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Line 14 man page, in case the conversion went wrong.	Line 14 man page, in case the conversion went wrong.
<br>	<br>
<ul>	<ul>
<li><a name="TOC1" href="#SEC1">PCRE REGULAR EXPRESSION DETAILS</a>	<li><a name="TOC1" href="#SEC1">PCRE REGULAR EXPRESSION DETAILS</a>
<li><a name="TOC2" href="#SEC2">NEWLINE CONVENTIONS</a>	<li><a name="TOC2" href="#SEC2">SPECIAL START-OF-PATTERN ITEMS</a>
<li><a name="TOC3" href="#SEC3">CHARACTERS AND METACHARACTERS</a>	<li><a name="TOC3" href="#SEC3">EBCDIC CHARACTER CODES</a>
<li><a name="TOC4" href="#SEC4">BACKSLASH</a>	<li><a name="TOC4" href="#SEC4">CHARACTERS AND METACHARACTERS</a>
<li><a name="TOC5" href="#SEC5">CIRCUMFLEX AND DOLLAR</a>	<li><a name="TOC5" href="#SEC5">BACKSLASH</a>
<li><a name="TOC6" href="#SEC6">FULL STOP (PERIOD, DOT) AND \N</a>	<li><a name="TOC6" href="#SEC6">CIRCUMFLEX AND DOLLAR</a>
<li><a name="TOC7" href="#SEC7">MATCHING A SINGLE BYTE</a>	<li><a name="TOC7" href="#SEC7">FULL STOP (PERIOD, DOT) AND \N</a>
<li><a name="TOC8" href="#SEC8">SQUARE BRACKETS AND CHARACTER CLASSES</a>	<li><a name="TOC8" href="#SEC8">MATCHING A SINGLE DATA UNIT</a>
<li><a name="TOC9" href="#SEC9">POSIX CHARACTER CLASSES</a>	<li><a name="TOC9" href="#SEC9">SQUARE BRACKETS AND CHARACTER CLASSES</a>
<li><a name="TOC10" href="#SEC10">VERTICAL BAR</a>	<li><a name="TOC10" href="#SEC10">POSIX CHARACTER CLASSES</a>
<li><a name="TOC11" href="#SEC11">INTERNAL OPTION SETTING</a>	<li><a name="TOC11" href="#SEC11">COMPATIBILITY FEATURE FOR WORD BOUNDARIES</a>
<li><a name="TOC12" href="#SEC12">SUBPATTERNS</a>	<li><a name="TOC12" href="#SEC12">VERTICAL BAR</a>
<li><a name="TOC13" href="#SEC13">DUPLICATE SUBPATTERN NUMBERS</a>	<li><a name="TOC13" href="#SEC13">INTERNAL OPTION SETTING</a>
<li><a name="TOC14" href="#SEC14">NAMED SUBPATTERNS</a>	<li><a name="TOC14" href="#SEC14">SUBPATTERNS</a>
<li><a name="TOC15" href="#SEC15">REPETITION</a>	<li><a name="TOC15" href="#SEC15">DUPLICATE SUBPATTERN NUMBERS</a>
<li><a name="TOC16" href="#SEC16">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a>	<li><a name="TOC16" href="#SEC16">NAMED SUBPATTERNS</a>
<li><a name="TOC17" href="#SEC17">BACK REFERENCES</a>	<li><a name="TOC17" href="#SEC17">REPETITION</a>
<li><a name="TOC18" href="#SEC18">ASSERTIONS</a>	<li><a name="TOC18" href="#SEC18">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a>
<li><a name="TOC19" href="#SEC19">CONDITIONAL SUBPATTERNS</a>	<li><a name="TOC19" href="#SEC19">BACK REFERENCES</a>
<li><a name="TOC20" href="#SEC20">COMMENTS</a>	<li><a name="TOC20" href="#SEC20">ASSERTIONS</a>
<li><a name="TOC21" href="#SEC21">RECURSIVE PATTERNS</a>	<li><a name="TOC21" href="#SEC21">CONDITIONAL SUBPATTERNS</a>
<li><a name="TOC22" href="#SEC22">SUBPATTERNS AS SUBROUTINES</a>	<li><a name="TOC22" href="#SEC22">COMMENTS</a>
<li><a name="TOC23" href="#SEC23">ONIGURUMA SUBROUTINE SYNTAX</a>	<li><a name="TOC23" href="#SEC23">RECURSIVE PATTERNS</a>
<li><a name="TOC24" href="#SEC24">CALLOUTS</a>	<li><a name="TOC24" href="#SEC24">SUBPATTERNS AS SUBROUTINES</a>
<li><a name="TOC25" href="#SEC25">BACKTRACKING CONTROL</a>	<li><a name="TOC25" href="#SEC25">ONIGURUMA SUBROUTINE SYNTAX</a>
<li><a name="TOC26" href="#SEC26">SEE ALSO</a>	<li><a name="TOC26" href="#SEC26">CALLOUTS</a>
<li><a name="TOC27" href="#SEC27">AUTHOR</a>	<li><a name="TOC27" href="#SEC27">BACKTRACKING CONTROL</a>
<li><a name="TOC28" href="#SEC28">REVISION</a>	<li><a name="TOC28" href="#SEC28">SEE ALSO</a>
	<li><a name="TOC29" href="#SEC29">AUTHOR</a>
	<li><a name="TOC30" href="#SEC30">REVISION</a>
</ul>	</ul>
<br><a name="SEC1" href="#TOC1">PCRE REGULAR EXPRESSION DETAILS</a><br>	<br><a name="SEC1" href="#TOC1">PCRE REGULAR EXPRESSION DETAILS</a><br>
<P>	<P>
Line 60 published by O'Reilly, covers regular expressions in g	Line 62 published by O'Reilly, covers regular expressions in g
description of PCRE's regular expressions is intended as reference material.	description of PCRE's regular expressions is intended as reference material.
</P>	</P>
<P>	<P>
	This document discusses the patterns that are supported by PCRE when one its
	main matching functions, <b>pcre_exec()</b> (8-bit) or <b>pcre[16\|32]_exec()</b>
	(16- or 32-bit), is used. PCRE also has alternative matching functions,
	<b>pcre_dfa_exec()</b> and <b>pcre[16\|32_dfa_exec()</b>, which match using a
	different algorithm that is not Perl-compatible. Some of the features discussed
	below are not available when DFA matching is used. The advantages and
	disadvantages of the alternative functions, and how they differ from the normal
	functions, are discussed in the
	<a href="pcrematching.html"><b>pcrematching</b></a>
	page.
	</P>
	<br><a name="SEC2" href="#TOC1">SPECIAL START-OF-PATTERN ITEMS</a><br>
	<P>
	A number of options that can be passed to <b>pcre_compile()</b> can also be set
	by special items at the start of a pattern. These are not Perl-compatible, but
	are provided to make these options accessible to pattern writers who are not
	able to change the program that processes the pattern. Any number of these
	items may appear, but they must all be together right at the start of the
	pattern string, and the letters must be in upper case.
	</P>
	<br><b>
	UTF support
	</b><br>
	<P>
The original operation of PCRE was on strings of one-byte characters. However,	The original operation of PCRE was on strings of one-byte characters. However,
there is now also support for UTF-8 character strings. To use this,	there is now also support for UTF-8 strings in the original library, an
PCRE must be built to include UTF-8 support, and you must call	extra library that supports 16-bit and UTF-16 character strings, and a
<b>pcre_compile()</b> or <b>pcre_compile2()</b> with the PCRE_UTF8 option. There	third library that supports 32-bit and UTF-32 character strings. To use these
is also a special sequence that can be given at the start of a pattern:	features, PCRE must be built to include appropriate support. When using UTF
	strings you must either call the compiling function with the PCRE_UTF8,
	PCRE_UTF16, or PCRE_UTF32 option, or the pattern must start with one of
	these special sequences:
<pre>	<pre>
(*UTF8)	(*UTF8)
	(*UTF16)
	(*UTF32)
	(*UTF)
</pre>	</pre>
Starting a pattern with this sequence is equivalent to setting the PCRE_UTF8	(*UTF) is a generic sequence that can be used with any of the libraries.
option. This feature is not Perl-compatible. How setting UTF-8 mode affects	Starting a pattern with such a sequence is equivalent to setting the relevant
pattern matching is mentioned in several places below. There is also a summary	option. How setting a UTF mode affects pattern matching is mentioned in several
of UTF-8 features in the	places below. There is also a summary of features in the
<a href="pcreunicode.html"><b>pcreunicode</b></a>	<a href="pcreunicode.html"><b>pcreunicode</b></a>
page.	page.
</P>	</P>
<P>	<P>
Another special sequence that may appear at the start of a pattern or in	Some applications that allow their users to supply patterns may wish to
combination with (*UTF8) is:	restrict them to non-UTF data for security reasons. If the PCRE_NEVER_UTF
<pre>	option is set at compile time, (*UTF) etc. are not allowed, and their
(*UCP)	appearance causes an error.
</pre>	</P>
	<br><b>
	Unicode property support
	</b><br>
	<P>
	Another special sequence that may appear at the start of a pattern is (*UCP).
This has the same effect as setting the PCRE_UCP option: it causes sequences	This has the same effect as setting the PCRE_UCP option: it causes sequences
such as \d and \w to use Unicode properties to determine character types,	such as \d and \w to use Unicode properties to determine character types,
instead of recognizing only characters with codes less than 128 via a lookup	instead of recognizing only characters with codes less than 128 via a lookup
table.	table.
</P>	</P>
	<br><b>
	Disabling auto-possessification
	</b><br>
<P>	<P>
If a pattern starts with (*NO_START_OPT), it has the same effect as setting the	If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as setting
PCRE_NO_START_OPTIMIZE option either at compile or matching time. There are	the PCRE_NO_AUTO_POSSESS option at compile time. This stops PCRE from making
also some more of these special sequences that are concerned with the handling	quantifiers possessive when what follows cannot match the repeated item. For
of newlines; they are described below.	example, by default a+b is treated as a++b. For more details, see the
	<a href="pcreapi.html"><b>pcreapi</b></a>
	documentation.
</P>	</P>
	<br><b>
	Disabling start-up optimizations
	</b><br>
<P>	<P>
The remainder of this document discusses the patterns that are supported by	If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
PCRE when its main matching function, <b>pcre_exec()</b>, is used.	PCRE_NO_START_OPTIMIZE option either at compile or matching time. This disables
From release 6.0, PCRE offers a second matching function,	several optimizations for quickly reaching "no match" results. For more
<b>pcre_dfa_exec()</b>, which matches using a different algorithm that is not	details, see the
Perl-compatible. Some of the features discussed below are not available when	<a href="pcreapi.html"><b>pcreapi</b></a>
<b>pcre_dfa_exec()</b> is used. The advantages and disadvantages of the	documentation.
alternative function, and how it differs from the normal function, are
discussed in the
<a href="pcrematching.html"><b>pcrematching</b></a>
page.
<a name="newlines"></a></P>	<a name="newlines"></a></P>
<br><a name="SEC2" href="#TOC1">NEWLINE CONVENTIONS</a><br>	<br><b>
	Newline conventions
	</b><br>
<P>	<P>
PCRE supports five different conventions for indicating line breaks in	PCRE supports five different conventions for indicating line breaks in
strings: a single CR (carriage return) character, a single LF (linefeed)	strings: a single CR (carriage return) character, a single LF (linefeed)
Line 126 string with one of the following five sequences:	Line 169 string with one of the following five sequences:
(*ANYCRLF) any of the three above	(*ANYCRLF) any of the three above
(*ANY) all Unicode newline sequences	(*ANY) all Unicode newline sequences
</pre>	</pre>
These override the default and the options given to <b>pcre_compile()</b> or	These override the default and the options given to the compiling function. For
<b>pcre_compile2()</b>. For example, on a Unix system where LF is the default	example, on a Unix system where LF is the default newline sequence, the pattern
newline sequence, the pattern
<pre>	<pre>
(*CR)a.b	(*CR)a.b
</pre>	</pre>
changes the convention to CR. That pattern matches "a\nb" because LF is no	changes the convention to CR. That pattern matches "a\nb" because LF is no
longer a newline. Note that these special settings, which are not	longer a newline. If more than one of these settings is present, the last one
Perl-compatible, are recognized only at the very start of a pattern, and that
they must be in upper case. If more than one of them is present, the last one
is used.	is used.
</P>	</P>
<P>	<P>
The newline convention affects the interpretation of the dot metacharacter when	The newline convention affects where the circumflex and dollar assertions are
PCRE_DOTALL is not set, and also the behaviour of \N. However, it does not	true. It also affects the interpretation of the dot metacharacter when
affect what the \R escape sequence matches. By default, this is any Unicode	PCRE_DOTALL is not set, and the behaviour of \N. However, it does not affect
newline sequence, for Perl compatibility. However, this can be changed; see the	what the \R escape sequence matches. By default, this is any Unicode newline
	sequence, for Perl compatibility. However, this can be changed; see the
description of \R in the section entitled	description of \R in the section entitled
<a href="#newlineseq">"Newline sequences"</a>	<a href="#newlineseq">"Newline sequences"</a>
below. A change of \R setting can be combined with a change of newline	below. A change of \R setting can be combined with a change of newline
convention.	convention.
</P>	</P>
<br><a name="SEC3" href="#TOC1">CHARACTERS AND METACHARACTERS</a><br>	<br><b>
	Setting match and recursion limits
	</b><br>
<P>	<P>
	The caller of <b>pcre_exec()</b> can set a limit on the number of times the
	internal <b>match()</b> function is called and on the maximum depth of
	recursive calls. These facilities are provided to catch runaway matches that
	are provoked by patterns with huge matching trees (a typical example is a
	pattern with nested unlimited repeats) and to avoid running out of system stack
	by too much recursion. When one of these limits is reached, <b>pcre_exec()</b>
	gives an error return. The limits can also be set by items at the start of the
	pattern of the form
	<pre>
	(*LIMIT_MATCH=d)
	(*LIMIT_RECURSION=d)
	</pre>
	where d is any number of decimal digits. However, the value of the setting must
	be less than the value set (or defaulted) by the caller of <b>pcre_exec()</b>
	for it to have any effect. In other words, the pattern writer can lower the
	limits set by the programmer, but not raise them. If there is more than one
	setting of one of these limits, the lower value is used.
	</P>
	<br><a name="SEC3" href="#TOC1">EBCDIC CHARACTER CODES</a><br>
	<P>
	PCRE can be compiled to run in an environment that uses EBCDIC as its character
	code rather than ASCII or Unicode (typically a mainframe system). In the
	sections below, character code values are ASCII or Unicode; in an EBCDIC
	environment these characters may have different code values, and there are no
	code points greater than 255.
	</P>
	<br><a name="SEC4" href="#TOC1">CHARACTERS AND METACHARACTERS</a><br>
	<P>
A regular expression is a pattern that is matched against a subject string from	A regular expression is a pattern that is matched against a subject string from
left to right. Most characters stand for themselves in a pattern, and match the	left to right. Most characters stand for themselves in a pattern, and match the
corresponding characters in the subject. As a trivial example, the pattern	corresponding characters in the subject. As a trivial example, the pattern
Line 158 corresponding characters in the subject. As a trivial	Line 229 corresponding characters in the subject. As a trivial
</pre>	</pre>
matches a portion of a subject string that is identical to itself. When	matches a portion of a subject string that is identical to itself. When
caseless matching is specified (the PCRE_CASELESS option), letters are matched	caseless matching is specified (the PCRE_CASELESS option), letters are matched
independently of case. In UTF-8 mode, PCRE always understands the concept of	independently of case. In a UTF mode, PCRE always understands the concept of
case for characters whose values are less than 128, so caseless matching is	case for characters whose values are less than 128, so caseless matching is
always possible. For characters with higher values, the concept of case is	always possible. For characters with higher values, the concept of case is
supported if PCRE is compiled with Unicode property support, but not otherwise.	supported if PCRE is compiled with Unicode property support, but not otherwise.
If you want to use caseless matching for characters 128 and above, you must	If you want to use caseless matching for characters 128 and above, you must
ensure that PCRE is compiled with Unicode property support as well as with	ensure that PCRE is compiled with Unicode property support as well as with
UTF-8 support.	UTF support.
</P>	</P>
<P>	<P>
The power of regular expressions comes from the ability to include alternatives	The power of regular expressions comes from the ability to include alternatives
Line 205 a character class the only metacharacters are:	Line 276 a character class the only metacharacters are:
</pre>	</pre>
The following sections describe the use of each of the metacharacters.	The following sections describe the use of each of the metacharacters.
</P>	</P>
<br><a name="SEC4" href="#TOC1">BACKSLASH</a><br>	<br><a name="SEC5" href="#TOC1">BACKSLASH</a><br>
<P>	<P>
The backslash character has several uses. Firstly, if it is followed by a	The backslash character has several uses. Firstly, if it is followed by a
character that is not a number or a letter, it takes away any special meaning	character that is not a number or a letter, it takes away any special meaning
Line 220 non-alphanumeric with backslash to specify that it sta	Line 291 non-alphanumeric with backslash to specify that it sta
particular, if you want to match a backslash, you write \\.	particular, if you want to match a backslash, you write \\.
</P>	</P>
<P>	<P>
In UTF-8 mode, only ASCII numbers and letters have any special meaning after a	In a UTF mode, only ASCII numbers and letters have any special meaning after a
backslash. All other characters (in particular, those whose codepoints are	backslash. All other characters (in particular, those whose codepoints are
greater than 127) are treated as literals.	greater than 127) are treated as literals.
</P>	</P>
<P>	<P>
If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the	If a pattern is compiled with the PCRE_EXTENDED option, most white space in the
pattern (other than in a character class) and characters between a # outside	pattern (other than in a character class), and characters between a # outside a
a character class and the next newline are ignored. An escaping backslash can	character class and the next newline, inclusive, are ignored. An escaping
be used to include a whitespace or # character as part of the pattern.	backslash can be used to include a white space or # character as part of the
	pattern.
</P>	</P>
<P>	<P>
If you want to remove the special meaning from a sequence of characters, you	If you want to remove the special meaning from a sequence of characters, you
Line 262 one of the following escape sequences than the binary	Line 334 one of the following escape sequences than the binary
\a alarm, that is, the BEL character (hex 07)	\a alarm, that is, the BEL character (hex 07)
\cx "control-x", where x is any ASCII character	\cx "control-x", where x is any ASCII character
\e escape (hex 1B)	\e escape (hex 1B)
\f formfeed (hex 0C)	\f form feed (hex 0C)
\n linefeed (hex 0A)	\n linefeed (hex 0A)
\r carriage return (hex 0D)	\r carriage return (hex 0D)
\t tab (hex 09)	\t tab (hex 09)
	\0dd character with octal code 0dd
\ddd character with octal code ddd, or back reference	\ddd character with octal code ddd, or back reference
	\o{ddd..} character with octal code ddd..
\xhh character with hex code hh	\xhh character with hex code hh
\x{hhh..} character with hex code hhh.. (non-JavaScript mode)	\x{hhh..} character with hex code hhh.. (non-JavaScript mode)
\uhhhh character with hex code hhhh (JavaScript mode only)	\uhhhh character with hex code hhhh (JavaScript mode only)
</pre>	</pre>
The precise effect of \cx is as follows: if x is a lower case letter, it	The precise effect of \cx on ASCII characters is as follows: if x is a lower
is converted to upper case. Then bit 6 of the character (hex 40) is inverted.	case letter, it is converted to upper case. Then bit 6 of the character (hex
Thus \cz becomes hex 1A (z is 7A), but \c{ becomes hex 3B ({ is 7B), while	40) is inverted. Thus \cA to \cZ become hex 01 to hex 1A (A is 41, Z is 5A),
\c; becomes hex 7B (; is 3B). If the byte following \c has a value greater	but \c{ becomes hex 3B ({ is 7B), and \c; becomes hex 7B (; is 3B). If the
than 127, a compile-time error occurs. This locks out non-ASCII characters in	data item (byte or 16-bit value) following \c has a value greater than 127, a
both byte mode and UTF-8 mode. (When PCRE is compiled in EBCDIC mode, all byte	compile-time error occurs. This locks out non-ASCII characters in all modes.
values are valid. A lower case letter is converted to upper case, and then the
0xc0 bits are flipped.)
</P>	</P>
<P>	<P>
By default, after \x, from zero to two hexadecimal digits are read (letters	The \c facility was designed for use with ASCII characters, but with the
can be in upper or lower case). Any number of hexadecimal digits may appear	extension to Unicode it is even less useful than it once was. It is, however,
between \x{ and }, but the value of the character code must be less than 256	recognized when PCRE is compiled in EBCDIC mode, where data items are always
in non-UTF-8 mode, and less than 2**31 in UTF-8 mode. That is, the maximum	bytes. In this mode, all values are valid after \c. If the next character is a
value in hexadecimal is 7FFFFFFF. Note that this is bigger than the largest	lower case letter, it is converted to upper case. Then the 0xc0 bits of the
Unicode code point, which is 10FFFF.	byte are inverted. Thus \cA becomes hex 01, as in ASCII (A is C1), but because
	the EBCDIC letters are disjoint, \cZ becomes hex 29 (Z is E9), and other
	characters also generate different values.
</P>	</P>
<P>	<P>
If characters other than hexadecimal digits appear between \x{ and }, or if
there is no terminating }, this form of escape is not recognized. Instead, the
initial \x will be interpreted as a basic hexadecimal escape, with no
following digits, giving a character whose value is zero.
</P>
<P>
If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x is
as just described only when it is followed by two hexadecimal digits.
Otherwise, it matches a literal "x" character. In JavaScript mode, support for
code points greater than 256 is provided by \u, which must be followed by
four hexadecimal digits; otherwise it matches a literal "u" character.
</P>
<P>
Characters whose value is less than 256 can be defined by either of the two
syntaxes for \x (or by \u in JavaScript mode). There is no difference in the
way they are handled. For example, \xdc is exactly the same as \x{dc} (or
\u00dc in JavaScript mode).
</P>
<P>
After \0 up to two further octal digits are read. If there are fewer than two	After \0 up to two further octal digits are read. If there are fewer than two
digits, just those that are present are used. Thus the sequence \0\x\07	digits, just those that are present are used. Thus the sequence \0\x\07
specifies two binary zeros followed by a BEL character (code value 7). Make	specifies two binary zeros followed by a BEL character (code value 7). Make
Line 315 sure you supply two digits after the initial zero if t	Line 370 sure you supply two digits after the initial zero if t
follows is itself an octal digit.	follows is itself an octal digit.
</P>	</P>
<P>	<P>
The handling of a backslash followed by a digit other than 0 is complicated.	The escape \o must be followed by a sequence of octal digits, enclosed in
Outside a character class, PCRE reads it and any following digits as a decimal	braces. An error occurs if this is not the case. This escape is a recent
number. If the number is less than 10, or if there have been at least that many	addition to Perl; it provides way of specifying character code points as octal
	numbers greater than 0777, and it also allows octal numbers and back references
	to be unambiguously specified.
	</P>
	<P>
	For greater clarity and unambiguity, it is best to avoid following \ by a
	digit greater than zero. Instead, use \o{} or \x{} to specify character
	numbers, and \g{} to specify back references. The following paragraphs
	describe the old, ambiguous syntax.
	</P>
	<P>
	The handling of a backslash followed by a digit other than 0 is complicated,
	and Perl has changed in recent releases, causing PCRE also to change. Outside a
	character class, PCRE reads the digit and any following digits as a decimal
	number. If the number is less than 8, or if there have been at least that many
previous capturing left parentheses in the expression, the entire sequence is	previous capturing left parentheses in the expression, the entire sequence is
taken as a <i>back reference</i>. A description of how this works is given	taken as a <i>back reference</i>. A description of how this works is given
<a href="#backreferences">later,</a>	<a href="#backreferences">later,</a>
Line 325 following the discussion of	Line 394 following the discussion of
<a href="#subpattern">parenthesized subpatterns.</a>	<a href="#subpattern">parenthesized subpatterns.</a>
</P>	</P>
<P>	<P>
Inside a character class, or if the decimal number is greater than 9 and there	Inside a character class, or if the decimal number following \ is greater than
have not been that many capturing subpatterns, PCRE re-reads up to three octal	7 and there have not been that many capturing subpatterns, PCRE handles \8 and
digits following the backslash, and uses them to generate a data character. Any	\9 as the literal characters "8" and "9", and otherwise re-reads up to three
subsequent digits stand for themselves. In non-UTF-8 mode, the value of a	octal digits following the backslash, using them to generate a data character.
character specified in octal must be less than \400. In UTF-8 mode, values up	Any subsequent digits stand for themselves. For example:
to \777 are permitted. For example:
<pre>	<pre>
\040 is another way of writing a space	\040 is another way of writing an ASCII space
\40 is the same, provided there are fewer than 40 previous capturing subpatterns	\40 is the same, provided there are fewer than 40 previous capturing subpatterns
\7 is always a back reference	\7 is always a back reference
\11 might be a back reference, or another way of writing a tab	\11 might be a back reference, or another way of writing a tab
\011 is always a tab	\011 is always a tab
\0113 is a tab followed by the character "3"	\0113 is a tab followed by the character "3"
\113 might be a back reference, otherwise the character with octal code 113	\113 might be a back reference, otherwise the character with octal code 113
\377 might be a back reference, otherwise the byte consisting entirely of 1 bits	\377 might be a back reference, otherwise the value 255 (decimal)
\81 is either a back reference, or a binary zero followed by the two characters "8" and "1"	\81 is either a back reference, or the two characters "8" and "1"
</pre>	</pre>
Note that octal values of 100 or greater must not be introduced by a leading	Note that octal values of 100 or greater that are specified using this syntax
zero, because no more than three octal digits are ever read.	must not be introduced by a leading zero, because no more than three octal
	digits are ever read.
</P>	</P>
<P>	<P>
	By default, after \x that is not followed by {, from zero to two hexadecimal
	digits are read (letters can be in upper or lower case). Any number of
	hexadecimal digits may appear between \x{ and }. If a character other than
	a hexadecimal digit appears between \x{ and }, or if there is no terminating
	}, an error occurs.
	</P>
	<P>
	If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \x is
	as just described only when it is followed by two hexadecimal digits.
	Otherwise, it matches a literal "x" character. In JavaScript mode, support for
	code points greater than 256 is provided by \u, which must be followed by
	four hexadecimal digits; otherwise it matches a literal "u" character.
	</P>
	<P>
	Characters whose value is less than 256 can be defined by either of the two
	syntaxes for \x (or by \u in JavaScript mode). There is no difference in the
	way they are handled. For example, \xdc is exactly the same as \x{dc} (or
	\u00dc in JavaScript mode).
	</P>
	<br><b>
	Constraints on character values
	</b><br>
	<P>
	Characters that are specified using octal or hexadecimal numbers are
	limited to certain values, as follows:
	<pre>
	8-bit non-UTF mode less than 0x100
	8-bit UTF-8 mode less than 0x10ffff and a valid codepoint
	16-bit non-UTF mode less than 0x10000
	16-bit UTF-16 mode less than 0x10ffff and a valid codepoint
	32-bit non-UTF mode less than 0x100000000
	32-bit UTF-32 mode less than 0x10ffff and a valid codepoint
	</pre>
	Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
	"surrogate" codepoints), and 0xffef.
	</P>
	<br><b>
	Escape sequences in character classes
	</b><br>
	<P>
All the sequences that define a single character value can be used both inside	All the sequences that define a single character value can be used both inside
and outside character classes. In addition, inside a character class, \b is	and outside character classes. In addition, inside a character class, \b is
interpreted as the backspace character (hex 08).	interpreted as the backspace character (hex 08).
Line 399 Another use of backslash is for specifying generic cha	Line 508 Another use of backslash is for specifying generic cha
<pre>	<pre>
\d any decimal digit	\d any decimal digit
\D any character that is not a decimal digit	\D any character that is not a decimal digit
\h any horizontal whitespace character	\h any horizontal white space character
\H any character that is not a horizontal whitespace character	\H any character that is not a horizontal white space character
\s any whitespace character	\s any white space character
\S any character that is not a whitespace character	\S any character that is not a white space character
\v any vertical whitespace character	\v any vertical white space character
\V any character that is not a vertical whitespace character	\V any character that is not a vertical white space character
\w any "word" character	\w any "word" character
\W any "non-word" character	\W any "non-word" character
</pre>	</pre>
Line 423 matching point is at the end of the subject string, al	Line 532 matching point is at the end of the subject string, al
there is no character to match.	there is no character to match.
</P>	</P>
<P>	<P>
For compatibility with Perl, \s does not match the VT character (code 11).	For compatibility with Perl, \s did not used to match the VT character (code
This makes it different from the the POSIX "space" class. The \s characters	11), which made it different from the the POSIX "space" class. However, Perl
are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is	added VT at release 5.18, and PCRE followed suit at release 8.34. The default
included in a Perl script, \s may match the VT character. In PCRE, it never	\s characters are now HT (9), LF (10), VT (11), FF (12), CR (13), and space
does.	(32), which are defined as white space in the "C" locale. This list may vary if
	locale-specific matching is taking place. For example, in some locales the
	"non-breaking space" character (\xA0) is recognized as white space, and in
	others the VT character is not.
</P>	</P>
<P>	<P>
A "word" character is an underscore or any character that is a letter or digit.	A "word" character is an underscore or any character that is a letter or digit.
Line 438 place (see	Line 550 place (see
in the	in the
<a href="pcreapi.html"><b>pcreapi</b></a>	<a href="pcreapi.html"><b>pcreapi</b></a>
page). For example, in a French locale such as "fr_FR" in Unix-like systems,	page). For example, in a French locale such as "fr_FR" in Unix-like systems,
or "french" in Windows, some character codes greater than 128 are used for	or "french" in Windows, some character codes greater than 127 are used for
accented letters, and these are then matched by \w. The use of locales with	accented letters, and these are then matched by \w. The use of locales with
Unicode is discouraged.	Unicode is discouraged.
</P>	</P>
<P>	<P>
By default, in UTF-8 mode, characters with values greater than 128 never match	By default, characters whose code points are greater than 127 never match \d,
\d, \s, or \w, and always match \D, \S, and \W. These sequences retain	\s, or \w, and always match \D, \S, and \W, although this may vary for
their original meanings from before UTF-8 support was available, mainly for	characters in the range 128-255 when locale-specific matching is happening.
efficiency reasons. However, if PCRE is compiled with Unicode property support,	These escape sequences retain their original meanings from before Unicode
and the PCRE_UCP option is set, the behaviour is changed so that Unicode	support was available, mainly for efficiency reasons. If PCRE is compiled with
properties are used to determine character types, as follows:	Unicode property support, and the PCRE_UCP option is set, the behaviour is
	changed so that Unicode properties are used to determine character types, as
	follows:
<pre>	<pre>
\d any character that \p{Nd} matches (decimal digit)	\d any character that matches \p{Nd} (decimal digit)
\s any character that \p{Z} matches, plus HT, LF, FF, CR	\s any character that matches \p{Z} or \h or \v
\w any character that \p{L} or \p{N} matches, plus underscore	\w any character that matches \p{L} or \p{N}, plus underscore
</pre>	</pre>
The upper case escapes match the inverse sets of characters. Note that \d	The upper case escapes match the inverse sets of characters. Note that \d
matches only decimal digits, whereas \w matches any Unicode digit, as well as	matches only decimal digits, whereas \w matches any Unicode digit, as well as
Line 463 is noticeably slower when PCRE_UCP is set.	Line 577 is noticeably slower when PCRE_UCP is set.
<P>	<P>
The sequences \h, \H, \v, and \V are features that were added to Perl at	The sequences \h, \H, \v, and \V are features that were added to Perl at
release 5.10. In contrast to the other sequences, which match only ASCII	release 5.10. In contrast to the other sequences, which match only ASCII
characters by default, these always match certain high-valued codepoints in	characters by default, these always match certain high-valued code points,
UTF-8 mode, whether or not PCRE_UCP is set. The horizontal space characters	whether or not PCRE_UCP is set. The horizontal space characters are:
are:
<pre>	<pre>
U+0009 Horizontal tab	U+0009 Horizontal tab (HT)
U+0020 Space	U+0020 Space
U+00A0 Non-break space	U+00A0 Non-break space
U+1680 Ogham space mark	U+1680 Ogham space mark
Line 489 are:	Line 602 are:
</pre>	</pre>
The vertical space characters are:	The vertical space characters are:
<pre>	<pre>
U+000A Linefeed	U+000A Linefeed (LF)
U+000B Vertical tab	U+000B Vertical tab (VT)
U+000C Formfeed	U+000C Form feed (FF)
U+000D Carriage return	U+000D Carriage return (CR)
U+0085 Next line	U+0085 Next line (NEL)
U+2028 Line separator	U+2028 Line separator
U+2029 Paragraph separator	U+2029 Paragraph separator
<a name="newlineseq"></a></PRE>	</pre>
</P>	In 8-bit, non-UTF-8 mode, only the characters with codepoints less than 256 are
	relevant.
	<a name="newlineseq"></a></P>
<br><b>	<br><b>
Newline sequences	Newline sequences
</b><br>	</b><br>
<P>	<P>
Outside a character class, by default, the escape sequence \R matches any	Outside a character class, by default, the escape sequence \R matches any
Unicode newline sequence. In non-UTF-8 mode \R is equivalent to the following:	Unicode newline sequence. In 8-bit non-UTF-8 mode \R is equivalent to the
	following:
<pre>	<pre>
(?>\r\n\|\n\|\x0b\|\f\|\r\|\x85)	(?>\r\n\|\n\|\x0b\|\f\|\r\|\x85)
</pre>	</pre>
Line 511 This is an example of an "atomic group", details of wh	Line 627 This is an example of an "atomic group", details of wh
<a href="#atomicgroup">below.</a>	<a href="#atomicgroup">below.</a>
This particular group matches either the two-character sequence CR followed by	This particular group matches either the two-character sequence CR followed by
LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,	LF, or one of the single characters LF (linefeed, U+000A), VT (vertical tab,
U+000B), FF (formfeed, U+000C), CR (carriage return, U+000D), or NEL (next	U+000B), FF (form feed, U+000C), CR (carriage return, U+000D), or NEL (next
line, U+0085). The two-character sequence is treated as a single unit that	line, U+0085). The two-character sequence is treated as a single unit that
cannot be split.	cannot be split.
</P>	</P>
<P>	<P>
In UTF-8 mode, two additional characters whose codepoints are greater than 255	In other modes, two additional characters whose codepoints are greater than 255
are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).	are added: LS (line separator, U+2028) and PS (paragraph separator, U+2029).
Unicode character property support is not needed for these characters to be	Unicode character property support is not needed for these characters to be
recognized.	recognized.
Line 533 one of the following sequences:	Line 649 one of the following sequences:
(*BSR_ANYCRLF) CR, LF, or CRLF only	(*BSR_ANYCRLF) CR, LF, or CRLF only
(*BSR_UNICODE) any Unicode newline sequence	(*BSR_UNICODE) any Unicode newline sequence
</pre>	</pre>
These override the default and the options given to <b>pcre_compile()</b> or	These override the default and the options given to the compiling function, but
<b>pcre_compile2()</b>, but they can be overridden by options given to	they can themselves be overridden by options given to a matching function. Note
<b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>. Note that these special settings,	that these special settings, which are not Perl-compatible, are recognized only
which are not Perl-compatible, are recognized only at the very start of a	at the very start of a pattern, and that they must be in upper case. If more
pattern, and that they must be in upper case. If more than one of them is	than one of them is present, the last one is used. They can be combined with a
present, the last one is used. They can be combined with a change of newline	change of newline convention; for example, a pattern can start with:
convention; for example, a pattern can start with:
<pre>	<pre>
(ANY)(BSR_ANYCRLF)	(ANY)(BSR_ANYCRLF)
</pre>	</pre>
They can also be combined with the (UTF8) or (UCP) special sequences. Inside	They can also be combined with the (UTF8), (UTF16), (UTF32), (UTF) or
a character class, \R is treated as an unrecognized escape sequence, and so	(*UCP) special sequences. Inside a character class, \R is treated as an
matches the letter "R" by default, but causes an error if PCRE_EXTRA is set.	unrecognized escape sequence, and so matches the letter "R" by default, but
	causes an error if PCRE_EXTRA is set.
<a name="uniextseq"></a></P>	<a name="uniextseq"></a></P>
<br><b>	<br><b>
Unicode character properties	Unicode character properties
Line 553 Unicode character properties	Line 669 Unicode character properties
<P>	<P>
When PCRE is built with Unicode character property support, three additional	When PCRE is built with Unicode character property support, three additional
escape sequences that match characters with specific properties are available.	escape sequences that match characters with specific properties are available.
When not in UTF-8 mode, these sequences are of course limited to testing	When in 8-bit non-UTF-8 mode, these sequences are of course limited to testing
characters whose codepoints are less than 256, but they do work in this mode.	characters whose codepoints are less than 256, but they do work in this mode.
The extra escape sequences are:	The extra escape sequences are:
<pre>	<pre>
\p{<i>xx</i>} a character with the <i>xx</i> property	\p{<i>xx</i>} a character with the <i>xx</i> property
\P{<i>xx</i>} a character without the <i>xx</i> property	\P{<i>xx</i>} a character without the <i>xx</i> property
\X an extended Unicode sequence	\X a Unicode extended grapheme cluster
</pre>	</pre>
The property names represented by <i>xx</i> above are limited to the Unicode	The property names represented by <i>xx</i> above are limited to the Unicode
script names, the general category properties, "Any", which matches any	script names, the general category properties, "Any", which matches any
Line 587 Armenian,	Line 703 Armenian,
Avestan,	Avestan,
Balinese,	Balinese,
Bamum,	Bamum,
	Batak,
Bengali,	Bengali,
Bopomofo,	Bopomofo,
	Brahmi,
Braille,	Braille,
Buginese,	Buginese,
Buhid,	Buhid,
Canadian_Aboriginal,	Canadian_Aboriginal,
Carian,	Carian,
	Chakma,
Cham,	Cham,
Cherokee,	Cherokee,
Common,	Common,
Line 636 Lisu,	Line 755 Lisu,
Lycian,	Lycian,
Lydian,	Lydian,
Malayalam,	Malayalam,
	Mandaic,
Meetei_Mayek,	Meetei_Mayek,
	Meroitic_Cursive,
	Meroitic_Hieroglyphs,
	Miao,
Mongolian,	Mongolian,
Myanmar,	Myanmar,
New_Tai_Lue,	New_Tai_Lue,
Line 655 Rejang,	Line 778 Rejang,
Runic,	Runic,
Samaritan,	Samaritan,
Saurashtra,	Saurashtra,
	Sharada,
Shavian,	Shavian,
Sinhala,	Sinhala,
	Sora_Sompeng,
Sundanese,	Sundanese,
Syloti_Nagri,	Syloti_Nagri,
Syriac,	Syriac,
Line 665 Tagbanwa,	Line 790 Tagbanwa,
Tai_Le,	Tai_Le,
Tai_Tham,	Tai_Tham,
Tai_Viet,	Tai_Viet,
	Takri,
Tamil,	Tamil,
Telugu,	Telugu,
Thaana,	Thaana,
Line 742 a modifier or "other".	Line 868 a modifier or "other".
</P>	</P>
<P>	<P>
The Cs (Surrogate) property applies only to characters in the range U+D800 to	The Cs (Surrogate) property applies only to characters in the range U+D800 to
U+DFFF. Such characters are not valid in UTF-8 strings (see RFC 3629) and so	U+DFFF. Such characters are not valid in Unicode strings and so
cannot be tested by PCRE, unless UTF-8 validity checking has been turned off	cannot be tested by PCRE, unless UTF validity checking has been turned off
(see the discussion of PCRE_NO_UTF8_CHECK in the	(see the discussion of PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK and
	PCRE_NO_UTF32_CHECK in the
<a href="pcreapi.html"><b>pcreapi</b></a>	<a href="pcreapi.html"><b>pcreapi</b></a>
page). Perl does not support the Cs property.	page). Perl does not support the Cs property.
</P>	</P>
Line 760 Unicode table.	Line 887 Unicode table.
</P>	</P>
<P>	<P>
Specifying caseless matching does not affect these escape sequences. For	Specifying caseless matching does not affect these escape sequences. For
example, \p{Lu} always matches only upper case letters.	example, \p{Lu} always matches only upper case letters. This is different from
	the behaviour of current versions of Perl.
</P>	</P>
<P>	<P>
The \X escape matches any number of Unicode characters that form an extended	Matching characters by Unicode property is not fast, because PCRE has to do a
Unicode sequence. \X is equivalent to	multistage table lookup in order to find a character's property. That is why
	the traditional escape sequences such as \d and \w do not use Unicode
	properties in PCRE by default, though you can make them do so by setting the
	PCRE_UCP option or by starting the pattern with (*UCP).
	</P>
	<br><b>
	Extended grapheme clusters
	</b><br>
	<P>
	The \X escape matches any number of Unicode characters that form an "extended
	grapheme cluster", and treats the sequence as an atomic group
	<a href="#atomicgroup">(see below).</a>
	Up to and including release 8.31, PCRE matched an earlier, simpler definition
	that was equivalent to
<pre>	<pre>
(?>\PM\pM*)	(?>\PM\pM*)
</pre>	</pre>
That is, it matches a character without the "mark" property, followed by zero	That is, it matched a character without the "mark" property, followed by zero
or more characters with the "mark" property, and treats the sequence as an	or more characters with the "mark" property. Characters with the "mark"
atomic group	property are typically non-spacing accents that affect the preceding character.
<a href="#atomicgroup">(see below).</a>
Characters with the "mark" property are typically accents that affect the
preceding character. None of them have codepoints less than 256, so in
non-UTF-8 mode \X matches any one character.
</P>	</P>
<P>	<P>
Note that recent versions of Perl have changed \X to match what Unicode calls	This simple definition was extended in Unicode to include more complicated
an "extended grapheme cluster", which has a more complicated definition.	kinds of composite character by giving each character a grapheme breaking
	property, and creating rules that use these properties to define the boundaries
	of extended grapheme clusters. In releases of PCRE later than 8.31, \X matches
	one of these clusters.
</P>	</P>
<P>	<P>
Matching characters by Unicode property is not fast, because PCRE has to search	\X always matches at least one character. Then it decides whether to add
a structure that contains data for over fifteen thousand characters. That is	additional characters according to the following rules for ending a cluster:
why the traditional escape sequences such as \d and \w do not use Unicode	</P>
properties in PCRE by default, though you can make them do so by setting the	<P>
PCRE_UCP option for <b>pcre_compile()</b> or by starting the pattern with	1. End at the end of the subject string.
(*UCP).	</P>
	<P>
	2. Do not end between CR and LF; otherwise end after any control character.
	</P>
	<P>
	3. Do not break Hangul (a Korean script) syllable sequences. Hangul characters
	are of five types: L, V, T, LV, and LVT. An L character may be followed by an
	L, V, LV, or LVT character; an LV or V character may be followed by a V or T
	character; an LVT or T character may be follwed only by a T character.
	</P>
	<P>
	4. Do not end before extending characters or spacing marks. Characters with
	the "mark" property always have the "extend" grapheme breaking property.
	</P>
	<P>
	5. Do not end after prepend characters.
	</P>
	<P>
	6. Otherwise, end the cluster.
<a name="extraprops"></a></P>	<a name="extraprops"></a></P>
<br><b>	<br><b>
PCRE's additional properties	PCRE's additional properties
</b><br>	</b><br>
<P>	<P>
As well as the standard Unicode properties described in the previous	As well as the standard Unicode properties described above, PCRE supports four
section, PCRE supports four more that make it possible to convert traditional	more that make it possible to convert traditional escape sequences such as \w
escape sequences such as \w and \s and POSIX character classes to use Unicode	and \s to use Unicode properties. PCRE uses these non-standard, non-Perl
properties. PCRE uses these non-standard, non-Perl properties internally when	properties internally when PCRE_UCP is set. However, they may also be used
PCRE_UCP is set. They are:	explicitly. These properties are:
<pre>	<pre>
Xan Any alphanumeric character	Xan Any alphanumeric character
Xps Any POSIX space character	Xps Any POSIX space character
Line 804 PCRE_UCP is set. They are:	Line 962 PCRE_UCP is set. They are:
Xwd Any Perl "word" character	Xwd Any Perl "word" character
</pre>	</pre>
Xan matches characters that have either the L (letter) or the N (number)	Xan matches characters that have either the L (letter) or the N (number)
property. Xps matches the characters tab, linefeed, vertical tab, formfeed, or	property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
carriage return, and any other character that has the Z (separator) property.	carriage return, and any other character that has the Z (separator) property.
Xsp is the same as Xps, except that vertical tab is excluded. Xwd matches the	Xsp is the same as Xps; it used to exclude vertical tab, for Perl
same characters as Xan, plus underscore.	compatibility, but Perl changed, and so PCRE followed at release 8.34. Xwd
	matches the same characters as Xan, plus underscore.
	</P>
	<P>
	There is another non-standard property, Xuc, which matches any character that
	can be represented by a Universal Character Name in C++ and other programming
	languages. These are the characters $, @, ` (grave accent), and all characters
	with Unicode code points greater than or equal to U+00A0, except for the
	surrogates U+D800 to U+DFFF. Note that most base (ASCII) characters are
	excluded. (Universal Character Names are of the form \uHHHH or \UHHHHHHHH
	where H is a hexadecimal digit. Note that the Xuc property does not match these
	sequences but the characters that they represent.)
<a name="resetmatchstart"></a></P>	<a name="resetmatchstart"></a></P>
<br><b>	<br><b>
Resetting the match start	Resetting the match start
Line 865 escape sequence" error is generated instead.	Line 1034 escape sequence" error is generated instead.
A word boundary is a position in the subject string where the current character	A word boundary is a position in the subject string where the current character
and the previous character do not both match \w or \W (i.e. one matches	and the previous character do not both match \w or \W (i.e. one matches
\w and the other matches \W), or the start or end of the string if the	\w and the other matches \W), or the start or end of the string if the
first or last character matches \w, respectively. In UTF-8 mode, the meanings	first or last character matches \w, respectively. In a UTF mode, the meanings
of \w and \W can be changed by setting the PCRE_UCP option. When this is	of \w and \W can be changed by setting the PCRE_UCP option. When this is
done, it also affects \b and \B. Neither PCRE nor Perl has a separate "start	done, it also affects \b and \B. Neither PCRE nor Perl has a separate "start
of word" or "end of word" metasequence. However, whatever follows \b normally	of word" or "end of word" metasequence. However, whatever follows \b normally
Line 904 If all the alternatives of a pattern begin with \G, th	Line 1073 If all the alternatives of a pattern begin with \G, th
to the starting match position, and the "anchored" flag is set in the compiled	to the starting match position, and the "anchored" flag is set in the compiled
regular expression.	regular expression.
</P>	</P>
<br><a name="SEC5" href="#TOC1">CIRCUMFLEX AND DOLLAR</a><br>	<br><a name="SEC6" href="#TOC1">CIRCUMFLEX AND DOLLAR</a><br>
<P>	<P>
	The circumflex and dollar metacharacters are zero-width assertions. That is,
	they test for a particular condition being true without consuming any
	characters from the subject string.
	</P>
	<P>
Outside a character class, in the default matching mode, the circumflex	Outside a character class, in the default matching mode, the circumflex
character is an assertion that is true only if the current matching point is	character is an assertion that is true only if the current matching point is at
at the start of the subject string. If the <i>startoffset</i> argument of	the start of the subject string. If the <i>startoffset</i> argument of
<b>pcre_exec()</b> is non-zero, circumflex can never match if the PCRE_MULTILINE	<b>pcre_exec()</b> is non-zero, circumflex can never match if the PCRE_MULTILINE
option is unset. Inside a character class, circumflex has an entirely different	option is unset. Inside a character class, circumflex has an entirely different
meaning	meaning
Line 924 constrained to match only at the start of the subject,	Line 1098 constrained to match only at the start of the subject,
to be anchored.)	to be anchored.)
</P>	</P>
<P>	<P>
A dollar character is an assertion that is true only if the current matching	The dollar character is an assertion that is true only if the current matching
point is at the end of the subject string, or immediately before a newline	point is at the end of the subject string, or immediately before a newline at
at the end of the string (by default). Dollar need not be the last character of	the end of the string (by default). Note, however, that it does not actually
the pattern if a number of alternatives are involved, but it should be the last	match the newline. Dollar need not be the last character of the pattern if a
item in any branch in which it appears. Dollar has no special meaning in a	number of alternatives are involved, but it should be the last item in any
character class.	branch in which it appears. Dollar has no special meaning in a character class.
</P>	</P>
<P>	<P>
The meaning of dollar can be changed so that it matches only at the very end of	The meaning of dollar can be changed so that it matches only at the very end of
Line 958 Note that the sequences \A, \Z, and \z can be used to	Line 1132 Note that the sequences \A, \Z, and \z can be used to
end of the subject in both modes, and if all branches of a pattern start with	end of the subject in both modes, and if all branches of a pattern start with
\A it is always anchored, whether or not PCRE_MULTILINE is set.	\A it is always anchored, whether or not PCRE_MULTILINE is set.
<a name="fullstopdot"></a></P>	<a name="fullstopdot"></a></P>
<br><a name="SEC6" href="#TOC1">FULL STOP (PERIOD, DOT) AND \N</a><br>	<br><a name="SEC7" href="#TOC1">FULL STOP (PERIOD, DOT) AND \N</a><br>
<P>	<P>
Outside a character class, a dot in the pattern matches any one character in	Outside a character class, a dot in the pattern matches any one character in
the subject string except (by default) a character that signifies the end of a	the subject string except (by default) a character that signifies the end of a
line. In UTF-8 mode, the matched character may be more than one byte long.	line.
</P>	</P>
<P>	<P>
When a line ending is defined as a single character, dot never matches that	When a line ending is defined as a single character, dot never matches that
Line 989 the PCRE_DOTALL option. In other words, it matches any	Line 1163 the PCRE_DOTALL option. In other words, it matches any
that signifies the end of a line. Perl also uses \N to match characters by	that signifies the end of a line. Perl also uses \N to match characters by
name; PCRE does not support this.	name; PCRE does not support this.
</P>	</P>
<br><a name="SEC7" href="#TOC1">MATCHING A SINGLE BYTE</a><br>	<br><a name="SEC8" href="#TOC1">MATCHING A SINGLE DATA UNIT</a><br>
<P>	<P>
Outside a character class, the escape sequence \C matches any one byte, both	Outside a character class, the escape sequence \C matches any one data unit,
in and out of UTF-8 mode. Unlike a dot, it always matches line-ending	whether or not a UTF mode is set. In the 8-bit library, one data unit is one
characters. The feature is provided in Perl in order to match individual bytes	byte; in the 16-bit library it is a 16-bit unit; in the 32-bit library it is
in UTF-8 mode, but it is unclear how it can usefully be used. Because \C	a 32-bit unit. Unlike a dot, \C always
breaks up characters into individual bytes, matching one byte with \C in UTF-8	matches line-ending characters. The feature is provided in Perl in order to
mode means that the rest of the string may start with a malformed UTF-8	match individual bytes in UTF-8 mode, but it is unclear how it can usefully be
character. This has undefined results, because PCRE assumes that it is dealing	used. Because \C breaks up characters into individual data units, matching one
with valid UTF-8 strings (and by default it checks this at the start of	unit with \C in a UTF mode means that the rest of the string may start with a
processing unless the PCRE_NO_UTF8_CHECK option is used).	malformed UTF character. This has undefined results, because PCRE assumes that
	it is dealing with valid UTF strings (and by default it checks this at the
	start of processing unless the PCRE_NO_UTF8_CHECK, PCRE_NO_UTF16_CHECK or
	PCRE_NO_UTF32_CHECK option is used).
</P>	</P>
<P>	<P>
PCRE does not allow \C to appear in lookbehind assertions	PCRE does not allow \C to appear in lookbehind assertions
<a href="#lookbehind">(described below)</a>	<a href="#lookbehind">(described below)</a>
in UTF-8 mode, because this would make it impossible to calculate the length of	in a UTF mode, because this would make it impossible to calculate the length of
the lookbehind.	the lookbehind.
</P>	</P>
<P>	<P>
In general, the \C escape sequence is best avoided in UTF-8 mode. However, one	In general, the \C escape sequence is best avoided. However, one
way of using it that avoids the problem of malformed UTF-8 characters is to	way of using it that avoids the problem of malformed UTF characters is to use a
use a lookahead to check the length of the next character, as in this pattern	lookahead to check the length of the next character, as in this pattern, which
(ignore white space and line breaks):	could be used with a UTF-8 string (ignore white space and line breaks):
<pre>	<pre>
(?\| (?=[\x00-\x7f])(\C) \|	(?\| (?=[\x00-\x7f])(\C) \|
(?=[\x80-\x{7ff}])(\C)(\C) \|	(?=[\x80-\x{7ff}])(\C)(\C) \|
Line 1026 character for values whose encoding uses 1, 2, 3, or 4	Line 1203 character for values whose encoding uses 1, 2, 3, or 4
character's individual bytes are then captured by the appropriate number of	character's individual bytes are then captured by the appropriate number of
groups.	groups.
<a name="characterclass"></a></P>	<a name="characterclass"></a></P>
<br><a name="SEC8" href="#TOC1">SQUARE BRACKETS AND CHARACTER CLASSES</a><br>	<br><a name="SEC9" href="#TOC1">SQUARE BRACKETS AND CHARACTER CLASSES</a><br>
<P>	<P>
An opening square bracket introduces a character class, terminated by a closing	An opening square bracket introduces a character class, terminated by a closing
square bracket. A closing square bracket on its own is not special by default.	square bracket. A closing square bracket on its own is not special by default.
Line 1036 a member of the class, it should be the first data cha	Line 1213 a member of the class, it should be the first data cha
(after an initial circumflex, if present) or escaped with a backslash.	(after an initial circumflex, if present) or escaped with a backslash.
</P>	</P>
<P>	<P>
A character class matches a single character in the subject. In UTF-8 mode, the	A character class matches a single character in the subject. In a UTF mode, the
character may be more than one byte long. A matched character must be in the	character may be more than one data unit long. A matched character must be in
set of characters defined by the class, unless the first character in the class	the set of characters defined by the class, unless the first character in the
definition is a circumflex, in which case the subject character must not be in	class definition is a circumflex, in which case the subject character must not
the set defined by the class. If a circumflex is actually required as a member	be in the set defined by the class. If a circumflex is actually required as a
of the class, ensure it is not the first character, or escape it with a	member of the class, ensure it is not the first character, or escape it with a
backslash.	backslash.
</P>	</P>
<P>	<P>
Line 1054 string, and therefore it fails if the current pointer	Line 1231 string, and therefore it fails if the current pointer
string.	string.
</P>	</P>
<P>	<P>
In UTF-8 mode, characters with values greater than 255 can be included in a	In UTF-8 (UTF-16, UTF-32) mode, characters with values greater than 255 (0xffff)
class as a literal string of bytes, or by using the \x{ escaping mechanism.	can be included in a class as a literal string of data units, or by using the
	\x{ escaping mechanism.
</P>	</P>
<P>	<P>
When caseless matching is set, any letters in a class represent both their	When caseless matching is set, any letters in a class represent both their
upper case and lower case versions, so for example, a caseless [aeiou] matches	upper case and lower case versions, so for example, a caseless [aeiou] matches
"A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a	"A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a
caseful version would. In UTF-8 mode, PCRE always understands the concept of	caseful version would. In a UTF mode, PCRE always understands the concept of
case for characters whose values are less than 128, so caseless matching is	case for characters whose values are less than 128, so caseless matching is
always possible. For characters with higher values, the concept of case is	always possible. For characters with higher values, the concept of case is
supported if PCRE is compiled with Unicode property support, but not otherwise.	supported if PCRE is compiled with Unicode property support, but not otherwise.
If you want to use caseless matching in UTF8-mode for characters 128 and above,	If you want to use caseless matching in a UTF mode for characters 128 and
you must ensure that PCRE is compiled with Unicode property support as well as	above, you must ensure that PCRE is compiled with Unicode property support as
with UTF-8 support.	well as with UTF support.
</P>	</P>
<P>	<P>
Characters that might indicate line breaks are never treated in any special way	Characters that might indicate line breaks are never treated in any special way
Line 1080 The minus (hyphen) character can be used to specify a	Line 1258 The minus (hyphen) character can be used to specify a
character class. For example, [d-m] matches any letter between d and m,	character class. For example, [d-m] matches any letter between d and m,
inclusive. If a minus character is required in a class, it must be escaped with	inclusive. If a minus character is required in a class, it must be escaped with
a backslash or appear in a position where it cannot be interpreted as	a backslash or appear in a position where it cannot be interpreted as
indicating a range, typically as the first or last character in the class.	indicating a range, typically as the first or last character in the class, or
	immediately after a range. For example, [b-d-z] matches letters in the range b
	to d, a hyphen character, or z.
</P>	</P>
<P>	<P>
It is not possible to have the literal character "]" as the end character of a	It is not possible to have the literal character "]" as the end character of a
Line 1092 followed by two other characters. The octal or hexadec	Line 1272 followed by two other characters. The octal or hexadec
"]" can also be used to end a range.	"]" can also be used to end a range.
</P>	</P>
<P>	<P>
	An error is generated if a POSIX character class (see below) or an escape
	sequence other than one that defines a single character appears at a point
	where a range ending character is expected. For example, [z-\xff] is valid,
	but [A-\d] and [A-[:digit:]] are not.
	</P>
	<P>
Ranges operate in the collating sequence of character values. They can also be	Ranges operate in the collating sequence of character values. They can also be
used for characters specified numerically, for example [\000-\037]. In UTF-8	used for characters specified numerically, for example [\000-\037]. Ranges
mode, ranges can include characters whose values are greater than 255, for	can include any characters that are valid for the current mode.
example [\x{100}-\x{2ff}].
</P>	</P>
<P>	<P>
If a range that includes letters is used when caseless matching is set, it	If a range that includes letters is used when caseless matching is set, it
matches the letters in either case. For example, [W-c] is equivalent to	matches the letters in either case. For example, [W-c] is equivalent to
[][\\^_`wxyzabc], matched caselessly, and in non-UTF-8 mode, if character	[][\\^_`wxyzabc], matched caselessly, and in a non-UTF mode, if character
tables for a French locale are in use, [\xc8-\xcb] matches accented E	tables for a French locale are in use, [\xc8-\xcb] matches accented E
characters in both cases. In UTF-8 mode, PCRE supports the concept of case for	characters in both cases. In UTF modes, PCRE supports the concept of case for
characters with values greater than 128 only when it is compiled with Unicode	characters with values greater than 128 only when it is compiled with Unicode
property support.	property support.
</P>	</P>
Line 1110 property support.	Line 1295 property support.
The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v,	The character escape sequences \d, \D, \h, \H, \p, \P, \s, \S, \v,
\V, \w, and \W may appear in a character class, and add the characters that	\V, \w, and \W may appear in a character class, and add the characters that
they match to the class. For example, [\dABCDEF] matches any hexadecimal	they match to the class. For example, [\dABCDEF] matches any hexadecimal
digit. In UTF-8 mode, the PCRE_UCP option affects the meanings of \d, \s, \w	digit. In UTF modes, the PCRE_UCP option affects the meanings of \d, \s, \w
and their upper case partners, just as it does when they appear outside a	and their upper case partners, just as it does when they appear outside a
character class, as described in the section entitled	character class, as described in the section entitled
<a href="#genericchartypes">"Generic character types"</a>	<a href="#genericchartypes">"Generic character types"</a>
Line 1132 something AND NOT ...".	Line 1317 something AND NOT ...".
The only metacharacters that are recognized in character classes are backslash,	The only metacharacters that are recognized in character classes are backslash,
hyphen (only where it can be interpreted as specifying a range), circumflex	hyphen (only where it can be interpreted as specifying a range), circumflex
(only at the start), opening square bracket (only when it can be interpreted as	(only at the start), opening square bracket (only when it can be interpreted as
introducing a POSIX class name - see the next section), and the terminating	introducing a POSIX class name, or for a special compatibility feature - see
closing square bracket. However, escaping other non-alphanumeric characters	the next two sections), and the terminating closing square bracket. However,
does no harm.	escaping other non-alphanumeric characters does no harm.
</P>	</P>
<br><a name="SEC9" href="#TOC1">POSIX CHARACTER CLASSES</a><br>	<br><a name="SEC10" href="#TOC1">POSIX CHARACTER CLASSES</a><br>
<P>	<P>
Perl supports the POSIX notation for character classes. This uses names	Perl supports the POSIX notation for character classes. This uses names
enclosed by [: and :] within the enclosing square brackets. PCRE also supports	enclosed by [: and :] within the enclosing square brackets. PCRE also supports
Line 1157 are:	Line 1342 are:
lower lower case letters	lower lower case letters
print printing characters, including space	print printing characters, including space
punct printing characters, excluding letters and digits and space	punct printing characters, excluding letters and digits and space
space white space (not quite the same as \s)	space white space (the same as \s from PCRE 8.34)
upper upper case letters	upper upper case letters
word "word" characters (same as \w)	word "word" characters (same as \w)
xdigit hexadecimal digits	xdigit hexadecimal digits
</pre>	</pre>
The "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13), and	The default "space" characters are HT (9), LF (10), VT (11), FF (12), CR (13),
space (32). Notice that this list includes the VT character (code 11). This	and space (32). If locale-specific matching is taking place, the list of space
makes "space" different to \s, which does not include VT (for Perl	characters may be different; there may be fewer or more of them. "Space" used
compatibility).	to be different to \s, which did not include VT, for Perl compatibility.
	However, Perl changed at release 5.18, and PCRE followed at release 8.34.
	"Space" and \s now match the same set of characters.
</P>	</P>
<P>	<P>
The name "word" is a Perl extension, and "blank" is a GNU extension from Perl	The name "word" is a Perl extension, and "blank" is a GNU extension from Perl
Line 1179 syntax [.ch.] and [=ch=] where "ch" is a "collating el	Line 1366 syntax [.ch.] and [=ch=] where "ch" is a "collating el
supported, and an error is given if they are encountered.	supported, and an error is given if they are encountered.
</P>	</P>
<P>	<P>
By default, in UTF-8 mode, characters with values greater than 128 do not match	By default, characters with values greater than 128 do not match any of the
any of the POSIX character classes. However, if the PCRE_UCP option is passed	POSIX character classes. However, if the PCRE_UCP option is passed to
to <b>pcre_compile()</b>, some of the classes are changed so that Unicode	<b>pcre_compile()</b>, some of the classes are changed so that Unicode character
character properties are used. This is achieved by replacing the POSIX classes	properties are used. This is achieved by replacing certain POSIX classes by
by other sequences, as follows:	other sequences, as follows:
<pre>	<pre>
[:alnum:] becomes \p{Xan}	[:alnum:] becomes \p{Xan}
[:alpha:] becomes \p{L}	[:alpha:] becomes \p{L}
Line 1194 by other sequences, as follows:	Line 1381 by other sequences, as follows:
[:upper:] becomes \p{Lu}	[:upper:] becomes \p{Lu}
[:word:] becomes \p{Xwd}	[:word:] becomes \p{Xwd}
</pre>	</pre>
Negated versions, such as [:^alpha:] use \P instead of \p. The other POSIX	Negated versions, such as [:^alpha:] use \P instead of \p. Three other POSIX
classes are unchanged, and match only characters with code points less than	classes are handled specially in UCP mode:
128.
</P>	</P>
<br><a name="SEC10" href="#TOC1">VERTICAL BAR</a><br>
<P>	<P>
	[:graph:]
	This matches characters that have glyphs that mark the page when printed. In
	Unicode property terms, it matches all characters with the L, M, N, P, S, or Cf
	properties, except for:
	<pre>
	U+061C Arabic Letter Mark
	U+180E Mongolian Vowel Separator
	U+2066 - U+2069 Various "isolate"s

	</PRE>
	</P>
	<P>
	[:print:]
	This matches the same characters as [:graph:] plus space characters that are
	not controls, that is, characters with the Zs property.
	</P>
	<P>
	[:punct:]
	This matches all characters that have the Unicode P (punctuation) property,
	plus those characters whose code points are less than 128 that have the S
	(Symbol) property.
	</P>
	<P>
	The other POSIX classes are unchanged, and match only characters with code
	points less than 128.
	</P>
	<br><a name="SEC11" href="#TOC1">COMPATIBILITY FEATURE FOR WORD BOUNDARIES</a><br>
	<P>
	In the POSIX.2 compliant library that was included in 4.4BSD Unix, the ugly
	syntax [[:<:]] and [[:>:]] is used for matching "start of word" and "end of
	word". PCRE treats these items as follows:
	<pre>
	[[:<:]] is converted to \b(?=\w)
	[[:>:]] is converted to \b(?<=\w)
	</pre>
	Only these exact character sequences are recognized. A sequence such as
	[a[:<:]b] provokes error for an unrecognized POSIX class name. This support is
	not compatible with Perl. It is provided to help migrations from other
	environments, and is best not used in any new patterns. Note that \b matches
	at the start and the end of a word (see
	<a href="#smallassertions">"Simple assertions"</a>
	above), and in a Perl-style pattern the preceding or following character
	normally shows which is wanted, without the need for the assertions that are
	used above in order to give exactly the POSIX behaviour.
	</P>
	<br><a name="SEC12" href="#TOC1">VERTICAL BAR</a><br>
	<P>
Vertical bar characters are used to separate alternative patterns. For example,	Vertical bar characters are used to separate alternative patterns. For example,
the pattern	the pattern
<pre>	<pre>
Line 1213 that succeeds is used. If the alternatives are within	Line 1445 that succeeds is used. If the alternatives are within
"succeeds" means matching the rest of the main pattern as well as the	"succeeds" means matching the rest of the main pattern as well as the
alternative in the subpattern.	alternative in the subpattern.
</P>	</P>
<br><a name="SEC11" href="#TOC1">INTERNAL OPTION SETTING</a><br>	<br><a name="SEC13" href="#TOC1">INTERNAL OPTION SETTING</a><br>
<P>	<P>
The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and	The settings of the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and
PCRE_EXTENDED options (which are Perl-compatible) can be changed from within	PCRE_EXTENDED options (which are Perl-compatible) can be changed from within
Line 1264 behaviour otherwise.	Line 1496 behaviour otherwise.
</P>	</P>
<P>	<P>
<b>Note:</b> There are other PCRE-specific options that can be set by the	<b>Note:</b> There are other PCRE-specific options that can be set by the
application when the compile or match functions are called. In some cases the	application when the compiling or matching functions are called. In some cases
pattern can contain special leading sequences such as (*CRLF) to override what	the pattern can contain special leading sequences such as (*CRLF) to override
the application has set or what has been defaulted. Details are given in the	what the application has set or what has been defaulted. Details are given in
section entitled	the section entitled
<a href="#newlineseq">"Newline sequences"</a>	<a href="#newlineseq">"Newline sequences"</a>
above. There are also the (UTF8) and (UCP) leading sequences that can be used	above. There are also the (UTF8), (UTF16),(UTF32), and (UCP) leading
to set UTF-8 and Unicode property modes; they are equivalent to setting the	sequences that can be used to set UTF and Unicode property modes; they are
PCRE_UTF8 and the PCRE_UCP options, respectively.	equivalent to setting the PCRE_UTF8, PCRE_UTF16, PCRE_UTF32 and the PCRE_UCP
	options, respectively. The (*UTF) sequence is a generic version that can be
	used with any of the libraries. However, the application can set the
	PCRE_NEVER_UTF option, which locks out the use of the (*UTF) sequences.
<a name="subpattern"></a></P>	<a name="subpattern"></a></P>
<br><a name="SEC12" href="#TOC1">SUBPATTERNS</a><br>	<br><a name="SEC14" href="#TOC1">SUBPATTERNS</a><br>
<P>	<P>
Subpatterns are delimited by parentheses (round brackets), which can be nested.	Subpatterns are delimited by parentheses (round brackets), which can be nested.
Turning part of a pattern into a subpattern does two things:	Turning part of a pattern into a subpattern does two things:
Line 1289 match "cataract", "erpillar" or an empty string.	Line 1524 match "cataract", "erpillar" or an empty string.
<br>	<br>
2. It sets up the subpattern as a capturing subpattern. This means that, when	2. It sets up the subpattern as a capturing subpattern. This means that, when
the whole pattern matches, that portion of the subject string that matched the	the whole pattern matches, that portion of the subject string that matched the
subpattern is passed back to the caller via the <i>ovector</i> argument of	subpattern is passed back to the caller via the <i>ovector</i> argument of the
<b>pcre_exec()</b>. Opening parentheses are counted from left to right (starting	matching function. (This applies only to the traditional matching functions;
from 1) to obtain numbers for the capturing subpatterns. For example, if the	the DFA matching functions do not support capturing.)
string "the red king" is matched against the pattern	</P>
	<P>
	Opening parentheses are counted from left to right (starting from 1) to obtain
	numbers for the capturing subpatterns. For example, if the string "the red
	king" is matched against the pattern
<pre>	<pre>
the ((red\|white) (king\|queen))	the ((red\|white) (king\|queen))
</pre>	</pre>
Line 1325 from left to right, and options are not reset until th	Line 1564 from left to right, and options are not reset until th
is reached, an option setting in one branch does affect subsequent branches, so	is reached, an option setting in one branch does affect subsequent branches, so
the above patterns match "SUNDAY" as well as "Saturday".	the above patterns match "SUNDAY" as well as "Saturday".
<a name="dupsubpatternnumber"></a></P>	<a name="dupsubpatternnumber"></a></P>
<br><a name="SEC13" href="#TOC1">DUPLICATE SUBPATTERN NUMBERS</a><br>	<br><a name="SEC15" href="#TOC1">DUPLICATE SUBPATTERN NUMBERS</a><br>
<P>	<P>
Perl 5.10 introduced a feature whereby each alternative in a subpattern uses	Perl 5.10 introduced a feature whereby each alternative in a subpattern uses
the same numbers for its capturing parentheses. Such a subpattern starts with	the same numbers for its capturing parentheses. Such a subpattern starts with
Line 1369 true if any of the subpatterns of that number have mat	Line 1608 true if any of the subpatterns of that number have mat
An alternative approach to using this "branch reset" feature is to use	An alternative approach to using this "branch reset" feature is to use
duplicate named subpatterns, as described in the next section.	duplicate named subpatterns, as described in the next section.
</P>	</P>
<br><a name="SEC14" href="#TOC1">NAMED SUBPATTERNS</a><br>	<br><a name="SEC16" href="#TOC1">NAMED SUBPATTERNS</a><br>
<P>	<P>
Identifying capturing parentheses by number is simple, but it can be very hard	Identifying capturing parentheses by number is simple, but it can be very hard
to keep track of the numbers in complicated regular expressions. Furthermore,	to keep track of the numbers in complicated regular expressions. Furthermore,
Line 1391 and	Line 1630 and
can be made by name as well as by number.	can be made by name as well as by number.
</P>	</P>
<P>	<P>
Names consist of up to 32 alphanumeric characters and underscores. Named	Names consist of up to 32 alphanumeric characters and underscores, but must
capturing parentheses are still allocated numbers as well as names, exactly as	start with a non-digit. Named capturing parentheses are still allocated numbers
if the names were not present. The PCRE API provides function calls for	as well as names, exactly as if the names were not present. The PCRE API
extracting the name-to-number translation table from a compiled pattern. There	provides function calls for extracting the name-to-number translation table
is also a convenience function for extracting a captured substring by name.	from a compiled pattern. There is also a convenience function for extracting a
	captured substring by name.
</P>	</P>
<P>	<P>
By default, a name must be unique within a pattern, but it is possible to relax	By default, a name must be unique within a pattern, but it is possible to relax
Line 1424 matched. This saves searching to find which numbered s	Line 1664 matched. This saves searching to find which numbered s
</P>	</P>
<P>	<P>
If you make a back reference to a non-unique named subpattern from elsewhere in	If you make a back reference to a non-unique named subpattern from elsewhere in
the pattern, the one that corresponds to the first occurrence of the name is	the pattern, the subpatterns to which the name refers are checked in the order
used. In the absence of duplicate numbers (see the previous section) this is	in which they appear in the overall pattern. The first one that is set is used
the one with the lowest number. If you use a named reference in a condition	for the reference. For example, this pattern matches both "foofoo" and
	"barbar" but not "foobar" or "barfoo":
	<pre>
	(?:(?<n>foo)\|(?<n>bar))\k<n>

	</PRE>
	</P>
	<P>
	If you make a subroutine call to a non-unique named subpattern, the one that
	corresponds to the first occurrence of the name is used. In the absence of
	duplicate numbers (see the previous section) this is the one with the lowest
	number.
	</P>
	<P>
	If you use a named reference in a condition
test (see the	test (see the
<a href="#conditions">section about conditions</a>	<a href="#conditions">section about conditions</a>
below), either to check whether a subpattern has matched, or to check for	below), either to check whether a subpattern has matched, or to check for
Line 1441 documentation.	Line 1695 documentation.
<b>Warning:</b> You cannot use different names to distinguish between two	<b>Warning:</b> You cannot use different names to distinguish between two
subpatterns with the same number because PCRE uses only the numbers when	subpatterns with the same number because PCRE uses only the numbers when
matching. For this reason, an error is given at compile time if different names	matching. For this reason, an error is given at compile time if different names
are given to subpatterns with the same number. However, you can give the same	are given to subpatterns with the same number. However, you can always give the
name to subpatterns with the same number, even when PCRE_DUPNAMES is not set.	same name to subpatterns with the same number, even when PCRE_DUPNAMES is not
	set.
</P>	</P>
<br><a name="SEC15" href="#TOC1">REPETITION</a><br>	<br><a name="SEC17" href="#TOC1">REPETITION</a><br>
<P>	<P>
Repetition is specified by quantifiers, which can follow any of the following	Repetition is specified by quantifiers, which can follow any of the following
items:	items:
Line 1452 items:	Line 1707 items:
a literal data character	a literal data character
the dot metacharacter	the dot metacharacter
the \C escape sequence	the \C escape sequence
the \X escape sequence (in UTF-8 mode with Unicode properties)	the \X escape sequence
the \R escape sequence	the \R escape sequence
an escape such as \d or \pL that matches a single character	an escape such as \d or \pL that matches a single character
a character class	a character class
Line 1484 quantifier, is taken as a literal character. For examp	Line 1739 quantifier, is taken as a literal character. For examp
quantifier, but a literal string of four characters.	quantifier, but a literal string of four characters.
</P>	</P>
<P>	<P>
In UTF-8 mode, quantifiers apply to UTF-8 characters rather than to individual	In UTF modes, quantifiers apply to characters rather than to individual data
bytes. Thus, for example, \x{100}{2} matches two UTF-8 characters, each of	units. Thus, for example, \x{100}{2} matches two characters, each of
which is represented by a two-byte sequence. Similarly, when Unicode property	which is represented by a two-byte sequence in a UTF-8 string. Similarly,
support is available, \X{3} matches three Unicode extended sequences, each of	\X{3} matches three Unicode extended grapheme clusters, each of which may be
which may be several bytes long (and they may be of different lengths).	several data units long (and they may be of different lengths).
</P>	</P>
<P>	<P>
The quantifier {0} is permitted, causing the expression to behave as if the	The quantifier {0} is permitted, causing the expression to behave as if the
Line 1577 worth setting PCRE_DOTALL in order to obtain this opti	Line 1832 worth setting PCRE_DOTALL in order to obtain this opti
alternatively using ^ to indicate anchoring explicitly.	alternatively using ^ to indicate anchoring explicitly.
</P>	</P>
<P>	<P>
However, there is one situation where the optimization cannot be used. When .*	However, there are some cases where the optimization cannot be used. When .*
is inside capturing parentheses that are the subject of a back reference	is inside capturing parentheses that are the subject of a back reference
elsewhere in the pattern, a match at the start may fail where a later one	elsewhere in the pattern, a match at the start may fail where a later one
succeeds. Consider, for example:	succeeds. Consider, for example:
Line 1588 If the subject is "xyz123abc123" the match point is th	Line 1843 If the subject is "xyz123abc123" the match point is th
this reason, such a pattern is not implicitly anchored.	this reason, such a pattern is not implicitly anchored.
</P>	</P>
<P>	<P>
	Another case where implicit anchoring is not applied is when the leading .* is
	inside an atomic group. Once again, a match at the start may fail where a later
	one succeeds. Consider this pattern:
	<pre>
	(?>.*?a)b
	</pre>
	It matches "ab" in the subject "aab". The use of the backtracking control verbs
	(PRUNE) and (SKIP) also disable this optimization.
	</P>
	<P>
When a capturing subpattern is repeated, the value captured is the substring	When a capturing subpattern is repeated, the value captured is the substring
that matched the final iteration. For example, after	that matched the final iteration. For example, after
<pre>	<pre>
Line 1602 example, after	Line 1867 example, after
</pre>	</pre>
matches "aba" the value of the second captured substring is "b".	matches "aba" the value of the second captured substring is "b".
<a name="atomicgroup"></a></P>	<a name="atomicgroup"></a></P>
<br><a name="SEC16" href="#TOC1">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a><br>	<br><a name="SEC18" href="#TOC1">ATOMIC GROUPING AND POSSESSIVE QUANTIFIERS</a><br>
<P>	<P>
With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")	With both maximizing ("greedy") and minimizing ("ungreedy" or "lazy")
repetition, failure of what follows normally causes the repeated item to be	repetition, failure of what follows normally causes the repeated item to be
Line 1706 an atomic group, like this:	Line 1971 an atomic group, like this:
</pre>	</pre>
sequences of non-digits cannot be broken, and failure happens quickly.	sequences of non-digits cannot be broken, and failure happens quickly.
<a name="backreferences"></a></P>	<a name="backreferences"></a></P>
<br><a name="SEC17" href="#TOC1">BACK REFERENCES</a><br>	<br><a name="SEC19" href="#TOC1">BACK REFERENCES</a><br>
<P>	<P>
Outside a character class, a backslash followed by a digit greater than 0 (and	Outside a character class, a backslash followed by a digit greater than 0 (and
possibly further digits) is a back reference to a capturing subpattern earlier	possibly further digits) is a back reference to a capturing subpattern earlier
Line 1805 Because there may be many capturing parentheses in a p	Line 2070 Because there may be many capturing parentheses in a p
following a backslash are taken as part of a potential back reference number.	following a backslash are taken as part of a potential back reference number.
If the pattern continues with a digit character, some delimiter must be used to	If the pattern continues with a digit character, some delimiter must be used to
terminate the back reference. If the PCRE_EXTENDED option is set, this can be	terminate the back reference. If the PCRE_EXTENDED option is set, this can be
whitespace. Otherwise, the \g{ syntax or an empty comment (see	white space. Otherwise, the \g{ syntax or an empty comment (see
<a href="#comments">"Comments"</a>	<a href="#comments">"Comments"</a>
below) can be used.	below) can be used.
</P>	</P>
Line 1834 as an	Line 2099 as an
Once the whole group has been matched, a subsequent matching failure cannot	Once the whole group has been matched, a subsequent matching failure cannot
cause backtracking into the middle of the group.	cause backtracking into the middle of the group.
<a name="bigassertions"></a></P>	<a name="bigassertions"></a></P>
<br><a name="SEC18" href="#TOC1">ASSERTIONS</a><br>	<br><a name="SEC20" href="#TOC1">ASSERTIONS</a><br>
<P>	<P>
An assertion is a test on the characters following or preceding the current	An assertion is a test on the characters following or preceding the current
matching point that does not actually consume any characters. The simple	matching point that does not actually consume any characters. The simple
Line 1851 except that it does not cause the current matching pos	Line 2116 except that it does not cause the current matching pos
Assertion subpatterns are not capturing subpatterns. If such an assertion	Assertion subpatterns are not capturing subpatterns. If such an assertion
contains capturing subpatterns within it, these are counted for the purposes of	contains capturing subpatterns within it, these are counted for the purposes of
numbering the capturing subpatterns in the whole pattern. However, substring	numbering the capturing subpatterns in the whole pattern. However, substring
capturing is carried out only for positive assertions, because it does not make	capturing is carried out only for positive assertions. (Perl sometimes, but not
sense for negative assertions.	always, does do capturing in negative assertions.)
</P>	</P>
<P>	<P>
For compatibility with Perl, assertion subpatterns may be repeated; though	For compatibility with Perl, assertion subpatterns may be repeated; though
Line 1950 match. If there are insufficient characters before the	Line 2215 match. If there are insufficient characters before the
assertion fails.	assertion fails.
</P>	</P>
<P>	<P>
In UTF-8 mode, PCRE does not allow the \C escape (which matches a single byte,	In a UTF mode, PCRE does not allow the \C escape (which matches a single data
even in UTF-8 mode) to appear in lookbehind assertions, because it makes it	unit even in a UTF mode) to appear in lookbehind assertions, because it makes
impossible to calculate the length of the lookbehind. The \X and \R escapes,	it impossible to calculate the length of the lookbehind. The \X and \R
which can match different numbers of bytes, are also not permitted.	escapes, which can match different numbers of data units, are also not
	permitted.
</P>	</P>
<P>	<P>
<a href="#subpatternsassubroutines">"Subroutine"</a>	<a href="#subpatternsassubroutines">"Subroutine"</a>
Line 2023 preceded by "foo", while	Line 2289 preceded by "foo", while
is another pattern that matches "foo" preceded by three digits and any three	is another pattern that matches "foo" preceded by three digits and any three
characters that are not "999".	characters that are not "999".
<a name="conditions"></a></P>	<a name="conditions"></a></P>
<br><a name="SEC19" href="#TOC1">CONDITIONAL SUBPATTERNS</a><br>	<br><a name="SEC21" href="#TOC1">CONDITIONAL SUBPATTERNS</a><br>
<P>	<P>
It is possible to cause the matching process to obey a subpattern	It is possible to cause the matching process to obey a subpattern
conditionally or to choose between two alternative subpatterns, depending on	conditionally or to choose between two alternative subpatterns, depending on
Line 2097 Checking for a used subpattern by name	Line 2363 Checking for a used subpattern by name
<P>	<P>
Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used	Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used
subpattern by name. For compatibility with earlier versions of PCRE, which had	subpattern by name. For compatibility with earlier versions of PCRE, which had
this facility before Perl, the syntax (?(name)...) is also recognized. However,	this facility before Perl, the syntax (?(name)...) is also recognized.
there is a possible ambiguity with this syntax, because subpattern names may
consist entirely of digits. PCRE looks first for a named subpattern; if it
cannot find one and the name consists entirely of digits, PCRE looks for a
subpattern of that number, which must be greater than zero. Using subpattern
names that consist entirely of digits is not recommended.
</P>	</P>
<P>	<P>
Rewriting the above example to use a named subpattern gives this:	Rewriting the above example to use a named subpattern gives this:
Line 2146 point in the pattern; the idea of DEFINE is that it ca	Line 2407 point in the pattern; the idea of DEFINE is that it ca
subroutines that can be referenced from elsewhere. (The use of	subroutines that can be referenced from elsewhere. (The use of
<a href="#subpatternsassubroutines">subroutines</a>	<a href="#subpatternsassubroutines">subroutines</a>
is described below.) For example, a pattern to match an IPv4 address such as	is described below.) For example, a pattern to match an IPv4 address such as
"192.168.23.245" could be written like this (ignore whitespace and line	"192.168.23.245" could be written like this (ignore white space and line
breaks):	breaks):
<pre>	<pre>
(?(DEFINE) (?<byte> 2[0-4]\d \| 25[0-5] \| 1\d\d \| [1-9]?\d) )	(?(DEFINE) (?<byte> 2[0-4]\d \| 25[0-5] \| 1\d\d \| [1-9]?\d) )
Line 2178 subject is matched against the first alternative; othe	Line 2439 subject is matched against the first alternative; othe
against the second. This pattern matches strings in one of the two forms	against the second. This pattern matches strings in one of the two forms
dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits.	dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits.
<a name="comments"></a></P>	<a name="comments"></a></P>
<br><a name="SEC20" href="#TOC1">COMMENTS</a><br>	<br><a name="SEC22" href="#TOC1">COMMENTS</a><br>
<P>	<P>
There are two ways of including comments in patterns that are processed by	There are two ways of including comments in patterns that are processed by
PCRE. In both cases, the start of the comment must not be in a character class,	PCRE. In both cases, the start of the comment must not be in a character class,
Line 2192 closing parenthesis. Nested parentheses are not permit	Line 2453 closing parenthesis. Nested parentheses are not permit
option is set, an unescaped # character also introduces a comment, which in	option is set, an unescaped # character also introduces a comment, which in
this case continues to immediately after the next newline character or	this case continues to immediately after the next newline character or
character sequence in the pattern. Which characters are interpreted as newlines	character sequence in the pattern. Which characters are interpreted as newlines
is controlled by the options passed to <b>pcre_compile()</b> or by a special	is controlled by the options passed to a compiling function or by a special
sequence at the start of the pattern, as described in the section entitled	sequence at the start of the pattern, as described in the section entitled
<a href="#newlines">"Newline conventions"</a>	<a href="#newlines">"Newline conventions"</a>
above. Note that the end of this type of comment is a literal newline sequence	above. Note that the end of this type of comment is a literal newline sequence
Line 2207 a newline in the pattern. The sequence \n is still lit	Line 2468 a newline in the pattern. The sequence \n is still lit
it does not terminate the comment. Only an actual character with the code value	it does not terminate the comment. Only an actual character with the code value
0x0a (the default newline) does so.	0x0a (the default newline) does so.
<a name="recursion"></a></P>	<a name="recursion"></a></P>
<br><a name="SEC21" href="#TOC1">RECURSIVE PATTERNS</a><br>	<br><a name="SEC23" href="#TOC1">RECURSIVE PATTERNS</a><br>
<P>	<P>
Consider the problem of matching a string in parentheses, allowing for	Consider the problem of matching a string in parentheses, allowing for
unlimited nested parentheses. Without the use of recursion, the best that can	unlimited nested parentheses. Without the use of recursion, the best that can
Line 2422 now match "b" and so the whole match succeeds. In Perl	Line 2683 now match "b" and so the whole match succeeds. In Perl
match because inside the recursive call \1 cannot access the externally set	match because inside the recursive call \1 cannot access the externally set
value.	value.
<a name="subpatternsassubroutines"></a></P>	<a name="subpatternsassubroutines"></a></P>
<br><a name="SEC22" href="#TOC1">SUBPATTERNS AS SUBROUTINES</a><br>	<br><a name="SEC24" href="#TOC1">SUBPATTERNS AS SUBROUTINES</a><br>
<P>	<P>
If the syntax for a recursive subpattern call (either by number or by	If the syntax for a recursive subpattern call (either by number or by
name) is used outside the parentheses to which it refers, it operates like a	name) is used outside the parentheses to which it refers, it operates like a
Line 2463 different calls. For example, consider this pattern:	Line 2724 different calls. For example, consider this pattern:
It matches "abcabc". It does not match "abcABC" because the change of	It matches "abcabc". It does not match "abcABC" because the change of
processing option does not affect the called subpattern.	processing option does not affect the called subpattern.
<a name="onigurumasubroutines"></a></P>	<a name="onigurumasubroutines"></a></P>
<br><a name="SEC23" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>	<br><a name="SEC25" href="#TOC1">ONIGURUMA SUBROUTINE SYNTAX</a><br>
<P>	<P>
For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or	For compatibility with Oniguruma, the non-Perl syntax \g followed by a name or
a number enclosed either in angle brackets or single quotes, is an alternative	a number enclosed either in angle brackets or single quotes, is an alternative
Line 2481 plus or a minus sign it is taken as a relative referen	Line 2742 plus or a minus sign it is taken as a relative referen
Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are <i>not</i>	Note that \g{...} (Perl syntax) and \g<...> (Oniguruma syntax) are <i>not</i>
synonymous. The former is a back reference; the latter is a subroutine call.	synonymous. The former is a back reference; the latter is a subroutine call.
</P>	</P>
<br><a name="SEC24" href="#TOC1">CALLOUTS</a><br>	<br><a name="SEC26" href="#TOC1">CALLOUTS</a><br>
<P>	<P>
Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl	Perl has a feature whereby using the sequence (?{...}) causes arbitrary Perl
code to be obeyed in the middle of matching a regular expression. This makes it	code to be obeyed in the middle of matching a regular expression. This makes it
Line 2491 same pair of parentheses when there is a repetition.	Line 2752 same pair of parentheses when there is a repetition.
<P>	<P>
PCRE provides a similar feature, but of course it cannot obey arbitrary Perl	PCRE provides a similar feature, but of course it cannot obey arbitrary Perl
code. The feature is called "callout". The caller of PCRE provides an external	code. The feature is called "callout". The caller of PCRE provides an external
function by putting its entry point in the global variable <i>pcre_callout</i>.	function by putting its entry point in the global variable <i>pcre_callout</i>
	(8-bit library) or <i>pcre[16\|32]_callout</i> (16-bit or 32-bit library).
By default, this variable contains NULL, which disables all calling out.	By default, this variable contains NULL, which disables all calling out.
</P>	</P>
<P>	<P>
Line 2502 For example, this pattern has two callout points:	Line 2764 For example, this pattern has two callout points:
<pre>	<pre>
(?C1)abc(?C2)def	(?C1)abc(?C2)def
</pre>	</pre>
If the PCRE_AUTO_CALLOUT flag is passed to <b>pcre_compile()</b>, callouts are	If the PCRE_AUTO_CALLOUT flag is passed to a compiling function, callouts are
automatically installed before each item in the pattern. They are all numbered	automatically installed before each item in the pattern. They are all numbered
255.	255. If there is a conditional group in the pattern whose condition is an
	assertion, an additional callout is inserted just before the condition. An
	explicit callout may also be set at this position, as in this example:
	<pre>
	(?(?C9)(?=a)abc\|def)
	</pre>
	Note that this applies only to assertion conditions, not to other types of
	condition.
</P>	</P>
<P>	<P>
During matching, when PCRE reaches a callout point (and <i>pcre_callout</i> is	During matching, when PCRE reaches a callout point, the external function is
set), the external function is called. It is provided with the number of the	called. It is provided with the number of the callout, the position in the
callout, the position in the pattern, and, optionally, one item of data	pattern, and, optionally, one item of data originally supplied by the caller of
originally supplied by the caller of <b>pcre_exec()</b>. The callout function	the matching function. The callout function may cause matching to proceed, to
may cause matching to proceed, to backtrack, or to fail altogether. A complete	backtrack, or to fail altogether.
description of the interface to the callout function is given in the	</P>
	<P>
	By default, PCRE implements a number of optimizations at compile time and
	matching time, and one side-effect is that sometimes callouts are skipped. If
	you need all possible callouts to happen, you need to set options that disable
	the relevant optimizations. More details, and a complete description of the
	interface to the callout function, are given in the
<a href="pcrecallout.html"><b>pcrecallout</b></a>	<a href="pcrecallout.html"><b>pcrecallout</b></a>
documentation.	documentation.
<a name="backtrackcontrol"></a></P>	<a name="backtrackcontrol"></a></P>
<br><a name="SEC25" href="#TOC1">BACKTRACKING CONTROL</a><br>	<br><a name="SEC27" href="#TOC1">BACKTRACKING CONTROL</a><br>
<P>	<P>
Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which	Perl 5.10 introduced a number of "Special Backtracking Control Verbs", which
are described in the Perl documentation as "experimental and subject to change	are still described in the Perl documentation as "experimental and subject to
or removal in a future version of Perl". It goes on to say: "Their usage in	change or removal in a future version of Perl". It goes on to say: "Their usage
production code should be noted to avoid problems during upgrades." The same	in production code should be noted to avoid problems during upgrades." The same
remarks apply to the PCRE features described in this section.	remarks apply to the PCRE features described in this section.
</P>	</P>
<P>	<P>
Since these verbs are specifically related to backtracking, most of them can be	The new verbs make use of what was previously invalid syntax: an opening
used only when the pattern is to be matched using <b>pcre_exec()</b>, which uses	parenthesis followed by an asterisk. They are generally of the form
a backtracking algorithm. With the exception of (*FAIL), which behaves like a	(VERB) or (VERB:NAME). Some may take either form, possibly behaving
failing negative assertion, they cause an error if encountered by	differently depending on whether or not a name is present. A name is any
<b>pcre_dfa_exec()</b>.	sequence of characters that does not include a closing parenthesis. The maximum
	length of name is 255 in the 8-bit library and 65535 in the 16-bit and 32-bit
	libraries. If the name is empty, that is, if the closing parenthesis
	immediately follows the colon, the effect is as if the colon were not there.
	Any number of these verbs may occur in a pattern.
</P>	</P>
<P>	<P>
If any of these verbs are used in an assertion or in a subpattern that is	Since these verbs are specifically related to backtracking, most of them can be
called as a subroutine (whether or not recursively), their effect is confined	used only when the pattern is to be matched using one of the traditional
to that subpattern; it does not extend to the surrounding pattern, with one	matching functions, because these use a backtracking algorithm. With the
exception: the name from a (MARK), (PRUNE), or (*THEN) that is encountered in	exception of (*FAIL), which behaves like a failing negative assertion, the
a successful positive assertion <i>is</i> passed back when a match succeeds	backtracking control verbs cause an error if encountered by a DFA matching
(compare capturing parentheses in assertions). Note that such subpatterns are	function.
processed as anchored at the point where they are tested. Note also that Perl's
treatment of subroutines is different in some cases.
</P>	</P>
<P>	<P>
The new verbs make use of what was previously invalid syntax: an opening	The behaviour of these verbs in
parenthesis followed by an asterisk. They are generally of the form	<a href="#btrepeat">repeated groups,</a>
(VERB) or (VERB:NAME). Some may take either form, with differing behaviour,	<a href="#btassert">assertions,</a>
depending on whether or not an argument is present. A name is any sequence of	and in
characters that does not include a closing parenthesis. If the name is empty,	<a href="#btsub">subpatterns called as subroutines</a>
that is, if the closing parenthesis immediately follows the colon, the effect	(whether or not recursively) is documented below.
is as if the colon were not there. Any number of these verbs may occur in a	<a name="nooptimize"></a></P>
pattern.	<br><b>
</P>	Optimizations that affect backtracking verbs
	</b><br>
<P>	<P>
PCRE contains some optimizations that are used to speed up matching by running	PCRE contains some optimizations that are used to speed up matching by running
some checks at the start of each match attempt. For example, it may know the	some checks at the start of each match attempt. For example, it may know the
minimum length of matching subject, or that a particular character must be	minimum length of matching subject, or that a particular character must be
present. When one of these optimizations suppresses the running of a match, any	present. When one of these optimizations bypasses the running of a match, any
included backtracking verbs will not, of course, be processed. You can suppress	included backtracking verbs will not, of course, be processed. You can suppress
the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option	the start-of-match optimizations by setting the PCRE_NO_START_OPTIMIZE option
when calling <b>pcre_compile()</b> or <b>pcre_exec()</b>, or by starting the	when calling <b>pcre_compile()</b> or <b>pcre_exec()</b>, or by starting the
pattern with (*NO_START_OPT).	pattern with (*NO_START_OPT). There is more discussion of this option in the
	section entitled
	<a href="pcreapi.html#execoptions">"Option bits for <b>pcre_exec()</b>"</a>
	in the
	<a href="pcreapi.html"><b>pcreapi</b></a>
	documentation.
</P>	</P>
<P>	<P>
Experiments with Perl suggest that it too has similar optimizations, sometimes	Experiments with Perl suggest that it too has similar optimizations, sometimes
Line 2577 followed by a name.	Line 2860 followed by a name.
This verb causes the match to end successfully, skipping the remainder of the	This verb causes the match to end successfully, skipping the remainder of the
pattern. However, when it is inside a subpattern that is called as a	pattern. However, when it is inside a subpattern that is called as a
subroutine, only that subpattern is ended successfully. Matching then continues	subroutine, only that subpattern is ended successfully. Matching then continues
at the outer level. If (*ACCEPT) is inside capturing parentheses, the data so	at the outer level. If (*ACCEPT) in triggered in a positive assertion, the
far is captured. For example:	assertion succeeds; in a negative assertion, the assertion fails.
	</P>
	<P>
	If (*ACCEPT) is inside capturing parentheses, the data so far is captured. For
	example:
<pre>	<pre>
A((?:A\|B(*ACCEPT)\|C)D)	A((?:A\|B(*ACCEPT)\|C)D)
</pre>	</pre>
Line 2612 A name is always required with this verb. There may be	Line 2899 A name is always required with this verb. There may be
(*MARK) as you like in a pattern, and their names do not have to be unique.	(*MARK) as you like in a pattern, and their names do not have to be unique.
</P>	</P>
<P>	<P>
When a match succeeds, the name of the last-encountered (*MARK) on the matching	When a match succeeds, the name of the last-encountered (*MARK:NAME),
path is passed back to the caller via the <i>pcre_extra</i> data structure, as	(PRUNE:NAME), or (THEN:NAME) on the matching path is passed back to the
described in the	caller as described in the section entitled
<a href="pcreapi.html#extradata">section on <i>pcre_extra</i></a>	<a href="pcreapi.html#extradata">"Extra data for <b>pcre_exec()</b>"</a>
in the	in the
<a href="pcreapi.html"><b>pcreapi</b></a>	<a href="pcreapi.html"><b>pcreapi</b></a>
documentation. Here is an example of <b>pcretest</b> output, where the /K	documentation. Here is an example of <b>pcretest</b> output, where the /K
Line 2635 of obtaining this information than putting each altern	Line 2922 of obtaining this information than putting each altern
capturing parentheses.	capturing parentheses.
</P>	</P>
<P>	<P>
If (*MARK) is encountered in a positive assertion, its name is recorded and	If a verb with a name is encountered in a positive assertion that is true, the
passed back if it is the last-encountered. This does not happen for negative	name is recorded and passed back if it is the last-encountered. This does not
assertions.	happen for negative assertions or failing positive assertions.
</P>	</P>
<P>	<P>
After a partial match or a failed match, the name of the last encountered	After a partial match or a failed match, the last encountered name in the
(*MARK) in the entire match process is returned. For example:	entire match process is returned. For example:
<pre>	<pre>
re> /X(MARK:A)Y\|X(MARK:B)Z/K	re> /X(MARK:A)Y\|X(MARK:B)Z/K
data> XP	data> XP
No match, mark = B	No match, mark = B
</pre>	</pre>
Note that in this unanchored example the mark is retained from the match	Note that in this unanchored example the mark is retained from the match
attempt that started at the letter "X". Subsequent match attempts starting at	attempt that started at the letter "X" in the subject. Subsequent match
"P" and then with an empty string do not get as far as the (*MARK) item, but	attempts starting at "P" and then with an empty string do not get as far as the
nevertheless do not reset it.	(*MARK) item, but nevertheless do not reset it.
</P>	</P>
	<P>
	If you are interested in (*MARK) values after failed matches, you should
	probably set the PCRE_NO_START_OPTIMIZE option
	<a href="#nooptimize">(see above)</a>
	to ensure that the match is always attempted.
	</P>
<br><b>	<br><b>
Verbs that act after backtracking	Verbs that act after backtracking
</b><br>	</b><br>
Line 2659 Verbs that act after backtracking	Line 2952 Verbs that act after backtracking
The following verbs do nothing when they are encountered. Matching continues	The following verbs do nothing when they are encountered. Matching continues
with what follows, but if there is no subsequent match, causing a backtrack to	with what follows, but if there is no subsequent match, causing a backtrack to
the verb, a failure is forced. That is, backtracking cannot pass to the left of	the verb, a failure is forced. That is, backtracking cannot pass to the left of
the verb. However, when one of these verbs appears inside an atomic group, its	the verb. However, when one of these verbs appears inside an atomic group or an
effect is confined to that group, because once the group has been matched,	assertion that is true, its effect is confined to that group, because once the
there is never any backtracking into it. In this situation, backtracking can	group has been matched, there is never any backtracking into it. In this
"jump back" to the left of the entire atomic group. (Remember also, as stated	situation, backtracking can "jump back" to the left of the entire atomic group
above, that this localization also applies in subroutine calls and assertions.)	or assertion. (Remember also, as stated above, that this localization also
	applies in subroutine calls.)
</P>	</P>
<P>	<P>
These verbs differ in exactly what kind of failure occurs when backtracking	These verbs differ in exactly what kind of failure occurs when backtracking
reaches them.	reaches them. The behaviour described below is what happens when the verb is
	not in a subroutine or an assertion. Subsequent sections cover these special
	cases.
<pre>	<pre>
(*COMMIT)	(*COMMIT)
</pre>	</pre>
This verb, which may not be followed by a name, causes the whole match to fail	This verb, which may not be followed by a name, causes the whole match to fail
outright if the rest of the pattern does not match. Even if the pattern is	outright if there is a later matching failure that causes backtracking to reach
unanchored, no further attempts to find a match by advancing the starting point	it. Even if the pattern is unanchored, no further attempts to find a match by
take place. Once (*COMMIT) has been passed, <b>pcre_exec()</b> is committed to	advancing the starting point take place. If (*COMMIT) is the only backtracking
finding a match at the current starting point, or not at all. For example:	verb that is encountered, once it has been passed <b>pcre_exec()</b> is
	committed to finding a match at the current starting point, or not at all. For
	example:
<pre>	<pre>
a+(*COMMIT)b	a+(*COMMIT)b
</pre>	</pre>
Line 2685 recently passed (*MARK) in the path is passed back whe	Line 2983 recently passed (*MARK) in the path is passed back whe
match failure.	match failure.
</P>	</P>
<P>	<P>
	If there is more than one backtracking verb in a pattern, a different one that
	follows (COMMIT) may be triggered first, so merely passing (COMMIT) during a
	match does not always guarantee that a match must be at this starting point.
	</P>
	<P>
Note that (*COMMIT) at the start of a pattern is not the same as an anchor,	Note that (*COMMIT) at the start of a pattern is not the same as an anchor,
unless PCRE's start-of-match optimizations are turned off, as shown in this	unless PCRE's start-of-match optimizations are turned off, as shown in this
<b>pcretest</b> example:	<b>pcretest</b> example:
Line 2704 starting points.	Line 3007 starting points.
(PRUNE) or (PRUNE:NAME)	(PRUNE) or (PRUNE:NAME)
</pre>	</pre>
This verb causes the match to fail at the current starting position in the	This verb causes the match to fail at the current starting position in the
subject if the rest of the pattern does not match. If the pattern is	subject if there is a later matching failure that causes backtracking to reach
unanchored, the normal "bumpalong" advance to the next starting character then	it. If the pattern is unanchored, the normal "bumpalong" advance to the next
happens. Backtracking can occur as usual to the left of (*PRUNE), before it is	starting character then happens. Backtracking can occur as usual to the left of
reached, or when matching to the right of (*PRUNE), but if there is no match to	(PRUNE), before it is reached, or when matching to the right of (PRUNE), but
the right, backtracking cannot cross (*PRUNE). In simple cases, the use of	if there is no match to the right, backtracking cannot cross (*PRUNE). In
(*PRUNE) is just an alternative to an atomic group or possessive quantifier,	simple cases, the use of (*PRUNE) is just an alternative to an atomic group or
but there are some uses of (*PRUNE) that cannot be expressed in any other way.	possessive quantifier, but there are some uses of (*PRUNE) that cannot be
The behaviour of (PRUNE:NAME) is the same as (MARK:NAME)(*PRUNE). In an	expressed in any other way. In an anchored pattern (*PRUNE) has the same effect
anchored pattern (PRUNE) has the same effect as (COMMIT).	as (*COMMIT).
	</P>
	<P>
	The behaviour of (PRUNE:NAME) is the not the same as (MARK:NAME)(*PRUNE).
	It is like (*MARK:NAME) in that the name is remembered for passing back to the
	caller. However, (SKIP:NAME) searches only for names set with (MARK).
<pre>	<pre>
(*SKIP)	(*SKIP)
</pre>	</pre>
Line 2733 instead of skipping on to "c".	Line 3041 instead of skipping on to "c".
<pre>	<pre>
(*SKIP:NAME)	(*SKIP:NAME)
</pre>	</pre>
When (*SKIP) has an associated name, its behaviour is modified. If the	When (*SKIP) has an associated name, its behaviour is modified. When it is
following pattern fails to match, the previous path through the pattern is	triggered, the previous path through the pattern is searched for the most
searched for the most recent (*MARK) that has the same name. If one is found,	recent (*MARK) that has the same name. If one is found, the "bumpalong" advance
the "bumpalong" advance is to the subject position that corresponds to that	is to the subject position that corresponds to that (*MARK) instead of to where
(MARK) instead of to where (SKIP) was encountered. If no (*MARK) with a	(SKIP) was encountered. If no (MARK) with a matching name is found, the
matching name is found, the (*SKIP) is ignored.	(*SKIP) is ignored.
	</P>
	<P>
	Note that (SKIP:NAME) searches only for names set by (MARK:NAME). It ignores
	names that are set by (PRUNE:NAME) or (THEN:NAME).
<pre>	<pre>
(THEN) or (THEN:NAME)	(THEN) or (THEN:NAME)
</pre>	</pre>
This verb causes a skip to the next innermost alternative if the rest of the	This verb causes a skip to the next innermost alternative when backtracking
pattern does not match. That is, it cancels pending backtracking, but only	reaches it. That is, it cancels any further backtracking within the current
within the current alternative. Its name comes from the observation that it can	alternative. Its name comes from the observation that it can be used for a
be used for a pattern-based if-then-else block:	pattern-based if-then-else block:
<pre>	<pre>
( COND1 (THEN) FOO \| COND2 (THEN) BAR \| COND3 (*THEN) BAZ ) ...	( COND1 (THEN) FOO \| COND2 (THEN) BAR \| COND3 (*THEN) BAZ ) ...
</pre>	</pre>
If the COND1 pattern matches, FOO is tried (and possibly further items after	If the COND1 pattern matches, FOO is tried (and possibly further items after
the end of the group if FOO succeeds); on failure, the matcher skips to the	the end of the group if FOO succeeds); on failure, the matcher skips to the
second alternative and tries COND2, without backtracking into COND1. The	second alternative and tries COND2, without backtracking into COND1. If that
behaviour of (THEN:NAME) is exactly the same as (MARK:NAME)(*THEN).	succeeds and BAR fails, COND3 is tried. If subsequently BAZ fails, there are no
If (THEN) is not inside an alternation, it acts like (PRUNE).	more alternatives, so there is a backtrack to whatever came before the entire
	group. If (THEN) is not inside an alternation, it acts like (PRUNE).
</P>	</P>
<P>	<P>
Note that a subpattern that does not contain a \| character is just a part of	The behaviour of (THEN:NAME) is the not the same as (MARK:NAME)(*THEN).
the enclosing alternative; it is not a nested alternation with only one	It is like (*MARK:NAME) in that the name is remembered for passing back to the
	caller. However, (SKIP:NAME) searches only for names set with (MARK).
	</P>
	<P>
	A subpattern that does not contain a \| character is just a part of the
	enclosing alternative; it is not a nested alternation with only one
alternative. The effect of (*THEN) extends beyond such a subpattern to the	alternative. The effect of (*THEN) extends beyond such a subpattern to the
enclosing alternative. Consider this pattern, where A, B, etc. are complex	enclosing alternative. Consider this pattern, where A, B, etc. are complex
pattern fragments that do not contain any \| characters at this level:	pattern fragments that do not contain any \| characters at this level:
Line 2777 because there are no more alternatives to try. In this	Line 3095 because there are no more alternatives to try. In this
backtrack into A.	backtrack into A.
</P>	</P>
<P>	<P>
Note also that a conditional subpattern is not considered as having two	Note that a conditional subpattern is not considered as having two
alternatives, because only one is ever used. In other words, the \| character in	alternatives, because only one is ever used. In other words, the \| character in
a conditional subpattern has a different meaning. Ignoring white space,	a conditional subpattern has a different meaning. Ignoring white space,
consider:	consider:
Line 2801 unanchored pattern). (*SKIP) is similar, except that t	Line 3119 unanchored pattern). (*SKIP) is similar, except that t
than one character. (*COMMIT) is the strongest, causing the entire match to	than one character. (*COMMIT) is the strongest, causing the entire match to
fail.	fail.
</P>	</P>
	<br><b>
	More than one backtracking verb
	</b><br>
<P>	<P>
If more than one such verb is present in a pattern, the "strongest" one wins.	If more than one backtracking verb is present in a pattern, the one that is
For example, consider this pattern, where A, B, etc. are complex pattern	backtracked onto first acts. For example, consider this pattern, where A, B,
fragments:	etc. are complex pattern fragments:
<pre>	<pre>
(A(COMMIT)B(THEN)C\|D)	(A(COMMIT)B(THEN)C\|ABD)
</pre>	</pre>
Once A has matched, PCRE is committed to this match, at the current starting	If A matches but B fails, the backtrack to (*COMMIT) causes the entire match to
position. If subsequently B matches, but C does not, the normal (*THEN) action	fail. However, if A and B match, but C fails, the backtrack to (*THEN) causes
of trying the next alternative (that is, D) does not happen because (*COMMIT)	the next alternative (ABD) to be tried. This behaviour is consistent, but is
overrides.	not always the same as Perl's. It means that if two or more backtracking verbs
	appear in succession, all the the last of them has no effect. Consider this
	example:
	<pre>
	...(COMMIT)(PRUNE)...
	</pre>
	If there is a matching failure to the right, backtracking onto (*PRUNE) causes
	it to be triggered, and its action is taken. There can never be a backtrack
	onto (*COMMIT).
	<a name="btrepeat"></a></P>
	<br><b>
	Backtracking verbs in repeated groups
	</b><br>
	<P>
	PCRE differs from Perl in its handling of backtracking verbs in repeated
	groups. For example, consider:
	<pre>
	/(a(*COMMIT)b)+ac/
	</pre>
	If the subject is "abac", Perl matches, but PCRE fails because the (*COMMIT) in
	the second repeat of the group acts.
	<a name="btassert"></a></P>
	<br><b>
	Backtracking verbs in assertions
	</b><br>
	<P>
	(*FAIL) in an assertion has its normal effect: it forces an immediate backtrack.
</P>	</P>
<br><a name="SEC26" href="#TOC1">SEE ALSO</a><br>
<P>	<P>
	(*ACCEPT) in a positive assertion causes the assertion to succeed without any
	further processing. In a negative assertion, (*ACCEPT) causes the assertion to
	fail without any further processing.
	</P>
	<P>
	The other backtracking verbs are not treated specially if they appear in a
	positive assertion. In particular, (*THEN) skips to the next alternative in the
	innermost enclosing group that has alternations, whether or not this is within
	the assertion.
	</P>
	<P>
	Negative assertions are, however, different, in order to ensure that changing a
	positive assertion into a negative assertion changes its result. Backtracking
	into (COMMIT), (SKIP), or (*PRUNE) causes a negative assertion to be true,
	without considering any further alternative branches in the assertion.
	Backtracking into (*THEN) causes it to skip to the next enclosing alternative
	within the assertion (the normal behaviour), but if the assertion does not have
	such an alternative, (THEN) behaves like (PRUNE).
	<a name="btsub"></a></P>
	<br><b>
	Backtracking verbs in subroutines
	</b><br>
	<P>
	These behaviours occur whether or not the subpattern is called recursively.
	Perl's treatment of subroutines is different in some cases.
	</P>
	<P>
	(*FAIL) in a subpattern called as a subroutine has its normal effect: it forces
	an immediate backtrack.
	</P>
	<P>
	(*ACCEPT) in a subpattern called as a subroutine causes the subroutine match to
	succeed without any further processing. Matching then continues after the
	subroutine call.
	</P>
	<P>
	(COMMIT), (SKIP), and (*PRUNE) in a subpattern called as a subroutine cause
	the subroutine match to fail.
	</P>
	<P>
	(*THEN) skips to the next alternative in the innermost enclosing group within
	the subpattern that has alternatives. If there is no such group within the
	subpattern, (*THEN) causes the subroutine match to fail.
	</P>
	<br><a name="SEC28" href="#TOC1">SEE ALSO</a><br>
	<P>
<b>pcreapi</b>(3), <b>pcrecallout</b>(3), <b>pcrematching</b>(3),	<b>pcreapi</b>(3), <b>pcrecallout</b>(3), <b>pcrematching</b>(3),
<b>pcresyntax</b>(3), <b>pcre</b>(3).	<b>pcresyntax</b>(3), <b>pcre</b>(3), <b>pcre16(3)</b>, <b>pcre32(3)</b>.
</P>	</P>
<br><a name="SEC27" href="#TOC1">AUTHOR</a><br>	<br><a name="SEC29" href="#TOC1">AUTHOR</a><br>
<P>	<P>
Philip Hazel	Philip Hazel
<br>	<br>
Line 2827 University Computing Service	Line 3219 University Computing Service
Cambridge CB2 3QH, England.	Cambridge CB2 3QH, England.
<br>	<br>
</P>	</P>
<br><a name="SEC28" href="#TOC1">REVISION</a><br>	<br><a name="SEC30" href="#TOC1">REVISION</a><br>
<P>	<P>
Last updated: 29 November 2011	Last updated: 03 December 2013
<br>	<br>
Copyright © 1997-2011 University of Cambridge.	Copyright © 1997-2013 University of Cambridge.
<br>	<br>
<p>	<p>
Return to the <a href="index.html">PCRE index page</a>.	Return to the <a href="index.html">PCRE index page</a>.

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