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1 .TH PCREAPI 3
2 .SH NAME
3 PCRE - Perl-compatible regular expressions
4 .SH "PCRE NATIVE API BASIC FUNCTIONS"
5 .rs
6 .sp
7 .B #include <pcre.h>
8 .PP
9 .SM
10 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
11 .ti +5n
12 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
13 .ti +5n
14 .B const unsigned char *\fItableptr\fP);
15 .PP
16 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
17 .ti +5n
18 .B int *\fIerrorcodeptr\fP,
19 .ti +5n
20 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
21 .ti +5n
22 .B const unsigned char *\fItableptr\fP);
23 .PP
24 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
25 .ti +5n
26 .B const char **\fIerrptr\fP);
27 .PP
28 .B void pcre_free_study(pcre_extra *\fIextra\fP);
29 .PP
30 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
31 .ti +5n
32 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
33 .ti +5n
34 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
35 .
36 .
37 .SH "PCRE NATIVE API AUXILIARY FUNCTIONS"
38 .rs
39 .sp
40 .B pcre_jit_stack *pcre_jit_stack_alloc(int \fIstartsize\fP, int \fImaxsize\fP);
41 .PP
42 .B void pcre_jit_stack_free(pcre_jit_stack *\fIstack\fP);
43 .PP
44 .B void pcre_assign_jit_stack(pcre_extra *\fIextra\fP,
45 .ti +5n
46 .B pcre_jit_callback \fIcallback\fP, void *\fIdata\fP);
47 .PP
48 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
49 .ti +5n
50 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
51 .ti +5n
52 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
53 .ti +5n
54 .B int *\fIworkspace\fP, int \fIwscount\fP);
55 .PP
56 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
57 .ti +5n
58 .B const char *\fIsubject\fP, int *\fIovector\fP,
59 .ti +5n
60 .B int \fIstringcount\fP, const char *\fIstringname\fP,
61 .ti +5n
62 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
63 .PP
64 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
65 .ti +5n
66 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
67 .ti +5n
68 .B int \fIbuffersize\fP);
69 .PP
70 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
71 .ti +5n
72 .B const char *\fIsubject\fP, int *\fIovector\fP,
73 .ti +5n
74 .B int \fIstringcount\fP, const char *\fIstringname\fP,
75 .ti +5n
76 .B const char **\fIstringptr\fP);
77 .PP
78 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
79 .ti +5n
80 .B const char *\fIname\fP);
81 .PP
82 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
83 .ti +5n
84 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
85 .PP
86 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
87 .ti +5n
88 .B int \fIstringcount\fP, int \fIstringnumber\fP,
89 .ti +5n
90 .B const char **\fIstringptr\fP);
91 .PP
92 .B int pcre_get_substring_list(const char *\fIsubject\fP,
93 .ti +5n
94 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
95 .PP
96 .B void pcre_free_substring(const char *\fIstringptr\fP);
97 .PP
98 .B void pcre_free_substring_list(const char **\fIstringptr\fP);
99 .PP
100 .B const unsigned char *pcre_maketables(void);
101 .PP
102 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
103 .ti +5n
104 .B int \fIwhat\fP, void *\fIwhere\fP);
105 .PP
106 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
107 .B *\fIfirstcharptr\fP);
108 .PP
109 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
110 .PP
111 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
112 .PP
113 .B char *pcre_version(void);
114 .
115 .
116 .SH "PCRE NATIVE API INDIRECTED FUNCTIONS"
117 .rs
118 .sp
119 .B void *(*pcre_malloc)(size_t);
120 .PP
121 .B void (*pcre_free)(void *);
122 .PP
123 .B void *(*pcre_stack_malloc)(size_t);
124 .PP
125 .B void (*pcre_stack_free)(void *);
126 .PP
127 .B int (*pcre_callout)(pcre_callout_block *);
128 .
129 .
130 .SH "PCRE API OVERVIEW"
131 .rs
132 .sp
133 PCRE has its own native API, which is described in this document. There are
134 also some wrapper functions that correspond to the POSIX regular expression
135 API, but they do not give access to all the functionality. They are described
136 in the
137 .\" HREF
138 \fBpcreposix\fP
139 .\"
140 documentation. Both of these APIs define a set of C function calls. A C++
141 wrapper is also distributed with PCRE. It is documented in the
142 .\" HREF
143 \fBpcrecpp\fP
144 .\"
145 page.
146 .P
147 The native API C function prototypes are defined in the header file
148 \fBpcre.h\fP, and on Unix systems the library itself is called \fBlibpcre\fP.
149 It can normally be accessed by adding \fB-lpcre\fP to the command for linking
150 an application that uses PCRE. The header file defines the macros PCRE_MAJOR
151 and PCRE_MINOR to contain the major and minor release numbers for the library.
152 Applications can use these to include support for different releases of PCRE.
153 .P
154 In a Windows environment, if you want to statically link an application program
155 against a non-dll \fBpcre.a\fP file, you must define PCRE_STATIC before
156 including \fBpcre.h\fP or \fBpcrecpp.h\fP, because otherwise the
157 \fBpcre_malloc()\fP and \fBpcre_free()\fP exported functions will be declared
158 \fB__declspec(dllimport)\fP, with unwanted results.
159 .P
160 The functions \fBpcre_compile()\fP, \fBpcre_compile2()\fP, \fBpcre_study()\fP,
161 and \fBpcre_exec()\fP are used for compiling and matching regular expressions
162 in a Perl-compatible manner. A sample program that demonstrates the simplest
163 way of using them is provided in the file called \fIpcredemo.c\fP in the PCRE
164 source distribution. A listing of this program is given in the
165 .\" HREF
166 \fBpcredemo\fP
167 .\"
168 documentation, and the
169 .\" HREF
170 \fBpcresample\fP
171 .\"
172 documentation describes how to compile and run it.
173 .P
174 Just-in-time compiler support is an optional feature of PCRE that can be built
175 in appropriate hardware environments. It greatly speeds up the matching
176 performance of many patterns. Simple programs can easily request that it be
177 used if available, by setting an option that is ignored when it is not
178 relevant. More complicated programs might need to make use of the functions
179 \fBpcre_jit_stack_alloc()\fP, \fBpcre_jit_stack_free()\fP, and
180 \fBpcre_assign_jit_stack()\fP in order to control the JIT code's memory usage.
181 These functions are discussed in the
182 .\" HREF
183 \fBpcrejit\fP
184 .\"
185 documentation.
186 .P
187 A second matching function, \fBpcre_dfa_exec()\fP, which is not
188 Perl-compatible, is also provided. This uses a different algorithm for the
189 matching. The alternative algorithm finds all possible matches (at a given
190 point in the subject), and scans the subject just once (unless there are
191 lookbehind assertions). However, this algorithm does not return captured
192 substrings. A description of the two matching algorithms and their advantages
193 and disadvantages is given in the
194 .\" HREF
195 \fBpcrematching\fP
196 .\"
197 documentation.
198 .P
199 In addition to the main compiling and matching functions, there are convenience
200 functions for extracting captured substrings from a subject string that is
201 matched by \fBpcre_exec()\fP. They are:
202 .sp
203 \fBpcre_copy_substring()\fP
204 \fBpcre_copy_named_substring()\fP
205 \fBpcre_get_substring()\fP
206 \fBpcre_get_named_substring()\fP
207 \fBpcre_get_substring_list()\fP
208 \fBpcre_get_stringnumber()\fP
209 \fBpcre_get_stringtable_entries()\fP
210 .sp
211 \fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
212 provided, to free the memory used for extracted strings.
213 .P
214 The function \fBpcre_maketables()\fP is used to build a set of character tables
215 in the current locale for passing to \fBpcre_compile()\fP, \fBpcre_exec()\fP,
216 or \fBpcre_dfa_exec()\fP. This is an optional facility that is provided for
217 specialist use. Most commonly, no special tables are passed, in which case
218 internal tables that are generated when PCRE is built are used.
219 .P
220 The function \fBpcre_fullinfo()\fP is used to find out information about a
221 compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
222 some of the available information, but is retained for backwards compatibility.
223 The function \fBpcre_version()\fP returns a pointer to a string containing the
224 version of PCRE and its date of release.
225 .P
226 The function \fBpcre_refcount()\fP maintains a reference count in a data block
227 containing a compiled pattern. This is provided for the benefit of
228 object-oriented applications.
229 .P
230 The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
231 the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
232 respectively. PCRE calls the memory management functions via these variables,
233 so a calling program can replace them if it wishes to intercept the calls. This
234 should be done before calling any PCRE functions.
235 .P
236 The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
237 indirections to memory management functions. These special functions are used
238 only when PCRE is compiled to use the heap for remembering data, instead of
239 recursive function calls, when running the \fBpcre_exec()\fP function. See the
240 .\" HREF
241 \fBpcrebuild\fP
242 .\"
243 documentation for details of how to do this. It is a non-standard way of
244 building PCRE, for use in environments that have limited stacks. Because of the
245 greater use of memory management, it runs more slowly. Separate functions are
246 provided so that special-purpose external code can be used for this case. When
247 used, these functions are always called in a stack-like manner (last obtained,
248 first freed), and always for memory blocks of the same size. There is a
249 discussion about PCRE's stack usage in the
250 .\" HREF
251 \fBpcrestack\fP
252 .\"
253 documentation.
254 .P
255 The global variable \fBpcre_callout\fP initially contains NULL. It can be set
256 by the caller to a "callout" function, which PCRE will then call at specified
257 points during a matching operation. Details are given in the
258 .\" HREF
259 \fBpcrecallout\fP
260 .\"
261 documentation.
262 .
263 .
264 .\" HTML <a name="newlines"></a>
265 .SH NEWLINES
266 .rs
267 .sp
268 PCRE supports five different conventions for indicating line breaks in
269 strings: a single CR (carriage return) character, a single LF (linefeed)
270 character, the two-character sequence CRLF, any of the three preceding, or any
271 Unicode newline sequence. The Unicode newline sequences are the three just
272 mentioned, plus the single characters VT (vertical tab, U+000B), FF (formfeed,
273 U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS
274 (paragraph separator, U+2029).
275 .P
276 Each of the first three conventions is used by at least one operating system as
277 its standard newline sequence. When PCRE is built, a default can be specified.
278 The default default is LF, which is the Unix standard. When PCRE is run, the
279 default can be overridden, either when a pattern is compiled, or when it is
280 matched.
281 .P
282 At compile time, the newline convention can be specified by the \fIoptions\fP
283 argument of \fBpcre_compile()\fP, or it can be specified by special text at the
284 start of the pattern itself; this overrides any other settings. See the
285 .\" HREF
286 \fBpcrepattern\fP
287 .\"
288 page for details of the special character sequences.
289 .P
290 In the PCRE documentation the word "newline" is used to mean "the character or
291 pair of characters that indicate a line break". The choice of newline
292 convention affects the handling of the dot, circumflex, and dollar
293 metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
294 recognized line ending sequence, the match position advancement for a
295 non-anchored pattern. There is more detail about this in the
296 .\" HTML <a href="#execoptions">
297 .\" </a>
298 section on \fBpcre_exec()\fP options
299 .\"
300 below.
301 .P
302 The choice of newline convention does not affect the interpretation of
303 the \en or \er escape sequences, nor does it affect what \eR matches, which is
304 controlled in a similar way, but by separate options.
305 .
306 .
307 .SH MULTITHREADING
308 .rs
309 .sp
310 The PCRE functions can be used in multi-threading applications, with the
311 proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
312 \fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
313 callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
314 .P
315 The compiled form of a regular expression is not altered during matching, so
316 the same compiled pattern can safely be used by several threads at once.
317 .P
318 If the just-in-time optimization feature is being used, it needs separate
319 memory stack areas for each thread. See the
320 .\" HREF
321 \fBpcrejit\fP
322 .\"
323 documentation for more details.
324 .
325 .
326 .SH "SAVING PRECOMPILED PATTERNS FOR LATER USE"
327 .rs
328 .sp
329 The compiled form of a regular expression can be saved and re-used at a later
330 time, possibly by a different program, and even on a host other than the one on
331 which it was compiled. Details are given in the
332 .\" HREF
333 \fBpcreprecompile\fP
334 .\"
335 documentation. However, compiling a regular expression with one version of PCRE
336 for use with a different version is not guaranteed to work and may cause
337 crashes.
338 .
339 .
340 .SH "CHECKING BUILD-TIME OPTIONS"
341 .rs
342 .sp
343 .B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
344 .PP
345 The function \fBpcre_config()\fP makes it possible for a PCRE client to
346 discover which optional features have been compiled into the PCRE library. The
347 .\" HREF
348 \fBpcrebuild\fP
349 .\"
350 documentation has more details about these optional features.
351 .P
352 The first argument for \fBpcre_config()\fP is an integer, specifying which
353 information is required; the second argument is a pointer to a variable into
354 which the information is placed. The following information is available:
355 .sp
356 PCRE_CONFIG_UTF8
357 .sp
358 The output is an integer that is set to one if UTF-8 support is available;
359 otherwise it is set to zero.
360 .sp
361 PCRE_CONFIG_UNICODE_PROPERTIES
362 .sp
363 The output is an integer that is set to one if support for Unicode character
364 properties is available; otherwise it is set to zero.
365 .sp
366 PCRE_CONFIG_JIT
367 .sp
368 The output is an integer that is set to one if support for just-in-time
369 compiling is available; otherwise it is set to zero.
370 .sp
371 PCRE_CONFIG_NEWLINE
372 .sp
373 The output is an integer whose value specifies the default character sequence
374 that is recognized as meaning "newline". The four values that are supported
375 are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF, and -1 for ANY.
376 Though they are derived from ASCII, the same values are returned in EBCDIC
377 environments. The default should normally correspond to the standard sequence
378 for your operating system.
379 .sp
380 PCRE_CONFIG_BSR
381 .sp
382 The output is an integer whose value indicates what character sequences the \eR
383 escape sequence matches by default. A value of 0 means that \eR matches any
384 Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
385 or CRLF. The default can be overridden when a pattern is compiled or matched.
386 .sp
387 PCRE_CONFIG_LINK_SIZE
388 .sp
389 The output is an integer that contains the number of bytes used for internal
390 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
391 allow larger regular expressions to be compiled, at the expense of slower
392 matching. The default value of 2 is sufficient for all but the most massive
393 patterns, since it allows the compiled pattern to be up to 64K in size.
394 .sp
395 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
396 .sp
397 The output is an integer that contains the threshold above which the POSIX
398 interface uses \fBmalloc()\fP for output vectors. Further details are given in
399 the
400 .\" HREF
401 \fBpcreposix\fP
402 .\"
403 documentation.
404 .sp
405 PCRE_CONFIG_MATCH_LIMIT
406 .sp
407 The output is a long integer that gives the default limit for the number of
408 internal matching function calls in a \fBpcre_exec()\fP execution. Further
409 details are given with \fBpcre_exec()\fP below.
410 .sp
411 PCRE_CONFIG_MATCH_LIMIT_RECURSION
412 .sp
413 The output is a long integer that gives the default limit for the depth of
414 recursion when calling the internal matching function in a \fBpcre_exec()\fP
415 execution. Further details are given with \fBpcre_exec()\fP below.
416 .sp
417 PCRE_CONFIG_STACKRECURSE
418 .sp
419 The output is an integer that is set to one if internal recursion when running
420 \fBpcre_exec()\fP is implemented by recursive function calls that use the stack
421 to remember their state. This is the usual way that PCRE is compiled. The
422 output is zero if PCRE was compiled to use blocks of data on the heap instead
423 of recursive function calls. In this case, \fBpcre_stack_malloc\fP and
424 \fBpcre_stack_free\fP are called to manage memory blocks on the heap, thus
425 avoiding the use of the stack.
426 .
427 .
428 .SH "COMPILING A PATTERN"
429 .rs
430 .sp
431 .B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
432 .ti +5n
433 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
434 .ti +5n
435 .B const unsigned char *\fItableptr\fP);
436 .sp
437 .B pcre *pcre_compile2(const char *\fIpattern\fP, int \fIoptions\fP,
438 .ti +5n
439 .B int *\fIerrorcodeptr\fP,
440 .ti +5n
441 .B const char **\fIerrptr\fP, int *\fIerroffset\fP,
442 .ti +5n
443 .B const unsigned char *\fItableptr\fP);
444 .P
445 Either of the functions \fBpcre_compile()\fP or \fBpcre_compile2()\fP can be
446 called to compile a pattern into an internal form. The only difference between
447 the two interfaces is that \fBpcre_compile2()\fP has an additional argument,
448 \fIerrorcodeptr\fP, via which a numerical error code can be returned. To avoid
449 too much repetition, we refer just to \fBpcre_compile()\fP below, but the
450 information applies equally to \fBpcre_compile2()\fP.
451 .P
452 The pattern is a C string terminated by a binary zero, and is passed in the
453 \fIpattern\fP argument. A pointer to a single block of memory that is obtained
454 via \fBpcre_malloc\fP is returned. This contains the compiled code and related
455 data. The \fBpcre\fP type is defined for the returned block; this is a typedef
456 for a structure whose contents are not externally defined. It is up to the
457 caller to free the memory (via \fBpcre_free\fP) when it is no longer required.
458 .P
459 Although the compiled code of a PCRE regex is relocatable, that is, it does not
460 depend on memory location, the complete \fBpcre\fP data block is not
461 fully relocatable, because it may contain a copy of the \fItableptr\fP
462 argument, which is an address (see below).
463 .P
464 The \fIoptions\fP argument contains various bit settings that affect the
465 compilation. It should be zero if no options are required. The available
466 options are described below. Some of them (in particular, those that are
467 compatible with Perl, but some others as well) can also be set and unset from
468 within the pattern (see the detailed description in the
469 .\" HREF
470 \fBpcrepattern\fP
471 .\"
472 documentation). For those options that can be different in different parts of
473 the pattern, the contents of the \fIoptions\fP argument specifies their
474 settings at the start of compilation and execution. The PCRE_ANCHORED,
475 PCRE_BSR_\fIxxx\fP, PCRE_NEWLINE_\fIxxx\fP, PCRE_NO_UTF8_CHECK, and
476 PCRE_NO_START_OPT options can be set at the time of matching as well as at
477 compile time.
478 .P
479 If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
480 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
481 NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
482 error message. This is a static string that is part of the library. You must
483 not try to free it. Normally, the offset from the start of the pattern to the
484 byte that was being processed when the error was discovered is placed in the
485 variable pointed to by \fIerroffset\fP, which must not be NULL (if it is, an
486 immediate error is given). However, for an invalid UTF-8 string, the offset is
487 that of the first byte of the failing character. Also, some errors are not
488 detected until checks are carried out when the whole pattern has been scanned;
489 in these cases the offset passed back is the length of the pattern.
490 .P
491 Note that the offset is in bytes, not characters, even in UTF-8 mode. It may
492 sometimes point into the middle of a UTF-8 character.
493 .P
494 If \fBpcre_compile2()\fP is used instead of \fBpcre_compile()\fP, and the
495 \fIerrorcodeptr\fP argument is not NULL, a non-zero error code number is
496 returned via this argument in the event of an error. This is in addition to the
497 textual error message. Error codes and messages are listed below.
498 .P
499 If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
500 character tables that are built when PCRE is compiled, using the default C
501 locale. Otherwise, \fItableptr\fP must be an address that is the result of a
502 call to \fBpcre_maketables()\fP. This value is stored with the compiled
503 pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
504 passed to it. For more discussion, see the section on locale support below.
505 .P
506 This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
507 .sp
508 pcre *re;
509 const char *error;
510 int erroffset;
511 re = pcre_compile(
512 "^A.*Z", /* the pattern */
513 0, /* default options */
514 &error, /* for error message */
515 &erroffset, /* for error offset */
516 NULL); /* use default character tables */
517 .sp
518 The following names for option bits are defined in the \fBpcre.h\fP header
519 file:
520 .sp
521 PCRE_ANCHORED
522 .sp
523 If this bit is set, the pattern is forced to be "anchored", that is, it is
524 constrained to match only at the first matching point in the string that is
525 being searched (the "subject string"). This effect can also be achieved by
526 appropriate constructs in the pattern itself, which is the only way to do it in
527 Perl.
528 .sp
529 PCRE_AUTO_CALLOUT
530 .sp
531 If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
532 all with number 255, before each pattern item. For discussion of the callout
533 facility, see the
534 .\" HREF
535 \fBpcrecallout\fP
536 .\"
537 documentation.
538 .sp
539 PCRE_BSR_ANYCRLF
540 PCRE_BSR_UNICODE
541 .sp
542 These options (which are mutually exclusive) control what the \eR escape
543 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
544 match any Unicode newline sequence. The default is specified when PCRE is
545 built. It can be overridden from within the pattern, or by setting an option
546 when a compiled pattern is matched.
547 .sp
548 PCRE_CASELESS
549 .sp
550 If this bit is set, letters in the pattern match both upper and lower case
551 letters. It is equivalent to Perl's /i option, and it can be changed within a
552 pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
553 concept of case for characters whose values are less than 128, so caseless
554 matching is always possible. For characters with higher values, the concept of
555 case is supported if PCRE is compiled with Unicode property support, but not
556 otherwise. If you want to use caseless matching for characters 128 and above,
557 you must ensure that PCRE is compiled with Unicode property support as well as
558 with UTF-8 support.
559 .sp
560 PCRE_DOLLAR_ENDONLY
561 .sp
562 If this bit is set, a dollar metacharacter in the pattern matches only at the
563 end of the subject string. Without this option, a dollar also matches
564 immediately before a newline at the end of the string (but not before any other
565 newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
566 There is no equivalent to this option in Perl, and no way to set it within a
567 pattern.
568 .sp
569 PCRE_DOTALL
570 .sp
571 If this bit is set, a dot metacharacter in the pattern matches a character of
572 any value, including one that indicates a newline. However, it only ever
573 matches one character, even if newlines are coded as CRLF. Without this option,
574 a dot does not match when the current position is at a newline. This option is
575 equivalent to Perl's /s option, and it can be changed within a pattern by a
576 (?s) option setting. A negative class such as [^a] always matches newline
577 characters, independent of the setting of this option.
578 .sp
579 PCRE_DUPNAMES
580 .sp
581 If this bit is set, names used to identify capturing subpatterns need not be
582 unique. This can be helpful for certain types of pattern when it is known that
583 only one instance of the named subpattern can ever be matched. There are more
584 details of named subpatterns below; see also the
585 .\" HREF
586 \fBpcrepattern\fP
587 .\"
588 documentation.
589 .sp
590 PCRE_EXTENDED
591 .sp
592 If this bit is set, whitespace data characters in the pattern are totally
593 ignored except when escaped or inside a character class. Whitespace does not
594 include the VT character (code 11). In addition, characters between an
595 unescaped # outside a character class and the next newline, inclusive, are also
596 ignored. This is equivalent to Perl's /x option, and it can be changed within a
597 pattern by a (?x) option setting.
598 .P
599 Which characters are interpreted as newlines is controlled by the options
600 passed to \fBpcre_compile()\fP or by a special sequence at the start of the
601 pattern, as described in the section entitled
602 .\" HTML <a href="pcrepattern.html#newlines">
603 .\" </a>
604 "Newline conventions"
605 .\"
606 in the \fBpcrepattern\fP documentation. Note that the end of this type of
607 comment is a literal newline sequence in the pattern; escape sequences that
608 happen to represent a newline do not count.
609 .P
610 This option makes it possible to include comments inside complicated patterns.
611 Note, however, that this applies only to data characters. Whitespace characters
612 may never appear within special character sequences in a pattern, for example
613 within the sequence (?( that introduces a conditional subpattern.
614 .sp
615 PCRE_EXTRA
616 .sp
617 This option was invented in order to turn on additional functionality of PCRE
618 that is incompatible with Perl, but it is currently of very little use. When
619 set, any backslash in a pattern that is followed by a letter that has no
620 special meaning causes an error, thus reserving these combinations for future
621 expansion. By default, as in Perl, a backslash followed by a letter with no
622 special meaning is treated as a literal. (Perl can, however, be persuaded to
623 give an error for this, by running it with the -w option.) There are at present
624 no other features controlled by this option. It can also be set by a (?X)
625 option setting within a pattern.
626 .sp
627 PCRE_FIRSTLINE
628 .sp
629 If this option is set, an unanchored pattern is required to match before or at
630 the first newline in the subject string, though the matched text may continue
631 over the newline.
632 .sp
633 PCRE_JAVASCRIPT_COMPAT
634 .sp
635 If this option is set, PCRE's behaviour is changed in some ways so that it is
636 compatible with JavaScript rather than Perl. The changes are as follows:
637 .P
638 (1) A lone closing square bracket in a pattern causes a compile-time error,
639 because this is illegal in JavaScript (by default it is treated as a data
640 character). Thus, the pattern AB]CD becomes illegal when this option is set.
641 .P
642 (2) At run time, a back reference to an unset subpattern group matches an empty
643 string (by default this causes the current matching alternative to fail). A
644 pattern such as (\e1)(a) succeeds when this option is set (assuming it can find
645 an "a" in the subject), whereas it fails by default, for Perl compatibility.
646 .sp
647 PCRE_MULTILINE
648 .sp
649 By default, PCRE treats the subject string as consisting of a single line of
650 characters (even if it actually contains newlines). The "start of line"
651 metacharacter (^) matches only at the start of the string, while the "end of
652 line" metacharacter ($) matches only at the end of the string, or before a
653 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
654 Perl.
655 .P
656 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
657 match immediately following or immediately before internal newlines in the
658 subject string, respectively, as well as at the very start and end. This is
659 equivalent to Perl's /m option, and it can be changed within a pattern by a
660 (?m) option setting. If there are no newlines in a subject string, or no
661 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
662 .sp
663 PCRE_NEWLINE_CR
664 PCRE_NEWLINE_LF
665 PCRE_NEWLINE_CRLF
666 PCRE_NEWLINE_ANYCRLF
667 PCRE_NEWLINE_ANY
668 .sp
669 These options override the default newline definition that was chosen when PCRE
670 was built. Setting the first or the second specifies that a newline is
671 indicated by a single character (CR or LF, respectively). Setting
672 PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character
673 CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three
674 preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies
675 that any Unicode newline sequence should be recognized. The Unicode newline
676 sequences are the three just mentioned, plus the single characters VT (vertical
677 tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS (line
678 separator, U+2028), and PS (paragraph separator, U+2029). The last two are
679 recognized only in UTF-8 mode.
680 .P
681 The newline setting in the options word uses three bits that are treated
682 as a number, giving eight possibilities. Currently only six are used (default
683 plus the five values above). This means that if you set more than one newline
684 option, the combination may or may not be sensible. For example,
685 PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but
686 other combinations may yield unused numbers and cause an error.
687 .P
688 The only time that a line break in a pattern is specially recognized when
689 compiling is when PCRE_EXTENDED is set. CR and LF are whitespace characters,
690 and so are ignored in this mode. Also, an unescaped # outside a character class
691 indicates a comment that lasts until after the next line break sequence. In
692 other circumstances, line break sequences in patterns are treated as literal
693 data.
694 .P
695 The newline option that is set at compile time becomes the default that is used
696 for \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, but it can be overridden.
697 .sp
698 PCRE_NO_AUTO_CAPTURE
699 .sp
700 If this option is set, it disables the use of numbered capturing parentheses in
701 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
702 were followed by ?: but named parentheses can still be used for capturing (and
703 they acquire numbers in the usual way). There is no equivalent of this option
704 in Perl.
705 .sp
706 NO_START_OPTIMIZE
707 .sp
708 This is an option that acts at matching time; that is, it is really an option
709 for \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. If it is set at compile time,
710 it is remembered with the compiled pattern and assumed at matching time. For
711 details see the discussion of PCRE_NO_START_OPTIMIZE
712 .\" HTML <a href="#execoptions">
713 .\" </a>
714 below.
715 .\"
716 .sp
717 PCRE_UCP
718 .sp
719 This option changes the way PCRE processes \eB, \eb, \eD, \ed, \eS, \es, \eW,
720 \ew, and some of the POSIX character classes. By default, only ASCII characters
721 are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
722 classify characters. More details are given in the section on
723 .\" HTML <a href="pcre.html#genericchartypes">
724 .\" </a>
725 generic character types
726 .\"
727 in the
728 .\" HREF
729 \fBpcrepattern\fP
730 .\"
731 page. If you set PCRE_UCP, matching one of the items it affects takes much
732 longer. The option is available only if PCRE has been compiled with Unicode
733 property support.
734 .sp
735 PCRE_UNGREEDY
736 .sp
737 This option inverts the "greediness" of the quantifiers so that they are not
738 greedy by default, but become greedy if followed by "?". It is not compatible
739 with Perl. It can also be set by a (?U) option setting within the pattern.
740 .sp
741 PCRE_UTF8
742 .sp
743 This option causes PCRE to regard both the pattern and the subject as strings
744 of UTF-8 characters instead of single-byte character strings. However, it is
745 available only when PCRE is built to include UTF-8 support. If not, the use
746 of this option provokes an error. Details of how this option changes the
747 behaviour of PCRE are given in the
748 .\" HREF
749 \fBpcreunicode\fP
750 .\"
751 page.
752 .sp
753 PCRE_NO_UTF8_CHECK
754 .sp
755 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
756 automatically checked. There is a discussion about the
757 .\" HTML <a href="pcre.html#utf8strings">
758 .\" </a>
759 validity of UTF-8 strings
760 .\"
761 in the main
762 .\" HREF
763 \fBpcre\fP
764 .\"
765 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_compile()\fP
766 returns an error. If you already know that your pattern is valid, and you want
767 to skip this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK
768 option. When it is set, the effect of passing an invalid UTF-8 string as a
769 pattern is undefined. It may cause your program to crash. Note that this option
770 can also be passed to \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP, to suppress
771 the UTF-8 validity checking of subject strings.
772 .
773 .
774 .SH "COMPILATION ERROR CODES"
775 .rs
776 .sp
777 The following table lists the error codes than may be returned by
778 \fBpcre_compile2()\fP, along with the error messages that may be returned by
779 both compiling functions. As PCRE has developed, some error codes have fallen
780 out of use. To avoid confusion, they have not been re-used.
781 .sp
782 0 no error
783 1 \e at end of pattern
784 2 \ec at end of pattern
785 3 unrecognized character follows \e
786 4 numbers out of order in {} quantifier
787 5 number too big in {} quantifier
788 6 missing terminating ] for character class
789 7 invalid escape sequence in character class
790 8 range out of order in character class
791 9 nothing to repeat
792 10 [this code is not in use]
793 11 internal error: unexpected repeat
794 12 unrecognized character after (? or (?-
795 13 POSIX named classes are supported only within a class
796 14 missing )
797 15 reference to non-existent subpattern
798 16 erroffset passed as NULL
799 17 unknown option bit(s) set
800 18 missing ) after comment
801 19 [this code is not in use]
802 20 regular expression is too large
803 21 failed to get memory
804 22 unmatched parentheses
805 23 internal error: code overflow
806 24 unrecognized character after (?<
807 25 lookbehind assertion is not fixed length
808 26 malformed number or name after (?(
809 27 conditional group contains more than two branches
810 28 assertion expected after (?(
811 29 (?R or (?[+-]digits must be followed by )
812 30 unknown POSIX class name
813 31 POSIX collating elements are not supported
814 32 this version of PCRE is not compiled with PCRE_UTF8 support
815 33 [this code is not in use]
816 34 character value in \ex{...} sequence is too large
817 35 invalid condition (?(0)
818 36 \eC not allowed in lookbehind assertion
819 37 PCRE does not support \eL, \el, \eN{name}, \eU, or \eu
820 38 number after (?C is > 255
821 39 closing ) for (?C expected
822 40 recursive call could loop indefinitely
823 41 unrecognized character after (?P
824 42 syntax error in subpattern name (missing terminator)
825 43 two named subpatterns have the same name
826 44 invalid UTF-8 string
827 45 support for \eP, \ep, and \eX has not been compiled
828 46 malformed \eP or \ep sequence
829 47 unknown property name after \eP or \ep
830 48 subpattern name is too long (maximum 32 characters)
831 49 too many named subpatterns (maximum 10000)
832 50 [this code is not in use]
833 51 octal value is greater than \e377 (not in UTF-8 mode)
834 52 internal error: overran compiling workspace
835 53 internal error: previously-checked referenced subpattern
836 not found
837 54 DEFINE group contains more than one branch
838 55 repeating a DEFINE group is not allowed
839 56 inconsistent NEWLINE options
840 57 \eg is not followed by a braced, angle-bracketed, or quoted
841 name/number or by a plain number
842 58 a numbered reference must not be zero
843 59 an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
844 60 (*VERB) not recognized
845 61 number is too big
846 62 subpattern name expected
847 63 digit expected after (?+
848 64 ] is an invalid data character in JavaScript compatibility mode
849 65 different names for subpatterns of the same number are
850 not allowed
851 66 (*MARK) must have an argument
852 67 this version of PCRE is not compiled with PCRE_UCP support
853 68 \ec must be followed by an ASCII character
854 69 \ek is not followed by a braced, angle-bracketed, or quoted name
855 .sp
856 The numbers 32 and 10000 in errors 48 and 49 are defaults; different values may
857 be used if the limits were changed when PCRE was built.
858 .
859 .
860 .\" HTML <a name="studyingapattern"></a>
861 .SH "STUDYING A PATTERN"
862 .rs
863 .sp
864 .B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP
865 .ti +5n
866 .B const char **\fIerrptr\fP);
867 .PP
868 If a compiled pattern is going to be used several times, it is worth spending
869 more time analyzing it in order to speed up the time taken for matching. The
870 function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
871 argument. If studying the pattern produces additional information that will
872 help speed up matching, \fBpcre_study()\fP returns a pointer to a
873 \fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
874 results of the study.
875 .P
876 The returned value from \fBpcre_study()\fP can be passed directly to
877 \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP. However, a \fBpcre_extra\fP block
878 also contains other fields that can be set by the caller before the block is
879 passed; these are described
880 .\" HTML <a href="#extradata">
881 .\" </a>
882 below
883 .\"
884 in the section on matching a pattern.
885 .P
886 If studying the pattern does not produce any useful information,
887 \fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
888 wants to pass any of the other fields to \fBpcre_exec()\fP or
889 \fBpcre_dfa_exec()\fP, it must set up its own \fBpcre_extra\fP block.
890 .P
891 The second argument of \fBpcre_study()\fP contains option bits. There is only
892 one option: PCRE_STUDY_JIT_COMPILE. If this is set, and the just-in-time
893 compiler is available, the pattern is further compiled into machine code that
894 executes much faster than the \fBpcre_exec()\fP matching function. If
895 the just-in-time compiler is not available, this option is ignored. All other
896 bits in the \fIoptions\fP argument must be zero.
897 .P
898 JIT compilation is a heavyweight optimization. It can take some time for
899 patterns to be analyzed, and for one-off matches and simple patterns the
900 benefit of faster execution might be offset by a much slower study time.
901 Not all patterns can be optimized by the JIT compiler. For those that cannot be
902 handled, matching automatically falls back to the \fBpcre_exec()\fP
903 interpreter. For more details, see the
904 .\" HREF
905 \fBpcrejit\fP
906 .\"
907 documentation.
908 .P
909 The third argument for \fBpcre_study()\fP is a pointer for an error message. If
910 studying succeeds (even if no data is returned), the variable it points to is
911 set to NULL. Otherwise it is set to point to a textual error message. This is a
912 static string that is part of the library. You must not try to free it. You
913 should test the error pointer for NULL after calling \fBpcre_study()\fP, to be
914 sure that it has run successfully.
915 .P
916 When you are finished with a pattern, you can free the memory used for the
917 study data by calling \fBpcre_free_study()\fP. This function was added to the
918 API for release 8.20. For earlier versions, the memory could be freed with
919 \fBpcre_free()\fP, just like the pattern itself. This will still work in cases
920 where PCRE_STUDY_JIT_COMPILE is not used, but it is advisable to change to the
921 new function when convenient.
922 .P
923 This is a typical way in which \fBpcre_study\fP() is used (except that in a
924 real application there should be tests for errors):
925 .sp
926 int rc;
927 pcre *re;
928 pcre_extra *sd;
929 re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
930 sd = pcre_study(
931 re, /* result of pcre_compile() */
932 0, /* no options */
933 &error); /* set to NULL or points to a message */
934 rc = pcre_exec( /* see below for details of pcre_exec() options */
935 re, sd, "subject", 7, 0, 0, ovector, 30);
936 ...
937 pcre_free_study(sd);
938 pcre_free(re);
939 .sp
940 Studying a pattern does two things: first, a lower bound for the length of
941 subject string that is needed to match the pattern is computed. This does not
942 mean that there are any strings of that length that match, but it does
943 guarantee that no shorter strings match. The value is used by
944 \fBpcre_exec()\fP and \fBpcre_dfa_exec()\fP to avoid wasting time by trying to
945 match strings that are shorter than the lower bound. You can find out the value
946 in a calling program via the \fBpcre_fullinfo()\fP function.
947 .P
948 Studying a pattern is also useful for non-anchored patterns that do not have a
949 single fixed starting character. A bitmap of possible starting bytes is
950 created. This speeds up finding a position in the subject at which to start
951 matching.
952 .P
953 These two optimizations apply to both \fBpcre_exec()\fP and
954 \fBpcre_dfa_exec()\fP. However, they are not used by \fBpcre_exec()\fP if
955 \fBpcre_study()\fP is called with the PCRE_STUDY_JIT_COMPILE option, and
956 just-in-time compiling is successful. The optimizations can be disabled by
957 setting the PCRE_NO_START_OPTIMIZE option when calling \fBpcre_exec()\fP or
958 \fBpcre_dfa_exec()\fP. You might want to do this if your pattern contains
959 callouts or (*MARK) (which cannot be handled by the JIT compiler), and you want
960 to make use of these facilities in cases where matching fails. See the
961 discussion of PCRE_NO_START_OPTIMIZE
962 .\" HTML <a href="#execoptions">
963 .\" </a>
964 below.
965 .\"
966 .
967 .
968 .\" HTML <a name="localesupport"></a>
969 .SH "LOCALE SUPPORT"
970 .rs
971 .sp
972 PCRE handles caseless matching, and determines whether characters are letters,
973 digits, or whatever, by reference to a set of tables, indexed by character
974 value. When running in UTF-8 mode, this applies only to characters with codes
975 less than 128. By default, higher-valued codes never match escapes such as \ew
976 or \ed, but they can be tested with \ep if PCRE is built with Unicode character
977 property support. Alternatively, the PCRE_UCP option can be set at compile
978 time; this causes \ew and friends to use Unicode property support instead of
979 built-in tables. The use of locales with Unicode is discouraged. If you are
980 handling characters with codes greater than 128, you should either use UTF-8
981 and Unicode, or use locales, but not try to mix the two.
982 .P
983 PCRE contains an internal set of tables that are used when the final argument
984 of \fBpcre_compile()\fP is NULL. These are sufficient for many applications.
985 Normally, the internal tables recognize only ASCII characters. However, when
986 PCRE is built, it is possible to cause the internal tables to be rebuilt in the
987 default "C" locale of the local system, which may cause them to be different.
988 .P
989 The internal tables can always be overridden by tables supplied by the
990 application that calls PCRE. These may be created in a different locale from
991 the default. As more and more applications change to using Unicode, the need
992 for this locale support is expected to die away.
993 .P
994 External tables are built by calling the \fBpcre_maketables()\fP function,
995 which has no arguments, in the relevant locale. The result can then be passed
996 to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
997 example, to build and use tables that are appropriate for the French locale
998 (where accented characters with values greater than 128 are treated as letters),
999 the following code could be used:
1000 .sp
1001 setlocale(LC_CTYPE, "fr_FR");
1002 tables = pcre_maketables();
1003 re = pcre_compile(..., tables);
1004 .sp
1005 The locale name "fr_FR" is used on Linux and other Unix-like systems; if you
1006 are using Windows, the name for the French locale is "french".
1007 .P
1008 When \fBpcre_maketables()\fP runs, the tables are built in memory that is
1009 obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
1010 that the memory containing the tables remains available for as long as it is
1011 needed.
1012 .P
1013 The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
1014 pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
1015 and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
1016 pattern, compilation, studying and matching all happen in the same locale, but
1017 different patterns can be compiled in different locales.
1018 .P
1019 It is possible to pass a table pointer or NULL (indicating the use of the
1020 internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
1021 this facility could be used to match a pattern in a different locale from the
1022 one in which it was compiled. Passing table pointers at run time is discussed
1023 below in the section on matching a pattern.
1024 .
1025 .
1026 .\" HTML <a name="infoaboutpattern"></a>
1027 .SH "INFORMATION ABOUT A PATTERN"
1028 .rs
1029 .sp
1030 .B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1031 .ti +5n
1032 .B int \fIwhat\fP, void *\fIwhere\fP);
1033 .PP
1034 The \fBpcre_fullinfo()\fP function returns information about a compiled
1035 pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
1036 nevertheless retained for backwards compability (and is documented below).
1037 .P
1038 The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
1039 pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
1040 the pattern was not studied. The third argument specifies which piece of
1041 information is required, and the fourth argument is a pointer to a variable
1042 to receive the data. The yield of the function is zero for success, or one of
1043 the following negative numbers:
1044 .sp
1045 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1046 the argument \fIwhere\fP was NULL
1047 PCRE_ERROR_BADMAGIC the "magic number" was not found
1048 PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
1049 .sp
1050 The "magic number" is placed at the start of each compiled pattern as an simple
1051 check against passing an arbitrary memory pointer. Here is a typical call of
1052 \fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
1053 .sp
1054 int rc;
1055 size_t length;
1056 rc = pcre_fullinfo(
1057 re, /* result of pcre_compile() */
1058 sd, /* result of pcre_study(), or NULL */
1059 PCRE_INFO_SIZE, /* what is required */
1060 &length); /* where to put the data */
1061 .sp
1062 The possible values for the third argument are defined in \fBpcre.h\fP, and are
1063 as follows:
1064 .sp
1065 PCRE_INFO_BACKREFMAX
1066 .sp
1067 Return the number of the highest back reference in the pattern. The fourth
1068 argument should point to an \fBint\fP variable. Zero is returned if there are
1069 no back references.
1070 .sp
1071 PCRE_INFO_CAPTURECOUNT
1072 .sp
1073 Return the number of capturing subpatterns in the pattern. The fourth argument
1074 should point to an \fBint\fP variable.
1075 .sp
1076 PCRE_INFO_DEFAULT_TABLES
1077 .sp
1078 Return a pointer to the internal default character tables within PCRE. The
1079 fourth argument should point to an \fBunsigned char *\fP variable. This
1080 information call is provided for internal use by the \fBpcre_study()\fP
1081 function. External callers can cause PCRE to use its internal tables by passing
1082 a NULL table pointer.
1083 .sp
1084 PCRE_INFO_FIRSTBYTE
1085 .sp
1086 Return information about the first byte of any matched string, for a
1087 non-anchored pattern. The fourth argument should point to an \fBint\fP
1088 variable. (This option used to be called PCRE_INFO_FIRSTCHAR; the old name is
1089 still recognized for backwards compatibility.)
1090 .P
1091 If there is a fixed first byte, for example, from a pattern such as
1092 (cat|cow|coyote), its value is returned. Otherwise, if either
1093 .sp
1094 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
1095 starts with "^", or
1096 .sp
1097 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
1098 (if it were set, the pattern would be anchored),
1099 .sp
1100 -1 is returned, indicating that the pattern matches only at the start of a
1101 subject string or after any newline within the string. Otherwise -2 is
1102 returned. For anchored patterns, -2 is returned.
1103 .sp
1104 PCRE_INFO_FIRSTTABLE
1105 .sp
1106 If the pattern was studied, and this resulted in the construction of a 256-bit
1107 table indicating a fixed set of bytes for the first byte in any matching
1108 string, a pointer to the table is returned. Otherwise NULL is returned. The
1109 fourth argument should point to an \fBunsigned char *\fP variable.
1110 .sp
1111 PCRE_INFO_HASCRORLF
1112 .sp
1113 Return 1 if the pattern contains any explicit matches for CR or LF characters,
1114 otherwise 0. The fourth argument should point to an \fBint\fP variable. An
1115 explicit match is either a literal CR or LF character, or \er or \en.
1116 .sp
1117 PCRE_INFO_JCHANGED
1118 .sp
1119 Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
1120 0. The fourth argument should point to an \fBint\fP variable. (?J) and
1121 (?-J) set and unset the local PCRE_DUPNAMES option, respectively.
1122 .sp
1123 PCRE_INFO_JIT
1124 .sp
1125 Return 1 if the pattern was studied with the PCRE_STUDY_JIT_COMPILE option, and
1126 just-in-time compiling was successful. The fourth argument should point to an
1127 \fBint\fP variable. A return value of 0 means that JIT support is not available
1128 in this version of PCRE, or that the pattern was not studied with the
1129 PCRE_STUDY_JIT_COMPILE option, or that the JIT compiler could not handle this
1130 particular pattern. See the
1131 .\" HREF
1132 \fBpcrejit\fP
1133 .\"
1134 documentation for details of what can and cannot be handled.
1135 .sp
1136 PCRE_INFO_LASTLITERAL
1137 .sp
1138 Return the value of the rightmost literal byte that must exist in any matched
1139 string, other than at its start, if such a byte has been recorded. The fourth
1140 argument should point to an \fBint\fP variable. If there is no such byte, -1 is
1141 returned. For anchored patterns, a last literal byte is recorded only if it
1142 follows something of variable length. For example, for the pattern
1143 /^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
1144 is -1.
1145 .sp
1146 PCRE_INFO_MINLENGTH
1147 .sp
1148 If the pattern was studied and a minimum length for matching subject strings
1149 was computed, its value is returned. Otherwise the returned value is -1. The
1150 value is a number of characters, not bytes (this may be relevant in UTF-8
1151 mode). The fourth argument should point to an \fBint\fP variable. A
1152 non-negative value is a lower bound to the length of any matching string. There
1153 may not be any strings of that length that do actually match, but every string
1154 that does match is at least that long.
1155 .sp
1156 PCRE_INFO_NAMECOUNT
1157 PCRE_INFO_NAMEENTRYSIZE
1158 PCRE_INFO_NAMETABLE
1159 .sp
1160 PCRE supports the use of named as well as numbered capturing parentheses. The
1161 names are just an additional way of identifying the parentheses, which still
1162 acquire numbers. Several convenience functions such as
1163 \fBpcre_get_named_substring()\fP are provided for extracting captured
1164 substrings by name. It is also possible to extract the data directly, by first
1165 converting the name to a number in order to access the correct pointers in the
1166 output vector (described with \fBpcre_exec()\fP below). To do the conversion,
1167 you need to use the name-to-number map, which is described by these three
1168 values.
1169 .P
1170 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
1171 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
1172 entry; both of these return an \fBint\fP value. The entry size depends on the
1173 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
1174 entry of the table (a pointer to \fBchar\fP). The first two bytes of each entry
1175 are the number of the capturing parenthesis, most significant byte first. The
1176 rest of the entry is the corresponding name, zero terminated.
1177 .P
1178 The names are in alphabetical order. Duplicate names may appear if (?| is used
1179 to create multiple groups with the same number, as described in the
1180 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
1181 .\" </a>
1182 section on duplicate subpattern numbers
1183 .\"
1184 in the
1185 .\" HREF
1186 \fBpcrepattern\fP
1187 .\"
1188 page. Duplicate names for subpatterns with different numbers are permitted only
1189 if PCRE_DUPNAMES is set. In all cases of duplicate names, they appear in the
1190 table in the order in which they were found in the pattern. In the absence of
1191 (?| this is the order of increasing number; when (?| is used this is not
1192 necessarily the case because later subpatterns may have lower numbers.
1193 .P
1194 As a simple example of the name/number table, consider the following pattern
1195 (assume PCRE_EXTENDED is set, so white space - including newlines - is
1196 ignored):
1197 .sp
1198 .\" JOIN
1199 (?<date> (?<year>(\ed\ed)?\ed\ed) -
1200 (?<month>\ed\ed) - (?<day>\ed\ed) )
1201 .sp
1202 There are four named subpatterns, so the table has four entries, and each entry
1203 in the table is eight bytes long. The table is as follows, with non-printing
1204 bytes shows in hexadecimal, and undefined bytes shown as ??:
1205 .sp
1206 00 01 d a t e 00 ??
1207 00 05 d a y 00 ?? ??
1208 00 04 m o n t h 00
1209 00 02 y e a r 00 ??
1210 .sp
1211 When writing code to extract data from named subpatterns using the
1212 name-to-number map, remember that the length of the entries is likely to be
1213 different for each compiled pattern.
1214 .sp
1215 PCRE_INFO_OKPARTIAL
1216 .sp
1217 Return 1 if the pattern can be used for partial matching with
1218 \fBpcre_exec()\fP, otherwise 0. The fourth argument should point to an
1219 \fBint\fP variable. From release 8.00, this always returns 1, because the
1220 restrictions that previously applied to partial matching have been lifted. The
1221 .\" HREF
1222 \fBpcrepartial\fP
1223 .\"
1224 documentation gives details of partial matching.
1225 .sp
1226 PCRE_INFO_OPTIONS
1227 .sp
1228 Return a copy of the options with which the pattern was compiled. The fourth
1229 argument should point to an \fBunsigned long int\fP variable. These option bits
1230 are those specified in the call to \fBpcre_compile()\fP, modified by any
1231 top-level option settings at the start of the pattern itself. In other words,
1232 they are the options that will be in force when matching starts. For example,
1233 if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
1234 result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.
1235 .P
1236 A pattern is automatically anchored by PCRE if all of its top-level
1237 alternatives begin with one of the following:
1238 .sp
1239 ^ unless PCRE_MULTILINE is set
1240 \eA always
1241 \eG always
1242 .\" JOIN
1243 .* if PCRE_DOTALL is set and there are no back
1244 references to the subpattern in which .* appears
1245 .sp
1246 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
1247 \fBpcre_fullinfo()\fP.
1248 .sp
1249 PCRE_INFO_SIZE
1250 .sp
1251 Return the size of the compiled pattern, that is, the value that was passed as
1252 the argument to \fBpcre_malloc()\fP when PCRE was getting memory in which to
1253 place the compiled data. The fourth argument should point to a \fBsize_t\fP
1254 variable.
1255 .sp
1256 PCRE_INFO_STUDYSIZE
1257 .sp
1258 Return the size of the data block pointed to by the \fIstudy_data\fP field in a
1259 \fBpcre_extra\fP block. If \fBpcre_extra\fP is NULL, or there is no study data,
1260 zero is returned. The fourth argument should point to a \fBsize_t\fP variable.
1261 The \fIstudy_data\fP field is set by \fBpcre_study()\fP to record information
1262 that will speed up matching (see the section entitled
1263 .\" HTML <a href="#studyingapattern">
1264 .\" </a>
1265 "Studying a pattern"
1266 .\"
1267 above). The format of the \fIstudy_data\fP block is private, but its length
1268 is made available via this option so that it can be saved and restored (see the
1269 .\" HREF
1270 \fBpcreprecompile\fP
1271 .\"
1272 documentation for details).
1273 .
1274 .
1275 .SH "OBSOLETE INFO FUNCTION"
1276 .rs
1277 .sp
1278 .B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
1279 .B *\fIfirstcharptr\fP);
1280 .PP
1281 The \fBpcre_info()\fP function is now obsolete because its interface is too
1282 restrictive to return all the available data about a compiled pattern. New
1283 programs should use \fBpcre_fullinfo()\fP instead. The yield of
1284 \fBpcre_info()\fP is the number of capturing subpatterns, or one of the
1285 following negative numbers:
1286 .sp
1287 PCRE_ERROR_NULL the argument \fIcode\fP was NULL
1288 PCRE_ERROR_BADMAGIC the "magic number" was not found
1289 .sp
1290 If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
1291 pattern was compiled is placed in the integer it points to (see
1292 PCRE_INFO_OPTIONS above).
1293 .P
1294 If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
1295 it is used to pass back information about the first character of any matched
1296 string (see PCRE_INFO_FIRSTBYTE above).
1297 .
1298 .
1299 .SH "REFERENCE COUNTS"
1300 .rs
1301 .sp
1302 .B int pcre_refcount(pcre *\fIcode\fP, int \fIadjust\fP);
1303 .PP
1304 The \fBpcre_refcount()\fP function is used to maintain a reference count in the
1305 data block that contains a compiled pattern. It is provided for the benefit of
1306 applications that operate in an object-oriented manner, where different parts
1307 of the application may be using the same compiled pattern, but you want to free
1308 the block when they are all done.
1309 .P
1310 When a pattern is compiled, the reference count field is initialized to zero.
1311 It is changed only by calling this function, whose action is to add the
1312 \fIadjust\fP value (which may be positive or negative) to it. The yield of the
1313 function is the new value. However, the value of the count is constrained to
1314 lie between 0 and 65535, inclusive. If the new value is outside these limits,
1315 it is forced to the appropriate limit value.
1316 .P
1317 Except when it is zero, the reference count is not correctly preserved if a
1318 pattern is compiled on one host and then transferred to a host whose byte-order
1319 is different. (This seems a highly unlikely scenario.)
1320 .
1321 .
1322 .SH "MATCHING A PATTERN: THE TRADITIONAL FUNCTION"
1323 .rs
1324 .sp
1325 .B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
1326 .ti +5n
1327 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
1328 .ti +5n
1329 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
1330 .P
1331 The function \fBpcre_exec()\fP is called to match a subject string against a
1332 compiled pattern, which is passed in the \fIcode\fP argument. If the
1333 pattern was studied, the result of the study should be passed in the
1334 \fIextra\fP argument. You can call \fBpcre_exec()\fP with the same \fIcode\fP
1335 and \fIextra\fP arguments as many times as you like, in order to match
1336 different subject strings with the same pattern.
1337 .P
1338 This function is the main matching facility of the library, and it operates in
1339 a Perl-like manner. For specialist use there is also an alternative matching
1340 function, which is described
1341 .\" HTML <a href="#dfamatch">
1342 .\" </a>
1343 below
1344 .\"
1345 in the section about the \fBpcre_dfa_exec()\fP function.
1346 .P
1347 In most applications, the pattern will have been compiled (and optionally
1348 studied) in the same process that calls \fBpcre_exec()\fP. However, it is
1349 possible to save compiled patterns and study data, and then use them later
1350 in different processes, possibly even on different hosts. For a discussion
1351 about this, see the
1352 .\" HREF
1353 \fBpcreprecompile\fP
1354 .\"
1355 documentation.
1356 .P
1357 Here is an example of a simple call to \fBpcre_exec()\fP:
1358 .sp
1359 int rc;
1360 int ovector[30];
1361 rc = pcre_exec(
1362 re, /* result of pcre_compile() */
1363 NULL, /* we didn't study the pattern */
1364 "some string", /* the subject string */
1365 11, /* the length of the subject string */
1366 0, /* start at offset 0 in the subject */
1367 0, /* default options */
1368 ovector, /* vector of integers for substring information */
1369 30); /* number of elements (NOT size in bytes) */
1370 .
1371 .
1372 .\" HTML <a name="extradata"></a>
1373 .SS "Extra data for \fBpcre_exec()\fR"
1374 .rs
1375 .sp
1376 If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
1377 data block. The \fBpcre_study()\fP function returns such a block (when it
1378 doesn't return NULL), but you can also create one for yourself, and pass
1379 additional information in it. The \fBpcre_extra\fP block contains the following
1380 fields (not necessarily in this order):
1381 .sp
1382 unsigned long int \fIflags\fP;
1383 void *\fIstudy_data\fP;
1384 void *\fIexecutable_jit\fP;
1385 unsigned long int \fImatch_limit\fP;
1386 unsigned long int \fImatch_limit_recursion\fP;
1387 void *\fIcallout_data\fP;
1388 const unsigned char *\fItables\fP;
1389 unsigned char **\fImark\fP;
1390 .sp
1391 The \fIflags\fP field is a bitmap that specifies which of the other fields
1392 are set. The flag bits are:
1393 .sp
1394 PCRE_EXTRA_STUDY_DATA
1395 PCRE_EXTRA_EXECUTABLE_JIT
1396 PCRE_EXTRA_MATCH_LIMIT
1397 PCRE_EXTRA_MATCH_LIMIT_RECURSION
1398 PCRE_EXTRA_CALLOUT_DATA
1399 PCRE_EXTRA_TABLES
1400 PCRE_EXTRA_MARK
1401 .sp
1402 Other flag bits should be set to zero. The \fIstudy_data\fP field and sometimes
1403 the \fIexecutable_jit\fP field are set in the \fBpcre_extra\fP block that is
1404 returned by \fBpcre_study()\fP, together with the appropriate flag bits. You
1405 should not set these yourself, but you may add to the block by setting the
1406 other fields and their corresponding flag bits.
1407 .P
1408 The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
1409 vast amount of resources when running patterns that are not going to match,
1410 but which have a very large number of possibilities in their search trees. The
1411 classic example is a pattern that uses nested unlimited repeats.
1412 .P
1413 Internally, \fBpcre_exec()\fP uses a function called \fBmatch()\fP, which it
1414 calls repeatedly (sometimes recursively). The limit set by \fImatch_limit\fP is
1415 imposed on the number of times this function is called during a match, which
1416 has the effect of limiting the amount of backtracking that can take place. For
1417 patterns that are not anchored, the count restarts from zero for each position
1418 in the subject string.
1419 .P
1420 When \fBpcre_exec()\fP is called with a pattern that was successfully studied
1421 with the PCRE_STUDY_JIT_COMPILE option, the way that the matching is executed
1422 is entirely different. However, there is still the possibility of runaway
1423 matching that goes on for a very long time, and so the \fImatch_limit\fP value
1424 is also used in this case (but in a different way) to limit how long the
1425 matching can continue.
1426 .P
1427 The default value for the limit can be set when PCRE is built; the default
1428 default is 10 million, which handles all but the most extreme cases. You can
1429 override the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP
1430 block in which \fImatch_limit\fP is set, and PCRE_EXTRA_MATCH_LIMIT is set in
1431 the \fIflags\fP field. If the limit is exceeded, \fBpcre_exec()\fP returns
1432 PCRE_ERROR_MATCHLIMIT.
1433 .P
1434 The \fImatch_limit_recursion\fP field is similar to \fImatch_limit\fP, but
1435 instead of limiting the total number of times that \fBmatch()\fP is called, it
1436 limits the depth of recursion. The recursion depth is a smaller number than the
1437 total number of calls, because not all calls to \fBmatch()\fP are recursive.
1438 This limit is of use only if it is set smaller than \fImatch_limit\fP.
1439 .P
1440 Limiting the recursion depth limits the amount of machine stack that can be
1441 used, or, when PCRE has been compiled to use memory on the heap instead of the
1442 stack, the amount of heap memory that can be used. This limit is not relevant,
1443 and is ignored, if the pattern was successfully studied with
1444 PCRE_STUDY_JIT_COMPILE.
1445 .P
1446 The default value for \fImatch_limit_recursion\fP can be set when PCRE is
1447 built; the default default is the same value as the default for
1448 \fImatch_limit\fP. You can override the default by suppling \fBpcre_exec()\fP
1449 with a \fBpcre_extra\fP block in which \fImatch_limit_recursion\fP is set, and
1450 PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the \fIflags\fP field. If the limit
1451 is exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_RECURSIONLIMIT.
1452 .P
1453 The \fIcallout_data\fP field is used in conjunction with the "callout" feature,
1454 and is described in the
1455 .\" HREF
1456 \fBpcrecallout\fP
1457 .\"
1458 documentation.
1459 .P
1460 The \fItables\fP field is used to pass a character tables pointer to
1461 \fBpcre_exec()\fP; this overrides the value that is stored with the compiled
1462 pattern. A non-NULL value is stored with the compiled pattern only if custom
1463 tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
1464 If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
1465 internal tables to be used. This facility is helpful when re-using patterns
1466 that have been saved after compiling with an external set of tables, because
1467 the external tables might be at a different address when \fBpcre_exec()\fP is
1468 called. See the
1469 .\" HREF
1470 \fBpcreprecompile\fP
1471 .\"
1472 documentation for a discussion of saving compiled patterns for later use.
1473 .P
1474 If PCRE_EXTRA_MARK is set in the \fIflags\fP field, the \fImark\fP field must
1475 be set to point to a \fBchar *\fP variable. If the pattern contains any
1476 backtracking control verbs such as (*MARK:NAME), and the execution ends up with
1477 a name to pass back, a pointer to the name string (zero terminated) is placed
1478 in the variable pointed to by the \fImark\fP field. The names are within the
1479 compiled pattern; if you wish to retain such a name you must copy it before
1480 freeing the memory of a compiled pattern. If there is no name to pass back, the
1481 variable pointed to by the \fImark\fP field set to NULL. For details of the
1482 backtracking control verbs, see the section entitled
1483 .\" HTML <a href="pcrepattern#backtrackcontrol">
1484 .\" </a>
1485 "Backtracking control"
1486 .\"
1487 in the
1488 .\" HREF
1489 \fBpcrepattern\fP
1490 .\"
1491 documentation.
1492 .
1493 .
1494 .\" HTML <a name="execoptions"></a>
1495 .SS "Option bits for \fBpcre_exec()\fP"
1496 .rs
1497 .sp
1498 The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
1499 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
1500 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
1501 PCRE_NO_START_OPTIMIZE, PCRE_NO_UTF8_CHECK, PCRE_PARTIAL_SOFT, and
1502 PCRE_PARTIAL_HARD.
1503 .P
1504 If the pattern was successfully studied with the PCRE_STUDY_JIT_COMPILE option,
1505 the only supported options for JIT execution are PCRE_NO_UTF8_CHECK,
1506 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, and PCRE_NOTEMPTY_ATSTART. Note in
1507 particular that partial matching is not supported. If an unsupported option is
1508 used, JIT execution is disabled and the normal interpretive code in
1509 \fBpcre_exec()\fP is run.
1510 .sp
1511 PCRE_ANCHORED
1512 .sp
1513 The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
1514 matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
1515 to be anchored by virtue of its contents, it cannot be made unachored at
1516 matching time.
1517 .sp
1518 PCRE_BSR_ANYCRLF
1519 PCRE_BSR_UNICODE
1520 .sp
1521 These options (which are mutually exclusive) control what the \eR escape
1522 sequence matches. The choice is either to match only CR, LF, or CRLF, or to
1523 match any Unicode newline sequence. These options override the choice that was
1524 made or defaulted when the pattern was compiled.
1525 .sp
1526 PCRE_NEWLINE_CR
1527 PCRE_NEWLINE_LF
1528 PCRE_NEWLINE_CRLF
1529 PCRE_NEWLINE_ANYCRLF
1530 PCRE_NEWLINE_ANY
1531 .sp
1532 These options override the newline definition that was chosen or defaulted when
1533 the pattern was compiled. For details, see the description of
1534 \fBpcre_compile()\fP above. During matching, the newline choice affects the
1535 behaviour of the dot, circumflex, and dollar metacharacters. It may also alter
1536 the way the match position is advanced after a match failure for an unanchored
1537 pattern.
1538 .P
1539 When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a
1540 match attempt for an unanchored pattern fails when the current position is at a
1541 CRLF sequence, and the pattern contains no explicit matches for CR or LF
1542 characters, the match position is advanced by two characters instead of one, in
1543 other words, to after the CRLF.
1544 .P
1545 The above rule is a compromise that makes the most common cases work as
1546 expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not
1547 set), it does not match the string "\er\enA" because, after failing at the
1548 start, it skips both the CR and the LF before retrying. However, the pattern
1549 [\er\en]A does match that string, because it contains an explicit CR or LF
1550 reference, and so advances only by one character after the first failure.
1551 .P
1552 An explicit match for CR of LF is either a literal appearance of one of those
1553 characters, or one of the \er or \en escape sequences. Implicit matches such as
1554 [^X] do not count, nor does \es (which includes CR and LF in the characters
1555 that it matches).
1556 .P
1557 Notwithstanding the above, anomalous effects may still occur when CRLF is a
1558 valid newline sequence and explicit \er or \en escapes appear in the pattern.
1559 .sp
1560 PCRE_NOTBOL
1561 .sp
1562 This option specifies that first character of the subject string is not the
1563 beginning of a line, so the circumflex metacharacter should not match before
1564 it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
1565 never to match. This option affects only the behaviour of the circumflex
1566 metacharacter. It does not affect \eA.
1567 .sp
1568 PCRE_NOTEOL
1569 .sp
1570 This option specifies that the end of the subject string is not the end of a
1571 line, so the dollar metacharacter should not match it nor (except in multiline
1572 mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
1573 compile time) causes dollar never to match. This option affects only the
1574 behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
1575 .sp
1576 PCRE_NOTEMPTY
1577 .sp
1578 An empty string is not considered to be a valid match if this option is set. If
1579 there are alternatives in the pattern, they are tried. If all the alternatives
1580 match the empty string, the entire match fails. For example, if the pattern
1581 .sp
1582 a?b?
1583 .sp
1584 is applied to a string not beginning with "a" or "b", it matches an empty
1585 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
1586 valid, so PCRE searches further into the string for occurrences of "a" or "b".
1587 .sp
1588 PCRE_NOTEMPTY_ATSTART
1589 .sp
1590 This is like PCRE_NOTEMPTY, except that an empty string match that is not at
1591 the start of the subject is permitted. If the pattern is anchored, such a match
1592 can occur only if the pattern contains \eK.
1593 .P
1594 Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
1595 does make a special case of a pattern match of the empty string within its
1596 \fBsplit()\fP function, and when using the /g modifier. It is possible to
1597 emulate Perl's behaviour after matching a null string by first trying the match
1598 again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
1599 if that fails, by advancing the starting offset (see below) and trying an
1600 ordinary match again. There is some code that demonstrates how to do this in
1601 the
1602 .\" HREF
1603 \fBpcredemo\fP
1604 .\"
1605 sample program. In the most general case, you have to check to see if the
1606 newline convention recognizes CRLF as a newline, and if so, and the current
1607 character is CR followed by LF, advance the starting offset by two characters
1608 instead of one.
1609 .sp
1610 PCRE_NO_START_OPTIMIZE
1611 .sp
1612 There are a number of optimizations that \fBpcre_exec()\fP uses at the start of
1613 a match, in order to speed up the process. For example, if it is known that an
1614 unanchored match must start with a specific character, it searches the subject
1615 for that character, and fails immediately if it cannot find it, without
1616 actually running the main matching function. This means that a special item
1617 such as (*COMMIT) at the start of a pattern is not considered until after a
1618 suitable starting point for the match has been found. When callouts or (*MARK)
1619 items are in use, these "start-up" optimizations can cause them to be skipped
1620 if the pattern is never actually used. The start-up optimizations are in effect
1621 a pre-scan of the subject that takes place before the pattern is run.
1622 .P
1623 The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly
1624 causing performance to suffer, but ensuring that in cases where the result is
1625 "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK)
1626 are considered at every possible starting position in the subject string. If
1627 PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching
1628 time.
1629 .P
1630 Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
1631 Consider the pattern
1632 .sp
1633 (*COMMIT)ABC
1634 .sp
1635 When this is compiled, PCRE records the fact that a match must start with the
1636 character "A". Suppose the subject string is "DEFABC". The start-up
1637 optimization scans along the subject, finds "A" and runs the first match
1638 attempt from there. The (*COMMIT) item means that the pattern must match the
1639 current starting position, which in this case, it does. However, if the same
1640 match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
1641 subject string does not happen. The first match attempt is run starting from
1642 "D" and when this fails, (*COMMIT) prevents any further matches being tried, so
1643 the overall result is "no match". If the pattern is studied, more start-up
1644 optimizations may be used. For example, a minimum length for the subject may be
1645 recorded. Consider the pattern
1646 .sp
1647 (*MARK:A)(X|Y)
1648 .sp
1649 The minimum length for a match is one character. If the subject is "ABC", there
1650 will be attempts to match "ABC", "BC", "C", and then finally an empty string.
1651 If the pattern is studied, the final attempt does not take place, because PCRE
1652 knows that the subject is too short, and so the (*MARK) is never encountered.
1653 In this case, studying the pattern does not affect the overall match result,
1654 which is still "no match", but it does affect the auxiliary information that is
1655 returned.
1656 .sp
1657 PCRE_NO_UTF8_CHECK
1658 .sp
1659 When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
1660 string is automatically checked when \fBpcre_exec()\fP is subsequently called.
1661 The value of \fIstartoffset\fP is also checked to ensure that it points to the
1662 start of a UTF-8 character. There is a discussion about the validity of UTF-8
1663 strings in the
1664 .\" HTML <a href="pcre.html#utf8strings">
1665 .\" </a>
1666 section on UTF-8 support
1667 .\"
1668 in the main
1669 .\" HREF
1670 \fBpcre\fP
1671 .\"
1672 page. If an invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fP returns
1673 the error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is
1674 a truncated UTF-8 character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
1675 both cases, information about the precise nature of the error may also be
1676 returned (see the descriptions of these errors in the section entitled \fIError
1677 return values from\fP \fBpcre_exec()\fP
1678 .\" HTML <a href="#errorlist">
1679 .\" </a>
1680 below).
1681 .\"
1682 If \fIstartoffset\fP contains a value that does not point to the start of a
1683 UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
1684 returned.
1685 .P
1686 If you already know that your subject is valid, and you want to skip these
1687 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
1688 calling \fBpcre_exec()\fP. You might want to do this for the second and
1689 subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
1690 all the matches in a single subject string. However, you should be sure that
1691 the value of \fIstartoffset\fP points to the start of a UTF-8 character (or the
1692 end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an
1693 invalid UTF-8 string as a subject or an invalid value of \fIstartoffset\fP is
1694 undefined. Your program may crash.
1695 .sp
1696 PCRE_PARTIAL_HARD
1697 PCRE_PARTIAL_SOFT
1698 .sp
1699 These options turn on the partial matching feature. For backwards
1700 compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match
1701 occurs if the end of the subject string is reached successfully, but there are
1702 not enough subject characters to complete the match. If this happens when
1703 PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by
1704 testing any remaining alternatives. Only if no complete match can be found is
1705 PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words,
1706 PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match,
1707 but only if no complete match can be found.
1708 .P
1709 If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a
1710 partial match is found, \fBpcre_exec()\fP immediately returns
1711 PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words,
1712 when PCRE_PARTIAL_HARD is set, a partial match is considered to be more
1713 important that an alternative complete match.
1714 .P
1715 In both cases, the portion of the string that was inspected when the partial
1716 match was found is set as the first matching string. There is a more detailed
1717 discussion of partial and multi-segment matching, with examples, in the
1718 .\" HREF
1719 \fBpcrepartial\fP
1720 .\"
1721 documentation.
1722 .
1723 .
1724 .SS "The string to be matched by \fBpcre_exec()\fP"
1725 .rs
1726 .sp
1727 The subject string is passed to \fBpcre_exec()\fP as a pointer in
1728 \fIsubject\fP, a length (in bytes) in \fIlength\fP, and a starting byte offset
1729 in \fIstartoffset\fP. If this is negative or greater than the length of the
1730 subject, \fBpcre_exec()\fP returns PCRE_ERROR_BADOFFSET. When the starting
1731 offset is zero, the search for a match starts at the beginning of the subject,
1732 and this is by far the most common case. In UTF-8 mode, the byte offset must
1733 point to the start of a UTF-8 character (or the end of the subject). Unlike the
1734 pattern string, the subject may contain binary zero bytes.
1735 .P
1736 A non-zero starting offset is useful when searching for another match in the
1737 same subject by calling \fBpcre_exec()\fP again after a previous success.
1738 Setting \fIstartoffset\fP differs from just passing over a shortened string and
1739 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
1740 lookbehind. For example, consider the pattern
1741 .sp
1742 \eBiss\eB
1743 .sp
1744 which finds occurrences of "iss" in the middle of words. (\eB matches only if
1745 the current position in the subject is not a word boundary.) When applied to
1746 the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
1747 occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
1748 subject, namely "issipi", it does not match, because \eB is always false at the
1749 start of the subject, which is deemed to be a word boundary. However, if
1750 \fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
1751 set to 4, it finds the second occurrence of "iss" because it is able to look
1752 behind the starting point to discover that it is preceded by a letter.
1753 .P
1754 Finding all the matches in a subject is tricky when the pattern can match an
1755 empty string. It is possible to emulate Perl's /g behaviour by first trying the
1756 match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
1757 PCRE_ANCHORED options, and then if that fails, advancing the starting offset
1758 and trying an ordinary match again. There is some code that demonstrates how to
1759 do this in the
1760 .\" HREF
1761 \fBpcredemo\fP
1762 .\"
1763 sample program. In the most general case, you have to check to see if the
1764 newline convention recognizes CRLF as a newline, and if so, and the current
1765 character is CR followed by LF, advance the starting offset by two characters
1766 instead of one.
1767 .P
1768 If a non-zero starting offset is passed when the pattern is anchored, one
1769 attempt to match at the given offset is made. This can only succeed if the
1770 pattern does not require the match to be at the start of the subject.
1771 .
1772 .
1773 .SS "How \fBpcre_exec()\fP returns captured substrings"
1774 .rs
1775 .sp
1776 In general, a pattern matches a certain portion of the subject, and in
1777 addition, further substrings from the subject may be picked out by parts of the
1778 pattern. Following the usage in Jeffrey Friedl's book, this is called
1779 "capturing" in what follows, and the phrase "capturing subpattern" is used for
1780 a fragment of a pattern that picks out a substring. PCRE supports several other
1781 kinds of parenthesized subpattern that do not cause substrings to be captured.
1782 .P
1783 Captured substrings are returned to the caller via a vector of integers whose
1784 address is passed in \fIovector\fP. The number of elements in the vector is
1785 passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP: this
1786 argument is NOT the size of \fIovector\fP in bytes.
1787 .P
1788 The first two-thirds of the vector is used to pass back captured substrings,
1789 each substring using a pair of integers. The remaining third of the vector is
1790 used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
1791 and is not available for passing back information. The number passed in
1792 \fIovecsize\fP should always be a multiple of three. If it is not, it is
1793 rounded down.
1794 .P
1795 When a match is successful, information about captured substrings is returned
1796 in pairs of integers, starting at the beginning of \fIovector\fP, and
1797 continuing up to two-thirds of its length at the most. The first element of
1798 each pair is set to the byte offset of the first character in a substring, and
1799 the second is set to the byte offset of the first character after the end of a
1800 substring. \fBNote\fP: these values are always byte offsets, even in UTF-8
1801 mode. They are not character counts.
1802 .P
1803 The first pair of integers, \fIovector[0]\fP and \fIovector[1]\fP, identify the
1804 portion of the subject string matched by the entire pattern. The next pair is
1805 used for the first capturing subpattern, and so on. The value returned by
1806 \fBpcre_exec()\fP is one more than the highest numbered pair that has been set.
1807 For example, if two substrings have been captured, the returned value is 3. If
1808 there are no capturing subpatterns, the return value from a successful match is
1809 1, indicating that just the first pair of offsets has been set.
1810 .P
1811 If a capturing subpattern is matched repeatedly, it is the last portion of the
1812 string that it matched that is returned.
1813 .P
1814 If the vector is too small to hold all the captured substring offsets, it is
1815 used as far as possible (up to two-thirds of its length), and the function
1816 returns a value of zero. If neither the actual string matched not any captured
1817 substrings are of interest, \fBpcre_exec()\fP may be called with \fIovector\fP
1818 passed as NULL and \fIovecsize\fP as zero. However, if the pattern contains
1819 back references and the \fIovector\fP is not big enough to remember the related
1820 substrings, PCRE has to get additional memory for use during matching. Thus it
1821 is usually advisable to supply an \fIovector\fP of reasonable size.
1822 .P
1823 There are some cases where zero is returned (indicating vector overflow) when
1824 in fact the vector is exactly the right size for the final match. For example,
1825 consider the pattern
1826 .sp
1827 (a)(?:(b)c|bd)
1828 .sp
1829 If a vector of 6 elements (allowing for only 1 captured substring) is given
1830 with subject string "abd", \fBpcre_exec()\fP will try to set the second
1831 captured string, thereby recording a vector overflow, before failing to match
1832 "c" and backing up to try the second alternative. The zero return, however,
1833 does correctly indicate that the maximum number of slots (namely 2) have been
1834 filled. In similar cases where there is temporary overflow, but the final
1835 number of used slots is actually less than the maximum, a non-zero value is
1836 returned.
1837 .P
1838 The \fBpcre_fullinfo()\fP function can be used to find out how many capturing
1839 subpatterns there are in a compiled pattern. The smallest size for
1840 \fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
1841 the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
1842 .P
1843 It is possible for capturing subpattern number \fIn+1\fP to match some part of
1844 the subject when subpattern \fIn\fP has not been used at all. For example, if
1845 the string "abc" is matched against the pattern (a|(z))(bc) the return from the
1846 function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this
1847 happens, both values in the offset pairs corresponding to unused subpatterns
1848 are set to -1.
1849 .P
1850 Offset values that correspond to unused subpatterns at the end of the
1851 expression are also set to -1. For example, if the string "abc" is matched
1852 against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The
1853 return from the function is 2, because the highest used capturing subpattern
1854 number is 1, and the offsets for for the second and third capturing subpatterns
1855 (assuming the vector is large enough, of course) are set to -1.
1856 .P
1857 \fBNote\fP: Elements in the first two-thirds of \fIovector\fP that do not
1858 correspond to capturing parentheses in the pattern are never changed. That is,
1859 if a pattern contains \fIn\fP capturing parentheses, no more than
1860 \fIovector[0]\fP to \fIovector[2n+1]\fP are set by \fBpcre_exec()\fP. The other
1861 elements (in the first two-thirds) retain whatever values they previously had.
1862 .P
1863 Some convenience functions are provided for extracting the captured substrings
1864 as separate strings. These are described below.
1865 .
1866 .
1867 .\" HTML <a name="errorlist"></a>
1868 .SS "Error return values from \fBpcre_exec()\fP"
1869 .rs
1870 .sp
1871 If \fBpcre_exec()\fP fails, it returns a negative number. The following are
1872 defined in the header file:
1873 .sp
1874 PCRE_ERROR_NOMATCH (-1)
1875 .sp
1876 The subject string did not match the pattern.
1877 .sp
1878 PCRE_ERROR_NULL (-2)
1879 .sp
1880 Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
1881 NULL and \fIovecsize\fP was not zero.
1882 .sp
1883 PCRE_ERROR_BADOPTION (-3)
1884 .sp
1885 An unrecognized bit was set in the \fIoptions\fP argument.
1886 .sp
1887 PCRE_ERROR_BADMAGIC (-4)
1888 .sp
1889 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
1890 the case when it is passed a junk pointer and to detect when a pattern that was
1891 compiled in an environment of one endianness is run in an environment with the
1892 other endianness. This is the error that PCRE gives when the magic number is
1893 not present.
1894 .sp
1895 PCRE_ERROR_UNKNOWN_OPCODE (-5)
1896 .sp
1897 While running the pattern match, an unknown item was encountered in the
1898 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
1899 of the compiled pattern.
1900 .sp
1901 PCRE_ERROR_NOMEMORY (-6)
1902 .sp
1903 If a pattern contains back references, but the \fIovector\fP that is passed to
1904 \fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
1905 gets a block of memory at the start of matching to use for this purpose. If the
1906 call via \fBpcre_malloc()\fP fails, this error is given. The memory is
1907 automatically freed at the end of matching.
1908 .P
1909 This error is also given if \fBpcre_stack_malloc()\fP fails in
1910 \fBpcre_exec()\fP. This can happen only when PCRE has been compiled with
1911 \fB--disable-stack-for-recursion\fP.
1912 .sp
1913 PCRE_ERROR_NOSUBSTRING (-7)
1914 .sp
1915 This error is used by the \fBpcre_copy_substring()\fP,
1916 \fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
1917 below). It is never returned by \fBpcre_exec()\fP.
1918 .sp
1919 PCRE_ERROR_MATCHLIMIT (-8)
1920 .sp
1921 The backtracking limit, as specified by the \fImatch_limit\fP field in a
1922 \fBpcre_extra\fP structure (or defaulted) was reached. See the description
1923 above.
1924 .sp
1925 PCRE_ERROR_CALLOUT (-9)
1926 .sp
1927 This error is never generated by \fBpcre_exec()\fP itself. It is provided for
1928 use by callout functions that want to yield a distinctive error code. See the
1929 .\" HREF
1930 \fBpcrecallout\fP
1931 .\"
1932 documentation for details.
1933 .sp
1934 PCRE_ERROR_BADUTF8 (-10)
1935 .sp
1936 A string that contains an invalid UTF-8 byte sequence was passed as a subject,
1937 and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
1938 (\fIovecsize\fP) is at least 2, the byte offset to the start of the the invalid
1939 UTF-8 character is placed in the first element, and a reason code is placed in
1940 the second element. The reason codes are listed in the
1941 .\" HTML <a href="#badutf8reasons">
1942 .\" </a>
1943 following section.
1944 .\"
1945 For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
1946 truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
1947 PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
1948 .sp
1949 PCRE_ERROR_BADUTF8_OFFSET (-11)
1950 .sp
1951 The UTF-8 byte sequence that was passed as a subject was checked and found to
1952 be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
1953 \fIstartoffset\fP did not point to the beginning of a UTF-8 character or the
1954 end of the subject.
1955 .sp
1956 PCRE_ERROR_PARTIAL (-12)
1957 .sp
1958 The subject string did not match, but it did match partially. See the
1959 .\" HREF
1960 \fBpcrepartial\fP
1961 .\"
1962 documentation for details of partial matching.
1963 .sp
1964 PCRE_ERROR_BADPARTIAL (-13)
1965 .sp
1966 This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
1967 option was used with a compiled pattern containing items that were not
1968 supported for partial matching. From release 8.00 onwards, there are no
1969 restrictions on partial matching.
1970 .sp
1971 PCRE_ERROR_INTERNAL (-14)
1972 .sp
1973 An unexpected internal error has occurred. This error could be caused by a bug
1974 in PCRE or by overwriting of the compiled pattern.
1975 .sp
1976 PCRE_ERROR_BADCOUNT (-15)
1977 .sp
1978 This error is given if the value of the \fIovecsize\fP argument is negative.
1979 .sp
1980 PCRE_ERROR_RECURSIONLIMIT (-21)
1981 .sp
1982 The internal recursion limit, as specified by the \fImatch_limit_recursion\fP
1983 field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
1984 description above.
1985 .sp
1986 PCRE_ERROR_BADNEWLINE (-23)
1987 .sp
1988 An invalid combination of PCRE_NEWLINE_\fIxxx\fP options was given.
1989 .sp
1990 PCRE_ERROR_BADOFFSET (-24)
1991 .sp
1992 The value of \fIstartoffset\fP was negative or greater than the length of the
1993 subject, that is, the value in \fIlength\fP.
1994 .sp
1995 PCRE_ERROR_SHORTUTF8 (-25)
1996 .sp
1997 This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
1998 ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
1999 Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
2000 fact sufficient to detect this case, but this special error code for
2001 PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
2002 retained for backwards compatibility.
2003 .sp
2004 PCRE_ERROR_RECURSELOOP (-26)
2005 .sp
2006 This error is returned when \fBpcre_exec()\fP detects a recursion loop within
2007 the pattern. Specifically, it means that either the whole pattern or a
2008 subpattern has been called recursively for the second time at the same position
2009 in the subject string. Some simple patterns that might do this are detected and
2010 faulted at compile time, but more complicated cases, in particular mutual
2011 recursions between two different subpatterns, cannot be detected until run
2012 time.
2013 .sp
2014 PCRE_ERROR_JIT_STACKLIMIT (-27)
2015 .sp
2016 This error is returned when a pattern that was successfully studied using the
2017 PCRE_STUDY_JIT_COMPILE option is being matched, but the memory available for
2018 the just-in-time processing stack is not large enough. See the
2019 .\" HREF
2020 \fBpcrejit\fP
2021 .\"
2022 documentation for more details.
2023 .P
2024 Error numbers -16 to -20 and -22 are not used by \fBpcre_exec()\fP.
2025 .
2026 .
2027 .\" HTML <a name="badutf8reasons"></a>
2028 .SS "Reason codes for invalid UTF-8 strings"
2029 .rs
2030 .sp
2031 When \fBpcre_exec()\fP returns either PCRE_ERROR_BADUTF8 or
2032 PCRE_ERROR_SHORTUTF8, and the size of the output vector (\fIovecsize\fP) is at
2033 least 2, the offset of the start of the invalid UTF-8 character is placed in
2034 the first output vector element (\fIovector[0]\fP) and a reason code is placed
2035 in the second element (\fIovector[1]\fP). The reason codes are given names in
2036 the \fBpcre.h\fP header file:
2037 .sp
2038 PCRE_UTF8_ERR1
2039 PCRE_UTF8_ERR2
2040 PCRE_UTF8_ERR3
2041 PCRE_UTF8_ERR4
2042 PCRE_UTF8_ERR5
2043 .sp
2044 The string ends with a truncated UTF-8 character; the code specifies how many
2045 bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be
2046 no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279)
2047 allows for up to 6 bytes, and this is checked first; hence the possibility of
2048 4 or 5 missing bytes.
2049 .sp
2050 PCRE_UTF8_ERR6
2051 PCRE_UTF8_ERR7
2052 PCRE_UTF8_ERR8
2053 PCRE_UTF8_ERR9
2054 PCRE_UTF8_ERR10
2055 .sp
2056 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the
2057 character do not have the binary value 0b10 (that is, either the most
2058 significant bit is 0, or the next bit is 1).
2059 .sp
2060 PCRE_UTF8_ERR11
2061 PCRE_UTF8_ERR12
2062 .sp
2063 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long;
2064 these code points are excluded by RFC 3629.
2065 .sp
2066 PCRE_UTF8_ERR13
2067 .sp
2068 A 4-byte character has a value greater than 0x10fff; these code points are
2069 excluded by RFC 3629.
2070 .sp
2071 PCRE_UTF8_ERR14
2072 .sp
2073 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of
2074 code points are reserved by RFC 3629 for use with UTF-16, and so are excluded
2075 from UTF-8.
2076 .sp
2077 PCRE_UTF8_ERR15
2078 PCRE_UTF8_ERR16
2079 PCRE_UTF8_ERR17
2080 PCRE_UTF8_ERR18
2081 PCRE_UTF8_ERR19
2082 .sp
2083 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a
2084 value that can be represented by fewer bytes, which is invalid. For example,
2085 the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just
2086 one byte.
2087 .sp
2088 PCRE_UTF8_ERR20
2089 .sp
2090 The two most significant bits of the first byte of a character have the binary
2091 value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a
2092 byte can only validly occur as the second or subsequent byte of a multi-byte
2093 character.
2094 .sp
2095 PCRE_UTF8_ERR21
2096 .sp
2097 The first byte of a character has the value 0xfe or 0xff. These values can
2098 never occur in a valid UTF-8 string.
2099 .
2100 .
2101 .SH "EXTRACTING CAPTURED SUBSTRINGS BY NUMBER"
2102 .rs
2103 .sp
2104 .B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2105 .ti +5n
2106 .B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
2107 .ti +5n
2108 .B int \fIbuffersize\fP);
2109 .PP
2110 .B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
2111 .ti +5n
2112 .B int \fIstringcount\fP, int \fIstringnumber\fP,
2113 .ti +5n
2114 .B const char **\fIstringptr\fP);
2115 .PP
2116 .B int pcre_get_substring_list(const char *\fIsubject\fP,
2117 .ti +5n
2118 .B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
2119 .PP
2120 Captured substrings can be accessed directly by using the offsets returned by
2121 \fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
2122 \fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
2123 \fBpcre_get_substring_list()\fP are provided for extracting captured substrings
2124 as new, separate, zero-terminated strings. These functions identify substrings
2125 by number. The next section describes functions for extracting named
2126 substrings.
2127 .P
2128 A substring that contains a binary zero is correctly extracted and has a
2129 further zero added on the end, but the result is not, of course, a C string.
2130 However, you can process such a string by referring to the length that is
2131 returned by \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP.
2132 Unfortunately, the interface to \fBpcre_get_substring_list()\fP is not adequate
2133 for handling strings containing binary zeros, because the end of the final
2134 string is not independently indicated.
2135 .P
2136 The first three arguments are the same for all three of these functions:
2137 \fIsubject\fP is the subject string that has just been successfully matched,
2138 \fIovector\fP is a pointer to the vector of integer offsets that was passed to
2139 \fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
2140 captured by the match, including the substring that matched the entire regular
2141 expression. This is the value returned by \fBpcre_exec()\fP if it is greater
2142 than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
2143 space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
2144 number of elements in the vector divided by three.
2145 .P
2146 The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
2147 extract a single substring, whose number is given as \fIstringnumber\fP. A
2148 value of zero extracts the substring that matched the entire pattern, whereas
2149 higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
2150 the string is placed in \fIbuffer\fP, whose length is given by
2151 \fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
2152 obtained via \fBpcre_malloc\fP, and its address is returned via
2153 \fIstringptr\fP. The yield of the function is the length of the string, not
2154 including the terminating zero, or one of these error codes:
2155 .sp
2156 PCRE_ERROR_NOMEMORY (-6)
2157 .sp
2158 The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
2159 memory failed for \fBpcre_get_substring()\fP.
2160 .sp
2161 PCRE_ERROR_NOSUBSTRING (-7)
2162 .sp
2163 There is no substring whose number is \fIstringnumber\fP.
2164 .P
2165 The \fBpcre_get_substring_list()\fP function extracts all available substrings
2166 and builds a list of pointers to them. All this is done in a single block of
2167 memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
2168 is returned via \fIlistptr\fP, which is also the start of the list of string
2169 pointers. The end of the list is marked by a NULL pointer. The yield of the
2170 function is zero if all went well, or the error code
2171 .sp
2172 PCRE_ERROR_NOMEMORY (-6)
2173 .sp
2174 if the attempt to get the memory block failed.
2175 .P
2176 When any of these functions encounter a substring that is unset, which can
2177 happen when capturing subpattern number \fIn+1\fP matches some part of the
2178 subject, but subpattern \fIn\fP has not been used at all, they return an empty
2179 string. This can be distinguished from a genuine zero-length substring by
2180 inspecting the appropriate offset in \fIovector\fP, which is negative for unset
2181 substrings.
2182 .P
2183 The two convenience functions \fBpcre_free_substring()\fP and
2184 \fBpcre_free_substring_list()\fP can be used to free the memory returned by
2185 a previous call of \fBpcre_get_substring()\fP or
2186 \fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
2187 the function pointed to by \fBpcre_free\fP, which of course could be called
2188 directly from a C program. However, PCRE is used in some situations where it is
2189 linked via a special interface to another programming language that cannot use
2190 \fBpcre_free\fP directly; it is for these cases that the functions are
2191 provided.
2192 .
2193 .
2194 .SH "EXTRACTING CAPTURED SUBSTRINGS BY NAME"
2195 .rs
2196 .sp
2197 .B int pcre_get_stringnumber(const pcre *\fIcode\fP,
2198 .ti +5n
2199 .B const char *\fIname\fP);
2200 .PP
2201 .B int pcre_copy_named_substring(const pcre *\fIcode\fP,
2202 .ti +5n
2203 .B const char *\fIsubject\fP, int *\fIovector\fP,
2204 .ti +5n
2205 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2206 .ti +5n
2207 .B char *\fIbuffer\fP, int \fIbuffersize\fP);
2208 .PP
2209 .B int pcre_get_named_substring(const pcre *\fIcode\fP,
2210 .ti +5n
2211 .B const char *\fIsubject\fP, int *\fIovector\fP,
2212 .ti +5n
2213 .B int \fIstringcount\fP, const char *\fIstringname\fP,
2214 .ti +5n
2215 .B const char **\fIstringptr\fP);
2216 .PP
2217 To extract a substring by name, you first have to find associated number.
2218 For example, for this pattern
2219 .sp
2220 (a+)b(?<xxx>\ed+)...
2221 .sp
2222 the number of the subpattern called "xxx" is 2. If the name is known to be
2223 unique (PCRE_DUPNAMES was not set), you can find the number from the name by
2224 calling \fBpcre_get_stringnumber()\fP. The first argument is the compiled
2225 pattern, and the second is the name. The yield of the function is the
2226 subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
2227 that name.
2228 .P
2229 Given the number, you can extract the substring directly, or use one of the
2230 functions described in the previous section. For convenience, there are also
2231 two functions that do the whole job.
2232 .P
2233 Most of the arguments of \fBpcre_copy_named_substring()\fP and
2234 \fBpcre_get_named_substring()\fP are the same as those for the similarly named
2235 functions that extract by number. As these are described in the previous
2236 section, they are not re-described here. There are just two differences:
2237 .P
2238 First, instead of a substring number, a substring name is given. Second, there
2239 is an extra argument, given at the start, which is a pointer to the compiled
2240 pattern. This is needed in order to gain access to the name-to-number
2241 translation table.
2242 .P
2243 These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
2244 then call \fBpcre_copy_substring()\fP or \fBpcre_get_substring()\fP, as
2245 appropriate. \fBNOTE:\fP If PCRE_DUPNAMES is set and there are duplicate names,
2246 the behaviour may not be what you want (see the next section).
2247 .P
2248 \fBWarning:\fP If the pattern uses the (?| feature to set up multiple
2249 subpatterns with the same number, as described in the
2250 .\" HTML <a href="pcrepattern.html#dupsubpatternnumber">
2251 .\" </a>
2252 section on duplicate subpattern numbers
2253 .\"
2254 in the
2255 .\" HREF
2256 \fBpcrepattern\fP
2257 .\"
2258 page, you cannot use names to distinguish the different subpatterns, because
2259 names are not included in the compiled code. The matching process uses only
2260 numbers. For this reason, the use of different names for subpatterns of the
2261 same number causes an error at compile time.
2262 .
2263 .
2264 .SH "DUPLICATE SUBPATTERN NAMES"
2265 .rs
2266 .sp
2267 .B int pcre_get_stringtable_entries(const pcre *\fIcode\fP,
2268 .ti +5n
2269 .B const char *\fIname\fP, char **\fIfirst\fP, char **\fIlast\fP);
2270 .PP
2271 When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns
2272 are not required to be unique. (Duplicate names are always allowed for
2273 subpatterns with the same number, created by using the (?| feature. Indeed, if
2274 such subpatterns are named, they are required to use the same names.)
2275 .P
2276 Normally, patterns with duplicate names are such that in any one match, only
2277 one of the named subpatterns participates. An example is shown in the
2278 .\" HREF
2279 \fBpcrepattern\fP
2280 .\"
2281 documentation.
2282 .P
2283 When duplicates are present, \fBpcre_copy_named_substring()\fP and
2284 \fBpcre_get_named_substring()\fP return the first substring corresponding to
2285 the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is
2286 returned; no data is returned. The \fBpcre_get_stringnumber()\fP function
2287 returns one of the numbers that are associated with the name, but it is not
2288 defined which it is.
2289 .P
2290 If you want to get full details of all captured substrings for a given name,
2291 you must use the \fBpcre_get_stringtable_entries()\fP function. The first
2292 argument is the compiled pattern, and the second is the name. The third and
2293 fourth are pointers to variables which are updated by the function. After it
2294 has run, they point to the first and last entries in the name-to-number table
2295 for the given name. The function itself returns the length of each entry, or
2296 PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
2297 described above in the section entitled \fIInformation about a pattern\fP
2298 .\" HTML <a href="#infoaboutpattern">
2299 .\" </a>
2300 above.
2301 .\"
2302 Given all the relevant entries for the name, you can extract each of their
2303 numbers, and hence the captured data, if any.
2304 .
2305 .
2306 .SH "FINDING ALL POSSIBLE MATCHES"
2307 .rs
2308 .sp
2309 The traditional matching function uses a similar algorithm to Perl, which stops
2310 when it finds the first match, starting at a given point in the subject. If you
2311 want to find all possible matches, or the longest possible match, consider
2312 using the alternative matching function (see below) instead. If you cannot use
2313 the alternative function, but still need to find all possible matches, you
2314 can kludge it up by making use of the callout facility, which is described in
2315 the
2316 .\" HREF
2317 \fBpcrecallout\fP
2318 .\"
2319 documentation.
2320 .P
2321 What you have to do is to insert a callout right at the end of the pattern.
2322 When your callout function is called, extract and save the current matched
2323 substring. Then return 1, which forces \fBpcre_exec()\fP to backtrack and try
2324 other alternatives. Ultimately, when it runs out of matches, \fBpcre_exec()\fP
2325 will yield PCRE_ERROR_NOMATCH.
2326 .
2327 .
2328 .\" HTML <a name="dfamatch"></a>
2329 .SH "MATCHING A PATTERN: THE ALTERNATIVE FUNCTION"
2330 .rs
2331 .sp
2332 .B int pcre_dfa_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
2333 .ti +5n
2334 .B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
2335 .ti +5n
2336 .B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP,
2337 .ti +5n
2338 .B int *\fIworkspace\fP, int \fIwscount\fP);
2339 .P
2340 The function \fBpcre_dfa_exec()\fP is called to match a subject string against
2341 a compiled pattern, using a matching algorithm that scans the subject string
2342 just once, and does not backtrack. This has different characteristics to the
2343 normal algorithm, and is not compatible with Perl. Some of the features of PCRE
2344 patterns are not supported. Nevertheless, there are times when this kind of
2345 matching can be useful. For a discussion of the two matching algorithms, and a
2346 list of features that \fBpcre_dfa_exec()\fP does not support, see the
2347 .\" HREF
2348 \fBpcrematching\fP
2349 .\"
2350 documentation.
2351 .P
2352 The arguments for the \fBpcre_dfa_exec()\fP function are the same as for
2353 \fBpcre_exec()\fP, plus two extras. The \fIovector\fP argument is used in a
2354 different way, and this is described below. The other common arguments are used
2355 in the same way as for \fBpcre_exec()\fP, so their description is not repeated
2356 here.
2357 .P
2358 The two additional arguments provide workspace for the function. The workspace
2359 vector should contain at least 20 elements. It is used for keeping track of
2360 multiple paths through the pattern tree. More workspace will be needed for
2361 patterns and subjects where there are a lot of potential matches.
2362 .P
2363 Here is an example of a simple call to \fBpcre_dfa_exec()\fP:
2364 .sp
2365 int rc;
2366 int ovector[10];
2367 int wspace[20];
2368 rc = pcre_dfa_exec(
2369 re, /* result of pcre_compile() */
2370 NULL, /* we didn't study the pattern */
2371 "some string", /* the subject string */
2372 11, /* the length of the subject string */
2373 0, /* start at offset 0 in the subject */
2374 0, /* default options */
2375 ovector, /* vector of integers for substring information */
2376 10, /* number of elements (NOT size in bytes) */
2377 wspace, /* working space vector */
2378 20); /* number of elements (NOT size in bytes) */
2379 .
2380 .SS "Option bits for \fBpcre_dfa_exec()\fP"
2381 .rs
2382 .sp
2383 The unused bits of the \fIoptions\fP argument for \fBpcre_dfa_exec()\fP must be
2384 zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NEWLINE_\fIxxx\fP,
2385 PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART,
2386 PCRE_NO_UTF8_CHECK, PCRE_BSR_ANYCRLF, PCRE_BSR_UNICODE, PCRE_NO_START_OPTIMIZE,
2387 PCRE_PARTIAL_HARD, PCRE_PARTIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.
2388 All but the last four of these are exactly the same as for \fBpcre_exec()\fP,
2389 so their description is not repeated here.
2390 .sp
2391 PCRE_PARTIAL_HARD
2392 PCRE_PARTIAL_SOFT
2393 .sp
2394 These have the same general effect as they do for \fBpcre_exec()\fP, but the
2395 details are slightly different. When PCRE_PARTIAL_HARD is set for
2396 \fBpcre_dfa_exec()\fP, it returns PCRE_ERROR_PARTIAL if the end of the subject
2397 is reached and there is still at least one matching possibility that requires
2398 additional characters. This happens even if some complete matches have also
2399 been found. When PCRE_PARTIAL_SOFT is set, the return code PCRE_ERROR_NOMATCH
2400 is converted into PCRE_ERROR_PARTIAL if the end of the subject is reached,
2401 there have been no complete matches, but there is still at least one matching
2402 possibility. The portion of the string that was inspected when the longest
2403 partial match was found is set as the first matching string in both cases.
2404 There is a more detailed discussion of partial and multi-segment matching, with
2405 examples, in the
2406 .\" HREF
2407 \fBpcrepartial\fP
2408 .\"
2409 documentation.
2410 .sp
2411 PCRE_DFA_SHORTEST
2412 .sp
2413 Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as
2414 soon as it has found one match. Because of the way the alternative algorithm
2415 works, this is necessarily the shortest possible match at the first possible
2416 matching point in the subject string.
2417 .sp
2418 PCRE_DFA_RESTART
2419 .sp
2420 When \fBpcre_dfa_exec()\fP returns a partial match, it is possible to call it
2421 again, with additional subject characters, and have it continue with the same
2422 match. The PCRE_DFA_RESTART option requests this action; when it is set, the
2423 \fIworkspace\fP and \fIwscount\fP options must reference the same vector as
2424 before because data about the match so far is left in them after a partial
2425 match. There is more discussion of this facility in the
2426 .\" HREF
2427 \fBpcrepartial\fP
2428 .\"
2429 documentation.
2430 .
2431 .
2432 .SS "Successful returns from \fBpcre_dfa_exec()\fP"
2433 .rs
2434 .sp
2435 When \fBpcre_dfa_exec()\fP succeeds, it may have matched more than one
2436 substring in the subject. Note, however, that all the matches from one run of
2437 the function start at the same point in the subject. The shorter matches are
2438 all initial substrings of the longer matches. For example, if the pattern
2439 .sp
2440 <.*>
2441 .sp
2442 is matched against the string
2443 .sp
2444 This is <something> <something else> <something further> no more
2445 .sp
2446 the three matched strings are
2447 .sp
2448 <something>
2449 <something> <something else>
2450 <something> <something else> <something further>
2451 .sp
2452 On success, the yield of the function is a number greater than zero, which is
2453 the number of matched substrings. The substrings themselves are returned in
2454 \fIovector\fP. Each string uses two elements; the first is the offset to the
2455 start, and the second is the offset to the end. In fact, all the strings have
2456 the same start offset. (Space could have been saved by giving this only once,
2457 but it was decided to retain some compatibility with the way \fBpcre_exec()\fP
2458 returns data, even though the meaning of the strings is different.)
2459 .P
2460 The strings are returned in reverse order of length; that is, the longest
2461 matching string is given first. If there were too many matches to fit into
2462 \fIovector\fP, the yield of the function is zero, and the vector is filled with
2463 the longest matches. Unlike \fBpcre_exec()\fP, \fBpcre_dfa_exec()\fP can use
2464 the entire \fIovector\fP for returning matched strings.
2465 .
2466 .
2467 .SS "Error returns from \fBpcre_dfa_exec()\fP"
2468 .rs
2469 .sp
2470 The \fBpcre_dfa_exec()\fP function returns a negative number when it fails.
2471 Many of the errors are the same as for \fBpcre_exec()\fP, and these are
2472 described
2473 .\" HTML <a href="#errorlist">
2474 .\" </a>
2475 above.
2476 .\"
2477 There are in addition the following errors that are specific to
2478 \fBpcre_dfa_exec()\fP:
2479 .sp
2480 PCRE_ERROR_DFA_UITEM (-16)
2481 .sp
2482 This return is given if \fBpcre_dfa_exec()\fP encounters an item in the pattern
2483 that it does not support, for instance, the use of \eC or a back reference.
2484 .sp
2485 PCRE_ERROR_DFA_UCOND (-17)
2486 .sp
2487 This return is given if \fBpcre_dfa_exec()\fP encounters a condition item that
2488 uses a back reference for the condition, or a test for recursion in a specific
2489 group. These are not supported.
2490 .sp
2491 PCRE_ERROR_DFA_UMLIMIT (-18)
2492 .sp
2493 This return is given if \fBpcre_dfa_exec()\fP is called with an \fIextra\fP
2494 block that contains a setting of the \fImatch_limit\fP or
2495 \fImatch_limit_recursion\fP fields. This is not supported (these fields are
2496 meaningless for DFA matching).
2497 .sp
2498 PCRE_ERROR_DFA_WSSIZE (-19)
2499 .sp
2500 This return is given if \fBpcre_dfa_exec()\fP runs out of space in the
2501 \fIworkspace\fP vector.
2502 .sp
2503 PCRE_ERROR_DFA_RECURSE (-20)
2504 .sp
2505 When a recursive subpattern is processed, the matching function calls itself
2506 recursively, using private vectors for \fIovector\fP and \fIworkspace\fP. This
2507 error is given if the output vector is not large enough. This should be
2508 extremely rare, as a vector of size 1000 is used.
2509 .
2510 .
2511 .SH "SEE ALSO"
2512 .rs
2513 .sp
2514 \fBpcrebuild\fP(3), \fBpcrecallout\fP(3), \fBpcrecpp(3)\fP(3),
2515 \fBpcrematching\fP(3), \fBpcrepartial\fP(3), \fBpcreposix\fP(3),
2516 \fBpcreprecompile\fP(3), \fBpcresample\fP(3), \fBpcrestack\fP(3).
2517 .
2518 .
2519 .SH AUTHOR
2520 .rs
2521 .sp
2522 .nf
2523 Philip Hazel
2524 University Computing Service
2525 Cambridge CB2 3QH, England.
2526 .fi
2527 .
2528 .
2529 .SH REVISION
2530 .rs
2531 .sp
2532 .nf
2533 Last updated: 23 September 2011
2534 Copyright (c) 1997-2011 University of Cambridge.
2535 .fi

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