pcre2syntax(3) — Linux manual page

NAME | PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY | QUOTING | BRACED ITEMS | ESCAPED CHARACTERS | CHARACTER TYPES | GENERAL CATEGORY PROPERTIES FOR \p and \P | PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P | BINARY PROPERTIES FOR \p AND \P | SCRIPT MATCHING WITH \p AND \P | THE BIDI_CLASS PROPERTY FOR \p AND \P | CHARACTER CLASSES | QUANTIFIERS | ANCHORS AND SIMPLE ASSERTIONS | REPORTED MATCH POINT SETTING | ALTERNATION | CAPTURING | ATOMIC GROUPS | COMMENT | OPTION SETTING | NEWLINE CONVENTION | WHAT \R MATCHES | LOOKAHEAD AND LOOKBEHIND ASSERTIONS | NON-ATOMIC LOOKAROUND ASSERTIONS | SCRIPT RUNS | BACKREFERENCES | SUBROUTINE REFERENCES (POSSIBLY RECURSIVE) | CONDITIONAL PATTERNS | BACKTRACKING CONTROL | CALLOUTS | SEE ALSO | AUTHOR | REVISION | COLOPHON

PCRE2SYNTAX(3)          Library Functions Manual          PCRE2SYNTAX(3)

NAME         top

       PCRE2 - Perl-compatible regular expressions (revised API)

PCRE2 REGULAR EXPRESSION SYNTAX SUMMARY         top


       The full syntax and semantics of the regular expressions that are
       supported by PCRE2 are described in the pcre2pattern
       documentation. This document contains a quick-reference summary
       of the syntax.

QUOTING         top


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

       Note that white space inside \Q...\E is always treated as
       literal, even if PCRE2_EXTENDED is set, causing most other white
       space to be ignored.

BRACED ITEMS         top


       With one exception, wherever brace characters { and } are
       required to enclose data for constructions such as \g{2} or
       \k{name}, space and/or horizontal tab characters that follow { or
       precede } are allowed and are ignored. In the case of
       quantifiers, they may also appear before or after the comma. The
       exception is \u{...} which is not Perl-compatible and is
       recognized only when PCRE2_EXTRA_ALT_BSUX is set. This is an
       ECMAScript compatibility feature, and follows ECMAScript's
       behaviour.

ESCAPED CHARACTERS         top


       This table applies to ASCII and Unicode environments. An
       unrecognized escape sequence causes an error.

         \a         alarm, that is, the BEL character (hex 07)
         \cx        "control-x", where x is a non-control ASCII
       character
         \e         escape (hex 1B)
         \f         form feed (hex 0C)
         \n         newline (hex 0A)
         \r         carriage return (hex 0D)
         \t         tab (hex 09)
         \0dd       character with octal code 0dd
         \ddd       character with octal code ddd, or backreference
         \o{ddd..}  character with octal code ddd..
         \N{U+hh..} character with Unicode code point hh.. (Unicode mode
       only)
         \xhh       character with hex code hh
         \x{hh..}   character with hex code hh..

       If PCRE2_ALT_BSUX or PCRE2_EXTRA_ALT_BSUX is set ("ALT_BSUX
       mode"), the following are also recognized:

         \U         the character "U"
         \uhhhh     character with hex code hhhh
         \u{hh..}   character with hex code hh.. but only for
       EXTRA_ALT_BSUX

       When \x is not followed by {, from zero to two hexadecimal digits
       are read, but in ALT_BSUX mode \x must be followed by two
       hexadecimal digits to be recognized as a hexadecimal escape;
       otherwise it matches a literal "x".  Likewise, if \u (in ALT_BSUX
       mode) is not followed by four hexadecimal digits or (in
       EXTRA_ALT_BSUX mode) a sequence of hex digits in curly brackets,
       it matches a literal "u".

       Note that \0dd is always an octal code. The treatment of
       backslash followed by a non-zero digit is complicated; for
       details see the section "Non-printing characters" in the
       pcre2pattern documentation, where details of escape processing in
       EBCDIC environments are also given. \N{U+hh..} is synonymous with
       \x{hh..} in PCRE2 but is not supported in EBCDIC environments.
       Note that \N not followed by an opening curly bracket has a
       different meaning (see below).

CHARACTER TYPES         top


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

       \C is dangerous because it may leave the current matching point
       in the middle of a UTF-8 or UTF-16 character. The application can
       lock out the use of \C by setting the PCRE2_NEVER_BACKSLASH_C
       option. It is also possible to build PCRE2 with the use of \C
       permanently disabled.

       By default, \d, \s, and \w match only ASCII characters, even in
       UTF-8 mode or in the 16-bit and 32-bit libraries. However, if
       locale-specific matching is happening, \s and \w may also match
       characters with code points in the range 128-255. If the
       PCRE2_UCP option is set, the behaviour of these escape sequences
       is changed to use Unicode properties and they match many more
       characters, but there are some option settings that can restrict
       individual sequences to matching only ASCII characters.

       Property descriptions in \p and \P are matched caselessly;
       hyphens, underscores, and white space are ignored, in accordance
       with Unicode's "loose matching" rules.

GENERAL CATEGORY PROPERTIES FOR \p and \P         top


         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
         Lc         Ll, Lu, or Lt
         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

PCRE2 SPECIAL CATEGORY PROPERTIES FOR \p and \P         top


         Xan        Alphanumeric: union of properties L and N
         Xps        POSIX space: property Z or tab, NL, VT, FF, CR
         Xsp        Perl space: property Z or tab, NL, VT, FF, CR
         Xuc        Universally-named character: one that can be
                      represented by a Universal Character Name
         Xwd        Perl word: property Xan or underscore

       Perl and POSIX space are now the same. Perl added VT to its space
       character set at release 5.18.

BINARY PROPERTIES FOR \p AND \P         top


       Unicode defines a number of binary properties, that is,
       properties whose only values are true or false. You can obtain a
       list of those that are recognized by \p and \P, along with their
       abbreviations, by running this command:

         pcre2test -LP

SCRIPT MATCHING WITH \p AND \P         top


       Many script names and their 4-letter abbreviations are recognized
       in \p{sc:...} or \p{scx:...} items, or on their own with \p (and
       also \P of course). You can obtain a list of these scripts by
       running this command:

         pcre2test -LS

THE BIDI_CLASS PROPERTY FOR \p AND \P         top


         \p{Bidi_Class:<class>}   matches a character with the given
       class
         \p{BC:<class>}           matches a character with the given
       class

       The recognized classes are:

         AL          Arabic letter
         AN          Arabic number
         B           paragraph separator
         BN          boundary neutral
         CS          common separator
         EN          European number
         ES          European separator
         ET          European terminator
         FSI         first strong isolate
         L           left-to-right
         LRE         left-to-right embedding
         LRI         left-to-right isolate
         LRO         left-to-right override
         NSM         non-spacing mark
         ON          other neutral
         PDF         pop directional format
         PDI         pop directional isolate
         R           right-to-left
         RLE         right-to-left embedding
         RLI         right-to-left isolate
         RLO         right-to-left override
         S           segment separator
         WS          which space

CHARACTER CLASSES         top


         [...]       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       white space
         upper       upper case letter
         word        same as \w
         xdigit      hexadecimal digit

       In PCRE2, POSIX character set names recognize only ASCII
       characters by default, but some of them use Unicode properties if
       PCRE2_UCP is set. You can use \Q...\E inside a character class.

QUANTIFIERS         top


         ?           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
         {,m}        zero up to m, greedy
         {,m}+       zero up to m, possessive
         {,m}?       zero up to m, lazy

ANCHORS AND SIMPLE ASSERTIONS         top


         \b          word boundary
         \B          not a word boundary
         ^           start of subject
                       also after an internal newline in multiline mode
                       (after any newline if PCRE2_ALT_CIRCUMFLEX is
       set)
         \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

REPORTED MATCH POINT SETTING         top


         \K          set reported start of match

       From release 10.38 \K is not permitted by default in lookaround
       assertions, for compatibility with Perl. However, if the
       PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK option is set, the previous
       behaviour is re-enabled. When this option is set, \K is honoured
       in positive assertions, but ignored in negative ones.

ALTERNATION         top


         expr|expr|expr...

CAPTURING         top


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

       In non-UTF modes, names may contain underscores and ASCII letters
       and digits; in UTF modes, any Unicode letters and Unicode decimal
       digits are permitted. In both cases, a name must not start with a
       digit.

ATOMIC GROUPS         top


         (?>...)         atomic non-capture group
         (*atomic:...)   atomic non-capture group

COMMENT         top


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

OPTION SETTING         top

       Changes of these options within a group are automatically
       cancelled at the end of the group.

         (?a)            all ASCII options
         (?aD)           restrict \d to ASCII in UCP mode
         (?aS)           restrict \s to ASCII in UCP mode
         (?aW)           restrict \w to ASCII in UCP mode
         (?aP)           restrict all POSIX classes to ASCII in UCP mode
         (?aT)           restrict POSIX digit classes to ASCII in UCP
       mode
         (?i)            caseless
         (?J)            allow duplicate named groups
         (?m)            multiline
         (?n)            no auto capture
         (?r)            restrict caseless to either ASCII or non-ASCII
         (?s)            single line (dotall)
         (?U)            default ungreedy (lazy)
         (?x)            ignore white space except in classes or \Q...\E
         (?xx)           as (?x) but also ignore space and tab in
       classes
         (?-...)         unset the given option(s)
         (?^)            unset imnrsx options

       (?aP) implies (?aT) as well, though this has no additional
       effect. However, it means that (?-aP) is really (?-PT) which
       disables all ASCII restrictions for POSIX classes.

       Unsetting x or xx unsets both. Several options may be set at
       once, and a mixture of setting and unsetting such as (?i-x) is
       allowed, but there may be only one hyphen. Setting (but no
       unsetting) is allowed after (?^ for example (?^in). An option
       setting may appear at the start of a non-capture group, for
       example (?i:...).

       The following are recognized only at the very start of a pattern
       or after one of the newline or \R options with similar syntax.
       More than one of them may appear. For the first three, d is a
       decimal number.

         (*LIMIT_DEPTH=d) set the backtracking limit to d
         (*LIMIT_HEAP=d)  set the heap size limit to d * 1024 bytes
         (*LIMIT_MATCH=d) set the match limit to d
         (*NOTEMPTY)      set PCRE2_NOTEMPTY when matching
         (*NOTEMPTY_ATSTART) set PCRE2_NOTEMPTY_ATSTART when matching
         (*NO_AUTO_POSSESS) no auto-possessification
       (PCRE2_NO_AUTO_POSSESS)
         (*NO_DOTSTAR_ANCHOR) no .* anchoring (PCRE2_NO_DOTSTAR_ANCHOR)
         (*NO_JIT)       disable JIT optimization
         (*NO_START_OPT) no start-match optimization
       (PCRE2_NO_START_OPTIMIZE)
         (*UTF)          set appropriate UTF mode for the library in use
         (*UCP)          set PCRE2_UCP (use Unicode properties for \d
       etc)

       Note that LIMIT_DEPTH, LIMIT_HEAP, and LIMIT_MATCH can only
       reduce the value of the limits set by the caller of pcre2_match()
       or pcre2_dfa_match(), not increase them. LIMIT_RECURSION is an
       obsolete synonym for LIMIT_DEPTH. The application can lock out
       the use of (*UTF) and (*UCP) by setting the PCRE2_NEVER_UTF or
       PCRE2_NEVER_UCP options, respectively, at compile time.

NEWLINE CONVENTION         top


       These are recognized only at the very start of the pattern or
       after option settings with a similar syntax.

         (*CR)           carriage return only
         (*LF)           linefeed only
         (*CRLF)         carriage return followed by linefeed
         (*ANYCRLF)      all three of the above
         (*ANY)          any Unicode newline sequence
         (*NUL)          the NUL character (binary zero)

WHAT \R MATCHES         top


       These are recognized only at the very start of the pattern or
       after option setting with a similar syntax.

         (*BSR_ANYCRLF)  CR, LF, or CRLF
         (*BSR_UNICODE)  any Unicode newline sequence

LOOKAHEAD AND LOOKBEHIND ASSERTIONS         top


         (?=...)                     )
         (*pla:...)                  ) positive lookahead
         (*positive_lookahead:...)   )

         (?!...)                     )
         (*nla:...)                  ) negative lookahead
         (*negative_lookahead:...)   )

         (?<=...)                    )
         (*plb:...)                  ) positive lookbehind
         (*positive_lookbehind:...)  )

         (?<!...)                    )
         (*nlb:...)                  ) negative lookbehind
         (*negative_lookbehind:...)  )

       Each top-level branch of a lookbehind must have a limit for the
       number of characters it matches. If any branch can match a
       variable number of characters, the maximum for each branch is
       limited to a value set by the caller of pcre2_compile() or
       defaulted. The default is set when PCRE2 is built (ultimate
       default 255). If every branch matches a fixed number of
       characters, the limit for each branch is 65535 characters.

NON-ATOMIC LOOKAROUND ASSERTIONS         top


       These assertions are specific to PCRE2 and are not Perl-
       compatible.

         (?*...)                                )
         (*napla:...)                           ) synonyms
         (*non_atomic_positive_lookahead:...)   )

         (?<*...)                               )
         (*naplb:...)                           ) synonyms
         (*non_atomic_positive_lookbehind:...)  )

SCRIPT RUNS         top


         (*script_run:...)           ) script run, can be backtracked
       into
         (*sr:...)                   )

         (*atomic_script_run:...)    ) atomic script run
         (*asr:...)                  )

BACKREFERENCES         top


         \n              reference by number (can be ambiguous)
         \gn             reference by number
         \g{n}           reference by number
         \g+n            relative reference by number (PCRE2 extension)
         \g-n            relative reference by number
         \g{+n}          relative reference by number (PCRE2 extension)
         \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)         top


         (?R)            recurse whole pattern
         (?n)            call subroutine by absolute number
         (?+n)           call subroutine by relative number
         (?-n)           call subroutine by relative number
         (?&name)        call subroutine by name (Perl)
         (?P>name)       call subroutine by name (Python)
         \g<name>        call subroutine by name (Oniguruma)
         \g'name'        call subroutine by name (Oniguruma)
         \g<n>           call subroutine by absolute number (Oniguruma)
         \g'n'           call subroutine by absolute number (Oniguruma)
         \g<+n>          call subroutine by relative number (PCRE2
       extension)
         \g'+n'          call subroutine by relative number (PCRE2
       extension)
         \g<-n>          call subroutine by relative number (PCRE2
       extension)
         \g'-n'          call subroutine by relative number (PCRE2
       extension)

CONDITIONAL PATTERNS         top


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

         (?(n)               absolute reference condition
         (?(+n)              relative reference condition (PCRE2
       extension)
         (?(-n)              relative reference condition (PCRE2
       extension)
         (?(<name>)          named reference condition (Perl)
         (?('name')          named reference condition (Perl)
         (?(name)            named reference condition (PCRE2,
       deprecated)
         (?(R)               overall recursion condition
         (?(Rn)              specific numbered group recursion condition
         (?(R&name)          specific named group recursion condition
         (?(DEFINE)          define groups for reference
         (?(VERSION[>]=n.m)  test PCRE2 version
         (?(assert)          assertion condition

       Note the ambiguity of (?(R) and (?(Rn) which might be named
       reference conditions or recursion tests. Such a condition is
       interpreted as a reference condition if the relevant named group
       exists.

BACKTRACKING CONTROL         top


       All backtracking control verbs may be in the form (*VERB:NAME).
       For (*MARK) the name is mandatory, for the others it is optional.
       (*SKIP) changes its behaviour if :NAME is present. The others
       just set a name for passing back to the caller, but this is not a
       name that (*SKIP) can see. The following act immediately they are
       reached:

         (*ACCEPT)       force successful match
         (*FAIL)         force backtrack; synonym (*F)
         (*MARK:NAME)    set name to be passed back; synonym (*:NAME)

       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 to current matching position
         (*SKIP:NAME)    advance to position corresponding to an earlier
                         (*MARK:NAME); if not found, the (*SKIP) is
       ignored
         (*THEN)         local failure, backtrack to next alternation

       The effect of one of these verbs in a group called as a
       subroutine is confined to the subroutine call.

CALLOUTS         top


         (?C)            callout (assumed number 0)
         (?Cn)           callout with numerical data n
         (?C"text")      callout with string data

       The allowed string delimiters are ` ' " ^ % # $ (which are the
       same for the start and the end), and the starting delimiter {
       matched with the ending delimiter }. To encode the ending
       delimiter within the string, double it.

SEE ALSO         top


       pcre2pattern(3), pcre2api(3), pcre2callout(3), pcre2matching(3),
       pcre2(3).

AUTHOR         top


       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.

REVISION         top


       Last updated: 12 October 2023
       Copyright (c) 1997-2023 University of Cambridge.

COLOPHON         top

       This page is part of the PCRE (Perl Compatible Regular
       Expressions) project.  Information about the project can be found
       at ⟨http://www.pcre.org/⟩.  If you have a bug report for this
       manual page, see
       ⟨http://bugs.exim.org/enter_bug.cgi?product=PCRE⟩.  This page was
       obtained from the tarball fetched from
       ⟨https://github.com/PhilipHazel/pcre2.git⟩ on 2024-06-14.  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

PCRE2 10.43                  12 October 2023              PCRE2SYNTAX(3)

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