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Basic Regular expression summary

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These are the main regular expression characters that you should learn. For the full set of regular expression characters, see Regular expression summary. [Attribution: Much of this is copied from the Java API documentation. I'm rewriting it and will Sun's text soon.]

Character classes

Character classes provide a way to specify a set of characters. The set can be explicitly enclosed in []. The set can also be expressed by what must not be in it by beginning the set with a caret, "^". There are a number of predefined sets (eg, d, s, etc). The minus, "-", can be used to indicate a range of character values. Altho a character class matches only one character, a quantifier following it can be used to match multiple characters.
[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)
Predefined character classes
. Any character (may or may not match line terminators)
d A digit: [0-9]
D A non-digit: [^0-9]
s A whitespace character: [ x0Bf ]
S A non-whitespace character: [^s]
w A word character: [a-zA-Z_0-9]
W A non-word character: [^w]

Quantifiers (repeating the previous element)

Greedy quantifiers - Expand as much as possible
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
Reluctant quantifiers - Expand only if forced by later failure to match
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

Boundary matchers - Zero-width matches.

^ The beginning of a line. Very useful.
$ The end of a line. Very userful. ^$ matches all emtpy lines.
 A word boundary
B A non-word boundary
A The beginning of the input
G The end of the previous match
 The end of the input but for the final terminator, if any
z The end of the input


Logical operators
XY X followed by Y
X|Y Either X or Y
Grouping - Parentheses both group and create a numbered element that can be used later.
(X) X. This capturing group is remembered so it can be referenced later. Numbered starting at 1.
Nothing, but quotes the following character.
x The character x
The backslash character
The tab character ('u0009')
The newline (line feed) character ('u000A')
The carriage-return character ('u000D')
f The form-feed character ('u000C')

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