Appendix H Regular Expressions

2017-11-03 09:05:02

A regular expression is a pattern of text that consists of ordinary characters (such as letters a through z) and special characters that are known as metacharacters . The pattern is used to describe one or more strings to match when searching a body of text. The regular expression acts as a template for matching a character pattern to the string that is being searched for.

The following table contains the complete list of metacharacters and their behavior in the context of a regular expression.

Character	Description
	Marks the next character as either a special character or a literal
^	Matches the beginning of input
$	Matches the end of input
*	Matches the preceding character zero or more times
+	Matches the preceding character one or more times
?	Matches the preceding character zero or one time
.	Matches any single character except a newline character
(pattern)	Matches pattern and remembers the match. The matched substring can be retrieved from the resulting Matches collection, using Item [0]...[n] To match the parentheses characters themselves , precede with slash-use ³ ³ or ³ ( ³)
(?:pattern)	Matches pattern but does not capture the match, that is, it is a noncapturing match that is not stored for possible later use. This is useful for combining parts of a pattern with the ³or ³ character (!). For example, ² anomol (?:y ! ies) ² is a more economical expression than ²anomoly ! anomolies ²
(?=pattern)	Positive lookahead matches the search string at any point where a string matching pattern begins. This is a noncapturing match, that is, the match is not captured for possible later use. For example ²Windows (?= 95 98 NT 2000 XP) ² matches ³Windows ³ in ³Windows XP ³ but not ³Windows ³ in ³Windows 3.1 ³
(?!pattern)	Negative lookahead matches the search string at any point where a string not matching pattern begins. This is a noncapturing match, that is, the match is not captured for possible later use. For example, ³Windows ( ? ! 95 98 NT 2000 XP ) ³ matches ³Windows ³ in ³Windows 3.1 ³ but does not match ³Windows ³ in ³Windows XP ³
xy	Matches either x or y
{n }	Matches exactly n times n must always be a nonnegative integer)
{n, }	Matches at least n times ( n must always be a nonnegative integer-note the terminating comma)
{n,m}	Matches at least n and at most m times ( m and n must always be nonnegative integers)
[xyz]	Matches any one of the enclosed characters ( xyz represents a character set)
[^xyz]	Matches any character not enclosed ( ^xyz represents a negative character set)
[a-z]	Matches any character in the specified range ( a-z represents a range of characters)
[^m-z]	Matches any character not in the specified range ( ^m-z represents a negative range of characters)
	Matches a word boundary, that is, the position between a word and a space
B	Matches a nonword boundary
d	Matches a digit character. Equivalent to [0 - 9]
D	Matches a nondigit character. Equivalent to [^ 0-9]
f	Matches a form-feed character
	Matches a newline character
	Matches a carriage return character
s	Matches any white space including space, tab, form-feed, and so on. Equivalent to ' [f v]"
	Matches a tab character ' [^f v]
v	Matches a vertical tab character
w	Matches any word character including underscore . Equivalent to ³ [A-Za-z0-9_] ³
W	Matches any nonword character. Equivalent to ³ [^A-Za-z0-9_] ³
.	Matches .
	Matches
{	Matches {
}	Matches }
\	Matches
[	Matches [
]	Matches ]
(	Matches (
)	Matches )
$ num	Matches num, where num is a positive integer. A reference back to remembered matches (note the $ symbol- differs from some Microsoft documentation)
	Matches n , where n is an octal escape value. Octal escape values must be 1, 2, or 3 digits long
uxxxx	Matches the ASCII character expressed by the UNICODE xxxx
xn	Matches n , where n is a hexadecimal escape value. Hexadecimal escape values must be exactly two digits long

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