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--- regex:cheat_sheet [2020/08/22 13:07] – [Inline Modifiers] 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 183: / Line 214: @@
 ^Modifier^Legend^Example^Sample Match^
 |(?i)|Case-insensitive mode (except JavaScript)|(?i)Monday|monDAY|
-|(?s)|DOTALL mode (except JS and Ruby). The dot (.) matches new line characters (\r\n).  Also known as "single-line mode" because the dot treats the entire input as a single line|(?s)From A.*to Z|From A to Z|
+|(?s)|DOTALL mode (except JS and Ruby). The dot (.) matches new line characters (\r\n).  Also known as "single-line mode" because the dot treats the entire input as a single line.|(?s)From A.*to Z|From A to Z|
-|(?m)|Multiline mode (except Ruby and JS) <nowiki>^ and $</nowiki> match at the beginning and end of every line|<nowiki>(?m)1\r\n^2$\r\n^3$</nowiki>|1|
+|(?m)|Multiline mode (except Ruby and JS) <nowiki>^ and $</nowiki> match at the beginning and end of every line.|<nowiki>(?m)1\r\n^2$\r\n^3$</nowiki>|1|
 |:::|:::|:::|2|
 |:::|:::|:::|3|
-|(?m)|In Ruby: the same as (?s) in other engines, i.e. DOTALL mode, i.e. dot matches line breaks|(?m)From A.*to Z|From A to Z|
+|(?m)|In Ruby: the same as (?s) in other engines, i.e. DOTALL mode, i.e. dot matches line breaks.|(?m)From A.*to Z|From A to Z|
-|(?x)|Free-Spacing Mode mode (except JavaScript).  Also known as comment mode or whitespace mode|(?x) # this is a  # comment|
+|(?x)|Free-Spacing Mode mode (except JavaScript).  Also known as comment mode or whitespace mode.|(?x)abc<nowiki>[ ]</nowiki>d|abc d|
-|:::|:::|:::|abc # write on multiple # lines
+|:::|Spaces must be in brackets|abc<nowiki>[ ]</nowiki>d| |
-|:::|:::|:::|<nowiki>[ ]</nowiki>d # spaces must be # in brackets|abc d|
 |(?n)|.NET, PCRE 10.30+: named capture only|Turns all (parentheses) into non-capture groups. To capture, use named groups.| |
 |(?d)|Java: Unix linebreaks only|The dot and the <nowiki>^ and $</nowiki> anchors are only affected by \n| |
-|(?^)|PCRE 10.32+: unset modifiers|Unsets ismnx modifiers| |
+|<nowiki>(?^)</nowiki>|PCRE 10.32+: unset modifiers|Unsets ismnx modifiers| |
+----
+===== Lookarounds =====
+^Lookaround^Legend^Example^Sample Match^
+|(?=…)|Positive lookahead|(?=\d{10})\d{5}|01234 in 0123456789|
+|<nowiki>(?<=…)</nowiki>|Positive lookbehind|<nowiki>(?<=\d)cat</nowiki>|cat in 1cat|
+|(?!…)|Negative lookahead|(?!theatre)the\w+|theme|
+|(?<!…)|Negative lookbehind|\w{3}(?<!mon)ster|Munster|
+----
+===== Character Class Operations =====
+^Class Operation^Legend^Example^Sample Match^
+|<nowiki>[…-[…]]</nowiki>|.NET: character class subtraction. One character that is in those on the left, but not in the subtracted class.|<nowiki>[a-z-[aeiou]]</nowiki>|Any lowercase consonant|
+|<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]]</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|<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++ ?)|