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Regular Expression Basics

Regular Expression Basics

Regular Expression Basics
.    Any character except newline
a   The character a
ab   The string ab
a|b    a or b
a*  0 or more a’s
\   Escapes a special character
Regular Expression Quantifiers
*  0 or more
+  1 or more
?  0 or 1
{2}  Exactly 2
{2, 5}  Between 2 and 5
{2,}  2 or more

Regular Expression Groups
(…)  Capturing group
(?:…)  Non-capturing group
\Y  Match the Y’th captured group
Regular Expression Character Classes
[ab-d]  One character of: a, b, c, d
[^ab-d]  One character except: a, b, c, d
[\b]  Backspace character
\d  One digit
\D  One non-digit
\s  One whitespace
\S  One non-whitespace
\w  One word character
\W  One non-word character
Regular Expression Assertions
^  Start of string
$  End of string
\b  Word boundary
\B   Non-word boundary
(?=…)  Positive lookahead
(?!…)  Negative lookahead
Regular Expression Flags
g  Global Match
i  Ignore case
m ^ and $ match start and end of line
Regular Expression Special Characters
\n  Newline
\r  Carriage return
\t  Tab
\0  Null character
\YYY  Octal character YYY
\xYY  Hexadecimal character YY
\uYYYY  Hexadecimal character YYYY
\cY  Control character Y
Regular Expression Replacement
$$  Inserts $
$&  Insert entire match
$`  Insert preceding string
$’  Insert following string
$Y  Insert Y’th captured group

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