the first three o in "Fooooood". ' o{0,1} ' is equivalent to ' O? '. Note that there can be no spaces between a comma and two numbers.