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

/
/
xu

Test String

Code Generator

Language

Generated Code

const regex = /(?x) # XML 1.0 well-formed validation implemented as a single regular expression. # dedicated to the public domain # Advanced features of regex engine used: Example: Alternative: # - utf8 matching expand UTF8 sequences in char classes # - utf8 \x{D800}-\x{DFFF} disallowed and max value make explicit if not enforced by regex engine # - fixed number of repetitions {3} expand (max 5) # - ignore whitespacd extended syntax (?x) remove spaces and comment lines # - ascii escaped hex characters \xhh alt escape notation # - unicode hex in character class \x{hhh} \uhhhh \Uhhhhhhhh or raw utf8 # - named capture group aka subroutine definition (?<xyz>) flatten + numbered # - function call \g<nm> flatten # - recursive function call for {element}, {kids} \g<element> programmatic check # - back reference (end tag matching) \k<tag> programmatic check # Tested with: # - PCRE2 # Implemented well-formedness constraints: # - PEs in Internal subset # - External Subset (by virtue of not loading externals) # - Element Type Match # - Legal Character # - In DTD # TODO: # - optimisation: make anon groups non capturing (?: ) # - optimisation: atomic groups, eager/lazy, etc # - unicode order character at start # - support character set other than assume engine is utf8 and ignore encoding... ^ (<\?xml (?<s> [\t\n\r\x20])+ version \g<s>*=\g<s>* ( "1\.0" | '1\.0' ) ( \g<s>+ encoding \g<s>*=\g<s>* ( "[A-Za-z][A-Za-z0-9._-]*" | '[A-Za-z][A-Za-z0-9._-]*' ) )? ( \g<s>+ standalone \g<s>*=\g<s>* ( "(yes|no)" | '(yes|no)' ) )? \g<s>* \?>)? (?<misc> \g<s>+ | (?<comment> <!-- ( -? [^\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}-] )* -->) | (?<procinst> <\? ( [MmLl] | (?<firstnoxml> [a-kn-wyzA-KN-WYZ_:] | [\xC0-\xD6\xD8-\xF6\xF8-\x{2FF}\x{370}-\x{37D}\x{37F}-\x{1FFF}] | [\x{200C}-\x{200D}\x{2070}-\x{218F}\x{2C00}-\x{2FEF}\x{3001}-\x{D7FF}\x{F900}-\x{FDCF}\x{FDF0}-\x{FFFD}\x{10000}-\x{EFFFF}] ) (?<latter> [XxMmLl] | (?<xmlatter> [0-9.-] | \g<firstnoxml> | [\xB7\x{300}-\x{36F}\x{203F}-\x{2040}] ) )* | [Xx] ( [XxLl] | \g<xmlatter> ) \g<latter>* | [Xx] [Mm] ( [XxMm] | \g<xmlatter> ) \g<latter>* | [Xx] [Mm] [Ll] \g<latter>+ ) ( \g<s>+ ( \? [^>\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}] | [^?\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}] )* \?? )? \?> ) )* ( <!DOCTYPE \g<s>+ (?<nm> ([XxMmLl] | \g<firstnoxml>) \g<latter>*) ( \g<s>+ (?<world> ( SYSTEM | (?<idpublic> PUBLIC \g<s>+ ('[\r\n\x20a-zA-Z0-9()+,.\x2F:=?;!*\#@$_%-]*' | "['\r\n\x20a-zA-Z0-9()+,.\x2F:=?;!*\#@$_%-]*" ) ) ) \g<s>+ ( " [^"\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]* " | ' [^'\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]* ' ) ) )? \g<s>* ( \[ ( <!ELEMENT \g<s>+ \g<nm> \g<s>+ ( EMPTY | ANY | \( \g<s>* \#PCDATA ( \g<s>* \) | ( (?<or> \g<s>* \| \g<s>*) \g<nm> )* \g<s>* \)\* ) | (?<kids> \( \g<s>* ( \g<nm> [?*+]? | \g<kids> ) ( ( \g<or> ( \g<nm> [?*+]? | \g<kids> ) )+ | ( \g<s>* , \g<s>* ( \g<nm> [?*+]? | \g<kids> ) )* ) \g<s>* \) [?*+]? ) ) \g<s>* > | <!ENTITY \g<s>+ ( ( % \g<s>+ )? \g<nm> \g<s>+ ( " ( [^"%&\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]+ # WFC: PEs in Internal Subset | % \g<nm> ; | (?<ref> & \g<nm> ; ) | (?<hash> &\# ( 0* ( 9 | 10 | 13 | 3[2-9] | [4-9][0-9] | [1-9][0-9][0-9][0-9]? | [1-47-9][0-9]{4} | 5[0-48-9][0-9]{3} | 55[0-1][0-9][0-9] | 552[0-8][0-9] | 5529[0-5] | 5734[4-9] | 573[5-9][0-9] | 57[4-9][0-9][0-9] | 6[0-46-9][0-9]{3} | 65[0-46-9][0-9][0-9] | 655[0-24-9][0-9] | 6553[0-36-9] | [1-9][0-9]{5} | 10[0-9]{5} | 110[0-9]{4} | 111[0-3][0-9]{3} | 11140[0-9][0-9] | 111410[0-9] | 111411[01] ) | x 0* ( [9aAdD] | [2-9a-f] [0-9a-fA-F] | [1-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] | [1-9a-cA-CeE] [0-9a-fA-F]{3} | [dD] [0-7] [0-9a-fA-F] [0-9a-fA-F] | [fF] [0-9a-eA-E] [0-9a-fA-F] [0-9a-fA-F] | [fF] [fF] [0-9a-eA-E] [0-9a-fA-F] | [fF] [fF] [fF] [0-9a-dA-D] | (10|[1-9a-fA-F]) [0-9a-fA-F]{4} ) ) ; ) )* " | ' ( [^'%&\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]+ # | % \g<nm> ; | \g<ref> | \g<hash> )* ' ) | \g<nm> \g<s>+ \g<world> ( \g<s>+ NDATA \g<s>+ \g<nm> )? | % \g<s>+ \g<nm> \g<s>+ \g<world> ) \g<s>* > | <!NOTATION \g<s>+ \g<nm> \g<s>+ ( \g<world> | \g<idpublic> ) \g<s>* > | <!ATTLIST \g<s>+ \g<nm> ( \g<s>+ \g<nm> \g<s>+ ( CDATA | ID | IDREF | IDREFS | ENTITY | ENTITIES | NMTOKEN | NMTOKENS | NOTATION \g<s>+ \( \g<s>* \g<nm> ( \g<or> \g<nm> )* \g<s>* \) | \( \g<s>* \g<latter>+ ( \g<or> \g<latter>+ )* \g<s>* \) ) \g<s>+ ( \#REQUIRED | \#IMPLIED | ( \#FIXED \g<s>+ )? (?<attvalue> " ( [^"<&\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]+ | \g<ref> | \g<hash> )* " | ' ( [^'<&\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]+ | \g<ref> | \g<hash> )* ' ) ) )* \g<s>* > | \g<procinst> | \g<comment> | % \g<nm> ; | \g<s>+ )* ] \g<s>* )? > )? \g<misc>* (?<element> < (?<tag> \g<nm>) ( \g<s>+ \g<nm> \g<s>*=\g<s>* \g<attvalue> )* \g<s>* ( \x2F > | > (?<data> >+ | ( >* ( [^><&\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]+ | [^\]<&\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}] ]? > )+ ) )? ( ( \g<element> | \g<ref> | \g<hash> | <!\[CDATA\[ >* ( [^>\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}]+ | [^\]\x00-\x08\x0B\x0C\x0E-\x1F\x{FFFE}\x{FFFF}] ]? > )* ]]> | \g<procinst> | \g<comment> ) \g<data>? )* < \x2F \k<tag> \g<s>* > ) ) \g<misc>* $ /u; // Alternative syntax using RegExp constructor // const regex = new RegExp('(?x) # XML 1.0 well-formed validation implemented as a single regular expression. # dedicated to the public domain # Advanced features of regex engine used: Example: Alternative: # - utf8 matching expand UTF8 sequences in char classes # - utf8 \\x{D800}-\\x{DFFF} disallowed and max value make explicit if not enforced by regex engine # - fixed number of repetitions {3} expand (max 5) # - ignore whitespacd extended syntax (?x) remove spaces and comment lines # - ascii escaped hex characters \\xhh alt escape notation # - unicode hex in character class \\x{hhh} \\uhhhh \\Uhhhhhhhh or raw utf8 # - named capture group aka subroutine definition (?<xyz>) flatten + numbered # - function call \\g<nm> flatten # - recursive function call for {element}, {kids} \\g<element> programmatic check # - back reference (end tag matching) \\k<tag> programmatic check # Tested with: # - PCRE2 # Implemented well-formedness constraints: # - PEs in Internal subset # - External Subset (by virtue of not loading externals) # - Element Type Match # - Legal Character # - In DTD # TODO: # - optimisation: make anon groups non capturing (?: ) # - optimisation: atomic groups, eager\/lazy, etc # - unicode order character at start # - support character set other than assume engine is utf8 and ignore encoding... ^ (<\\?xml (?<s> [\\t\\n\\r\\x20])+ version \\g<s>*=\\g<s>* ( "1\\.0" | \'1\\.0\' ) ( \\g<s>+ encoding \\g<s>*=\\g<s>* ( "[A-Za-z][A-Za-z0-9._-]*" | \'[A-Za-z][A-Za-z0-9._-]*\' ) )? ( \\g<s>+ standalone \\g<s>*=\\g<s>* ( "(yes|no)" | \'(yes|no)\' ) )? \\g<s>* \\?>)? (?<misc> \\g<s>+ | (?<comment> <!-- ( -? [^\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}-] )* -->) | (?<procinst> <\\? ( [MmLl] | (?<firstnoxml> [a-kn-wyzA-KN-WYZ_:] | [\\xC0-\\xD6\\xD8-\\xF6\\xF8-\\x{2FF}\\x{370}-\\x{37D}\\x{37F}-\\x{1FFF}] | [\\x{200C}-\\x{200D}\\x{2070}-\\x{218F}\\x{2C00}-\\x{2FEF}\\x{3001}-\\x{D7FF}\\x{F900}-\\x{FDCF}\\x{FDF0}-\\x{FFFD}\\x{10000}-\\x{EFFFF}] ) (?<latter> [XxMmLl] | (?<xmlatter> [0-9.-] | \\g<firstnoxml> | [\\xB7\\x{300}-\\x{36F}\\x{203F}-\\x{2040}] ) )* | [Xx] ( [XxLl] | \\g<xmlatter> ) \\g<latter>* | [Xx] [Mm] ( [XxMm] | \\g<xmlatter> ) \\g<latter>* | [Xx] [Mm] [Ll] \\g<latter>+ ) ( \\g<s>+ ( \\? [^>\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}] | [^?\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}] )* \\?? )? \\?> ) )* ( <!DOCTYPE \\g<s>+ (?<nm> ([XxMmLl] | \\g<firstnoxml>) \\g<latter>*) ( \\g<s>+ (?<world> ( SYSTEM | (?<idpublic> PUBLIC \\g<s>+ (\'[\\r\\n\\x20a-zA-Z0-9()+,.\\x2F:=?;!*\\#@$_%-]*\' | "[\'\\r\\n\\x20a-zA-Z0-9()+,.\\x2F:=?;!*\\#@$_%-]*" ) ) ) \\g<s>+ ( " [^"\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]* " | \' [^\'\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]* \' ) ) )? \\g<s>* ( \\[ ( <!ELEMENT \\g<s>+ \\g<nm> \\g<s>+ ( EMPTY | ANY | \\( \\g<s>* \\#PCDATA ( \\g<s>* \\) | ( (?<or> \\g<s>* \\| \\g<s>*) \\g<nm> )* \\g<s>* \\)\\* ) | (?<kids> \\( \\g<s>* ( \\g<nm> [?*+]? | \\g<kids> ) ( ( \\g<or> ( \\g<nm> [?*+]? | \\g<kids> ) )+ | ( \\g<s>* , \\g<s>* ( \\g<nm> [?*+]? | \\g<kids> ) )* ) \\g<s>* \\) [?*+]? ) ) \\g<s>* > | <!ENTITY \\g<s>+ ( ( % \\g<s>+ )? \\g<nm> \\g<s>+ ( " ( [^"%&\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]+ # WFC: PEs in Internal Subset | % \\g<nm> ; | (?<ref> & \\g<nm> ; ) | (?<hash> &\\# ( 0* ( 9 | 10 | 13 | 3[2-9] | [4-9][0-9] | [1-9][0-9][0-9][0-9]? | [1-47-9][0-9]{4} | 5[0-48-9][0-9]{3} | 55[0-1][0-9][0-9] | 552[0-8][0-9] | 5529[0-5] | 5734[4-9] | 573[5-9][0-9] | 57[4-9][0-9][0-9] | 6[0-46-9][0-9]{3} | 65[0-46-9][0-9][0-9] | 655[0-24-9][0-9] | 6553[0-36-9] | [1-9][0-9]{5} | 10[0-9]{5} | 110[0-9]{4} | 111[0-3][0-9]{3} | 11140[0-9][0-9] | 111410[0-9] | 111411[01] ) | x 0* ( [9aAdD] | [2-9a-f] [0-9a-fA-F] | [1-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] | [1-9a-cA-CeE] [0-9a-fA-F]{3} | [dD] [0-7] [0-9a-fA-F] [0-9a-fA-F] | [fF] [0-9a-eA-E] [0-9a-fA-F] [0-9a-fA-F] | [fF] [fF] [0-9a-eA-E] [0-9a-fA-F] | [fF] [fF] [fF] [0-9a-dA-D] | (10|[1-9a-fA-F]) [0-9a-fA-F]{4} ) ) ; ) )* " | \' ( [^\'%&\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]+ # | % \\g<nm> ; | \\g<ref> | \\g<hash> )* \' ) | \\g<nm> \\g<s>+ \\g<world> ( \\g<s>+ NDATA \\g<s>+ \\g<nm> )? | % \\g<s>+ \\g<nm> \\g<s>+ \\g<world> ) \\g<s>* > | <!NOTATION \\g<s>+ \\g<nm> \\g<s>+ ( \\g<world> | \\g<idpublic> ) \\g<s>* > | <!ATTLIST \\g<s>+ \\g<nm> ( \\g<s>+ \\g<nm> \\g<s>+ ( CDATA | ID | IDREF | IDREFS | ENTITY | ENTITIES | NMTOKEN | NMTOKENS | NOTATION \\g<s>+ \\( \\g<s>* \\g<nm> ( \\g<or> \\g<nm> )* \\g<s>* \\) | \\( \\g<s>* \\g<latter>+ ( \\g<or> \\g<latter>+ )* \\g<s>* \\) ) \\g<s>+ ( \\#REQUIRED | \\#IMPLIED | ( \\#FIXED \\g<s>+ )? (?<attvalue> " ( [^"<&\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]+ | \\g<ref> | \\g<hash> )* " | \' ( [^\'<&\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]+ | \\g<ref> | \\g<hash> )* \' ) ) )* \\g<s>* > | \\g<procinst> | \\g<comment> | % \\g<nm> ; | \\g<s>+ )* ] \\g<s>* )? > )? \\g<misc>* (?<element> < (?<tag> \\g<nm>) ( \\g<s>+ \\g<nm> \\g<s>*=\\g<s>* \\g<attvalue> )* \\g<s>* ( \\x2F > | > (?<data> >+ | ( >* ( [^><&\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]+ | [^\\]<&\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}] ]? > )+ ) )? ( ( \\g<element> | \\g<ref> | \\g<hash> | <!\\[CDATA\\[ >* ( [^>\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}]+ | [^\\]\\x00-\\x08\\x0B\\x0C\\x0E-\\x1F\\x{FFFE}\\x{FFFF}] ]? > )* ]]> | \\g<procinst> | \\g<comment> ) \\g<data>? )* < \\x2F \\k<tag> \\g<s>* > ) ) \\g<misc>* $ ', 'u') const str = `<doc>hello</doc>`; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; if ((m = regex.exec(str)) !== null) { // 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