1) Overview
Regular expressions (regular expression) describes a set of strings (pattern), it can be used to check whether a string containing the certain substring, replacing the sub-string matching or removed from a string meet a certain criteria substring and so on.
Regular expression pattern by a common text characters (e.g. characters a to z) and special characters (referred to as "meta character") thereof. Modes are described in the text search to match one or more strings. Regular expression as a template, a character pattern to match with the search string.
2) basic symbols :( are special characters to match the character itself, and needs in front of the escape character)
^ Represents the start position of the matched string (with the exception when in square brackets [], can be understood as the inverse of the parentheses represents a character string does not match)
$ Means match the end position of the string
* Indicates a match several times to zero
+ Indicates a match to a plurality of times (at least once)
? Represents zero or one match
Indicates that matches a single character
| Expressed as or, in the two take a
() Parentheses indicate match all characters in brackets
[] Brackets represents a range of characters as described in [0-9 az AZ] matching brackets
Braces {} for defining the number of matches as {n} {n characters which matches n, n} represents at least match the characters {n, m} indicates at least n, m at most
\ Escape character matching basic symbols as required as an escape character \ * * number indicates a match
\ W represent letters and numbers \ W non-alphanumeric
\ D represents a number \ D non-digital
3) non-printing characters
Character Description
\ Cx matches control characters specified by the x. For example, \ cM matches a Control-M or carriage return. The value of x must be AZ or az. Otherwise, c as a literal 'c' character.
\ F match for a website page. Equivalent to \ x0c and \ cL.
\ N Matches a newline. Equivalent to \ x0a and \ cJ.
\ R match a carriage return. Equivalent to \ x0d and \ cM.
\ S Matches any whitespace characters, including spaces, tabs, page breaks, and so on. Is equivalent to [\ f \ n \ r \ t \ v]. Note Unicode Regular Expressions will match full-width space character.
\ S Matches any non-whitespace characters. Is equivalent to [^ \ f \ n \ r \ t \ v].
\ T matches a tab. Equivalent to \ x09 and \ cI.
\ V matches a vertical tab. Equivalent to \ x0b and \ cK.
4) qualifier
Qualifier is used to specify the regular expression of a given component must appear many times to meet the match. There * or + or? Or {n} or {n,} or {n, m} total of six kinds.
* Matches the preceding subexpression zero or more times. For example, zo * matches "z" and "zoo". * Is equivalent to {0}.
+ Matches the preceding subexpression one or more times. For example, 'zo +' will match "zo" and "zoo", but can not match the "z". + Is equivalent to {1}.
? Matches the preceding subexpression zero or one. For example, "do (es)?" Matches "do", "does" in the "does", "doxy" in the "do". ? Is equivalent to {0,1}.
{N} n is a non-negative integer. Matching the determined n times. For example, 'o {2}' does not match the "Bob" in the 'o', but can match the "food" in the two o.
{N,} n is a non-negative integer. Matching at least n times. For example, 'o {2,}' does not match the "Bob" in the 'o', but it can match all o "foooood" in. 'O {1,}' is equivalent to 'o +'. 'O {0,}' is equivalent to 'o *'.
{N, m} m and n are non-negative integers, where n <= m. Match at least n times and match up to m times. For example, "o {1,3}" will match "fooooood" in the previous three o. 'O {0,1}' is equivalent to 'o?'. Please note that no spaces between the comma and the two numbers.