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revision 172 by ph10, Tue Jun 5 10:40:13 2007 UTC revision 208 by ph10, Mon Aug 6 15:23:29 2007 UTC
# Line 4  PCRE - Perl-compatible regular expressio Line 4  PCRE - Perl-compatible regular expressio
4  .SH "PCRE REGULAR EXPRESSION DETAILS"  .SH "PCRE REGULAR EXPRESSION DETAILS"
5  .rs  .rs
6  .sp  .sp
7  The syntax and semantics of the regular expressions supported by PCRE are  The syntax and semantics of the regular expressions that are supported by PCRE
8  described below. Regular expressions are also described in the Perl  are described in detail below. There is a quick-reference syntax summary in the
9  documentation and in a number of books, some of which have copious examples.  .\" HREF
10  Jeffrey Friedl's "Mastering Regular Expressions", published by O'Reilly, covers  \fBpcresyntax\fP
11  regular expressions in great detail. This description of PCRE's regular  .\"
12  expressions is intended as reference material.  page. Perl's regular expressions are described in its own documentation, and
13    regular expressions in general are covered in a number of books, some of which
14    have copious examples. Jeffrey Friedl's "Mastering Regular Expressions",
15    published by O'Reilly, covers regular expressions in great detail. This
16    description of PCRE's regular expressions is intended as reference material.
17  .P  .P
18  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,
19  there is now also support for UTF-8 character strings. To use this, you must  there is now also support for UTF-8 character strings. To use this, you must
# Line 240  meanings Line 244  meanings
244  .SS "Absolute and relative back references"  .SS "Absolute and relative back references"
245  .rs  .rs
246  .sp  .sp
247  The sequence \eg followed by a positive or negative number, optionally enclosed  The sequence \eg followed by an unsigned or a negative number, optionally
248  in braces, is an absolute or relative back reference. A named back reference  enclosed in braces, is an absolute or relative back reference. A named back
249  can be coded as \eg{name}. Back references are discussed  reference can be coded as \eg{name}. Back references are discussed
250  .\" HTML <a href="#backreferences">  .\" HTML <a href="#backreferences">
251  .\" </a>  .\" </a>
252  later,  later,
# Line 262  following are always recognized: Line 266  following are always recognized:
266  .sp  .sp
267    \ed     any decimal digit    \ed     any decimal digit
268    \eD     any character that is not a decimal digit    \eD     any character that is not a decimal digit
269      \eh     any horizontal whitespace character
270      \eH     any character that is not a horizontal whitespace character
271    \es     any whitespace character    \es     any whitespace character
272    \eS     any character that is not a whitespace character    \eS     any character that is not a whitespace character
273      \ev     any vertical whitespace character
274      \eV     any character that is not a vertical whitespace character
275    \ew     any "word" character    \ew     any "word" character
276    \eW     any "non-word" character    \eW     any "non-word" character
277  .sp  .sp
# Line 277  there is no character to match. Line 285  there is no character to match.
285  .P  .P
286  For compatibility with Perl, \es does not match the VT character (code 11).  For compatibility with Perl, \es does not match the VT character (code 11).
287  This makes it different from the the POSIX "space" class. The \es characters  This makes it different from the the POSIX "space" class. The \es characters
288  are HT (9), LF (10), FF (12), CR (13), and space (32). (If "use locale;" is  are HT (9), LF (10), FF (12), CR (13), and space (32). If "use locale;" is
289  included in a Perl script, \es may match the VT character. In PCRE, it never  included in a Perl script, \es may match the VT character. In PCRE, it never
290  does.)  does.
291    .P
292    In UTF-8 mode, characters with values greater than 128 never match \ed, \es, or
293    \ew, and always match \eD, \eS, and \eW. This is true even when Unicode
294    character property support is available. These sequences retain their original
295    meanings from before UTF-8 support was available, mainly for efficiency
296    reasons.
297    .P
298    The sequences \eh, \eH, \ev, and \eV are Perl 5.10 features. In contrast to the
299    other sequences, these do match certain high-valued codepoints in UTF-8 mode.
300    The horizontal space characters are:
301    .sp
302      U+0009     Horizontal tab
303      U+0020     Space
304      U+00A0     Non-break space
305      U+1680     Ogham space mark
306      U+180E     Mongolian vowel separator
307      U+2000     En quad
308      U+2001     Em quad
309      U+2002     En space
310      U+2003     Em space
311      U+2004     Three-per-em space
312      U+2005     Four-per-em space
313      U+2006     Six-per-em space
314      U+2007     Figure space
315      U+2008     Punctuation space
316      U+2009     Thin space
317      U+200A     Hair space
318      U+202F     Narrow no-break space
319      U+205F     Medium mathematical space
320      U+3000     Ideographic space
321    .sp
322    The vertical space characters are:
323    .sp
324      U+000A     Linefeed
325      U+000B     Vertical tab
326      U+000C     Formfeed
327      U+000D     Carriage return
328      U+0085     Next line
329      U+2028     Line separator
330      U+2029     Paragraph separator
331  .P  .P
332  A "word" character is an underscore or any character less than 256 that is a  A "word" character is an underscore or any character less than 256 that is a
333  letter or digit. The definition of letters and digits is controlled by PCRE's  letter or digit. The definition of letters and digits is controlled by PCRE's
# Line 295  in the Line 343  in the
343  .\"  .\"
344  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,
345  or "french" in Windows, some character codes greater than 128 are used for  or "french" in Windows, some character codes greater than 128 are used for
346  accented letters, and these are matched by \ew.  accented letters, and these are matched by \ew. The use of locales with Unicode
347  .P  is discouraged.
 In UTF-8 mode, characters with values greater than 128 never match \ed, \es, or  
 \ew, and always match \eD, \eS, and \eW. This is true even when Unicode  
 character property support is available. The use of locales with Unicode is  
 discouraged.  
348  .  .
349  .  .
350  .SS "Newline sequences"  .SS "Newline sequences"
351  .rs  .rs
352  .sp  .sp
353  Outside a character class, the escape sequence \eR matches any Unicode newline  Outside a character class, the escape sequence \eR matches any Unicode newline
354  sequence. This is an extension to Perl. In non-UTF-8 mode \eR is equivalent to  sequence. This is a Perl 5.10 feature. In non-UTF-8 mode \eR is equivalent to
355  the following:  the following:
356  .sp  .sp
357    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)    (?>\er\en|\en|\ex0b|\ef|\er|\ex85)
# Line 336  Inside a character class, \eR matches th Line 380  Inside a character class, \eR matches th
380  .rs  .rs
381  .sp  .sp
382  When PCRE is built with Unicode character property support, three additional  When PCRE is built with Unicode character property support, three additional
383  escape sequences to match character properties are available when UTF-8 mode  escape sequences that match characters with specific properties are available.
384  is selected. They are:  When not in UTF-8 mode, these sequences are of course limited to testing
385    characters whose codepoints are less than 256, but they do work in this mode.
386    The extra escape sequences are:
387  .sp  .sp
388    \ep{\fIxx\fP}   a character with the \fIxx\fP property    \ep{\fIxx\fP}   a character with the \fIxx\fP property
389    \eP{\fIxx\fP}   a character without the \fIxx\fP property    \eP{\fIxx\fP}   a character without the \fIxx\fP property
# Line 513  atomic group Line 559  atomic group
559  (see below).  (see below).
560  .\"  .\"
561  Characters with the "mark" property are typically accents that affect the  Characters with the "mark" property are typically accents that affect the
562  preceding character.  preceding character. None of them have codepoints less than 256, so in
563    non-UTF-8 mode \eX matches any one character.
564  .P  .P
565  Matching characters by Unicode property is not fast, because PCRE has to search  Matching characters by Unicode property is not fast, because PCRE has to search
566  a structure that contains data for over fifteen thousand characters. That is  a structure that contains data for over fifteen thousand characters. That is
# Line 958  is reached, an option setting in one bra Line 1005  is reached, an option setting in one bra
1005  the above patterns match "SUNDAY" as well as "Saturday".  the above patterns match "SUNDAY" as well as "Saturday".
1006  .  .
1007  .  .
1008    .SH "DUPLICATE SUBPATTERN NUMBERS"
1009    .rs
1010    .sp
1011    Perl 5.10 introduced a feature whereby each alternative in a subpattern uses
1012    the same numbers for its capturing parentheses. Such a subpattern starts with
1013    (?| and is itself a non-capturing subpattern. For example, consider this
1014    pattern:
1015    .sp
1016      (?|(Sat)ur|(Sun))day
1017    .sp
1018    Because the two alternatives are inside a (?| group, both sets of capturing
1019    parentheses are numbered one. Thus, when the pattern matches, you can look
1020    at captured substring number one, whichever alternative matched. This construct
1021    is useful when you want to capture part, but not all, of one of a number of
1022    alternatives. Inside a (?| group, parentheses are numbered as usual, but the
1023    number is reset at the start of each branch. The numbers of any capturing
1024    buffers that follow the subpattern start after the highest number used in any
1025    branch. The following example is taken from the Perl documentation.
1026    The numbers underneath show in which buffer the captured content will be
1027    stored.
1028    .sp
1029      # before  ---------------branch-reset----------- after
1030      / ( a )  (?| x ( y ) z | (p (q) r) | (t) u (v) ) ( z ) /x
1031      # 1            2         2  3        2     3     4
1032    .sp
1033    A backreference or a recursive call to a numbered subpattern always refers to
1034    the first one in the pattern with the given number.
1035    .P
1036    An alternative approach to using this "branch reset" feature is to use
1037    duplicate named subpatterns, as described in the next section.
1038    .
1039    .
1040  .SH "NAMED SUBPATTERNS"  .SH "NAMED SUBPATTERNS"
1041  .rs  .rs
1042  .sp  .sp
# Line 1007  abbreviation. This pattern (ignoring the Line 1086  abbreviation. This pattern (ignoring the
1086    (?<DN>Sat)(?:urday)?    (?<DN>Sat)(?:urday)?
1087  .sp  .sp
1088  There are five capturing substrings, but only one is ever set after a match.  There are five capturing substrings, but only one is ever set after a match.
1089    (An alternative way of solving this problem is to use a "branch reset"
1090    subpattern, as described in the previous section.)
1091    .P
1092  The convenience function for extracting the data by name returns the substring  The convenience function for extracting the data by name returns the substring
1093  for the first (and in this example, the only) subpattern of that name that  for the first (and in this example, the only) subpattern of that name that
1094  matched. This saves searching to find which numbered subpattern it was. If you  matched. This saves searching to find which numbered subpattern it was. If you
# Line 1212  previous example can be rewritten as Line 1294  previous example can be rewritten as
1294  .sp  .sp
1295    \ed++foo    \ed++foo
1296  .sp  .sp
1297    Note that a possessive quantifier can be used with an entire group, for
1298    example:
1299    .sp
1300      (abc|xyz){2,3}+
1301    .sp
1302  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY  Possessive quantifiers are always greedy; the setting of the PCRE_UNGREEDY
1303  option is ignored. They are a convenient notation for the simpler forms of  option is ignored. They are a convenient notation for the simpler forms of
1304  atomic group. However, there is no difference in the meaning of a possessive  atomic group. However, there is no difference in the meaning of a possessive
# Line 1286  subpattern is possible using named paren Line 1373  subpattern is possible using named paren
1373  .P  .P
1374  Another way of avoiding the ambiguity inherent in the use of digits following a  Another way of avoiding the ambiguity inherent in the use of digits following a
1375  backslash is to use the \eg escape sequence, which is a feature introduced in  backslash is to use the \eg escape sequence, which is a feature introduced in
1376  Perl 5.10. This escape must be followed by a positive or a negative number,  Perl 5.10. This escape must be followed by an unsigned number or a negative
1377  optionally enclosed in braces. These examples are all identical:  number, optionally enclosed in braces. These examples are all identical:
1378  .sp  .sp
1379    (ring), \e1    (ring), \e1
1380    (ring), \eg1    (ring), \eg1
1381    (ring), \eg{1}    (ring), \eg{1}
1382  .sp  .sp
1383  A positive number specifies an absolute reference without the ambiguity that is  An unsigned number specifies an absolute reference without the ambiguity that
1384  present in the older syntax. It is also useful when literal digits follow the  is present in the older syntax. It is also useful when literal digits follow
1385  reference. A negative number is a relative reference. Consider this example:  the reference. A negative number is a relative reference. Consider this
1386    example:
1387  .sp  .sp
1388    (abc(def)ghi)\eg{-1}    (abc(def)ghi)\eg{-1}
1389  .sp  .sp
# Line 1898  Cambridge CB2 3QH, England. Line 1986  Cambridge CB2 3QH, England.
1986  .rs  .rs
1987  .sp  .sp
1988  .nf  .nf
1989  Last updated: 29 May 2007  Last updated: 06 August 2007
1990  Copyright (c) 1997-2007 University of Cambridge.  Copyright (c) 1997-2007 University of Cambridge.
1991  .fi  .fi

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