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
| Symbol | Descriptions |
|---|---|
| . | replaces any character |
| ^ | matches start of string |
| $ | matches end of string |
| * | matches up zero or more times the preceding character |
| \ | Represent special characters |
| () | Groups regular expressions |
| ? | Matches up exactly one character |
| 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 |
| 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 |
These expressions tell us about the number of occurrences of a character in a string.
| Expression | Description |
|---|---|
| {n} | Matches the preceding character appearing 'n' times exactly |
| {n,m} | Matches the preceding character appearing 'n' times but not more than m |
| {n, } | Matches the preceding character only when it appears 'n' times or more |
These regular expressions contain combinations of more than one expression.
| Expression | Description |
|---|---|
| \+ | Matches one or more occurrence of the previous character |
| \? | Matches zero or one occurrence of the previous character |
The syntax for brace expansion is either a sequence or a comma separated list of items inside curly braces “{}”.
The starting and ending items in a sequence are separated by two periods “..”.
| Expression | Description |
|---|---|
| {a,b,c,d} | Matches the actual characters in the braces. Example: echo {a,b,c,d} |
| {a..z} | Matches a thru z. Example: echo {a..z} |
| {0..9} | Matches 0 thru 9. Example: echo {0..9} |
| 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 | \[\{\(\)\}\] | [{()}] |
| 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 |
| 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) |
| 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 |
| 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, including 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 |
| 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 | 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:]]+ | ‽,:〽⁆ |
NOTE: None of these are supported in JavaScript. In Ruby, beware of (?s) and (?m).
| 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)abc[ ]d | abc 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 |
| 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 |
| 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 |
| 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++ ?) |