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--- regex:cheat_sheet [2020/08/25 19:32] – 192.168.1.1
+++ regex:cheat_sheet [2021/05/20 23:54] (current) – peter
@@ Line 1: / Line 1: @@
 ====== Regex - Cheat Sheet ======
+<code>
+Cheat Sheet
+Character classes
+. 	any character except newline
+\w \d \s 	word, digit, whitespace
+\W \D \S 	not word, digit, whitespace
+[abc] 	any of a, b, or c
+[^abc] 	not a, b, or c
+[a-g] 	character between a & g
+Anchors
+^abc$ 	start / end of the string
+\b 	word boundary
+Escaped characters
+\. \* \\ 	escaped special characters
+\t \n \r 	tab, linefeed, carriage return
+\u00A9 	unicode escaped ©
+Groups & Lookaround
+(abc) 	capture group
+\1 	backreference to group #1
+(?:abc) 	non-capturing group
+(?=abc) 	positive lookahead
+(?!abc) 	negative lookahead
+Quantifiers & Alternation
+a* a+ a? 	0 or more, 1 or more, 0 or 1
+a{5} a{2,} 	exactly five, two or more
+a{1,3} 	between one & three
+a+? a{2,}? 	match as few as possible
+ab|cd 	match ab or cd
+</code>
+----
 ===== Basic regex =====
@@ Line 26: / Line 57: @@
 |\s|.NET, Python 3, JavaScript: "whitespace character": any Unicode separator|a\sb\sc|a b c|
 |\D|One character that is not a digit as defined by your engine's \d|\D\D\D|ABC|
-|\W|One character that is not a word character as defined by your engine's \w|\W\W\W\W\W|*-+=)|
+|\W|One character that is not a word character as defined by your engine's \w|\W\W\W\W\W|<nowiki>*-+=)</nowiki>|
 |\S|One character that is not a whitespace character as defined by your engine's \s|\S\S\S\S|Yoyo|
@@ Line 202: / Line 233: @@
 ^Lookaround^Legend^Example^Sample Match^
 |(?=…)|Positive lookahead|(?=\d{10})\d{5}|01234 in 0123456789|
-|(?<=…)|Positive lookbehind|(?<=\d)cat|cat in 1cat|
+|<nowiki>(?<=…)</nowiki>|Positive lookbehind|<nowiki>(?<=\d)cat</nowiki>|cat in 1cat|
 |(?!…)|Negative lookahead|(?!theatre)the\w+|theme|
 |(?<!…)|Negative lookbehind|\w{3}(?<!mon)ster|Munster|
@@ Line 214: / Line 245: @@
 |<nowiki>[…-[…]]</nowiki>|.NET: character class subtraction.|<nowiki>[\p{IsArabic}-[\D]]</nowiki>|An Arabic character that is not a non-digit, i.e., an Arabic digit|
 |<nowiki>[…&&[…]]</nowiki>|Java, Ruby 2+: character class intersection. One character that is both in those on the left and in the && class.|<nowiki>[\S&&[\D]]</nowiki>|An non-whitespace character that is a non-digit.|
-|<nowiki>[…&&[…]]</nowiki>|Java, Ruby 2+: character class intersection.|<nowiki>[\S&&[\D]&&[^a-zA-Z]]	An non-whitespace character that a non-digit and not a letter.|
+|<nowiki>[…&&[…]]</nowiki>|Java, Ruby 2+: character class intersection.|<nowiki>[\S&&[\D]&&[^a-zA-Z]]</nowiki>|An non-whitespace character that a non-digit and not a letter.|
-|<nowiki>[…&&[^…]]</nowiki>|Java, Ruby 2+: character class subtraction is obtained by intersecting a class with a negated class|.<nowiki>[a-z&&[^aeiou]]</nowiki>|An English lowercase letter that is not a vowel.|
+|<nowiki>[…&&[^…]]</nowiki>|Java, Ruby 2+: character class subtraction is obtained by intersecting a class with a negated class.|<nowiki>[a-z&&[^aeiou]]</nowiki>|An English lowercase letter that is not a vowel.|
 |<nowiki>[…&&[^…]]</nowiki>|Java, Ruby 2+: character class subtraction|<nowiki>[\p{InArabic}&&[^\p{L}\p{N}]]</nowiki>|An Arabic character that is not a letter or a number|
 ----
+===== Other Syntax =====
+^Syntax^Legend^Example^Sample Match^
+|\K|Keep Out.  Perl, PCRE (C, PHP, R…), Python's alternate regex engine, Ruby 2+: drop everything that was matched so far from the overall match to be returned.|prefix\K\d+|12|
+|\Q…\E|Perl, PCRE (C, PHP, R…), Java: treat anything between the delimiters as a literal string. Useful to escape metacharacters.|\Q(C++ ?)\E|(C++ ?)|