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

/
/
gxA

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