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Regex Cheat Sheet

Lâm
・13 min read

Reference

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++ ?)

Character Class Operations

Class Operation Legend Example Sample Match
[…-[…]] .NET: character class subtraction. One character that is in those on the left, but not in the subtracted class. [a-z-[aeiou]] Any lowercase consonant
[…-[…]] .NET: character class subtraction. [\p{IsArabic}-[\D]] An Arabic character that is not a non-digit, i.e., an Arabic digit
[…&&[…]] Java, Ruby 2+: character class intersection. One character that is both in those on the left and in the && class. [\S&&[\D]] An non-whitespace character that is a non-digit.
[…&&[…]] Java, Ruby 2+: character class intersection. [\S&&[\D]&&[^a-zA-Z]] An non-whitespace character that a non-digit and not a letter.
[…&&[^…]] Java, Ruby 2+: character class subtraction is obtained by intersecting a class with a negated class [a-z&&[^aeiou]] An English lowercase letter that is not a vowel.
[…&&[^…]] Java, Ruby 2+: character class subtraction [\p{InArabic}&&[^\p{L}\p{N}]] An Arabic character that is not a letter or a number

Lookarounds

Lookaround Legend Example Sample Match
(?=…) Positive lookahead (?=\d{10})\d{5} 01234 in 0123456789
(?<=…) Positive lookbehind (?<=\d)cat cat in 1cat
(?!…) Negative lookahead (?!theatre)the\w+ theme
(?<!…) Negative lookbehind \w{3}(?<!mon)ster Munster

Inline Modifiers

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
(?m) Multiline mode
(except Ruby and JS) ^ and $ match at the beginning and end of every line
(?m)1\r\n^2$\r\n^3$ 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
(?x) Free-Spacing Mode mode
(except JavaScript). Also known as comment mode or whitespace mode
(?x) # this is a
# comment
abc # write on multiple
# lines
[ ]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 ^ and $ anchors are only affected by \n
(?^) PCRE 10.32+: unset modifiers Unsets ismnx modifiers

POSIX Classes

Character Legend Example Sample Match
[:alpha:] PCRE (C, PHP, R…): ASCII letters A-Z and a-z [8[:alpha:]]+ WellDone88
[:alpha:] Ruby 2: Unicode letter or ideogram [[:alpha:]\d]+ кошка99
[:alnum:] PCRE (C, PHP, R…): ASCII digits and letters A-Z and a-z [[:alnum:]]{10} ABCDE12345
[:alnum:] Ruby 2: Unicode digit, letter or ideogram [[:alnum:]]{10} кошка90210
[:punct:] PCRE (C, PHP, R…): ASCII punctuation mark [[:punct:]]+ ?!.,:;
[:punct:] Ruby: Unicode punctuation mark [[:punct:]]+ ‽,:〽⁆

Anchors and Boundaries

Anchor Legend Example Sample Match
^ Start of string or start of line depending on multiline mode. (But when [^inside brackets], it means "not") ^abc .* abc (line start)
$ End of string or end of line depending on multiline mode. Many engine-dependent subtleties. .*? the end$ this is the end
\A Beginning of string
(all major engines except JS)
\Aabc[\d\D]* abc (string...
...start)
\z Very end of the string
Not available in Python and JS
the end\z this is...\n...the end
\Z End of string or (except Python) before final line break
Not available in JS
the end\Z this is...\n...the end\n
\G Beginning of String or End of Previous Match
.NET, Java, PCRE (C, PHP, R…), Perl, Ruby
\b Word boundary
Most engines: position where one side only is an ASCII letter, digit or underscore
Bob.*\bcat\b Bob ate the cat
\b Word boundary
.NET, Java, Python 3, Ruby: position where one side only is a Unicode letter, digit or underscore
Bob.*\b\кошка\b Bob ate the кошка
\B Not a word boundary c.*\Bcat\B.* copycats

Character Classes

Character Legend Example Sample Match
[ … ] One of the characters in the brackets [AEIOU] One uppercase vowel
[ … ] One of the characters in the brackets T[ao]p Tap or Top
- Range indicator [a-z] One lowercase letter
[x-y] One of the characters in the range from x to y [A-Z]+ GREAT
[ … ] One of the characters in the brackets [AB1-5w-z] One of either: A,B,1,2,3,4,5,w,x,y,z
[x-y] One of the characters in the range from x to y [ -~]+ Characters in the printable section of the ASCII table.
[^x] One character that is not x [^a-z]{3} A1!
[^x-y] One of the characters not in the range from x to y [^ -~]+ Characters that are not in the printable section of the ASCII table.
[\d\D] One character that is a digit or a non-digit [\d\D]+ Any characters, inc-
luding new lines, which the regular dot doesn't match
[\x41] Matches the character at hexadecimal position 41 in the ASCII table, i.e. A [\x41-\x45]{3} ABE

More Quantifiers

Quantifier Legend Example Sample Match
+ The + (one or more) is "greedy" \d+ 12345
? Makes quantifiers "lazy" \d+? 1 in 12345
* The * (zero or more) is "greedy" A* AAA
? Makes quantifiers "lazy" A*? empty in AAA
{2,4} Two to four times, "greedy" \w{2,4} abcd
? Makes quantifiers "lazy" \w{2,4}? ab in abcd

More White-Space

Character Legend Example Sample Match
\t Tab T\t\w{2} T     ab
\r Carriage return character see below
\n Line feed character see below
\r\n Line separator on Windows AB\r\nCD AB
CD
\N Perl, PCRE (C, PHP, R…): one character that is not a line break \N+ ABC
\h Perl, PCRE (C, PHP, R…), Java: one horizontal whitespace character: tab or Unicode space separator
\H One character that is not a horizontal whitespace
\v .NET, JavaScript, Python, Ruby: vertical tab
\v Perl, PCRE (C, PHP, R…), Java: one vertical whitespace character: line feed, carriage return, vertical tab, form feed, paragraph or line separator
\V Perl, PCRE (C, PHP, R…), Java: any character that is not a vertical whitespace
\R Perl, PCRE (C, PHP, R…), Java: one line break (carriage return + line feed pair, and all the characters matched by \v)

Logic

Logic Legend Example Sample Match
| Alternation / OR operand 22|33 33
( … ) Capturing group A(nt|pple) Apple (captures "pple")
\1 Contents of Group 1 r(\w)g\1x regex
\2 Contents of Group 2 (\d\d)\+(\d\d)=\2\+\1 12+65=65+12
(?: … ) Non-capturing group A(?:nt|pple) Apple

More Characters

Character Legend Example Sample Match
. Any character except line break a.c abc
. Any character except line break .* whatever, man.
\. A period (special character: needs to be escaped by a \) a\.c a.c
\ Escapes a special character \.\*\+\?    \$\^\/\\ .*+?    $^/\
\ Escapes a special character \[\{\(\)\}\] [{()}]

Quantifiers

Quantifier Legend Example Sample Match
+ One or more Version \w-\w+ Version A-b1_1
{3} Exactly three times \D{3} ABC
{2,4} Two to four times \d{2,4} 156
{3,} Three or more times \w{3,} regex_tutorial
* Zero or more times A*B*C* AAACC
? Once or none plurals? plural

Characters

Character Legend Example Sample Match
\d Most engines: one digit
from 0 to 9
file_\d\d file_25
\d .NET, Python 3: one Unicode digit in any script file_\d\d file_9੩
\w Most engines: "word character": ASCII letter, digit or underscore \w-\w\w\w A-b_1
\w .Python 3: "word character": Unicode letter, ideogram, digit, or underscore \w-\w\w\w 字-ま_۳
\w .NET: "word character": Unicode letter, ideogram, digit, or connector \w-\w\w\w 字-ま‿۳
\s Most engines: "whitespace character": space, tab, newline, carriage return, vertical tab a\sb\sc a b
c
\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 *-+=)
\S One character that is not a whitespace character as defined by your engine's \s \S\S\S\S Yoyo

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