Regular Expressions 101

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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

/
/
imxg

Test String

Code Generator

Language

Generated Code

const regex = /(?P<group_definition> \( (?P<options>[^\:\>\s\(\)]*[\:\>])? (?P<pattern> (?:[^\)\(]*(?R)*)* ) \) (?P<quantifier> (?:[\*\+\?])| (?: \{(?P<min>\d*) (?: , (?P<max>\d*)? )? \} ) )? )/img; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?P<group_definition> \\( (?P<options>[^\\:\\>\\s\\(\\)]*[\\:\\>])? (?P<pattern> (?:[^\\)\\(]*(?R)*)* ) \\) (?P<quantifier> (?:[\\*\\+\\?])| (?: \\{(?P<min>\\d*) (?: , (?P<max>\\d*)? )? \\} ) )? )', 'img') const str = `^(?P<line>(?P<junk>(?!(?:Message\\-ID:)\\s(?:\\<)|(?:&lt;)|(?:\\s))(?!(?:From:)\\s(?:\\<)|(?:&lt;)|(?:&quot;)|(?:["]))(?!(?:To:)\\s(?:\\<)|(?:&lt;)|(?:&quot;)|(?:["]))(?!(?:Reply\\-To:)\\s(?:\\<)|(?:&lt;)|(?:&quot;)|(?:["]))(?!(?:X\\-Sender:)\\s(?:\\<)|(?:&lt;)|(?:&quot;)|(?:["]))(?!(?:Return\\-Path:)\\s(?:\\<)|(?:&lt;)|(?:&quot;)|(?:["]))(?!(?:Received\\-SPF:))[^\\r\\n]*)(?P<wtf>(?:(?:\\"(?P<display_name>[^\\"\\r\\n]*)\\"\\s*)?\\b(?P<email>(?P<username>[A-Z0-9._%-]+)@(?P<domain_name>(?P<host>(?:[A-Z0-9.-]+\\.)*)?(?P<sld>[A-Z0-9.-]+)\\.(?P<tld>[A-Z]{2,4})))\\b)\\h*)(?P<trailing_data>[^\\r\\n]*))\$ (this is a group)? (another group (with a group inside)) and soem bogus test (and then another group) (?P<group_definition> (?P<pattern> \\( (?:[^\\)\\(]*(?R)*)* \\) ) (?P<quantifier> (?:[\\*\\+\\?])| (?: \\{(?P<min>\\d*) (?: , (?P<max>\\d*)? )? \\} ) )? )`; // 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