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revision 1369 by ph10, Tue Oct 8 15:06:46 2013 UTC revision 1401 by ph10, Tue Nov 12 17:44:07 2013 UTC
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1  .TH PCREPATTERN 3 "08 October 2013" "PCRE 8.34"  .TH PCREPATTERN 3 "12 November 2013" "PCRE 8.34"
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
# Line 80  appearance causes an error. Line 80  appearance causes an error.
80  .SS "Unicode property support"  .SS "Unicode property support"
81  .rs  .rs
82  .sp  .sp
83  Another special sequence that may appear at the start of a pattern is  Another special sequence that may appear at the start of a pattern is (*UCP).
 .sp  
   (*UCP)  
 .sp  
84  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
85  such as \ed and \ew to use Unicode properties to determine character types,  such as \ed and \ew to use Unicode properties to determine character types,
86  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
87  table.  table.
88  .  .
89  .  .
90    .SS "Disabling auto-possessification"
91    .rs
92    .sp
93    If a pattern starts with (*NO_AUTO_POSSESS), it has the same effect as setting
94    the PCRE_NO_AUTO_POSSESS option at compile time. This stops PCRE from making
95    quantifiers possessive when what follows cannot match the repeated item. For
96    example, by default a+b is treated as a++b. For more details, see the
97    .\" HREF
98    \fBpcreapi\fP
99    .\"
100    documentation.
101    .
102    .
103  .SS "Disabling start-up optimizations"  .SS "Disabling start-up optimizations"
104  .rs  .rs
105  .sp  .sp
106  If a pattern starts with (*NO_START_OPT), it has the same effect as setting the  If a pattern starts with (*NO_START_OPT), it has the same effect as setting the
107  PCRE_NO_START_OPTIMIZE option either at compile or matching time.  PCRE_NO_START_OPTIMIZE option either at compile or matching time. This disables
108    several optimizations for quickly reaching "no match" results. For more
109    details, see the
110    .\" HREF
111    \fBpcreapi\fP
112    .\"
113    documentation.
114  .  .
115  .  .
116  .\" HTML <a name="newlines"></a>  .\" HTML <a name="newlines"></a>
# Line 164  pattern of the form Line 180  pattern of the form
180    (*LIMIT_RECURSION=d)    (*LIMIT_RECURSION=d)
181  .sp  .sp
182  where d is any number of decimal digits. However, the value of the setting must  where d is any number of decimal digits. However, the value of the setting must
183  be less than the value set by the caller of \fBpcre_exec()\fP for it to have  be less than the value set (or defaulted) by the caller of \fBpcre_exec()\fP
184  any effect. In other words, the pattern writer can lower the limit set by the  for it to have any effect. In other words, the pattern writer can lower the
185  programmer, but not raise it. If there is more than one setting of one of these  limits set by the programmer, but not raise them. If there is more than one
186  limits, the lower value is used.  setting of one of these limits, the lower value is used.
187  .  .
188  .  .
189  .SH "EBCDIC CHARACTER CODES"  .SH "EBCDIC CHARACTER CODES"
# Line 257  In a UTF mode, only ASCII numbers and le Line 273  In a UTF mode, only ASCII numbers and le
273  backslash. All other characters (in particular, those whose codepoints are  backslash. All other characters (in particular, those whose codepoints are
274  greater than 127) are treated as literals.  greater than 127) are treated as literals.
275  .P  .P
276  If a pattern is compiled with the PCRE_EXTENDED option, white space in the  If a pattern is compiled with the PCRE_EXTENDED option, most white space in the
277  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
278  a character class and the next newline are ignored. An escaping backslash can  character class and the next newline, inclusive, are ignored. An escaping
279  be used to include a white space or # character as part of the pattern.  backslash can be used to include a white space or # character as part of the
280    pattern.
281  .P  .P
282  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
283  can do so by putting them between \eQ and \eE. This is different from Perl in  can do so by putting them between \eQ and \eE. This is different from Perl in
# Line 300  one of the following escape sequences th Line 317  one of the following escape sequences th
317    \en        linefeed (hex 0A)    \en        linefeed (hex 0A)
318    \er        carriage return (hex 0D)    \er        carriage return (hex 0D)
319    \et        tab (hex 09)    \et        tab (hex 09)
320      \e0dd      character with octal code 0dd
321    \eddd      character with octal code ddd, or back reference    \eddd      character with octal code ddd, or back reference
322      \eo{ddd..} character with octal code ddd..
323    \exhh      character with hex code hh    \exhh      character with hex code hh
324    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)    \ex{hhh..} character with hex code hhh.. (non-JavaScript mode)
325    \euhhhh    character with hex code hhhh (JavaScript mode only)    \euhhhh    character with hex code hhhh (JavaScript mode only)
# Line 321  byte are inverted. Thus \ecA becomes hex Line 340  byte are inverted. Thus \ecA becomes hex
340  the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other  the EBCDIC letters are disjoint, \ecZ becomes hex 29 (Z is E9), and other
341  characters also generate different values.  characters also generate different values.
342  .P  .P
 By default, after \ex, from zero to two hexadecimal digits are read (letters  
 can be in upper or lower case). Any number of hexadecimal digits may appear  
 between \ex{ and }, but the character code is constrained as follows:  
 .sp  
   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 0x80000000  
   32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint  
 .sp  
 Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called  
 "surrogate" codepoints), and 0xffef.  
 .P  
 If characters other than hexadecimal digits appear between \ex{ and }, or if  
 there is no terminating }, this form of escape is not recognized. Instead, the  
 initial \ex will be interpreted as a basic hexadecimal escape, with no  
 following digits, giving a character whose value is zero.  
 .P  
 If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex 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 \eu, which must be followed by  
 four hexadecimal digits; otherwise it matches a literal "u" character.  
 Character codes specified by \eu in JavaScript mode are constrained in the same  
 was as those specified by \ex in non-JavaScript mode.  
 .P  
 Characters whose value is less than 256 can be defined by either of the two  
 syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the  
 way they are handled. For example, \exdc is exactly the same as \ex{dc} (or  
 \eu00dc in JavaScript mode).  
 .P  
343  After \e0 up to two further octal digits are read. If there are fewer than two  After \e0 up to two further octal digits are read. If there are fewer than two
344  digits, just those that are present are used. Thus the sequence \e0\ex\e07  digits, just those that are present are used. Thus the sequence \e0\ex\e07
345  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
346  sure you supply two digits after the initial zero if the pattern character that  sure you supply two digits after the initial zero if the pattern character that
347  follows is itself an octal digit.  follows is itself an octal digit.
348  .P  .P
349    The escape \eo must be followed by a sequence of octal digits, enclosed in
350    braces. An error occurs if this is not the case. This escape is a recent
351    addition to Perl; it provides way of specifying character code points as octal
352    numbers greater than 0777, and it also allows octal numbers and back references
353    to be unambiguously specified.
354    .P
355    For greater clarity and unambiguity, it is best to avoid following \e by a
356    digit greater than zero. Instead, use \eo{} or \ex{} to specify character
357    numbers, and \eg{} to specify back references. The following paragraphs
358    describe the old, ambiguous syntax.
359    .P
360  The handling of a backslash followed by a digit other than 0 is complicated,  The handling of a backslash followed by a digit other than 0 is complicated,
361  and Perl has changed in recent releases, causing PCRE also to change. Outside a  and Perl has changed in recent releases, causing PCRE also to change. Outside a
362  character class, PCRE reads the digit and any following digits as a decimal  character class, PCRE reads the digit and any following digits as a decimal
# Line 379  Inside a character class, or if the deci Line 377  Inside a character class, or if the deci
377  7 and there have not been that many capturing subpatterns, PCRE handles \e8 and  7 and there have not been that many capturing subpatterns, PCRE handles \e8 and
378  \e9 as the literal characters "8" and "9", and otherwise re-reads up to three  \e9 as the literal characters "8" and "9", and otherwise re-reads up to three
379  octal digits following the backslash, using them to generate a data character.  octal digits following the backslash, using them to generate a data character.
380  Any subsequent digits stand for themselves. The value of the character is  Any subsequent digits stand for themselves. For example:
 constrained in the same way as characters specified in hexadecimal. For  
 example:  
381  .sp  .sp
382    \e040   is another way of writing an ASCII space    \e040   is another way of writing an ASCII space
383  .\" JOIN  .\" JOIN
# Line 403  example: Line 399  example:
399    \e81    is either a back reference, or the two    \e81    is either a back reference, or the two
400              characters "8" and "1"              characters "8" and "1"
401  .sp  .sp
402  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
403  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
404    digits are ever read.
405    .P
406    By default, after \ex that is not followed by {, from zero to two hexadecimal
407    digits are read (letters can be in upper or lower case). Any number of
408    hexadecimal digits may appear between \ex{ and }. If a character other than
409    a hexadecimal digit appears between \ex{ and }, or if there is no terminating
410    }, an error occurs.
411    .P
412    If the PCRE_JAVASCRIPT_COMPAT option is set, the interpretation of \ex is
413    as just described only when it is followed by two hexadecimal digits.
414    Otherwise, it matches a literal "x" character. In JavaScript mode, support for
415    code points greater than 256 is provided by \eu, which must be followed by
416    four hexadecimal digits; otherwise it matches a literal "u" character.
417  .P  .P
418    Characters whose value is less than 256 can be defined by either of the two
419    syntaxes for \ex (or by \eu in JavaScript mode). There is no difference in the
420    way they are handled. For example, \exdc is exactly the same as \ex{dc} (or
421    \eu00dc in JavaScript mode).
422    .
423    .
424    .SS "Constraints on character values"
425    .rs
426    .sp
427    Characters that are specified using octal or hexadecimal numbers are
428    limited to certain values, as follows:
429    .sp
430      8-bit non-UTF mode    less than 0x100
431      8-bit UTF-8 mode      less than 0x10ffff and a valid codepoint
432      16-bit non-UTF mode   less than 0x10000
433      16-bit UTF-16 mode    less than 0x10ffff and a valid codepoint
434      32-bit non-UTF mode   less than 0x100000000
435      32-bit UTF-32 mode    less than 0x10ffff and a valid codepoint
436    .sp
437    Invalid Unicode codepoints are the range 0xd800 to 0xdfff (the so-called
438    "surrogate" codepoints), and 0xffef.
439    .
440    .
441    .SS "Escape sequences in character classes"
442    .rs
443    .sp
444  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
445  and outside character classes. In addition, inside a character class, \eb is  and outside character classes. In addition, inside a character class, \eb is
446  interpreted as the backspace character (hex 08).  interpreted as the backspace character (hex 08).
# Line 498  there is no character to match. Line 533  there is no character to match.
533  .P  .P
534  For compatibility with Perl, \es did not used to match the VT character (code  For compatibility with Perl, \es did not used to match the VT character (code
535  11), which made it different from the the POSIX "space" class. However, Perl  11), which made it different from the the POSIX "space" class. However, Perl
536  added VT at release 5.18, and PCRE followed suit at release 8.34. The \es  added VT at release 5.18, and PCRE followed suit at release 8.34. The default
537  characters are now HT (9), LF (10), VT (11), FF (12), CR (13), and space (32).  \es characters are now HT (9), LF (10), VT (11), FF (12), CR (13), and space
538    (32), which are defined as white space in the "C" locale. This list may vary if
539    locale-specific matching is taking place; in particular, in some locales the
540    "non-breaking space" character (\exA0) is recognized as white space.
541  .P  .P
542  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.
543  By default, the definition of letters and digits is controlled by PCRE's  By default, the definition of letters and digits is controlled by PCRE's
# Line 514  in the Line 552  in the
552  \fBpcreapi\fP  \fBpcreapi\fP
553  .\"  .\"
554  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,
555  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
556  accented letters, and these are then matched by \ew. The use of locales with  accented letters, and these are then matched by \ew. The use of locales with
557  Unicode is discouraged.  Unicode is discouraged.
558  .P  .P
559  By default, in a UTF mode, characters with values greater than 128 never match  By default, characters whose code points are greater than 127 never match \ed,
560  \ed, \es, or \ew, and always match \eD, \eS, and \eW. These sequences retain  \es, or \ew, and always match \eD, \eS, and \eW, although this may vary for
561  their original meanings from before UTF support was available, mainly for  characters in the range 128-255 when locale-specific matching is happening.
562  efficiency reasons. However, if PCRE is compiled with Unicode property support,  These escape sequences retain their original meanings from before Unicode
563  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
564  properties are used to determine character types, as follows:  Unicode property support, and the PCRE_UCP option is set, the behaviour is
565  .sp  changed so that Unicode properties are used to determine character types, as
566    \ed  any character that \ep{Nd} matches (decimal digit)  follows:
567    \es  any character that \ep{Z} matches, plus HT, LF, FF, CR  .sp
568    \ew  any character that \ep{L} or \ep{N} matches, plus underscore    \ed  any character that matches \ep{Nd} (decimal digit)
569      \es  any character that matches \ep{Z} or \eh or \ev
570      \ew  any character that matches \ep{L} or \ep{N}, plus underscore
571  .sp  .sp
572  The upper case escapes match the inverse sets of characters. Note that \ed  The upper case escapes match the inverse sets of characters. Note that \ed
573  matches only decimal digits, whereas \ew matches any Unicode digit, as well as  matches only decimal digits, whereas \ew matches any Unicode digit, as well as
# Line 537  is noticeably slower when PCRE_UCP is se Line 577  is noticeably slower when PCRE_UCP is se
577  .P  .P
578  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at  The sequences \eh, \eH, \ev, and \eV are features that were added to Perl at
579  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
580  characters by default, these always match certain high-valued codepoints,  characters by default, these always match certain high-valued code points,
581  whether or not PCRE_UCP is set. The horizontal space characters are:  whether or not PCRE_UCP is set. The horizontal space characters are:
582  .sp  .sp
583    U+0009     Horizontal tab (HT)    U+0009     Horizontal tab (HT)
# Line 907  the "mark" property always have the "ext Line 947  the "mark" property always have the "ext
947  .sp  .sp
948  As well as the standard Unicode properties described above, PCRE supports four  As well as the standard Unicode properties described above, PCRE supports four
949  more that make it possible to convert traditional escape sequences such as \ew  more that make it possible to convert traditional escape sequences such as \ew
950  and \es and POSIX character classes to use Unicode properties. PCRE uses these  and \es to use Unicode properties. PCRE uses these non-standard, non-Perl
951  non-standard, non-Perl properties internally when PCRE_UCP is set. However,  properties internally when PCRE_UCP is set. However, they may also be used
952  they may also be used explicitly. These properties are:  explicitly. These properties are:
953  .sp  .sp
954    Xan   Any alphanumeric character    Xan   Any alphanumeric character
955    Xps   Any POSIX space character    Xps   Any POSIX space character
# Line 919  they may also be used explicitly. These Line 959  they may also be used explicitly. These
959  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)
960  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or  property. Xps matches the characters tab, linefeed, vertical tab, form feed, or
961  carriage return, and any other character that has the Z (separator) property.  carriage return, and any other character that has the Z (separator) property.
962  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
963  same characters as Xan, plus underscore.  compatibility, but Perl changed, and so PCRE followed at release 8.34. Xwd
964    matches the same characters as Xan, plus underscore.
965  .P  .P
966  There is another non-standard property, Xuc, which matches any character that  There is another non-standard property, Xuc, which matches any character that
967  can be represented by a Universal Character Name in C++ and other programming  can be represented by a Universal Character Name in C++ and other programming
# Line 1216  The minus (hyphen) character can be used Line 1257  The minus (hyphen) character can be used
1257  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,
1258  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
1259  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
1260  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
1261    immediately after a range. For example, [b-d-z] matches letters in the range b
1262    to d, a hyphen character, or z.
1263  .P  .P
1264  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
1265  range. A pattern such as [W-]46] is interpreted as a class of two characters  range. A pattern such as [W-]46] is interpreted as a class of two characters
# Line 1226  the end of range, so [W-\e]46] is interp Line 1269  the end of range, so [W-\e]46] is interp
1269  followed by two other characters. The octal or hexadecimal representation of  followed by two other characters. The octal or hexadecimal representation of
1270  "]" can also be used to end a range.  "]" can also be used to end a range.
1271  .P  .P
1272    An error is generated if a POSIX character class (see below) or an escape
1273    sequence other than one that defines a single character appears at a point
1274    where a range ending character is expected. For example, [z-\exff] is valid,
1275    but [A-\ed] and [A-[:digit:]] are not.
1276    .P
1277  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
1278  used for characters specified numerically, for example [\e000-\e037]. Ranges  used for characters specified numerically, for example [\e000-\e037]. Ranges
1279  can include any characters that are valid for the current mode.  can include any characters that are valid for the current mode.
# Line 1291  are: Line 1339  are:
1339    lower    lower case letters    lower    lower case letters
1340    print    printing characters, including space    print    printing characters, including space
1341    punct    printing characters, excluding letters and digits and space    punct    printing characters, excluding letters and digits and space
1342    space    white space (not quite the same as \es)    space    white space (the same as \es from PCRE 8.34)
1343    upper    upper case letters    upper    upper case letters
1344    word     "word" characters (same as \ew)    word     "word" characters (same as \ew)
1345    xdigit   hexadecimal digits    xdigit   hexadecimal digits
1346  .sp  .sp
1347  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),
1348  space (32). "Space" used to be different to \es, which did not include VT, for  and space (32). If locale-specific matching is taking place, there may be
1349  Perl compatibility. However, Perl changed at release 5.18, and PCRE followed at  additional space characters. "Space" used to be different to \es, which did not
1350  release 8.34. "Space" and \es now match the same set of characters.  include VT, for Perl compatibility. However, Perl changed at release 5.18, and
1351    PCRE followed at release 8.34. "Space" and \es now match the same set of
1352    characters.
1353  .P  .P
1354  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
1355  5.8. Another Perl extension is negation, which is indicated by a ^ character  5.8. Another Perl extension is negation, which is indicated by a ^ character
# Line 1311  matches "1", "2", or any non-digit. PCRE Line 1361  matches "1", "2", or any non-digit. PCRE
1361  syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not  syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not
1362  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1363  .P  .P
1364  By default, in UTF modes, characters with values greater than 128 do not match  By default, characters with values greater than 128 do not match any of the
1365  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
1366  to \fBpcre_compile()\fP, some of the classes are changed so that Unicode  \fBpcre_compile()\fP, some of the classes are changed so that Unicode character
1367  character properties are used. This is achieved by replacing the POSIX classes  properties are used. This is achieved by replacing certain POSIX classes by
1368  by other sequences, as follows:  other sequences, as follows:
1369  .sp  .sp
1370    [:alnum:]  becomes  \ep{Xan}    [:alnum:]  becomes  \ep{Xan}
1371    [:alpha:]  becomes  \ep{L}    [:alpha:]  becomes  \ep{L}
# Line 1326  by other sequences, as follows: Line 1376  by other sequences, as follows:
1376    [:upper:]  becomes  \ep{Lu}    [:upper:]  becomes  \ep{Lu}
1377    [:word:]   becomes  \ep{Xwd}    [:word:]   becomes  \ep{Xwd}
1378  .sp  .sp
1379  Negated versions, such as [:^alpha:] use \eP instead of \ep. The other POSIX  Negated versions, such as [:^alpha:] use \eP instead of \ep. Three other POSIX
1380  classes are unchanged, and match only characters with code points less than  classes are handled specially in UCP mode:
1381  128.  .TP 10
1382    [:graph:]
1383    This matches characters that have glyphs that mark the page when printed. In
1384    Unicode property terms, it matches all characters with the L, M, N, P, S, or Cf
1385    properties, except for:
1386    .sp
1387      U+061C           Arabic Letter Mark
1388      U+180E           Mongolian Vowel Separator
1389      U+2066 - U+2069  Various "isolate"s
1390    .sp
1391    .TP 10
1392    [:print:]
1393    This matches the same characters as [:graph:] plus space characters that are
1394    not controls, that is, characters with the Zs property.
1395    .TP 10
1396    [:punct:]
1397    This matches all characters that have the Unicode P (punctuation) property,
1398    plus those characters whose code points are less than 128 that have the S
1399    (Symbol) property.
1400    .P
1401    The other POSIX classes are unchanged, and match only characters with code
1402    points less than 128.
1403  .  .
1404  .  .
1405  .SH "VERTICAL BAR"  .SH "VERTICAL BAR"
# Line 1548  conditions, Line 1619  conditions,
1619  .\"  .\"
1620  can be made by name as well as by number.  can be made by name as well as by number.
1621  .P  .P
1622  Names consist of up to 32 alphanumeric characters and underscores. Named  Names consist of up to 32 alphanumeric characters and underscores, but must
1623  capturing parentheses are still allocated numbers as well as names, exactly as  start with a non-digit. Named capturing parentheses are still allocated numbers
1624  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
1625  extracting the name-to-number translation table from a compiled pattern. There  provides function calls for extracting the name-to-number translation table
1626  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
1627    captured substring by name.
1628  .P  .P
1629  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
1630  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate  this constraint by setting the PCRE_DUPNAMES option at compile time. (Duplicate
# Line 2284  This makes the fragment independent of t Line 2356  This makes the fragment independent of t
2356  .sp  .sp
2357  Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used  Perl uses the syntax (?(<name>)...) or (?('name')...) to test for a used
2358  subpattern by name. For compatibility with earlier versions of PCRE, which had  subpattern by name. For compatibility with earlier versions of PCRE, which had
2359  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.  
2360  .P  .P
2361  Rewriting the above example to use a named subpattern gives this:  Rewriting the above example to use a named subpattern gives this:
2362  .sp  .sp
# Line 2711  During matching, when PCRE reaches a cal Line 2778  During matching, when PCRE reaches a cal
2778  called. It is provided with the number of the callout, the position in the  called. It is provided with the number of the callout, the position in the
2779  pattern, and, optionally, one item of data originally supplied by the caller of  pattern, and, optionally, one item of data originally supplied by the caller of
2780  the matching function. The callout function may cause matching to proceed, to  the matching function. The callout function may cause matching to proceed, to
2781  backtrack, or to fail altogether. A complete description of the interface to  backtrack, or to fail altogether.
2782  the callout function is given in the  .P
2783    By default, PCRE implements a number of optimizations at compile time and
2784    matching time, and one side-effect is that sometimes callouts are skipped. If
2785    you need all possible callouts to happen, you need to set options that disable
2786    the relevant optimizations. More details, and a complete description of the
2787    interface to the callout function, are given in the
2788  .\" HREF  .\" HREF
2789  \fBpcrecallout\fP  \fBpcrecallout\fP
2790  .\"  .\"
# Line 3158  Cambridge CB2 3QH, England. Line 3230  Cambridge CB2 3QH, England.
3230  .rs  .rs
3231  .sp  .sp
3232  .nf  .nf
3233  Last updated: 08 October 2013  Last updated: 12 November 2013
3234  Copyright (c) 1997-2013 University of Cambridge.  Copyright (c) 1997-2013 University of Cambridge.
3235  .fi  .fi

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