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code/trunk/pcre.3 revision 11 by nigel, Sat Feb 24 21:38:17 2007 UTC code/tags/pcre-2.03/pcre.3 revision 30 by nigel, Sat Feb 24 21:38:55 2007 UTC
# Line 8  pcre - Perl-compatible regular expressio Line 8  pcre - Perl-compatible regular expressio
8  .br  .br
9  .B pcre *pcre_compile(const char *\fIpattern\fR, int \fIoptions\fR,  .B pcre *pcre_compile(const char *\fIpattern\fR, int \fIoptions\fR,
10  .ti +5n  .ti +5n
11  .B const char **\fIerrptr\fR, int *\fIerroffset\fR);  .B const char **\fIerrptr\fR, int *\fIerroffset\fR,
12    .ti +5n
13    .B const unsigned char *\fItableptr\fR);
14  .PP  .PP
15  .br  .br
16  .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,  .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
# Line 23  pcre - Perl-compatible regular expressio Line 25  pcre - Perl-compatible regular expressio
25  .B int *\fIovector\fR, int \fIovecsize\fR);  .B int *\fIovector\fR, int \fIovecsize\fR);
26  .PP  .PP
27  .br  .br
28  .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int  .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
29  .B *\fIfirstcharptr\fR);  .ti +5n
30    .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
31    .ti +5n
32    .B int \fIbuffersize\fR);
33  .PP  .PP
34  .br  .br
35  .B char *pcre_version(void);  .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
36    .ti +5n
37    .B int \fIstringcount\fR, int \fIstringnumber\fR,
38    .ti +5n
39    .B const char **\fIstringptr\fR);
40  .PP  .PP
41  .br  .br
42  .B void *(*pcre_malloc)(size_t);  .B int pcre_get_substring_list(const char *\fIsubject\fR,
43    .ti +5n
44    .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
45  .PP  .PP
46  .br  .br
47  .B void (*pcre_free)(void *);  .B const unsigned char *pcre_maketables(void);
48  .PP  .PP
49  .br  .br
50  .B unsigned char *pcre_cbits[128];  .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
51    .B *\fIfirstcharptr\fR);
52  .PP  .PP
53  .br  .br
54  .B unsigned char *pcre_ctypes[256];  .B char *pcre_version(void);
55  .PP  .PP
56  .br  .br
57  .B unsigned char *pcre_fcc[256];  .B void *(*pcre_malloc)(size_t);
58  .PP  .PP
59  .br  .br
60  .B unsigned char *pcre_lcc[256];  .B void (*pcre_free)(void *);
61    
62    
63    
64  .SH DESCRIPTION  .SH DESCRIPTION
65  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
66  pattern matching using the same syntax and semantics as Perl 5, with just a few  pattern matching using the same syntax and semantics as Perl 5, with just a few
67  differences (see below). The current implementation corresponds to Perl 5.004.  differences (see below). The current implementation corresponds to Perl 5.005.
68    
69  PCRE has its own native API, which is described in this man page. There is also  PCRE has its own native API, which is described in this man page. There is also
70  a set of wrapper functions that correspond to the POSIX API. See  a set of wrapper functions that correspond to the POSIX API. See
71  \fBpcreposix (3)\fR.  \fBpcreposix (3)\fR.
72    
73  The three functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and  The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR
74  \fBpcre_exec()\fR are used for compiling and matching regular expressions. The  are used for compiling and matching regular expressions, while
75  function \fBpcre_info()\fR is used to find out information about a compiled  \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
76    \fBpcre_get_substring_list()\fR are convenience functions for extracting
77    captured substrings from a matched subject string. The function
78    \fBpcre_maketables()\fR is used (optionally) to build a set of character tables
79    in the current locale for passing to \fBpcre_compile()\fR.
80    
81    The function \fBpcre_info()\fR is used to find out information about a compiled
82  pattern, while the function \fBpcre_version()\fR returns a pointer to a string  pattern, while the function \fBpcre_version()\fR returns a pointer to a string
83  containing the version of PCRE and its date of release.  containing the version of PCRE and its date of release.
84    
# Line 70  respectively. PCRE calls the memory mana Line 88  respectively. PCRE calls the memory mana
88  so a calling program can replace them if it wishes to intercept the calls. This  so a calling program can replace them if it wishes to intercept the calls. This
89  should be done before calling any PCRE functions.  should be done before calling any PCRE functions.
90    
 The other global variables are character tables. They are initialized when PCRE  
 is compiled, from source that is generated by reference to the C character type  
 functions, but which the maintainer of PCRE is free to modify. In principle  
 they could also be modified at runtime. See PCRE's README file for more  
 details.  
   
91    
92  .SH MULTI-THREADING  .SH MULTI-THREADING
93  The PCRE functions can be used in multi-threading applications, with the  The PCRE functions can be used in multi-threading applications, with the
94  proviso that the character tables and the memory management functions pointed  proviso that the memory management functions pointed to by \fBpcre_malloc\fR
95  to by \fBpcre_malloc\fR and \fBpcre_free\fR will be shared by all threads.  and \fBpcre_free\fR are shared by all threads.
96    
97  The compiled form of a regular expression is not altered during matching, so  The compiled form of a regular expression is not altered during matching, so
98  the same compiled pattern can safely be used by several threads at once.  the same compiled pattern can safely be used by several threads at once.
# Line 89  the same compiled pattern can safely be Line 101  the same compiled pattern can safely be
101  .SH COMPILING A PATTERN  .SH COMPILING A PATTERN
102  The function \fBpcre_compile()\fR is called to compile a pattern into an  The function \fBpcre_compile()\fR is called to compile a pattern into an
103  internal form. The pattern is a C string terminated by a binary zero, and  internal form. The pattern is a C string terminated by a binary zero, and
104  is passed in the argument \fIpattern\fR. A pointer to the compiled code block  is passed in the argument \fIpattern\fR. A pointer to a single block of memory
105  is returned. The \fBpcre\fR type is defined for this for convenience, but in  that is obtained via \fBpcre_malloc\fR is returned. This contains the
106  fact \fBpcre\fR is just a typedef for \fBvoid\fR, since the contents of the  compiled code and related data. The \fBpcre\fR type is defined for this for
107  block are not defined.  convenience, but in fact \fBpcre\fR is just a typedef for \fBvoid\fR, since the
108    contents of the block are not externally defined. It is up to the caller to
109    free the memory when it is no longer required.
110  .PP  .PP
111  The size of a compiled pattern is roughly proportional to the length of the  The size of a compiled pattern is roughly proportional to the length of the
112  pattern string, except that each character class (other than those containing  pattern string, except that each character class (other than those containing
# Line 101  quantifiers with a minimum greater than Line 115  quantifiers with a minimum greater than
115  relevant portions of the compiled pattern to be replicated.  relevant portions of the compiled pattern to be replicated.
116  .PP  .PP
117  The \fIoptions\fR argument contains independent bits that affect the  The \fIoptions\fR argument contains independent bits that affect the
118  compilation. It should be zero if no options are required. Those options that  compilation. It should be zero if no options are required. Some of the options,
119  are compabible with Perl can also be set at compile time from within the  in particular, those that are compatible with Perl, can also be set and unset
120  pattern (see the detailed description of regular expressions below) and all  from within the pattern (see the detailed description of regular expressions
121  options except PCRE_EXTENDED and PCRE_EXTRA can be set at the time of matching.  below). For these options, the contents of the \fIoptions\fR argument specifies
122    their initial settings at the start of compilation and execution. The
123    PCRE_ANCHORED option can be set at the time of matching as well as at compile
124    time.
125  .PP  .PP
126  If \fIerrptr\fR is NULL, \fBpcre_compile()\fR returns NULL immediately.  If \fIerrptr\fR is NULL, \fBpcre_compile()\fR returns NULL immediately.
127  Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fR returns  Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fR returns
128  NULL, and sets the variable pointed to by \fIerrptr\fR to point to a textual  NULL, and sets the variable pointed to by \fIerrptr\fR to point to a textual
129  error message.  error message. The offset from the start of the pattern to the character where
130    the error was discovered is placed in the variable pointed to by
131  The offset from the start of the pattern to the character where the error was  \fIerroffset\fR, which must not be NULL. If it is, an immediate error is given.
132  discovered is placed in the variable pointed to by \fIerroffset\fR, which must  .PP
133  not be NULL. If it is, an immediate error is given.  If the final argument, \fItableptr\fR, is NULL, PCRE uses a default set of
134    character tables which are built when it is compiled, using the default C
135    locale. Otherwise, \fItableptr\fR must be the result of a call to
136    \fBpcre_maketables()\fR. See the section on locale support below.
137  .PP  .PP
138  The following option bits are defined in the header file:  The following option bits are defined in the header file:
139    
# Line 127  constructs in the pattern itself, which Line 147  constructs in the pattern itself, which
147    PCRE_CASELESS    PCRE_CASELESS
148    
149  If this bit is set, letters in the pattern match both upper and lower case  If this bit is set, letters in the pattern match both upper and lower case
150  letters in any subject string. It is equivalent to Perl's /i option.  letters. It is equivalent to Perl's /i option.
151    
152    PCRE_DOLLAR_ENDONLY    PCRE_DOLLAR_ENDONLY
153    
154  If this bit is set, a dollar metacharacter in the pattern matches only at the  If this bit is set, a dollar metacharacter in the pattern matches only at the
155  end of the subject string. By default, it also matches immediately before the  end of the subject string. Without this option, a dollar also matches
156  final character if it is a newline (but not before any other newlines). The  immediately before the final character if it is a newline (but not before any
157  PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set. There is no  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
158  equivalent to this option in Perl.  set. There is no equivalent to this option in Perl.
159    
160    PCRE_DOTALL    PCRE_DOTALL
161    
162  If this bit is set, a dot metacharater in the pattern matches all characters,  If this bit is set, a dot metacharater in the pattern matches all characters,
163  including newlines. By default, newlines are excluded. This option is  including newlines. Without it, newlines are excluded. This option is
164  equivalent to Perl's /s option. A negative class such as [^a] always matches a  equivalent to Perl's /s option. A negative class such as [^a] always matches a
165  newline character, independent of the setting of this option.  newline character, independent of the setting of this option.
166    
167    PCRE_EXTENDED    PCRE_EXTENDED
168    
169  If this bit is set, whitespace characters in the pattern are totally ignored  If this bit is set, whitespace data characters in the pattern are totally
170  except when escaped or inside a character class, and characters between an  ignored except when escaped or inside a character class, and characters between
171  unescaped # outside a character class and the next newline character,  an unescaped # outside a character class and the next newline character,
172  inclusive, are also ignored. This is equivalent to Perl's /x option, and makes  inclusive, are also ignored. This is equivalent to Perl's /x option, and makes
173  it possible to include comments inside complicated patterns.  it possible to include comments inside complicated patterns. Note, however,
174    that this applies only to data characters. Whitespace characters may never
175    appear within special character sequences in a pattern, for example within the
176    sequence (?( which introduces a conditional subpattern.
177    
178      PCRE_EXTRA
179    
180    This option turns on additional functionality of PCRE that is incompatible with
181    Perl. Any backslash in a pattern that is followed by a letter that has no
182    special meaning causes an error, thus reserving these combinations for future
183    expansion. By default, as in Perl, a backslash followed by a letter with no
184    special meaning is treated as a literal. There are at present no other features
185    controlled by this option.
186    
187    PCRE_MULTILINE    PCRE_MULTILINE
188    
# Line 158  By default, PCRE treats the subject stri Line 190  By default, PCRE treats the subject stri
190  characters (even if it actually contains several newlines). The "start of line"  characters (even if it actually contains several newlines). The "start of line"
191  metacharacter (^) matches only at the start of the string, while the "end of  metacharacter (^) matches only at the start of the string, while the "end of
192  line" metacharacter ($) matches only at the end of the string, or before a  line" metacharacter ($) matches only at the end of the string, or before a
193  terminating newline. This is the same as Perl.  terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
194    Perl.
195    
196  When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs  When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
197  match immediately following or immediately before any newline in the subject  match immediately following or immediately before any newline in the subject
# Line 167  to Perl's /m option. If there are no "\\ Line 200  to Perl's /m option. If there are no "\\
200  no occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no  no occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no
201  effect.  effect.
202    
203    PCRE_EXTRA    PCRE_UNGREEDY
   
 This option turns on additional functionality of PCRE that is incompatible with  
 Perl. Any backslash in a pattern that is followed by a letter that has no  
 special meaning causes an error, thus reserving these combinations for future  
 expansion. By default, as in Perl, a backslash followed by a letter with no  
 special meaning is treated as a literal. There are two extra features currently  
 provided, and both are in some sense experimental additions that are useful for  
 influencing the progress of a match.  
   
   (1) The sequence \\X inserts a Prolog-like "cut" into the expression.  
   
   (2) Once a subpattern enclosed in (?>subpat) brackets has matched,  
       backtracking never goes back into the pattern.  
   
 See below for further details of both of these.  
204    
205    This option inverts the "greediness" of the quantifiers so that they are not
206    greedy by default, but become greedy if followed by "?". It is not compatible
207    with Perl. It can also be set by a (?U) option setting within the pattern.
208    
209    
210  .SH STUDYING A PATTERN  .SH STUDYING A PATTERN
# Line 195  typedef) containing additional informati Line 216  typedef) containing additional informati
216  passed to \fBpcre_exec()\fR. If no additional information is available, NULL  passed to \fBpcre_exec()\fR. If no additional information is available, NULL
217  is returned.  is returned.
218    
219  The second argument contains option bits. The only one currently supported is  The second argument contains option bits. At present, no options are defined
220  PCRE_CASELESS. It forces the studying to be done in a caseless manner, even if  for \fBpcre_study()\fR, and this argument should always be zero.
 the original pattern was compiled without PCRE_CASELESS. When the result of  
 \fBpcre_study()\fR is passed to \fBpcre_exec()\fR, it is used only if its  
 caseless state is the same as that of the matching process. A pattern that is  
 compiled without PCRE_CASELESS can be studied with and without PCRE_CASELESS,  
 and the appropriate data passed to \fBpcre_exec()\fR with and without the  
 PCRE_CASELESS flag.  
221    
222  The third argument for \fBpcre_study()\fR is a pointer to an error message. If  The third argument for \fBpcre_study()\fR is a pointer to an error message. If
223  studying succeeds (even if no data is returned), the variable it points to is  studying succeeds (even if no data is returned), the variable it points to is
# Line 213  not have a single fixed starting charact Line 228  not have a single fixed starting charact
228  characters is created.  characters is created.
229    
230    
231    .SH LOCALE SUPPORT
232    PCRE handles caseless matching, and determines whether characters are letters,
233    digits, or whatever, by reference to a set of tables. The library contains a
234    default set of tables which is created in the default C locale when PCRE is
235    compiled. This is used when the final argument of \fBpcre_compile()\fR is NULL,
236    and is sufficient for many applications.
237    
238    An alternative set of tables can, however, be supplied. Such tables are built
239    by calling the \fBpcre_maketables()\fR function, which has no arguments, in the
240    relevant locale. The result can then be passed to \fBpcre_compile()\ as often
241    as necessary. For example, to build and use tables that are appropriate for the
242    French locale (where accented characters with codes greater than 128 are
243    treated as letters), the following code could be used:
244    
245      setlocale(LC_CTYPE, "fr");
246      tables = pcre_maketables();
247      re = pcre_compile(..., tables);
248    
249    The tables are built in memory that is obtained via \fBpcre_malloc\fR. The
250    pointer that is passed to \fBpcre_compile\fR is saved with the compiled
251    pattern, and the same tables are used via this pointer by \fBpcre_study()\fR
252    and \fBpcre_match()\fR. Thus for any single pattern, compilation, studying and
253    matching all happen in the same locale, but different patterns can be compiled
254    in different locales. It is the caller's responsibility to ensure that the
255    memory containing the tables remains available for as long as it is needed.
256    
257    
258    .SH INFORMATION ABOUT A PATTERN
259    The \fBpcre_info()\fR function returns information about a compiled pattern.
260    Its yield is the number of capturing subpatterns, or one of the following
261    negative numbers:
262    
263      PCRE_ERROR_NULL       the argument \fIcode\fR was NULL
264      PCRE_ERROR_BADMAGIC   the "magic number" was not found
265    
266    If the \fIoptptr\fR argument is not NULL, a copy of the options with which the
267    pattern was compiled is placed in the integer it points to.
268    
269    If the \fIfirstcharptr\fR argument is not NULL, is is used to pass back
270    information about the first character of any matched string. If there is a
271    fixed first character, e.g. from a pattern such as (cat|cow|coyote), then it is
272    returned in the integer pointed to by \fIfirstcharptr\fR. Otherwise, if the
273    pattern was compiled with the PCRE_MULTILINE option, and every branch started
274    with "^", then -1 is returned, indicating that the pattern will match at the
275    start of a subject string or after any "\\n" within the string. Otherwise -2 is
276    returned.
277    
278    
279  .SH MATCHING A PATTERN  .SH MATCHING A PATTERN
280  The function \fBpcre_exec()\fR is called to match a subject string against a  The function \fBpcre_exec()\fR is called to match a subject string against a
281  pre-compiled pattern, which is passed in the \fIcode\fR argument. If the  pre-compiled pattern, which is passed in the \fIcode\fR argument. If the
# Line 222  pattern has been studied, the result of Line 285  pattern has been studied, the result of
285  The subject string is passed as a pointer in \fIsubject\fR and a length in  The subject string is passed as a pointer in \fIsubject\fR and a length in
286  \fIlength\fR. Unlike the pattern string, it may contain binary zero characters.  \fIlength\fR. Unlike the pattern string, it may contain binary zero characters.
287    
288  The options PCRE_ANCHORED, PCRE_CASELESS, PCRE_DOLLAR_ENDONLY, PCRE_DOTALL, and  The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose
289  PCRE_MULTILINE can be passed in the \fIoptions\fR argument, whose unused bits  unused bits must be zero. However, if a pattern was compiled with
290  must be zero. However, if a pattern is compiled with any of these options, they  PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it
291  cannot be unset when it is obeyed.  cannot be made unachored at matching time.
292    
293  There are also two further options that can be set only at matching time:  There are also two further options that can be set only at matching time:
294    
# Line 233  There are also two further options that Line 296  There are also two further options that
296    
297  The first character of the string is not the beginning of a line, so the  The first character of the string is not the beginning of a line, so the
298  circumflex metacharacter should not match before it. Setting this without  circumflex metacharacter should not match before it. Setting this without
299  PCRE_MULTILINE (at either compile or match time) causes circumflex never to  PCRE_MULTILINE (at compile time) causes circumflex never to match.
 match.  
300    
301    PCRE_NOTEOL    PCRE_NOTEOL
302    
303  The end of the string is not the end of a line, so the dollar metacharacter  The end of the string is not the end of a line, so the dollar metacharacter
304  should not match it. Setting this without PCRE_MULTILINE (at either compile or  should not match it nor (except in multiline mode) a newline immediately before
305  match time) causes dollar never to match.  it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
306    to match.
307    
308  In general, a pattern matches a certain portion of the subject, and in  In general, a pattern matches a certain portion of the subject, and in
309  addition, further substrings from the subject may be picked out by parts of the  addition, further substrings from the subject may be picked out by parts of the
# Line 251  kinds of parenthesized subpattern that d Line 314  kinds of parenthesized subpattern that d
314    
315  Captured substrings are returned to the caller via a vector of integer offsets  Captured substrings are returned to the caller via a vector of integer offsets
316  whose address is passed in \fIovector\fR. The number of elements in the vector  whose address is passed in \fIovector\fR. The number of elements in the vector
317  is passed in \fIovecsize\fR. This should always be an even number, because the  is passed in \fIovecsize\fR. The first two-thirds of the vector is used to pass
318  elements are used in pairs. If an odd number is passed, it is rounded down.  back captured substrings, each substring using a pair of integers. The
319    remaining third of the vector is used as workspace by \fBpcre_exec()\fR while
320    matching capturing subpatterns, and is not available for passing back
321    information. The length passed in \fIovecsize\fR should always be a multiple of
322    three. If it is not, it is rounded down.
323    
324    When a match has been successful, information about captured substrings is
325    returned in pairs of integers, starting at the beginning of \fIovector\fR, and
326    continuing up to two-thirds of its length at the most. The first element of a
327    pair is set to the offset of the first character in a substring, and the second
328    is set to the offset of the first character after the end of a substring. The
329    first pair, \fIovector[0]\fR and \fIovector[1]\fR, identify the portion of the
330    subject string matched by the entire pattern. The next pair is used for the
331    first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fR
332    is the number of pairs that have been set. If there are no capturing
333    subpatterns, the return value from a successful match is 1, indicating that
334    just the first pair of offsets has been set.
335    
336  The first element of a pair is set to the offset of the first character in a  Some convenience functions are provided for extracting the captured substrings
337  substring, and the second is set to the offset of the first character after the  as separate strings. These are described in the following section.
 end of a substring. The first pair, \fIovector[0]\fR and \fIovector[1]\fR,  
 identify the portion of the subject string matched by the entire pattern. The  
 next pair is used for the first capturing subpattern, and so on. The value  
 returned by \fBpcre_exec()\fR is the number of pairs that have been set. If  
 there are no capturing subpatterns, the return value from a successful match  
 is 1, indicating that just the first pair of offsets has been set.  
338    
339  It is possible for an capturing subpattern number \fIn+1\fR to match some  It is possible for an capturing subpattern number \fIn+1\fR to match some
340  part of the subject when subpattern \fIn\fR has not been used at all. For  part of the subject when subpattern \fIn\fR has not been used at all. For
341  example, if the string "abc" is matched against the pattern "(a|(z))(bc)",  example, if the string "abc" is matched against the pattern (a|(z))(bc)
342  subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset  subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
343  values corresponding to the unused subpattern are set to -1.  values corresponding to the unused subpattern are set to -1.
344    
# Line 273  If a capturing subpattern is matched rep Line 346  If a capturing subpattern is matched rep
346  string that it matched that gets returned.  string that it matched that gets returned.
347    
348  If the vector is too small to hold all the captured substrings, it is used as  If the vector is too small to hold all the captured substrings, it is used as
349  far as possible, and the function returns a value of zero. In particular, if  far as possible (up to two-thirds of its length), and the function returns a
350  the substring offsets are not of interest, \fBpcre_exec()\fR may be called with  value of zero. In particular, if the substring offsets are not of interest,
351  \fIovector\fR passed as NULL and \fIovecsize\fR as zero. However, if the  \fBpcre_exec()\fR may be called with \fIovector\fR passed as NULL and
352  pattern contains back references and the \fIovector\fR isn't big enough to  \fIovecsize\fR as zero. However, if the pattern contains back references and
353  remember the related substrings, PCRE has to get additional memory for use  the \fIovector\fR isn't big enough to remember the related substrings, PCRE has
354  during matching. Thus it is usually advisable to supply an \fIovector\fR.  to get additional memory for use during matching. Thus it is usually advisable
355    to supply an \fIovector\fR.
356    
357  Note that \fBpcre_info()\fR can be used to find out how many capturing  Note that \fBpcre_info()\fR can be used to find out how many capturing
358  subpatterns there are in a compiled pattern.  subpatterns there are in a compiled pattern. The smallest size for
359    \fIovector\fR that will allow for \fIn\fR captured substrings in addition to
360    the offsets of the substring matched by the whole pattern is (\fIn\fR+1)*3.
361    
362  If \fBpcre_exec()\fR fails, it returns a negative number. The following are  If \fBpcre_exec()\fR fails, it returns a negative number. The following are
363  defined in the header file:  defined in the header file:
# Line 290  defined in the header file: Line 366  defined in the header file:
366    
367  The subject string did not match the pattern.  The subject string did not match the pattern.
368    
369    PCRE_ERROR_BADREF         (-2)    PCRE_ERROR_NULL           (-2)
   
 There was a back-reference in the pattern to a capturing subpattern that had  
 not previously been set.  
   
   PCRE_ERROR_NULL           (-3)  
370    
371  Either \fIcode\fR or \fIsubject\fR was passed as NULL, or \fIovector\fR was  Either \fIcode\fR or \fIsubject\fR was passed as NULL, or \fIovector\fR was
372  NULL and \fIovecsize\fR was not zero.  NULL and \fIovecsize\fR was not zero.
373    
374    PCRE_ERROR_BADOPTION      (-4)    PCRE_ERROR_BADOPTION      (-3)
375    
376  An unrecognized bit was set in the \fIoptions\fR argument.  An unrecognized bit was set in the \fIoptions\fR argument.
377    
378    PCRE_ERROR_BADMAGIC       (-5)    PCRE_ERROR_BADMAGIC       (-4)
379    
380  PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch  PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
381  the case when it is passed a junk pointer. This is the error it gives when the  the case when it is passed a junk pointer. This is the error it gives when the
382  magic number isn't present.  magic number isn't present.
383    
384    PCRE_ERROR_UNKNOWN_NODE   (-6)    PCRE_ERROR_UNKNOWN_NODE   (-5)
385    
386  While running the pattern match, an unknown item was encountered in the  While running the pattern match, an unknown item was encountered in the
387  compiled pattern. This error could be caused by a bug in PCRE or by overwriting  compiled pattern. This error could be caused by a bug in PCRE or by overwriting
388  of the compiled pattern.  of the compiled pattern.
389    
390    PCRE_ERROR_NOMEMORY       (-7)    PCRE_ERROR_NOMEMORY       (-6)
391    
392  If a pattern contains back references, but the \fIovector\fR that is passed to  If a pattern contains back references, but the \fIovector\fR that is passed to
393  \fBpcre_exec()\fR is not big enough to remember the referenced substrings, PCRE  \fBpcre_exec()\fR is not big enough to remember the referenced substrings, PCRE
# Line 325  call via \fBpcre_malloc()\fR fails, this Line 396  call via \fBpcre_malloc()\fR fails, this
396  the end of matching.  the end of matching.
397    
398    
399  .SH INFORMATION ABOUT A PATTERN  .SH EXTRACTING CAPTURED SUBSTRINGS
400  The \fBpcre_info()\fR function returns information about a compiled pattern.  Captured substrings can be accessed directly by using the offsets returned by
401  Its yield is the number of capturing subpatterns, or one of the following  \fBpcre_exec()\fR in \fIovector\fR. For convenience, the functions
402  negative numbers:  \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
403    \fBpcre_get_substring_list()\fR are provided for extracting captured substrings
404    PCRE_ERROR_NULL       the argument \fIcode\fR was NULL  as new, separate, zero-terminated strings. A substring that contains a binary
405    PCRE_ERROR_BADMAGIC   the "magic number" was not found  zero is correctly extracted and has a further zero added on the end, but the
406    result does not, of course, function as a C string.
407  If the \fIoptptr\fR argument is not NULL, a copy of the options with which the  
408  pattern was compiled is placed in the integer it points to.  The first three arguments are the same for all three functions: \fIsubject\fR
409    is the subject string which has just been successfully matched, \fIovector\fR
410    is a pointer to the vector of integer offsets that was passed to
411    \fBpcre_exec()\fR, and \fIstringcount\fR is the number of substrings that
412    were captured by the match, including the substring that matched the entire
413    regular expression. This is the value returned by \fBpcre_exec\fR if it
414    is greater than zero. If \fBpcre_exec()\fR returned zero, indicating that it
415    ran out of space in \fIovector\fR, then the value passed as
416    \fIstringcount\fR should be the size of the vector divided by three.
417    
418    The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR
419    extract a single substring, whose number is given as \fIstringnumber\fR. A
420    value of zero extracts the substring that matched the entire pattern, while
421    higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,
422    the string is placed in \fIbuffer\fR, whose length is given by
423    \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of store is
424    obtained via \fBpcre_malloc\fR, and its address is returned via
425    \fIstringptr\fR. The yield of the function is the length of the string, not
426    including the terminating zero, or one of
427    
428      PCRE_ERROR_NOMEMORY       (-6)
429    
430    The buffer was too small for \fBpcre_copy_substring()\fR, or the attempt to get
431    memory failed for \fBpcre_get_substring()\fR.
432    
433      PCRE_ERROR_NOSUBSTRING    (-7)
434    
435    There is no substring whose number is \fIstringnumber\fR.
436    
437    The \fBpcre_get_substring_list()\fR function extracts all available substrings
438    and builds a list of pointers to them. All this is done in a single block of
439    memory which is obtained via \fBpcre_malloc\fR. The address of the memory block
440    is returned via \fIlistptr\fR, which is also the start of the list of string
441    pointers. The end of the list is marked by a NULL pointer. The yield of the
442    function is zero if all went well, or
443    
444      PCRE_ERROR_NOMEMORY       (-6)
445    
446    if the attempt to get the memory block failed.
447    
448    When any of these functions encounter a substring that is unset, which can
449    happen when capturing subpattern number \fIn+1\fR matches some part of the
450    subject, but subpattern \fIn\fR has not been used at all, they return an empty
451    string. This can be distinguished from a genuine zero-length substring by
452    inspecting the appropriate offset in \fIovector\fR, which is negative for unset
453    substrings.
454    
 If the \fIfirstcharptr\fR argument is not NULL, is is used to pass back  
 information about the first character of any matched string. If there is a  
 fixed first character, e.g. from a pattern such as (cat|cow|coyote), then it is  
 returned in the integer pointed to by \fIfirstcharptr\fR. Otherwise, if the  
 pattern was compiled with the PCRE_MULTILINE option, and every branch started  
 with "^", then -1 is returned, indicating that the pattern will match at the  
 start of a subject string or after any "\\n" within the string. Otherwise -2 is  
 returned.  
455    
456    
457  .SH LIMITATIONS  .SH LIMITATIONS
# Line 353  The maximum length of a compiled pattern Line 461  The maximum length of a compiled pattern
461  All values in repeating quantifiers must be less than 65536.  All values in repeating quantifiers must be less than 65536.
462  The maximum number of capturing subpatterns is 99.  The maximum number of capturing subpatterns is 99.
463  The maximum number of all parenthesized subpatterns, including capturing  The maximum number of all parenthesized subpatterns, including capturing
464  subpatterns and assertions, is 200.  subpatterns, assertions, and other types of subpattern, is 200.
465    
466  The maximum length of a subject string is the largest positive number that an  The maximum length of a subject string is the largest positive number that an
467  integer variable can hold. However, PCRE uses recursion to handle subpatterns  integer variable can hold. However, PCRE uses recursion to handle subpatterns
# Line 362  the size of a subject string that can be Line 470  the size of a subject string that can be
470    
471    
472  .SH DIFFERENCES FROM PERL  .SH DIFFERENCES FROM PERL
473  The differences described here are with respect to Perl 5.004.  The differences described here are with respect to Perl 5.005.
474    
475  1. By default, a whitespace character is any character that the C library  1. By default, a whitespace character is any character that the C library
476  function \fBisspace()\fR recognizes, though it is possible to compile PCRE with  function \fBisspace()\fR recognizes, though it is possible to compile PCRE with
# Line 371  formfeed, newline, carriage return, hori Line 479  formfeed, newline, carriage return, hori
479  no longer includes vertical tab in its set of whitespace characters. The \\v  no longer includes vertical tab in its set of whitespace characters. The \\v
480  escape that was in the Perl documentation for a long time was never in fact  escape that was in the Perl documentation for a long time was never in fact
481  recognized. However, the character itself was treated as whitespace at least  recognized. However, the character itself was treated as whitespace at least
482  up to 5.002. In 5.004 it does not match \\s.  up to 5.002. In 5.004 and 5.005 it does not match \\s.
483    
484  2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl permits  2. PCRE does not allow repeat quantifiers on lookahead assertions. Perl permits
485  them, but they do not mean what you might think. For example, "(?!a){3}" does  them, but they do not mean what you might think. For example, (?!a){3} does
486  not assert that the next three characters are not "a". It just asserts that the  not assert that the next three characters are not "a". It just asserts that the
487  next character is not "a" three times.  next character is not "a" three times.
488    
# Line 396  are not part of its pattern matching eng Line 504  are not part of its pattern matching eng
504  6. The Perl \\G assertion is not supported as it is not relevant to single  6. The Perl \\G assertion is not supported as it is not relevant to single
505  pattern matches.  pattern matches.
506    
507  7. If a backreference can never be matched, PCRE diagnoses an error. In a case  7. Fairly obviously, PCRE does not support the (?{code}) construction.
 like  
508    
509    /(123)\\2/  8. There are at the time of writing some oddities in Perl 5.005_02 concerned
510    with the settings of captured strings when part of a pattern is repeated. For
511    example, matching "aba" against the pattern /^(a(b)?)+$/ sets $2 to the value
512    "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves $2 unset. However, if
513    the pattern is changed to /^(aa(b(b))?)+$/ then $2 (and $3) get set.
514    
515  the error occurs at compile time. Perl gives no compile time error; version  In Perl 5.004 $2 is set in both cases, and that is also true of PCRE. If in the
516  5.004 either always fails to match, or gives a segmentation fault at runtime.  future Perl changes to a consistent state that is different, PCRE may change to
517  In more complicated cases such as  follow.
518    
519    /(1)(2)(3)(4)(5)(6)(7)(8)(9)(10\\10)/  9. Another as yet unresolved discrepancy is that in Perl 5.005_02 the pattern
520    /^(a)?(?(1)a|b)+$/ matches the string "a", whereas in PCRE it does not.
521    However, in both Perl and PCRE /^(a)?a/ matched against "a" leaves $1 unset.
522    
523  PCRE returns PCRE_ERROR_BADREF at run time. Perl always fails to match.  10. PCRE provides some extensions to the Perl regular expression facilities:
524    
525  8. PCRE provides some extensions to the Perl regular expression facilities:  (a) Although lookbehind assertions must match fixed length strings, each
526    alternative branch of a lookbehind assertion can match a different length of
527    string. Perl 5.005 requires them all to have the same length.
528    
529  (a) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $ meta-  (b) If PCRE_DOLLAR_ENDONLY is set and PCRE_MULTILINE is not set, the $ meta-
530  character matches only at the very end of the string.  character matches only at the very end of the string.
531    
532  (b) If PCRE_EXTRA is set, the \\X assertion (a Prolog-like "cut") is  (c) If PCRE_EXTRA is set, a backslash followed by a letter with no special
533  recognized, and a backslash followed by a letter with no special meaning is  meaning is faulted.
534  faulted. There is also a new kind of parenthesized subpattern starting with (?>  
535  which has a block on backtracking into it once it has matched.  (d) If PCRE_UNGREEDY is set, the greediness of the repetition quantifiers is
536    inverted, that is, by default they are not greedy, but if followed by a
537    question mark they are.
538    
539    
540  .SH REGULAR EXPRESSION DETAILS  .SH REGULAR EXPRESSION DETAILS
# Line 484  non-alphameric with "\\" to specify that Line 601  non-alphameric with "\\" to specify that
601  if you want to match a backslash, you write "\\\\".  if you want to match a backslash, you write "\\\\".
602    
603  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the  If a pattern is compiled with the PCRE_EXTENDED option, whitespace in the
604  pattern and characters between a "#" outside a character class and the next  pattern (other than in a character class) and characters between a "#" outside
605  newline character are ignored. An escaping backslash can be used to include a  a character class and the next newline character are ignored. An escaping
606  whitespace or "#" character as part of the pattern.  backslash can be used to include a whitespace or "#" character as part of the
607    pattern.
608    
609  A second use of backslash provides a way of encoding non-printing characters  A second use of backslash provides a way of encoding non-printing characters
610  in patterns in a visible manner. There is no restriction on the appearance of  in patterns in a visible manner. There is no restriction on the appearance of
# Line 503  represents: Line 621  represents:
621    \\r     carriage return (hex 0D)    \\r     carriage return (hex 0D)
622    \\t     tab (hex 09)    \\t     tab (hex 09)
623    \\xhh   character with hex code hh    \\xhh   character with hex code hh
624    \\ddd   character with octal code ddd or backreference    \\ddd   character with octal code ddd, or backreference
625    
626  The precise effect of "\\cx" is as follows: if "x" is a lower case letter, it  The precise effect of "\\cx" is as follows: if "x" is a lower case letter, it
627  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.  is converted to upper case. Then bit 6 of the character (hex 40) is inverted.
# Line 516  lower case). Line 634  lower case).
634  After "\\0" up to two further octal digits are read. In both cases, if there  After "\\0" up to two further octal digits are read. In both cases, if there
635  are fewer than two digits, just those that are present are used. Thus the  are fewer than two digits, just those that are present are used. Thus the
636  sequence "\\0\\x\\07" specifies two binary zeros followed by a BEL character.  sequence "\\0\\x\\07" specifies two binary zeros followed by a BEL character.
637  Make sure you supply two digits if the character that follows could otherwise  Make sure you supply two digits after the initial zero if the character that
638  be taken as another digit.  follows is itself an octal digit.
639    
640  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.
641  Outside a character class, PCRE reads it and any following digits as a decimal  Outside a character class, PCRE reads it and any following digits as a decimal
# Line 567  Each pair of escape sequences partitions Line 685  Each pair of escape sequences partitions
685  two disjoint sets. Any given character matches one, and only one, of each pair.  two disjoint sets. Any given character matches one, and only one, of each pair.
686    
687  A "word" character is any letter or digit or the underscore character, that is,  A "word" character is any letter or digit or the underscore character, that is,
688  any character which can be part of a Perl "word". These character type  any character which can be part of a Perl "word". The definition of letters and
689  sequences can appear both inside and outside character classes. They each match  digits is controlled by PCRE's character tables, and may vary if locale-
690  one character of the appropriate type. If the current matching point is at the  specific matching is taking place (see "Locale support" above). For example, in
691  end of the subject string, all of them fail, since there is no character to  the "fr" (French) locale, some character codes greater than 128 are used for
692  match.  accented letters, and these are matched by \\w.
693    
694  The fourth use of backslash is for certain assertions. An assertion specifies a  These character type sequences can appear both inside and outside character
695  condition that has to be met at a particular point in a match, without  classes. They each match one character of the appropriate type. If the current
696  consuming any characters from the subject string. The backslashed assertions  matching point is at the end of the subject string, all of them fail, since
697  are  there is no character to match.
698    
699    The fourth use of backslash is for certain simple assertions. An assertion
700    specifies a condition that has to be met at a particular point in a match,
701    without consuming any characters from the subject string. The use of
702    subpatterns for more complicated assertions is described below. The backslashed
703    assertions are
704    
705    \\b     word boundary    \\b     word boundary
706    \\B     not a word boundary    \\B     not a word boundary
707    \\A     start of subject (independent of multiline mode)    \\A     start of subject (independent of multiline mode)
708    \\Z     end of subject (independent of multiline mode)    \\Z     end of subject or newline at end (independent of multiline mode)
709      \\z     end of subject (independent of multiline mode)
710    
711  Assertions may not appear in character classes (but note that "\\b" has a  These assertions may not appear in character classes (but note that "\\b" has a
712  different meaning, namely the backspace character, inside a character class).  different meaning, namely the backspace character, inside a character class).
713    
714  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
715  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
716  "\\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
717  first or last character matches "\\w", respectively. More complicated  first or last character matches \\w, respectively.
718  assertions are also supported (see below).  
719    The \\A, \\Z, and \\z assertions differ from the traditional circumflex and
720  The "\\A" and "\\Z" assertions differ from the traditional "^" and "$"  dollar (described below) in that they only ever match at the very start and end
721  (described below) in that they only ever match at the very start and end of the  of the subject string, whatever options are set. They are not affected by the
722  subject string, respectively, whatever options are set.  PCRE_NOTBOL or PCRE_NOTEOL options. The difference between \\Z and \\z is that
723    \\Z matches before a newline that is the last character of the string as well
724  When the PCRE_EXTRA flag is set on a call to \fBpcre_compile()\fR, the  as at the end of the string, whereas \\z matches only at the end.
 additional assertion \\X, which has no equivalent in Perl, is recognized.  
 This operates like the "cut" operation in Prolog: it prevents the matching  
 operation from backtracking past it. For example, if the expression  
   
   .*/foo  
   
 is matched against the string "/this/string/is/not" then after the greedy .*  
 has swallowed the whole string, PCRE keeps backtracking all the way to the  
 beginning before failing. If, on the other hand, the expression is  
   
   .*/\\Xfoo  
   
 then once it has discovered that "/not" is not "/foo", backtracking ceases, and  
 the match fails. See also the section on "once-only" subpatterns below.  
   
725    
726    
727  .SH CIRCUMFLEX AND DOLLAR  .SH CIRCUMFLEX AND DOLLAR
728  Outside a character class, the circumflex character is an assertion which is  Outside a character class, in the default matching mode, the circumflex
729  true only if the current matching point is at the start of the subject string,  character is an assertion which is true only if the current matching point is
730  in the default matching mode. Inside a character class, circumflex has an  at the start of the subject string. Inside a character class, circumflex has an
731  entirely different meaning (see below).  entirely different meaning (see below).
732    
733  Circumflex need not be the first character of the pattern if a number of  Circumflex need not be the first character of the pattern if a number of
# Line 637  Dollar has no special meaning in a chara Line 747  Dollar has no special meaning in a chara
747    
748  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
749  the string, by setting the PCRE_DOLLAR_ENDONLY option at compile or matching  the string, by setting the PCRE_DOLLAR_ENDONLY option at compile or matching
750  time.  time. This does not affect the \\Z assertion.
751    
752  The meanings of the circumflex and dollar characters are changed if the  The meanings of the circumflex and dollar characters are changed if the
753  PCRE_MULTILINE option is set at compile or matching time. When this is the  PCRE_MULTILINE option is set. When this is the case, they match immediately
754  case, they match immediately after and immediately before an internal "\\n"  after and immediately before an internal "\\n" character, respectively, in
755  character, respectively, in addition to matching at the start and end of the  addition to matching at the start and end of the subject string. For example,
756  subject string. For example, the pattern /^abc$/ matches the subject string  the pattern /^abc$/ matches the subject string "def\\nabc" in multiline mode,
757  "def\\nabc" in multiline mode, but not otherwise. Consequently, patterns that  but not otherwise. Consequently, patterns that are anchored in single line mode
758  are anchored in single line mode because all branches start with "^" are not  because all branches start with "^" are not anchored in multiline mode. The
759  anchored in multiline mode. The PCRE_DOLLAR_ENDONLY option is ignored if  PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
760  PCRE_MULTILINE is set.  
761    Note that the sequences \\A, \\Z, and \\z can be used to match the start and
762  Note that the sequences "\\A" and "\\Z" can be used to match the start and end  end of the subject in both modes, and if all branches of a pattern start with
763  of the subject in both modes, and if all branches of a pattern start with "\\A"  \\A is it always anchored, whether PCRE_MULTILINE is set or not.
 is it always anchored.  
764    
765    
766  .SH FULL STOP (PERIOD, DOT)  .SH FULL STOP (PERIOD, DOT)
# Line 668  An opening square bracket introduces a c Line 777  An opening square bracket introduces a c
777  square bracket. A closing square bracket on its own is not special. If a  square bracket. A closing square bracket on its own is not special. If a
778  closing square bracket is required as a member of the class, it should be the  closing square bracket is required as a member of the class, it should be the
779  first data character in the class (after an initial circumflex, if present) or  first data character in the class (after an initial circumflex, if present) or
780  escaped with \\.  escaped with a backslash.
781    
782  A character class matches a single character in the subject; the character must  A character class matches a single character in the subject; the character must
783  be in the set of characters defined by the class, unless the first character in  be in the set of characters defined by the class, unless the first character in
784  the class is a circumflex, in which case the subject character must not be in  the class is a circumflex, in which case the subject character must not be in
785  the set defined by the class. If a circumflex is actually required as a member  the set defined by the class. If a circumflex is actually required as a member
786  of the class, ensure it is not the first character, or escape it with \\.  of the class, ensure it is not the first character, or escape it with a
787    backslash.
788    
789  For example, the character class [aeiou] matches any lower case vowel, while  For example, the character class [aeiou] matches any lower case vowel, while
790  [^aeiou] matches any character that is not a lower case vowel. Note that a  [^aeiou] matches any character that is not a lower case vowel. Note that a
# Line 683  are in the class by enumerating those th Line 793  are in the class by enumerating those th
793  still consumes a character from the subject string, and fails if the current  still consumes a character from the subject string, and fails if the current
794  pointer is at the end of the string.  pointer is at the end of the string.
795    
796    When caseless matching is set, any letters in a class represent both their
797    upper case and lower case versions, so for example, a caseless [aeiou] matches
798    "A" as well as "a", and a caseless [^aeiou] does not match "A", whereas a
799    caseful version would.
800    
801  The newline character is never treated in any special way in character classes,  The newline character is never treated in any special way in character classes,
802  whatever the setting of the PCRE_DOTALL or PCRE_MULTILINE options is. A class  whatever the setting of the PCRE_DOTALL or PCRE_MULTILINE options is. A class
803  such as [^a] will always match a newline.  such as [^a] will always match a newline.
# Line 690  such as [^a] will always match a newline Line 805  such as [^a] will always match a newline
805  The minus (hyphen) character can be used to specify a range of characters in a  The minus (hyphen) character can be used to specify a range of characters in a
806  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,
807  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
808  \\ or appear in a position where it cannot be interpreted as indicating a  a backslash or appear in a position where it cannot be interpreted as
809  range, typically as the first or last character in the class. It is not  indicating a range, typically as the first or last character in the class.
810  possible to have the character "]" as the end character of a range, since a  
811  sequence such as [w-] is interpreted as a class of two characters. The octal or  It is not possible to have the literal character "]" as the end character of a
812  hexadecimal representation of "]" can, however, be used to end a range.  range. A pattern such as [W-]46] is interpreted as a class of two characters
813    ("W" and "-") followed by a literal string "46]", so it would match "W46]" or
814    "-46]". However, if the "]" is escaped with a backslash it is interpreted as
815    the end of range, so [W-\\]46] is interpreted as a single class containing a
816    range followed by two separate characters. The octal or hexadecimal
817    representation of "]" can also be used to end a range.
818    
819  Ranges operate in ASCII collating sequence. They can also be used for  Ranges operate in ASCII collating sequence. They can also be used for
820  characters specified numerically, for example [\\000-\\037]. If a range such as  characters specified numerically, for example [\\000-\\037]. If a range that
821  [W-c] is used when PCRE_CASELESS is set, it matches the letters involved in  includes letters is used when caseless matching is set, it matches the letters
822  either case.  in either case. For example, [W-c] is equivalent to [][\\^_`wxyzabc], matched
823    caselessly, and if character tables for the "fr" locale are in use,
824    [\\xc8-\\xcb] matches accented E characters in both cases.
825    
826  The character types \\d, \\D, \\s, \\S, \\w, and \\W may also appear in a  The character types \\d, \\D, \\s, \\S, \\w, and \\W may also appear in a
827  character class, and add the characters that they match to the class. For  character class, and add the characters that they match to the class. For
828  example, the class [^\\W_] matches any letter or digit.  example, [\\dABCDEF] matches any hexadecimal digit. A circumflex can
829    conveniently be used with the upper case character types to specify a more
830    restricted set of characters than the matching lower case type. For example,
831    the class [^\\W_] matches any letter or digit, but not underscore.
832    
833  All non-alphameric characters other than \\, -, ^ (at the start) and the  All non-alphameric characters other than \\, -, ^ (at the start) and the
834  terminating ] are non-special in character classes, but it does no harm if they  terminating ] are non-special in character classes, but it does no harm if they
# Line 711  are escaped. Line 836  are escaped.
836    
837    
838  .SH VERTICAL BAR  .SH VERTICAL BAR
839  Vertical bar characters are used to separate alternative patterns. The matching  Vertical bar characters are used to separate alternative patterns. For example,
840  process tries all the alternatives in turn. For example, the pattern  the pattern
841    
842    gilbert|sullivan    gilbert|sullivan
843    
844  matches either "gilbert" or "sullivan". Any number of alternatives can be used,  matches either "gilbert" or "sullivan". Any number of alternatives may appear,
845  and an empty alternative is permitted (matching the empty string).  and an empty alternative is permitted (matching the empty string).
846    The matching process tries each alternative in turn, from left to right,
847    and the first one that succeeds is used. If the alternatives are within a
848    subpattern (defined below), "succeeds" means matching the rest of the main
849    pattern as well as the alternative in the subpattern.
850    
851    
852    .SH INTERNAL OPTION SETTING
853    The settings of PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, and PCRE_EXTENDED
854    can be changed from within the pattern by a sequence of Perl option letters
855    enclosed between "(?" and ")". The option letters are
856    
857      i  for PCRE_CASELESS
858      m  for PCRE_MULTILINE
859      s  for PCRE_DOTALL
860      x  for PCRE_EXTENDED
861    
862    For example, (?im) sets caseless, multiline matching. It is also possible to
863    unset these options by preceding the letter with a hyphen, and a combined
864    setting and unsetting such as (?im-sx), which sets PCRE_CASELESS and
865    PCRE_MULTILINE while unsetting PCRE_DOTALL and PCRE_EXTENDED, is also
866    permitted. If a letter appears both before and after the hyphen, the option is
867    unset.
868    
869    The scope of these option changes depends on where in the pattern the setting
870    occurs. For settings that are outside any subpattern (defined below), the
871    effect is the same as if the options were set or unset at the start of
872    matching. The following patterns all behave in exactly the same way:
873    
874      (?i)abc
875      a(?i)bc
876      ab(?i)c
877      abc(?i)
878    
879    which in turn is the same as compiling the pattern abc with PCRE_CASELESS set.
880    In other words, such "top level" settings apply to the whole pattern (unless
881    there are other changes inside subpatterns). If there is more than one setting
882    of the same option at top level, the rightmost setting is used.
883    
884    If an option change occurs inside a subpattern, the effect is different. This
885    is a change of behaviour in Perl 5.005. An option change inside a subpattern
886    affects only that part of the subpattern that follows it, so
887    
888      (a(?i)b)c
889    
890    matches abc and aBc and no other strings (assuming PCRE_CASELESS is not used).
891    By this means, options can be made to have different settings in different
892    parts of the pattern. Any changes made in one alternative do carry on
893    into subsequent branches within the same subpattern. For example,
894    
895      (a(?i)b|c)
896    
897    matches "ab", "aB", "c", and "C", even though when matching "C" the first
898    branch is abandoned before the option setting. This is because the effects of
899    option settings happen at compile time. There would be some very weird
900    behaviour otherwise.
901    
902    The PCRE-specific options PCRE_UNGREEDY and PCRE_EXTRA can be changed in the
903    same way as the Perl-compatible options by using the characters U and X
904    respectively. The (?X) flag setting is special in that it must always occur
905    earlier in the pattern than any of the additional features it turns on, even
906    when it is at top level. It is best put at the start.
907    
908    
909  .SH SUBPATTERNS  .SH SUBPATTERNS
# Line 757  the captured substrings are "white queen Line 943  the captured substrings are "white queen
943  2. The maximum number of captured substrings is 99, and the maximum number of  2. The maximum number of captured substrings is 99, and the maximum number of
944  all subpatterns, both capturing and non-capturing, is 200.  all subpatterns, both capturing and non-capturing, is 200.
945    
946    As a convenient shorthand, if any option settings are required at the start of
947  .SH BACK REFERENCES  a non-capturing subpattern, the option letters may appear between the "?" and
948  Outside a character class, a backslash followed by a digit greater than 0 (and  the ":". Thus the two patterns
949  possibly further digits) is a back reference to a capturing subpattern earlier  
950  (i.e. to its left) in the pattern, provided there have been that many previous    (?i:saturday|sunday)
951  capturing left parentheses. However, if the decimal number following the    (?:(?i)saturday|sunday)
952  backslash is less than 10, it is always taken as a back reference, and causes  
953  an error if there have not been that many previous capturing left parentheses.  match exactly the same set of strings. Because alternative branches are tried
954  See the section entitled "Backslash" above for further details of the handling  from left to right, and options are not reset until the end of the subpattern
955  of digits following a backslash.  is reached, an option setting in one branch does affect subsequent branches, so
956    the above patterns match "SUNDAY" as well as "Saturday".
 A back reference matches whatever actually matched the capturing subpattern in  
 the current subject string, rather than anything matching the subpattern  
 itself. So the pattern  
   
    (sens|respons)e and \\1ibility  
   
 matches "sense and sensibility" and "response and responsibility", but not  
 "sense and responsibility".  
   
 There may be more than one back reference to the same subpattern. If a  
 subpattern has not actually been used in a particular match, then any back  
 references to it always fail. For example, the pattern  
   
   (a|(bc))\\2  
   
 always fails if it starts to match "a" rather than "bc". Because there may be  
 up to 99 back references, all digits following the backslash are taken  
 as part of a potential back reference number. If the pattern continues with a  
 digit character, then some delimiter must be used to terminate the back  
 reference. If the PCRE_EXTENDED option is set, this can be whitespace.  
 Otherwise an empty comment can be used.  
957    
958    
959  .SH REPETITION  .SH REPETITION
# Line 798  items: Line 963  items:
963    a single character, possibly escaped    a single character, possibly escaped
964    the . metacharacter    the . metacharacter
965    a character class    a character class
966    a back reference    a back reference (see next section)
967    a parenthesized subpattern    a parenthesized subpattern (unless it is an assertion - see below)
968    
969  The general repetition quantifier specifies a minimum and maximum number of  The general repetition quantifier specifies a minimum and maximum number of
970  permitted matches, by giving the two numbers in curly brackets (braces),  permitted matches, by giving the two numbers in curly brackets (braces),
# Line 821  matches at least 3 successive vowels, bu Line 986  matches at least 3 successive vowels, bu
986    
987  matches exactly 8 digits. An opening curly bracket that appears in a position  matches exactly 8 digits. An opening curly bracket that appears in a position
988  where a quantifier is not allowed, or one that does not match the syntax of a  where a quantifier is not allowed, or one that does not match the syntax of a
989  quantifier, is taken as a literal character. For example, "{,6}" is not a  quantifier, is taken as a literal character. For example, {,6} is not a
990  quantifier, but a literal string of four characters.  quantifier, but a literal string of four characters.
991    
992  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 834  quantifiers have single-character abbrev Line 999  quantifiers have single-character abbrev
999    +    is equivalent to {1,}    +    is equivalent to {1,}
1000    ?    is equivalent to {0,1}    ?    is equivalent to {0,1}
1001    
1002    It is possible to construct infinite loops by following a subpattern that can
1003    match no characters with a quantifier that has no upper limit, for example:
1004    
1005      (a?)*
1006    
1007    Earlier versions of Perl and PCRE used to give an error at compile time for
1008    such patterns. However, because there are cases where this can be useful, such
1009    patterns are now accepted, but if any repetition of the subpattern does in fact
1010    match no characters, the loop is forcibly broken.
1011    
1012  By default, the quantifiers are "greedy", that is, they match as much as  By default, the quantifiers are "greedy", that is, they match as much as
1013  possible (up to the maximum number of permitted times), without causing the  possible (up to the maximum number of permitted times), without causing the
1014  rest of the pattern to fail. The classic example of where this gives problems  rest of the pattern to fail. The classic example of where this gives problems
# Line 861  quantifiers is not otherwise changed, ju Line 1036  quantifiers is not otherwise changed, ju
1036  Do not confuse this use of question mark with its use as a quantifier in its  Do not confuse this use of question mark with its use as a quantifier in its
1037  own right. Because it has two uses, it can sometimes appear doubled, as in  own right. Because it has two uses, it can sometimes appear doubled, as in
1038    
1039     \\d??\\d    \\d??\\d
1040    
1041  which matches one digit by preference, but can match two if that is the only  which matches one digit by preference, but can match two if that is the only
1042  way the rest of the pattern matches.  way the rest of the pattern matches.
1043    
1044    If the PCRE_UNGREEDY option is set (an option which is not available in Perl)
1045    then the quantifiers are not greedy by default, but individual ones can be made
1046    greedy by following them with a question mark. In other words, it inverts the
1047    default behaviour.
1048    
1049  When a parenthesized subpattern is quantified with a minimum repeat count that  When a parenthesized subpattern is quantified with a minimum repeat count that
1050  is greater than 1 or with a limited maximum, more store is required for the  is greater than 1 or with a limited maximum, more store is required for the
1051  compiled pattern, in proportion to the size of the minimum or maximum.  compiled pattern, in proportion to the size of the minimum or maximum.
# Line 875  follows will be tried against every char Line 1055  follows will be tried against every char
1055  PCRE treats this as though it were preceded by \\A.  PCRE treats this as though it were preceded by \\A.
1056    
1057  When a capturing subpattern is repeated, the value captured is the substring  When a capturing subpattern is repeated, the value captured is the substring
1058  that matched the final iteration. For example,  that matched the final iteration. For example, after
1059    
1060      (tweedle[dume]{3}\\s*)+
1061    
1062    has matched "tweedledum tweedledee" the value of the captured substring is
1063    "tweedledee". However, if there are nested capturing subpatterns, the
1064    corresponding captured values may have been set in previous iterations. For
1065    example, after
1066    
1067     (\s*tweedle[dume]{3})+\\1    /(a|(b))+/
1068    
1069  matches "tweedledum tweedledee tweedledee" but not "tweedledum tweedledee  matches "aba" the value of the second captured substring is "b".
1070  tweedledum".  
1071    
1072    .SH BACK REFERENCES
1073    Outside a character class, a backslash followed by a digit greater than 0 (and
1074    possibly further digits) is a back reference to a capturing subpattern earlier
1075    (i.e. to its left) in the pattern, provided there have been that many previous
1076    capturing left parentheses.
1077    
1078    However, if the decimal number following the backslash is less than 10, it is
1079    always taken as a back reference, and causes an error only if there are not
1080    that many capturing left parentheses in the entire pattern. In other words, the
1081    parentheses that are referenced need not be to the left of the reference for
1082    numbers less than 10. See the section entitled "Backslash" above for further
1083    details of the handling of digits following a backslash.
1084    
1085    A back reference matches whatever actually matched the capturing subpattern in
1086    the current subject string, rather than anything matching the subpattern
1087    itself. So the pattern
1088    
1089      (sens|respons)e and \\1ibility
1090    
1091    matches "sense and sensibility" and "response and responsibility", but not
1092    "sense and responsibility". If caseful matching is in force at the time of the
1093    back reference, then the case of letters is relevant. For example,
1094    
1095      ((?i)rah)\\s+\\1
1096    
1097    matches "rah rah" and "RAH RAH", but not "RAH rah", even though the original
1098    capturing subpattern is matched caselessly.
1099    
1100    There may be more than one back reference to the same subpattern. If a
1101    subpattern has not actually been used in a particular match, then any back
1102    references to it always fail. For example, the pattern
1103    
1104      (a|(bc))\\2
1105    
1106    always fails if it starts to match "a" rather than "bc". Because there may be
1107    up to 99 back references, all digits following the backslash are taken
1108    as part of a potential back reference number. If the pattern continues with a
1109    digit character, then some delimiter must be used to terminate the back
1110    reference. If the PCRE_EXTENDED option is set, this can be whitespace.
1111    Otherwise an empty comment can be used.
1112    
1113    A back reference that occurs inside the parentheses to which it refers fails
1114    when the subpattern is first used, so, for example, (a\\1) never matches.
1115    However, such references can be useful inside repeated subpatterns. For
1116    example, the pattern
1117    
1118      (a|b\\1)+
1119    
1120    matches any number of "a"s and also "aba", "ababaa" etc. At each iteration of
1121    the subpattern, the back reference matches the character string corresponding
1122    to the previous iteration. In order for this to work, the pattern must be such
1123    that the first iteration does not need to match the back reference. This can be
1124    done using alternation, as in the example above, or by a quantifier with a
1125    minimum of zero.
1126    
1127    
1128  .SH ASSERTIONS  .SH ASSERTIONS
1129  An assertion is a test on the characters following the current matching point  An assertion is a test on the characters following or preceding the current
1130  that does not actually consume any of those characters. The simple assertions  matching point that does not actually consume any characters. The simple
1131  coded as \\b, \\B, \\A, \\Z, ^ and $ are described above. More complicated  assertions coded as \\b, \\B, \\A, \\Z, \\z, ^ and $ are described above. More
1132  assertions are coded as subpatterns starting with (?= for positive assertions,  complicated assertions are coded as subpatterns. There are two kinds: those
1133  and (?! for negative assertions. For example,  that look ahead of the current position in the subject string, and those that
1134    look behind it.
1135    
1136    An assertion subpattern is matched in the normal way, except that it does not
1137    cause the current matching position to be changed. Lookahead assertions start
1138    with (?= for positive assertions and (?! for negative assertions. For example,
1139    
1140    \\w+(?=;)    \\w+(?=;)
1141    
# Line 904  apparently similar pattern Line 1151  apparently similar pattern
1151    
1152  does not find an occurrence of "bar" that is preceded by something other than  does not find an occurrence of "bar" that is preceded by something other than
1153  "foo"; it finds any occurrence of "bar" whatsoever, because the assertion  "foo"; it finds any occurrence of "bar" whatsoever, because the assertion
1154  (?!foo) is always true when the next three characters are "bar".  (?!foo) is always true when the next three characters are "bar". A
1155    lookbehind assertion is needed to achieve this effect.
1156    
1157    Lookbehind assertions start with (?<= for positive assertions and (?<! for
1158    negative assertions. For example,
1159    
1160      (?<!foo)bar
1161    
1162    does find an occurrence of "bar" that is not preceded by "foo". The contents of
1163    a lookbehind assertion are restricted such that all the strings it matches must
1164    have a fixed length. However, if there are several alternatives, they do not
1165    all have to have the same fixed length. Thus
1166    
1167      (?<=bullock|donkey)
1168    
1169    is permitted, but
1170    
1171      (?<!dogs?|cats?)
1172    
1173    causes an error at compile time. Branches that match different length strings
1174    are permitted only at the top level of a lookbehind assertion. This is an
1175    extension compared with Perl 5.005, which requires all branches to match the
1176    same length of string. An assertion such as
1177    
1178      (?<=ab(c|de))
1179    
1180    is not permitted, because its single top-level branch can match two different
1181    lengths, but it is acceptable if rewritten to use two top-level branches:
1182    
1183      (?<=abc|abde)
1184    
1185    The implementation of lookbehind assertions is, for each alternative, to
1186    temporarily move the current position back by the fixed width and then try to
1187    match. If there are insufficient characters before the current position, the
1188    match is deemed to fail. Lookbehinds in conjunction with once-only subpatterns
1189    can be particularly useful for matching at the ends of strings; an example is
1190    given at the end of the section on once-only subpatterns.
1191    
1192    Several assertions (of any sort) may occur in succession. For example,
1193    
1194      (?<=\\d{3})(?<!999)foo
1195    
1196    matches "foo" preceded by three digits that are not "999". Furthermore,
1197    assertions can be nested in any combination. For example,
1198    
1199      (?<=(?<!foo)bar)baz
1200    
1201    matches an occurrence of "baz" that is preceded by "bar" which in turn is not
1202    preceded by "foo".
1203    
1204  Assertion subpatterns are not capturing subpatterns, and may not be repeated,  Assertion subpatterns are not capturing subpatterns, and may not be repeated,
1205  because it makes no sense to assert the same thing several times. If an  because it makes no sense to assert the same thing several times. If an
# Line 917  Assertions count towards the maximum of Line 1212  Assertions count towards the maximum of
1212    
1213    
1214  .SH ONCE-ONLY SUBPATTERNS  .SH ONCE-ONLY SUBPATTERNS
 The facility described in this section is available only when the PCRE_EXTRA  
 option is set at compile time. It is an extension to Perl regular expressions.  
   
1215  With both maximizing and minimizing repetition, failure of what follows  With both maximizing and minimizing repetition, failure of what follows
1216  normally causes the repeated item to be re-evaluated to see if a different  normally causes the repeated item to be re-evaluated to see if a different
1217  number of repeats allows the rest of the pattern to match. Sometimes it is  number of repeats allows the rest of the pattern to match. Sometimes it is
1218  useful to prevent this, either to change the nature of the match, or to cause  useful to prevent this, either to change the nature of the match, or to cause
1219  it fail earlier than it otherwise might when the author of the pattern knows  it fail earlier than it otherwise might, when the author of the pattern knows
1220  there is no point in carrying on.  there is no point in carrying on.
1221    
1222  Consider, for example, the pattern \\d+foo when applied to the subject line  Consider, for example, the pattern \\d+foo when applied to the subject line
1223    
1224     123456bar    123456bar
1225    
1226  After matching all 6 digits and then failing to match "foo", the normal  After matching all 6 digits and then failing to match "foo", the normal
1227  action of the matcher is to try again with only 5 digits matching the \\d+  action of the matcher is to try again with only 5 digits matching the \\d+
# Line 939  has matched, it is not to be re-evaluate Line 1231  has matched, it is not to be re-evaluate
1231  give up immediately on failing to match "foo" the first time. The notation is  give up immediately on failing to match "foo" the first time. The notation is
1232  another kind of special parenthesis, starting with (?> as in this example:  another kind of special parenthesis, starting with (?> as in this example:
1233    
1234    (?>\d+)bar    (?>\\d+)bar
1235    
1236  This kind of parenthesis "locks up" the  part of the pattern it contains once  This kind of parenthesis "locks up" the  part of the pattern it contains once
1237  it has matched, and a failure further into the pattern is prevented from  it has matched, and a failure further into the pattern is prevented from
1238  backtracking into it. Backtracking past it to previous items, however, works as  backtracking into it. Backtracking past it to previous items, however, works as
1239  normal.  normal.
1240    
1241  For simple cases such as the above example, this feature can be though of as a  An alternative description is that a subpattern of this type matches the string
1242  maximizing repeat that must swallow everything it can. So, while both \\d+ and  of characters that an identical standalone pattern would match, if anchored at
1243  \\d+? are prepared to adjust the number of digits they match in order to make  the current point in the subject string.
1244  the rest of the pattern match, (?>\\d+) can only match an entire sequence of  
1245  digits.  Once-only subpatterns are not capturing subpatterns. Simple cases such as the
1246    above example can be thought of as a maximizing repeat that must swallow
1247    everything it can. So, while both \\d+ and \\d+? are prepared to adjust the
1248    number of digits they match in order to make the rest of the pattern match,
1249    (?>\\d+) can only match an entire sequence of digits.
1250    
1251  This construction can of course contain arbitrarily complicated subpatterns,  This construction can of course contain arbitrarily complicated subpatterns,
1252  and it can be nested. Contrast with the \\X assertion, which is a Prolog-like  and it can be nested.
1253  "cut".  
1254    Once-only subpatterns can be used in conjunction with lookbehind assertions to
1255    specify efficient matching at the end of the subject string. Consider a simple
1256    pattern such as
1257    
1258      abcd$
1259    
1260    when applied to a long string which does not match it. Because matching
1261    proceeds from left to right, PCRE will look for each "a" in the subject and
1262    then see if what follows matches the rest of the pattern. If the pattern is
1263    specified as
1264    
1265      .*abcd$
1266    
1267    then the initial .* matches the entire string at first, but when this fails, it
1268    backtracks to match all but the last character, then all but the last two
1269    characters, and so on. Once again the search for "a" covers the entire string,
1270    from right to left, so we are no better off. However, if the pattern is written
1271    as
1272    
1273      (?>.*)(?<=abcd)
1274    
1275    then there can be no backtracking for the .* item; it can match only the entire
1276    string. The subsequent lookbehind assertion does a single test on the last four
1277    characters. If it fails, the match fails immediately. For long strings, this
1278    approach makes a significant difference to the processing time.
1279    
1280    
1281    .SH CONDITIONAL SUBPATTERNS
1282    It is possible to cause the matching process to obey a subpattern
1283    conditionally or to choose between two alternative subpatterns, depending on
1284    the result of an assertion, or whether a previous capturing subpattern matched
1285    or not. The two possible forms of conditional subpattern are
1286    
1287      (?(condition)yes-pattern)
1288      (?(condition)yes-pattern|no-pattern)
1289    
1290    If the condition is satisfied, the yes-pattern is used; otherwise the
1291    no-pattern (if present) is used. If there are more than two alternatives in the
1292    subpattern, a compile-time error occurs.
1293    
1294    There are two kinds of condition. If the text between the parentheses consists
1295    of a sequence of digits, then the condition is satisfied if the capturing
1296    subpattern of that number has previously matched. Consider the following
1297    pattern, which contains non-significant white space to make it more readable
1298    (assume the PCRE_EXTENDED option) and to divide it into three parts for ease
1299    of discussion:
1300    
1301      ( \\( )?    [^()]+    (?(1) \\) )
1302    
1303    The first part matches an optional opening parenthesis, and if that
1304    character is present, sets it as the first captured substring. The second part
1305    matches one or more characters that are not parentheses. The third part is a
1306    conditional subpattern that tests whether the first set of parentheses matched
1307    or not. If they did, that is, if subject started with an opening parenthesis,
1308    the condition is true, and so the yes-pattern is executed and a closing
1309    parenthesis is required. Otherwise, since no-pattern is not present, the
1310    subpattern matches nothing. In other words, this pattern matches a sequence of
1311    non-parentheses, optionally enclosed in parentheses.
1312    
1313    If the condition is not a sequence of digits, it must be an assertion. This may
1314    be a positive or negative lookahead or lookbehind assertion. Consider this
1315    pattern, again containing non-significant white space, and with the two
1316    alternatives on the second line:
1317    
1318      (?(?=[^a-z]*[a-z])
1319      \\d{2}[a-z]{3}-\\d{2}  |  \\d{2}-\\d{2}-\\d{2} )
1320    
1321    The condition is a positive lookahead assertion that matches an optional
1322    sequence of non-letters followed by a letter. In other words, it tests for the
1323    presence of at least one letter in the subject. If a letter is found, the
1324    subject is matched against the first alternative; otherwise it is matched
1325    against the second. This pattern matches strings in one of the two forms
1326    dd-aaa-dd or dd-dd-dd, where aaa are letters and dd are digits.
1327    
1328    
1329  .SH COMMENTS  .SH COMMENTS
# Line 967  character class introduces a comment tha Line 1336  character class introduces a comment tha
1336  character in the pattern.  character in the pattern.
1337    
1338    
 .SH INTERNAL FLAG SETTING  
 If the sequence (?i) occurs anywhere in a pattern, it has the effect of setting  
 the PCRE_CASELESS option, that is, all letters are matched in a  
 case-independent manner. The option applies to the whole pattern, not just to  
 the portion that follows it.  
   
 If the sequence (?m) occurs anywhere in a pattern, it has the effect of setting  
 the PCRE_MULTILINE option, that is, subject strings matched by this pattern are  
 treated as consisting of multiple lines.  
   
 If the sequence (?s) occurs anywhere in a pattern, it has the effect of setting  
 the PCRE_DOTALL option, so that dot metacharacters match newlines as well as  
 all other characters.  
   
 If the sequence (?x) occurs anywhere in a pattern, it has the effect of setting  
 the PCRE_EXTENDED option, that is, whitespace is ignored and # introduces a  
 comment that lasts till the next newline. The option applies to the whole  
 pattern, not just to the portion that follows it.  
   
 If more than one option is required, they can be specified jointly, for example  
 as (?ix) or (?mi).  
   
   
1339  .SH PERFORMANCE  .SH PERFORMANCE
1340  Certain items that may appear in patterns are more efficient than others. It is  Certain items that may appear in patterns are more efficient than others. It is
1341  more efficient to use a character class like [aeiou] than a set of alternatives  more efficient to use a character class like [aeiou] than a set of alternatives
# Line 998  required behaviour is usually the most e Line 1344  required behaviour is usually the most e
1344  contains a lot of discussion about optimizing regular expressions for efficient  contains a lot of discussion about optimizing regular expressions for efficient
1345  performance.  performance.
1346    
 The use of PCRE_MULTILINE causes additional processing and should be avoided  
 when it is not necessary. Caseless matching of character classes is more  
 efficient if PCRE_CASELESS is set when the pattern is compiled.  
   
1347    
1348  .SH AUTHOR  .SH AUTHOR
1349  Philip Hazel <ph10@cam.ac.uk>  Philip Hazel <ph10@cam.ac.uk>
# Line 1014  Cambridge CB2 3QG, England. Line 1356  Cambridge CB2 3QG, England.
1356  .br  .br
1357  Phone: +44 1223 334714  Phone: +44 1223 334714
1358    
1359  Copyright (c) 1997 University of Cambridge.  Copyright (c) 1997-1999 University of Cambridge.

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