Regular Expressions

Creating Regular Expressions online, use this site.

Regex references

For more look here.

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

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 ABC* AAACC
? Once or none plurals? plural

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 [{()}] [{()}]

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 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 ABCD
\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)

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

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, 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

Examples

IP addresses

grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b"
$ nmcli | grep -oE "\b([0-9]{1,3}\.){3}[0-9]{1,3}\b"

10.10.10.32
0.0.0.0
10.10.10.0
169.254.0.0

Subdomains

grep -o '[^/]*\.<domain>\.com'

File extensions

grep -o '[^/]*\.js'

E-mail addresses

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9]))\.){3}(?:(2(5[0-5]|[0-4][0-9])|1[0-9][0-9]|[1-9]?[0-9])|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

Specific length

Line length

^.{16}$

Lines longer than x

.{22,}

Lines shorter than x

^.{0,31}$

Lines between x y

.{33,64}

URL list