Regular Expressions 101

Save & Share

  • Regex Version: ver. 7
  • Update Regex
    ctrl+⇧+s
  • Save new Regex
    ctrl+s
  • Add to Community Library

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

/
/
gxA

Test String

Code Generator

Language

Generated Code

$re = '/# Chess game validation regex (PCRE) (?!^(?!rnbqkbnr\np{8}(?:\n-{8}){4}\nP{8}\nRNBQKBNR\n\n)) # assert initial state of board, if this is the first move (?> (\n)? # \1 = capture \n if black moves next (ensuring that white moves first), or unset/NPCG if white moves next | # subroutines: ((.|\n(?=.)){2}) # (?3) = for moving within the board, without wrapping to the next board, (?2) = (?3){2} ((?= # (?4) = assert that position of just-consumed piece is vacated on the next turn (\X{72}) # (?5) = skip to the position of the just-consumed piece on the next turn -)) ((?! # (?6) = assert that the piece at the current position belongs to the current player ((?=(?(1)[-A-Z]|[-a-z]))) # (?7) = assert that the piece at the current position belongs to the current player\'s opponent or is empty )) ((?5)(?(?=(.*\n)\n)[qnrb]|p)) # (?8) = black pawn that might be promoted, (?9) = .*\n ( # (?10) = assert that the just-consumed piece never moved in all past turns (?<=(.)) ((?<!(?!_|\11(?12))\PM{74})) ) ((?5)(?(?=(?9){8}\n)[QNRB]|P)) # (?13) = white pawn that might be promoted ) ( # check if we\'re in check; \14 will be captured and empty if we\'re not in check, or unset if we are; call (?14) to assert we\'re not in check on the next turn (?! \X{,70} (?: # pawns (capture diagonally) (?(1)k|p)(?=(?3){7}(?2)?(?(1)P|K)) | # bishops, rooks, queens, or knights (?i: (?<E>(?6)K)? # decide between scanning forward (<E> is unset) or backwards (<E> is captured) (?: (?(E)|((?7)[BQ])) (?<B>()?((?(-1)-)(?3){7}(?(-2)(?2)))+) (?(E)(?-4)) | # bishops or queens (?(E)|((?7)[RQ])) (?<R>-*|((?(-1)-)(?3){8})+) (?(E)(?-3)) | # rooks or queens (?(E)|((?7) N )) (?<N>(?<=..)(?2){3}|(?=.)(?2){5}|(?2){8}(?2)?) (?(E)(?-2)) # knights ) (?(E)|(?&E)) | K(?<K>(?3){7,9})?K # kings ) ) ) )?? (?> (?> # Handle squares that don\'t change (empty->empty or pieces that doesn\'t move) (.)(?=(?5)\g{-1}) | # Handle a piece that moves (and optionally captures an enemy piece) (?(m)$) # allow only one move to be made per turn (?> (?(1) (?:p(?4)(?: # black pawn (?=(?3){8}((?3){9})? - (?8))(?(-1)(?=(?9){7}\n)) | # move 1 or 2 spaces forward (?=(?3){7}(?2)? [A-Z](?8)) ) | # capture diagonally (?=\X{73}--(?9){4}\n)(?|P(?=(p))|pP())(?<=(?=(?:-\X{8}){2}P)\PM{74}(?=\X{8}-(?5)p))\g{-1} ) # en passant | (?: # white pawn - (?=(?13))(?=(?3){8}((?3){9})?P(?4))(?(-1)(?=(?9){4}\n)) | # move 1 or 2 spaces forward [a-z](?=(?13))(?=(?3){7}(?2)? P(?4)) | # capture diagonally (?=\X{73}--(?9){5}\n)(?|p(?=(P))|Pp())(?<=(?=p(?:\X{8}-){2})\PM{82}(?=-(?5)P)\PM{10})\g{-1} ) # en passant ) | # Castling - must be tried before rook moves unless we give up atomicity # Leaves the rightmost changed square unconsumed, so that "only allow matching one of these per turn" below can\'t silently consume an illegal move (?6)([KkRr])(?10) (?! (?:--)?- # Verify that we aren\'t castling through check # There\'s no need to check for kings, because they can\'t threaten check at this spot without our king already being in check ()? # decide between bishops/queens or rooks/queens ()? # for bishops/queens, decide between one diagonal or the other (?(1) (?|\X{7}(?2)?P # pawns (capture diagonally) |(\X{6}|\X{10}|\X{16}(?2)?)N # knights |((?(-1)-)\X{7}(?(-2)(?2)))+[BQ] # bishops or queens |((?(-1)-)\X{8} )+[RQ]) # rooks or queens (only look downward, because left/right are impossible in this context) | (?<=p\PM{8}|p\PM{10} # pawns (capture diagonally) |(?=(?:|(?2)|\X{8}|\X{12})n)\PM{20} # knights |((?<= # bishops/queens or rooks/queens (?!.*\n\n) (?= (?(-4) \X # rooks or queens (only look upward, because left/right are impossible in this context) | (?(-3)(?2)) # bishops or queens ) (?:(?(-4)[rq]|[bq])|-(?-1)) ) \PM{11} ))) ) ) (?=(?5)-(-[Kk]|[Rr])\g{-6}-)--(?=\g{-1}(?10))-?\14 | # bishops, rooks, queens, knights, or kings (?<e>(?7).)? # decide between scanning forward (<e> is unset) or backwards (<e> is captured) (?= (?i: (?| (?(e)|(B|Q)) (?&B) (?(e)(B|Q)) | # bishops or queens (?(e)|(R|Q)) (?&R) (?(e)(R|Q)) | # rooks or queens (?(e)|(N )) (?&N) (?(e)(N )) | # knights (?(e)|(K )) (?&K)? (?(e)(K )) # kings ) ) (?(e)(?<=(?!(?7)).)(?4)|(?7).(?5)\g{-2}) # verify that the piece moved, and optionally captured piece, are of the correct color ) (?(e)(?=(?5)\g{-1})|(?6).(?4)) # verify that the piece moved is the same type and color at its destination in the next turn\'s board position )(?<m>) | (?(+1)$)(.) # handle the destination/source square that a piece moved to/from (only allow matching one of these per turn) )+\n )+ \k<m> # assert that a move has taken place (?=\n(?14)) # don\'t allow moving into check \1? # if white moved last, black moves next, and vice-versa/xA'; $str = 'rnbqkbnr pppppppp -------- -------- -------- -------- PPPPPPPP RNBQKBNR rnbqkbnr pppppppp -------- -------- ----P--- -------- PPPP-PPP RNBQKBNR rnbqkbnr pppp-ppp ----p--- -------- ----P--- -------- PPPP-PPP RNBQKBNR rnbqkbnr pppp-ppp ----p--- -------- ---PP--- -------- PPP--PPP RNBQKBNR rnbqkbnr ppp--ppp ----p--- ---p---- ---PP--- -------- PPP--PPP RNBQKBNR rnbqkbnr ppp--ppp ----p--- ---pP--- ---P---- -------- PPP--PPP RNBQKBNR rnbqkbnr pp---ppp ----p--- --ppP--- ---P---- -------- PPP--PPP RNBQKBNR rnbqkbnr pp---ppp ----p--- --ppP--- ---P---- --P----- PP---PPP RNBQKBNR rnbqkbnr pp---ppp ----p--- ---pP--- ---p---- --P----- PP---PPP RNBQKBNR rnbqkbnr pp---ppp ----p--- ---pP--- ---P---- -------- PP---PPP RNBQKBNR rnbqk-nr pp---ppp ----p--- ---pP--- -b-P---- -------- PP---PPP RNBQKBNR rnbqk-nr pp---ppp ----p--- ---pP--- -b-P---- --N----- PP---PPP R-BQKBNR r-bqk-nr pp---ppp --n-p--- ---pP--- -b-P---- --N----- PP---PPP R-BQKBNR r-bqk-nr pp---ppp --n-p--- ---pP--- -b-P---- --N--N-- PP---PPP R-BQKB-R r-bqk--r pp--nppp --n-p--- ---pP--- -b-P---- --N--N-- PP---PPP R-BQKB-R r-bqk--r pp--nppp --n-p--- ---pP--- -b-P---- --NB-N-- PP---PPP R-BQK--R r-bq-rk- pp--nppp --n-p--- ---pP--- -b-P---- --NB-N-- PP---PPP R-BQK--R r-bq-rk- pp--nppB --n-p--- ---pP--- -b-P---- --N--N-- PP---PPP R-BQK--R r-bq-r-- pp--nppk --n-p--- ---pP--- -b-P---- --N--N-- PP---PPP R-BQK--R r-bq-r-- pp--nppk --n-p--- ---pP-N- -b-P---- --N----- PP---PPP R-BQK--R r-bq-r-- pp--npp- --n-p-k- ---pP-N- -b-P---- --N----- PP---PPP R-BQK--R r-bq-r-- pp--npp- --n-p-k- ---pP-N- -b-P---P --N----- PP---PP- R-BQK--R r-bq-r-- pp--npp- ----p-k- ---pP-N- -b-n---P --N----- PP---PP- R-BQK--R r-bq-r-- pp--npp- ----p-k- ---pP-N- -b-n--QP --N----- PP---PP- R-B-K--R r-bq-r-- pp--n-p- ----p-k- ---pPpN- -b-n--QP --N----- PP---PP- R-B-K--R r-bq-r-- pp--n-p- ----p-k- ---pPpNP -b-n--Q- --N----- PP---PP- R-B-K--R r-bq-r-- pp--n-p- ----p--k ---pPpNP -b-n--Q- --N----- PP---PP- R-B-K--R r-bq-r-- pp--n-p- ----N--k ---pPp-P -b-n--Q- --N----- PP---PP- R-B-K--R r-bq-r-- pp--n--- ----N--k ---pPppP -b-n--Q- --N----- PP---PP- R-B-K--R r-bq-r-- pp--n--- ----N-Pk ---pPp-- -b-n--Q- --N----- PP---PP- R-B-K--R WIN BY CHECKMATE'; preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0); // Print the entire match result var_dump($matches);

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 PHP, please visit: http://php.net/manual/en/ref.pcre.php