Regular Expression Syntax Summary

Perl Compatible Regular Expressions

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pcresyntax man page

The full syntax and semantics of the regular expressions that are supported by PCRE are described in the pcrepattern documentation. This document contains just a quick-reference summary of the syntax.

QUOTING

  \x         where x is non-alphanumeric is a literal x
  \Q...\E    treat enclosed characters as literal

CHARACTERS

  \a         alarm, that is, the BEL character (hex 07)
  \cx        "control-x", where x is any character
  \e         escape (hex 1B)
  \f         formfeed (hex 0C)
  \n         newline (hex 0A)
  \r         carriage return (hex 0D)
  \t         tab (hex 09)
  \ddd       character with octal code ddd, or backreference
  \xhh       character with hex code hh
  \x{hhh..}  character with hex code hhh..

CHARACTER TYPES

  .          any character except newline;
               in dotall mode, any character whatsoever
  \C         one byte, even in UTF-8 mode (best avoided)
  \d         a decimal digit
  \D         a character that is not a decimal digit
  \h         a horizontal whitespace character
  \H         a character that is not a horizontal whitespace character
  \p{xx}     a character with the xx property
  \P{xx}     a character without the xx property
  \R         a newline sequence
  \s         a whitespace character
  \S         a character that is not a whitespace character
  \v         a vertical whitespace character
  \V         a character that is not a vertical whitespace character
  \w         a "word" character
  \W         a "non-word" character
  \X         an extended Unicode sequence

In PCRE, \d, \D, \s, \S, \w, and \W recognize only ASCII characters.

GENERAL CATEGORY PROPERTY CODES FOR \p and \P

  C          Other
  Cc         Control
  Cf         Format
  Cn         Unassigned
  Co         Private use
  Cs         Surrogate

  L          Letter
  Ll         Lower case letter
  Lm         Modifier letter
  Lo         Other letter
  Lt         Title case letter
  Lu         Upper case letter
  L&         Ll, Lu, or Lt

  M          Mark
  Mc         Spacing mark
  Me         Enclosing mark
  Mn         Non-spacing mark

  N          Number
  Nd         Decimal number
  Nl         Letter number
  No         Other number

  P          Punctuation
  Pc         Connector punctuation
  Pd         Dash punctuation
  Pe         Close punctuation
  Pf         Final punctuation
  Pi         Initial punctuation
  Po         Other punctuation
  Ps         Open punctuation

  S          Symbol
  Sc         Currency symbol
  Sk         Modifier symbol
  Sm         Mathematical symbol
  So         Other symbol

  Z          Separator
  Zl         Line separator
  Zp         Paragraph separator
  Zs         Space separator

SCRIPT NAMES FOR \p AND \P

Arabic, Armenian, Balinese, Bengali, Bopomofo, Braille, Buginese, Buhid, Canadian_Aboriginal, Cherokee, Common, Coptic, Cuneiform, Cypriot, Cyrillic, Deseret, Devanagari, Ethiopic, Georgian, Glagolitic, Gothic, Greek, Gujarati, Gurmukhi, Han, Hangul, Hanunoo, Hebrew, Hiragana, Inherited, Kannada, Katakana, Kharoshthi, Khmer, Lao, Latin, Limbu, Linear_B, Malayalam, Mongolian, Myanmar, New_Tai_Lue, Nko, Ogham, Old_Italic, Old_Persian, Oriya, Osmanya, Phags_Pa, Phoenician, Runic, Shavian, Sinhala, Syloti_Nagri, Syriac, Tagalog, Tagbanwa, Tai_Le, Tamil, Telugu, Thaana, Thai, Tibetan, Tifinagh, Ugaritic, Yi.

CHARACTER CLASSES

  [...]       positive character class
  [^...]      negative character class
  [x-y]       range (can be used for hex characters)
  [[:xxx:]]   positive POSIX named set
  [[:^xxx:]]  negative POSIX named set

  alnum       alphanumeric
  alpha       alphabetic
  ascii       0-127
  blank       space or tab
  cntrl       control character
  digit       decimal digit
  graph       printing, excluding space
  lower       lower case letter
  print       printing, including space
  punct       printing, excluding alphanumeric
  space       whitespace
  upper       upper case letter
  word        same as \w
  xdigit      hexadecimal digit

In PCRE, POSIX character set names recognize only ASCII characters. You can use \Q...\E inside a character class.

QUANTIFIERS

  ?           0 or 1, greedy
  ?+          0 or 1, possessive
  ??          0 or 1, lazy
  *           0 or more, greedy
  *+          0 or more, possessive
  *?          0 or more, lazy
  +           1 or more, greedy
  ++          1 or more, possessive
  +?          1 or more, lazy
  {n}         exactly n
  {n,m}       at least n, no more than m, greedy
  {n,m}+      at least n, no more than m, possessive
  {n,m}?      at least n, no more than m, lazy
  {n,}        n or more, greedy
  {n,}+       n or more, possessive
  {n,}?       n or more, lazy

ANCHORS AND SIMPLE ASSERTIONS

  \b          word boundary
  \B          not a word boundary
  ^           start of subject
               also after internal newline in multiline mode
  \A          start of subject
  $           end of subject
               also before newline at end of subject
               also before internal newline in multiline mode
  \Z          end of subject
               also before newline at end of subject
  \z          end of subject
  \G          first matching position in subject

MATCH POINT RESET

  \K          reset start of match

ALTERNATION

  expr|expr|expr...

CAPTURING

  (...)          capturing group
  (?<name>...)   named capturing group (Perl)
  (?'name'...)   named capturing group (Perl)
  (?P<name>...)  named capturing group (Python)
  (?:...)        non-capturing group
  (?|...)        non-capturing group; reset group numbers for
                  capturing groups in each alternative

ATOMIC GROUPS

  (?>...)        atomic, non-capturing group

COMMENT

  (?#....)       comment (not nestable)

OPTION SETTING

  (?i)           caseless
  (?J)           allow duplicate names
  (?m)           multiline
  (?s)           single line (dotall)
  (?U)           default ungreedy (lazy)
  (?x)           extended (ignore white space)
  (?-...)        unset option(s)

LOOKAHEAD AND LOOKBEHIND ASSERTIONS

  (?=...)        positive look ahead
  (?!...)        negative look ahead
  (?<=...)       positive look behind
  (?<!...)       negative look behind

Each top-level branch of a look behind must be of a fixed length.

BACKREFERENCES

  \n             reference by number (can be ambiguous)
  \gn            reference by number
  \g{n}          reference by number
  \g{-n}         relative reference by number
  \k<name>       reference by name (Perl)
  \k'name'       reference by name (Perl)
  \g{name}       reference by name (Perl)
  \k{name}       reference by name (.NET)
  (?P=name)      reference by name (Python)

SUBROUTINE REFERENCES (POSSIBLY RECURSIVE)

  (?R)           recurse whole pattern
  (?n)           call subpattern by absolute number
  (?+n)          call subpattern by relative number
  (?-n)          call subpattern by relative number
  (?&name;)       call subpattern by name (Perl)
  (?P>name)      call subpattern by name (Python)
  \g<name>       call subpattern by name (Oniguruma)
  \g'name'       call subpattern by name (Oniguruma)
  \g<n>          call subpattern by absolute number (Oniguruma)
  \g'n'          call subpattern by absolute number (Oniguruma)
  \g<+n>         call subpattern by relative number (PCRE extension)
  \g'+n'         call subpattern by relative number (PCRE extension)
  \g<-n>         call subpattern by relative number (PCRE extension)
  \g'-n'         call subpattern by relative number (PCRE extension)

CONDITIONAL PATTERNS

  (?(condition)yes-pattern)
  (?(condition)yes-pattern|no-pattern)

  (?(n)...       absolute reference condition
  (?(+n)...      relative reference condition
  (?(-n)...      relative reference condition
  (?(<name>)...  named reference condition (Perl)
  (?('name')...  named reference condition (Perl)
  (?(name)...    named reference condition (PCRE)
  (?(R)...       overall recursion condition
  (?(Rn)...      specific group recursion condition
  (?(R&name;)...  specific recursion condition
  (?(DEFINE)...  define subpattern for reference
  (?(assert)...  assertion condition

BACKTRACKING CONTROL

The following act immediately they are reached:

  (*ACCEPT)      force successful match
  (*FAIL)        force backtrack; synonym (*F)

The following act only when a subsequent match failure causes a backtrack to reach them. They all force a match failure, but they differ in what happens afterwards. Those that advance the start-of-match point do so only if the pattern is not anchored.

  (*COMMIT)      overall failure, no advance of starting point
  (*PRUNE)       advance to next starting character
  (*SKIP)        advance start to current matching position
  (*THEN)        local failure, backtrack to next alternation

NEWLINE CONVENTIONS

These are recognized only at the very start of the pattern or after a (*BSR_...) option.

  (*CR)
  (*LF)
  (*CRLF)
  (*ANYCRLF)
  (*ANY)

WHAT \R MATCHES

These are recognized only at the very start of the pattern or after a (*...) option that sets the newline convention.

  (*BSR_ANYCRLF)
  (*BSR_UNICODE)

CALLOUTS

  (?C)      callout
  (?Cn)     callout with data n