Metacharacters

---

The real power of regular expressions is in the use of metacharacters. Metacharacters allow you to construct expressions that match specific text patterns in an extremely flexible way.

Metacharacters and their meanings are listed below.

Metacharacter	Meaning
. (period)	Matches any one character no matter what the character is
?	Matches the character immediately before it either zero times or one time
*	Matches the character immediately before it any number of times including zero (the character may not be in the string at all)
+	Matches the character immediately before it one or more times (the character must be in the string at least once)
^	Indicates that the characters which follow are at the start of the string only
$	Indicates that the characters which precede it are at the end of the string
\d	Matches any decimal digit
\D	Matches any character that is not a decimal digit
\s	Matches a tab or space character
\S	Matches any character that is not a tab or a space
\w	Matches any letter, any digit, or the underscore character
\W	Matches any character which is not a letter, a digit, or the underscore
\	Escape character allowing the use of any of the metacharacters with their regular keyboard meaning. For instance, \. matches a period (.) in a regular expression. A period (.) matches any one character no matter what the character is.

Here are some examples which illustrate the use of metacharacters.

Regular Expression	Matches	Reason
up.own	uptown updown up own	Period (.) matches any character, even a space.
.exe	aexe 123exe 1exejfg	Period (.) matches any character, even a space.
\.exe	.exe	Backslash (\) tells NetTracker you are looking for a period, not using the period as a metacharacter.
ab?cdef	acdef abcdef abcdefg acdefghij	Question mark (?) matches both zero instances of b and one instance of b.
ntcgi\?johnswift	ntcgi?johnswift	Backslash (\) tells NetTracker you are looking for a question mark, not using the question mark as a metacharacter.
abc*defg	abdefg abcdefg abcdefghij abcccccdefg	Asterisk (*) matches the c zero or more times.
abc+defg	abcdefg abccdefg abcdefghij abcccdefghij	Plus (+) matches the c one or more times.
free	free freedom innisfree	By default, text is matched wherever it is found in the text string.
^free	free freedom	Caret (^) only matches the beginning of the text string.
free$	free innisfree	Dollar sign ($) only matches at the end of the text string.

In addition to metacharacters, you can use four other characters to indicate the relationships between various parts of the regular expression.

Character	Meaning
|	Tells NetTracker to match the text to the left of the pipe or the text to the right of the pipe
[ ]	Contains a set of characters and tells NetTracker to match any character within that set
( )	Indicates that the part of the expression that is within the parentheses is to be considered as one unit
^ (first character inside brackets)	Negates the set of characters in brackets so that text must contain a character at that point in the expression but it cannot be any of the characters inside the brackets

Here are some examples which illustrate the use of these characters.

Examples	Matches	Does Not Match	Reason
they (would|should)	they would they should they should have they would have		Parentheses and pipe indicate text must contain at least one instance of either would or should
[cz]one	cone zone	one	Brackets indicate either a c or a z must be present for a match
[^abc]xyz	dxyz mxyz	axyz bxyz cxyz xyz	Brackets indicate there must be a character at that point in the expression, but the caret indicates that character cannot be a, b, or c