Data mining – Regular expressions syntax reference

Characters

The following table shows characters.

Table 1. Characters
Construct	Matches
x	The character x
\\	The backslash character
\0n	The character with octal value 0n (0 <= n <= 7)
\0nn	The character with octal value 0nn (0 <= n <= 7)
\0mnn	The character with octal value 0mnn (0 <= m <= 3, 0 <= n <= 7)
\xhh	The character with hexadecimal value 0xhh
\uhhhh	The character with hexadecimal value 0xhhhh
\t	The tab character ('\u0009')
\n	The newline (line feed) character ('\u000A')
\r	The carriage-return character ('\u000D')
\f	The form-feed character ('\u000C')
\a	The alert (bell) character ('\u0007')
\e	The escape character ('\u001B')
\cx	The control character corresponding to x

The following table shows character classes.

Table 2. Character classes
Construct	Matches
[abc]	a, b, or c (simple class)
[^abc]	Any character except a, b, or c (negation)
[a-zA-Z]	a through z or A through Z, inclusive (range)
[a-d[m-p]]	a through d, or m through p: [a-dm-p] (union)
[a-z&&[def]]	d, e, or f (intersection)
[a-z&&[^bc]]	a through z, except for b and c: [ad-z] (subtraction)
[a-z&&[^m-p]]	a through z, and not m through p: [a-lq-z](subtraction)

The following table shows predefined character classes.

Table 3. Predefined character classes
Construct	Matches
.	Any character
\d	A digit: [0-9]
\D	A non-digit: [^0-9]
\s	A whitespace character: [ \t\n\x0B\f\r]
\S	A non-whitespace character: [^\s]
\w	A word character: [a-zA-Z_0-9]
\W	A non-word character: [^\w]

The following POSIX character classes apply to US-ASCII only.

Table 4. POSIX character classes that apply to US-ASCII only
Construct	Matches
\p{Lower}	A lower-case alphabetic character: [a-z]
\p{Upper}	An upper-case alphabetic character:[A-Z]
\p{ASCII}	All ASCII:[\x00-\x7F]
\p{Alpha}	An alphabetic character:[\p{Lower}\p{Upper}]
\p{Digit}	A decimal digit: [0-9]
\p{Alnum}	An alphanumeric character:[\p{Alpha}\p{Digit}]
\p{Punct}	Punctuation: One of !"#$%&'()*+,-./:;<=>?@[\]^_`{\|}~
\p{Graph}	A visible character: [\p{Alnum}\p{Punct}]
\p{Print}	A printable character: [\p{Graph}\x20]
\p{Blank}	A space or a tab: [ \t]
\p{Cntrl}	A control character: [\x00-\x1F\x7F]
\p{XDigit}	A hexadecimal digit: [0-9a-fA-F]
\p{Space}	A whitespace character: [ \t\n\x0B\f\r]

The following java.lang.Character classes are of simple java character type.

Table 5. java.lang.Character classes of simple java character type
Construct	Matches
\p{javaLowerCase}	Equivalent to java.lang.Character.isLowerCase()
\p{javaUpperCase}	Equivalent to java.lang.Character.isUpperCase()
\p{javaWhitespace}	Equivalent to java.lang.Character.isWhitespace()
\p{javaMirrored}	Equivalent to java.lang.Character.isMirrored()

The following table shows classes for Unicode blocks and categories.

Table 6. Classes for Unicode blocks and categories
Construct	Matches
\p{InGreek}	A character in the Greek block (simple block)
\p{Lu}	An uppercase letter (simple category)
\p{Sc}	A currency symbol
\P{InGreek}	Any character except one in the Greek block (negation)
[\p{L}&&[^\p{Lu}]]	Any letter except an uppercase letter (subtraction)

The following table shows boundary matchers.

Table 7. Boundary matchers
Construct	Matches
^	The beginning of a line
$	The end of a line
\b	A word boundary
\B	A non-word boundary
\A	The beginning of the input
\G	The end of the previous match
\Z	The end of the input but for the final terminator, if any
\z	The end of the input

The following table shows greedy quantifiers.

Table 8. Greedy quantifiers
Construct	Matches
X?	X, once or not at all
X*	X, zero or more times
X+	X, one or more times
X{n}	X, exactly n times
X{n,}	X, at least n times
X{n,m}	X, at least n but not more than m times

The following table shows reluctant quantifiers.

Table 9. Reluctant quantifiers
Construct	Matches
X??	X, once or not at all
X*?	X, zero or more times
X+?	X, one or more times
X{n}?	X, exactly n times
X{n,}?	X, at least n times
X{n,m}?	X, at least n but not more than m times

The following table shows possessive quantifiers.

Table 10. Possessive quantifiers
Construct	Matches
X?+	X, once or not at all
X*+	X, zero or more times
X++	X, one or more times
X{n}+	X, exactly n times
X{n,}+	X, at least n times
X{n,m}+	X, at least n but not more than m times

The following table shows logical operators.

Table 11. Logical operators
Construct	Matches	Notes®
XY	X followed by Y	-
X \| Y	Either X or Y	Use this with care. In the regular-expression implementation of the Java runtime environment, the usage of alternations might cause a stack-overflow runtime-exception depending on the size of the text to be analyzed. A pattern that works fine on a short input text might still fail on a longer input text.
(X )	X, as a capturing group	Use capturing groups to assign matching subparts of a regular expression to annotation features. Capturing groups are numbered from left to right, beginning with 1. Group 0 matches the whole regular expression.

The following table shows the back reference.

Table 12. POSIX character classes (US-ASCII only)
Construct	Matches
\n	Whatever the n^th capturing group matched

The following table shows quotations.

Table 13. POSIX character classes (US-ASCII only)
Construct	Matches
\	Nothing, but quotes the following character
\Q	Nothing, but quotes all characters until \E
\E	Nothing, but ends quoting started by \Q

The following table shows special constructs.

Table 14. Special constructs (non-capturing)
Construct	Matches
(?:X)	X, as a non-capturing group
(?idmsux-idmsux)	Nothing, but turns match flags i d m s u x on - off
(?idmsux-idmsux:X)	X, as a non-capturing group with the given flags i d m s u x on - off
(?=X)	X, via zero-width positive lookahead
(?!X)	X, via zero-width negative lookahead
(?<=X)	X, via zero-width positive lookbehind
(?X)	X, via zero-width negative lookbehind
(?>X)	X, as an independent, non-capturing group
(?<!X)	Does not match if X occurs before the rule. For example, if X=Bill\s, the regular expression pattern (?<Bill\s) Ford matches only terms that match the string Ford and that are not preceded by the term Bill.

The following table shows the most important match flags.

Table 15. The most important match flags
Construct	Matches
(?i)	Case insensitive matching
(?d)	Enables UNIX lines mode
(?m)	Enables multiline mode
(?s)	Enables dotall mode
(?u)	Enables Unicode-aware case sensitivity
(?x)	Permits whitespace and comments in pattern. In this mode, whitespace is ignored, and embedded comments starting with # are ignored until the end of a line