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

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

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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html