Regular Expressions 101

Save & Share

Flavor

  • PCRE2 (PHP >=7.3)
  • PCRE (PHP <7.3)
  • ECMAScript (JavaScript)
  • Python
  • Golang
  • Java 8
  • .NET 7.0 (C#)
  • Rust
  • Regex Flavor Guide

Function

  • Match
  • Substitution
  • List
  • Unit Tests

Tools

Sponsors
There are currently no sponsors. Become a sponsor today!
An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/
xmg

Test String

Code Generator

Language

Generated Code

const regex = /(?(DEFINE) (?<addr_spec> (?&local_part) @ (?&domain) ) (?<local_part> (?&dot_atom) | (?&quoted_string) | (?&obs_local_part) ) (?<domain> (?&dot_atom) | (?&domain_literal) | (?&obs_domain) ) (?<domain_literal> (?&CFWS)? \[ (?: (?&FWS)? (?&dtext) )* (?&FWS)? \] (?&CFWS)? ) (?<dtext> [\x21-\x5a] | [\x5e-\x7e] | (?&obs_dtext) ) (?<quoted_pair> \\ (?: (?&VCHAR) | (?&WSP) ) | (?&obs_qp) ) (?<dot_atom> (?&CFWS)? (?&dot_atom_text) (?&CFWS)? ) (?<dot_atom_text> (?&atext) (?: \. (?&atext) )* ) (?<atext> [a-zA-Z0-9!#$%&'*+\/=?^_`{|}~-]+ ) (?<atom> (?&CFWS)? (?&atext) (?&CFWS)? ) (?<word> (?&atom) | (?&quoted_string) ) (?<quoted_string> (?&CFWS)? " (?: (?&FWS)? (?&qcontent) )* (?&FWS)? " (?&CFWS)? ) (?<qcontent> (?&qtext) | (?&quoted_pair) ) (?<qtext> \x21 | [\x23-\x5b] | [\x5d-\x7e] | (?&obs_qtext) ) # comments and whitespace (?<FWS> (?: (?&WSP)* \r\n )? (?&WSP)+ | (?&obs_FWS) ) (?<CFWS> (?: (?&FWS)? (?&comment) )+ (?&FWS)? | (?&FWS) ) (?<comment> \( (?: (?&FWS)? (?&ccontent) )* (?&FWS)? \) ) (?<ccontent> (?&ctext) | (?&quoted_pair) | (?&comment) ) (?<ctext> [\x21-\x27] | [\x2a-\x5b] | [\x5d-\x7e] | (?&obs_ctext) ) # obsolete tokens (?<obs_domain> (?&atom) (?: \. (?&atom) )* ) (?<obs_local_part> (?&word) (?: \. (?&word) )* ) (?<obs_dtext> (?&obs_NO_WS_CTL) | (?&quoted_pair) ) (?<obs_qp> \\ (?: \x00 | (?&obs_NO_WS_CTL) | \n | \r ) ) (?<obs_FWS> (?&WSP)+ (?: \r\n (?&WSP)+ )* ) (?<obs_ctext> (?&obs_NO_WS_CTL) ) (?<obs_qtext> (?&obs_NO_WS_CTL) ) (?<obs_NO_WS_CTL> [\x01-\x08] | \x0b | \x0c | [\x0e-\x1f] | \x7f ) # character class definitions (?<VCHAR> [\x21-\x7E] ) (?<WSP> [ \t] ) ) ^(?&addr_spec)$/mg; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?(DEFINE) (?<addr_spec> (?&local_part) @ (?&domain) ) (?<local_part> (?&dot_atom) | (?&quoted_string) | (?&obs_local_part) ) (?<domain> (?&dot_atom) | (?&domain_literal) | (?&obs_domain) ) (?<domain_literal> (?&CFWS)? \\[ (?: (?&FWS)? (?&dtext) )* (?&FWS)? \\] (?&CFWS)? ) (?<dtext> [\\x21-\\x5a] | [\\x5e-\\x7e] | (?&obs_dtext) ) (?<quoted_pair> \\\\ (?: (?&VCHAR) | (?&WSP) ) | (?&obs_qp) ) (?<dot_atom> (?&CFWS)? (?&dot_atom_text) (?&CFWS)? ) (?<dot_atom_text> (?&atext) (?: \\. (?&atext) )* ) (?<atext> [a-zA-Z0-9!#$%&\'*+\\\/=?^_`{|}~-]+ ) (?<atom> (?&CFWS)? (?&atext) (?&CFWS)? ) (?<word> (?&atom) | (?&quoted_string) ) (?<quoted_string> (?&CFWS)? " (?: (?&FWS)? (?&qcontent) )* (?&FWS)? " (?&CFWS)? ) (?<qcontent> (?&qtext) | (?&quoted_pair) ) (?<qtext> \\x21 | [\\x23-\\x5b] | [\\x5d-\\x7e] | (?&obs_qtext) ) # comments and whitespace (?<FWS> (?: (?&WSP)* \\r\\n )? (?&WSP)+ | (?&obs_FWS) ) (?<CFWS> (?: (?&FWS)? (?&comment) )+ (?&FWS)? | (?&FWS) ) (?<comment> \\( (?: (?&FWS)? (?&ccontent) )* (?&FWS)? \\) ) (?<ccontent> (?&ctext) | (?&quoted_pair) | (?&comment) ) (?<ctext> [\\x21-\\x27] | [\\x2a-\\x5b] | [\\x5d-\\x7e] | (?&obs_ctext) ) # obsolete tokens (?<obs_domain> (?&atom) (?: \\. (?&atom) )* ) (?<obs_local_part> (?&word) (?: \\. (?&word) )* ) (?<obs_dtext> (?&obs_NO_WS_CTL) | (?&quoted_pair) ) (?<obs_qp> \\\\ (?: \\x00 | (?&obs_NO_WS_CTL) | \\n | \\r ) ) (?<obs_FWS> (?&WSP)+ (?: \\r\\n (?&WSP)+ )* ) (?<obs_ctext> (?&obs_NO_WS_CTL) ) (?<obs_qtext> (?&obs_NO_WS_CTL) ) (?<obs_NO_WS_CTL> [\\x01-\\x08] | \\x0b | \\x0c | [\\x0e-\\x1f] | \\x7f ) # character class definitions (?<VCHAR> [\\x21-\\x7E] ) (?<WSP> [ \\t] ) ) ^(?&addr_spec)$', 'mg') const str = ` Valid ------- first.last@iana.org 1234567890123456789012345678901234567890123456789012345678901234@iana.org "first\\"last"@iana.org "first@last"@iana.org "first\\\\last"@iana.org x@x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x23456789.x2 1234567890123456789012345678901234567890123456789012345678@12345678901234567890123456789012345678901234567890123456789.12345678901234567890123456789012345678901234567890123456789.123456789012345678901234567890123456789012345678901234567890123.iana.org first.last@[12.34.56.78] first.last@[IPv6:::12.34.56.78] first.last@[IPv6:::b3:b4] first.last@[IPv6:::] first.last@[IPv6:1111:2222:3333::4444:12.34.56.78] "first\\last"@iana.org user+mailbox@iana.org customer/department@iana.org customer/department=shipping@iana.org "Doug \\"Ace\\" L."@iana.org +1~1+@iana.org {_test_}@iana.org "[[ test ]]"@iana.org "test&#13;&#10; blah"@iana.org (foo)cal(bar)@(baz)iamcal.com(quux) cal(woo(yay)hoopla)@iamcal.com cal(foo\\@bar)@iamcal.com cal(foo\\)bar)@iamcal.com first(Welcome to&#13;&#10; the ("wonderful" (!)) world&#13;&#10; of email)@iana.org pete(his account)@silly.test(his host) c@(Chris's host.)public.example Invalid --------- first@...........com first.last@sub.do,com first\\@last@iana.org first.last .first.last@iana.org first.last.@iana.org "first"last"@iana.org """@iana.org first\\\\@last@iana.org Doug\\ \\"Ace\\"\\ Lovell@iana.org ()[]\\;:,><@iana.org test@. test@[123.123.123.123 test@123.123.123.123] `; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions