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1 .TH PCRE 3
2 .SH NAME
3 PCRE - Perl-compatible regular expressions
4 .SH SYNOPSIS OF PCRE API
5 .rs
6 .sp
7 .B #include <pcre.h>
8 .PP
9 .SM
10 .br
11 .B pcre *pcre_compile(const char *\fIpattern\fR, int \fIoptions\fR,
12 .ti +5n
13 .B const char **\fIerrptr\fR, int *\fIerroffset\fR,
14 .ti +5n
15 .B const unsigned char *\fItableptr\fR);
16 .PP
17 .br
18 .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
19 .ti +5n
20 .B const char **\fIerrptr\fR);
21 .PP
22 .br
23 .B int pcre_exec(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
24 .ti +5n
25 .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIstartoffset\fR,
26 .ti +5n
27 .B int \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
28 .PP
29 .br
30 .B int pcre_copy_named_substring(const pcre *\fIcode\fR,
31 .ti +5n
32 .B const char *\fIsubject\fR, int *\fIovector\fR,
33 .ti +5n
34 .B int \fIstringcount\fR, const char *\fIstringname\fR,
35 .ti +5n
36 .B char *\fIbuffer\fR, int \fIbuffersize\fR);
37 .PP
38 .br
39 .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
40 .ti +5n
41 .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
42 .ti +5n
43 .B int \fIbuffersize\fR);
44 .PP
45 .br
46 .B int pcre_get_named_substring(const pcre *\fIcode\fR,
47 .ti +5n
48 .B const char *\fIsubject\fR, int *\fIovector\fR,
49 .ti +5n
50 .B int \fIstringcount\fR, const char *\fIstringname\fR,
51 .ti +5n
52 .B const char **\fIstringptr\fR);
53 .PP
54 .br
55 .B int pcre_get_stringnumber(const pcre *\fIcode\fR,
56 .ti +5n
57 .B const char *\fIname\fR);
58 .PP
59 .br
60 .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
61 .ti +5n
62 .B int \fIstringcount\fR, int \fIstringnumber\fR,
63 .ti +5n
64 .B const char **\fIstringptr\fR);
65 .PP
66 .br
67 .B int pcre_get_substring_list(const char *\fIsubject\fR,
68 .ti +5n
69 .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
70 .PP
71 .br
72 .B void pcre_free_substring(const char *\fIstringptr\fR);
73 .PP
74 .br
75 .B void pcre_free_substring_list(const char **\fIstringptr\fR);
76 .PP
77 .br
78 .B const unsigned char *pcre_maketables(void);
79 .PP
80 .br
81 .B int pcre_fullinfo(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
82 .ti +5n
83 .B int \fIwhat\fR, void *\fIwhere\fR);
84 .PP
85 .br
86 .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
87 .B *\fIfirstcharptr\fR);
88 .PP
89 .br
90 .B int pcre_config(int \fIwhat\fR, void *\fIwhere\fR);
91 .PP
92 .br
93 .B char *pcre_version(void);
94 .PP
95 .br
96 .B void *(*pcre_malloc)(size_t);
97 .PP
98 .br
99 .B void (*pcre_free)(void *);
100 .PP
101 .br
102 .B void *(*pcre_stack_malloc)(size_t);
103 .PP
104 .br
105 .B void (*pcre_stack_free)(void *);
106 .PP
107 .br
108 .B int (*pcre_callout)(pcre_callout_block *);
109
110 .SH PCRE API
111 .rs
112 .sp
113 PCRE has its own native API, which is described in this document. There is also
114 a set of wrapper functions that correspond to the POSIX regular expression API.
115 These are described in the \fBpcreposix\fR documentation.
116
117 The native API function prototypes are defined in the header file \fBpcre.h\fR,
118 and on Unix systems the library itself is called \fBlibpcre.a\fR, so can be
119 accessed by adding \fB-lpcre\fR to the command for linking an application which
120 calls it. The header file defines the macros PCRE_MAJOR and PCRE_MINOR to
121 contain the major and minor release numbers for the library. Applications can
122 use these to include support for different releases.
123
124 The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR
125 are used for compiling and matching regular expressions. A sample program that
126 demonstrates the simplest way of using them is given in the file
127 \fIpcredemo.c\fR. The \fBpcresample\fR documentation describes how to run it.
128
129 There are convenience functions for extracting captured substrings from a
130 matched subject string. They are:
131
132 \fBpcre_copy_substring()\fR
133 \fBpcre_copy_named_substring()\fR
134 \fBpcre_get_substring()\fR
135 \fBpcre_get_named_substring()\fR
136 \fBpcre_get_substring_list()\fR
137
138 \fBpcre_free_substring()\fR and \fBpcre_free_substring_list()\fR are also
139 provided, to free the memory used for extracted strings.
140
141 The function \fBpcre_maketables()\fR is used (optionally) to build a set of
142 character tables in the current locale for passing to \fBpcre_compile()\fR.
143
144 The function \fBpcre_fullinfo()\fR is used to find out information about a
145 compiled pattern; \fBpcre_info()\fR is an obsolete version which returns only
146 some of the available information, but is retained for backwards compatibility.
147 The function \fBpcre_version()\fR returns a pointer to a string containing the
148 version of PCRE and its date of release.
149
150 The global variables \fBpcre_malloc\fR and \fBpcre_free\fR initially contain
151 the entry points of the standard \fBmalloc()\fR and \fBfree()\fR functions
152 respectively. PCRE calls the memory management functions via these variables,
153 so a calling program can replace them if it wishes to intercept the calls. This
154 should be done before calling any PCRE functions.
155
156 The global variables \fBpcre_stack_malloc\fR and \fBpcre_stack_free\fR are also
157 indirections to memory management functions. These special functions are used
158 only when PCRE is compiled to use the heap for remembering data, instead of
159 recursive function calls. This is a non-standard way of building PCRE, for use
160 in environments that have limited stacks. Because of the greater use of memory
161 management, it runs more slowly. Separate functions are provided so that
162 special-purpose external code can be used for this case. When used, these
163 functions are always called in a stack-like manner (last obtained, first
164 freed), and always for memory blocks of the same size.
165
166 The global variable \fBpcre_callout\fR initially contains NULL. It can be set
167 by the caller to a "callout" function, which PCRE will then call at specified
168 points during a matching operation. Details are given in the \fBpcrecallout\fR
169 documentation.
170
171 .SH MULTITHREADING
172 .rs
173 .sp
174 The PCRE functions can be used in multi-threading applications, with the
175 proviso that the memory management functions pointed to by \fBpcre_malloc\fR,
176 \fBpcre_free\fR, \fBpcre_stack_malloc\fR, and \fBpcre_stack_free\fR, and the
177 callout function pointed to by \fBpcre_callout\fR, are shared by all threads.
178
179 The compiled form of a regular expression is not altered during matching, so
180 the same compiled pattern can safely be used by several threads at once.
181
182 .SH CHECKING BUILD-TIME OPTIONS
183 .rs
184 .sp
185 .B int pcre_config(int \fIwhat\fR, void *\fIwhere\fR);
186 .PP
187 The function \fBpcre_config()\fR makes it possible for a PCRE client to
188 discover which optional features have been compiled into the PCRE library. The
189 .\" HREF
190 \fBpcrebuild\fR
191 .\"
192 documentation has more details about these optional features.
193
194 The first argument for \fBpcre_config()\fR is an integer, specifying which
195 information is required; the second argument is a pointer to a variable into
196 which the information is placed. The following information is available:
197
198 PCRE_CONFIG_UTF8
199
200 The output is an integer that is set to one if UTF-8 support is available;
201 otherwise it is set to zero.
202
203 PCRE_CONFIG_NEWLINE
204
205 The output is an integer that is set to the value of the code that is used for
206 the newline character. It is either linefeed (10) or carriage return (13), and
207 should normally be the standard character for your operating system.
208
209 PCRE_CONFIG_LINK_SIZE
210
211 The output is an integer that contains the number of bytes used for internal
212 linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
213 allow larger regular expressions to be compiled, at the expense of slower
214 matching. The default value of 2 is sufficient for all but the most massive
215 patterns, since it allows the compiled pattern to be up to 64K in size.
216
217 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
218
219 The output is an integer that contains the threshold above which the POSIX
220 interface uses \fBmalloc()\fR for output vectors. Further details are given in
221 the \fBpcreposix\fR documentation.
222
223 PCRE_CONFIG_MATCH_LIMIT
224
225 The output is an integer that gives the default limit for the number of
226 internal matching function calls in a \fBpcre_exec()\fR execution. Further
227 details are given with \fBpcre_exec()\fR below.
228
229 PCRE_CONFIG_STACKRECURSE
230
231 The output is an integer that is set to one if internal recursion is
232 implemented by recursive function calls that use the stack to remember their
233 state. This is the usual way that PCRE is compiled. The output is zero if PCRE
234 was compiled to use blocks of data on the heap instead of recursive function
235 calls. In this case, \fBpcre_stack_malloc\fR and \fBpcre_stack_free\fR are
236 called to manage memory blocks on the heap, thus avoiding the use of the stack.
237
238 .SH COMPILING A PATTERN
239 .rs
240 .sp
241 .B pcre *pcre_compile(const char *\fIpattern\fR, int \fIoptions\fR,
242 .ti +5n
243 .B const char **\fIerrptr\fR, int *\fIerroffset\fR,
244 .ti +5n
245 .B const unsigned char *\fItableptr\fR);
246 .PP
247
248 The function \fBpcre_compile()\fR is called to compile a pattern into an
249 internal form. The pattern is a C string terminated by a binary zero, and
250 is passed in the argument \fIpattern\fR. A pointer to a single block of memory
251 that is obtained via \fBpcre_malloc\fR is returned. This contains the compiled
252 code and related data. The \fBpcre\fR type is defined for the returned block;
253 this is a typedef for a structure whose contents are not externally defined. It
254 is up to the caller to free the memory when it is no longer required.
255
256 Although the compiled code of a PCRE regex is relocatable, that is, it does not
257 depend on memory location, the complete \fBpcre\fR data block is not
258 fully relocatable, because it contains a copy of the \fItableptr\fR argument,
259 which is an address (see below).
260
261 The \fIoptions\fR argument contains independent bits that affect the
262 compilation. It should be zero if no options are required. Some of the options,
263 in particular, those that are compatible with Perl, can also be set and unset
264 from within the pattern (see the detailed description of regular expressions
265 in the \fBpcrepattern\fR documentation). For these options, the contents of the
266 \fIoptions\fR argument specifies their initial settings at the start of
267 compilation and execution. The PCRE_ANCHORED option can be set at the time of
268 matching as well as at compile time.
269
270 If \fIerrptr\fR is NULL, \fBpcre_compile()\fR returns NULL immediately.
271 Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fR returns
272 NULL, and sets the variable pointed to by \fIerrptr\fR to point to a textual
273 error message. The offset from the start of the pattern to the character where
274 the error was discovered is placed in the variable pointed to by
275 \fIerroffset\fR, which must not be NULL. If it is, an immediate error is given.
276
277 If the final argument, \fItableptr\fR, is NULL, PCRE uses a default set of
278 character tables which are built when it is compiled, using the default C
279 locale. Otherwise, \fItableptr\fR must be the result of a call to
280 \fBpcre_maketables()\fR. See the section on locale support below.
281
282 This code fragment shows a typical straightforward call to \fBpcre_compile()\fR:
283
284 pcre *re;
285 const char *error;
286 int erroffset;
287 re = pcre_compile(
288 "^A.*Z", /* the pattern */
289 0, /* default options */
290 &error, /* for error message */
291 &erroffset, /* for error offset */
292 NULL); /* use default character tables */
293
294 The following option bits are defined:
295
296 PCRE_ANCHORED
297
298 If this bit is set, the pattern is forced to be "anchored", that is, it is
299 constrained to match only at the first matching point in the string which is
300 being searched (the "subject string"). This effect can also be achieved by
301 appropriate constructs in the pattern itself, which is the only way to do it in
302 Perl.
303
304 PCRE_CASELESS
305
306 If this bit is set, letters in the pattern match both upper and lower case
307 letters. It is equivalent to Perl's /i option, and it can be changed within a
308 pattern by a (?i) option setting.
309
310 PCRE_DOLLAR_ENDONLY
311
312 If this bit is set, a dollar metacharacter in the pattern matches only at the
313 end of the subject string. Without this option, a dollar also matches
314 immediately before the final character if it is a newline (but not before any
315 other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
316 set. There is no equivalent to this option in Perl, and no way to set it within
317 a pattern.
318
319 PCRE_DOTALL
320
321 If this bit is set, a dot metacharater in the pattern matches all characters,
322 including newlines. Without it, newlines are excluded. This option is
323 equivalent to Perl's /s option, and it can be changed within a pattern by a
324 (?s) option setting. A negative class such as [^a] always matches a newline
325 character, independent of the setting of this option.
326
327 PCRE_EXTENDED
328
329 If this bit is set, whitespace data characters in the pattern are totally
330 ignored except when escaped or inside a character class. Whitespace does not
331 include the VT character (code 11). In addition, characters between an
332 unescaped # outside a character class and the next newline character,
333 inclusive, are also ignored. This is equivalent to Perl's /x option, and it can
334 be changed within a pattern by a (?x) option setting.
335
336 This option makes it possible to include comments inside complicated patterns.
337 Note, however, that this applies only to data characters. Whitespace characters
338 may never appear within special character sequences in a pattern, for example
339 within the sequence (?( which introduces a conditional subpattern.
340
341 PCRE_EXTRA
342
343 This option was invented in order to turn on additional functionality of PCRE
344 that is incompatible with Perl, but it is currently of very little use. When
345 set, any backslash in a pattern that is followed by a letter that has no
346 special meaning causes an error, thus reserving these combinations for future
347 expansion. By default, as in Perl, a backslash followed by a letter with no
348 special meaning is treated as a literal. There are at present no other features
349 controlled by this option. It can also be set by a (?X) option setting within a
350 pattern.
351
352 PCRE_MULTILINE
353
354 By default, PCRE treats the subject string as consisting of a single "line" of
355 characters (even if it actually contains several newlines). The "start of line"
356 metacharacter (^) matches only at the start of the string, while the "end of
357 line" metacharacter ($) matches only at the end of the string, or before a
358 terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
359 Perl.
360
361 When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
362 match immediately following or immediately before any newline in the subject
363 string, respectively, as well as at the very start and end. This is equivalent
364 to Perl's /m option, and it can be changed within a pattern by a (?m) option
365 setting. If there are no "\\n" characters in a subject string, or no
366 occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
367
368 PCRE_NO_AUTO_CAPTURE
369
370 If this option is set, it disables the use of numbered capturing parentheses in
371 the pattern. Any opening parenthesis that is not followed by ? behaves as if it
372 were followed by ?: but named parentheses can still be used for capturing (and
373 they acquire numbers in the usual way). There is no equivalent of this option
374 in Perl.
375
376 PCRE_UNGREEDY
377
378 This option inverts the "greediness" of the quantifiers so that they are not
379 greedy by default, but become greedy if followed by "?". It is not compatible
380 with Perl. It can also be set by a (?U) option setting within the pattern.
381
382 PCRE_UTF8
383
384 This option causes PCRE to regard both the pattern and the subject as strings
385 of UTF-8 characters instead of single-byte character strings. However, it is
386 available only if PCRE has been built to include UTF-8 support. If not, the use
387 of this option provokes an error. Details of how this option changes the
388 behaviour of PCRE are given in the
389 .\" HTML <a href="pcre.html#utf8support">
390 .\" </a>
391 section on UTF-8 support
392 .\"
393 in the main
394 .\" HREF
395 \fBpcre\fR
396 .\"
397 page.
398
399 PCRE_NO_UTF8_CHECK
400
401 When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
402 automatically checked. If an invalid UTF-8 sequence of bytes is found,
403 \fBpcre_compile()\fR returns an error. If you already know that your pattern is
404 valid, and you want to skip this check for performance reasons, you can set the
405 PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
406 UTF-8 string as a pattern is undefined. It may cause your program to crash.
407 Note that there is a similar option for suppressing the checking of subject
408 strings passed to \fBpcre_exec()\fR.
409
410
411 .SH STUDYING A PATTERN
412 .rs
413 .sp
414 .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
415 .ti +5n
416 .B const char **\fIerrptr\fR);
417 .PP
418 When a pattern is going to be used several times, it is worth spending more
419 time analyzing it in order to speed up the time taken for matching. The
420 function \fBpcre_study()\fR takes a pointer to a compiled pattern as its first
421 argument. If studing the pattern produces additional information that will help
422 speed up matching, \fBpcre_study()\fR returns a pointer to a \fBpcre_extra\fR
423 block, in which the \fIstudy_data\fR field points to the results of the study.
424
425 The returned value from a \fBpcre_study()\fR can be passed directly to
426 \fBpcre_exec()\fR. However, the \fBpcre_extra\fR block also contains other
427 fields that can be set by the caller before the block is passed; these are
428 described below. If studying the pattern does not produce any additional
429 information, \fBpcre_study()\fR returns NULL. In that circumstance, if the
430 calling program wants to pass some of the other fields to \fBpcre_exec()\fR, it
431 must set up its own \fBpcre_extra\fR block.
432
433 The second argument contains option bits. At present, no options are defined
434 for \fBpcre_study()\fR, and this argument should always be zero.
435
436 The third argument for \fBpcre_study()\fR is a pointer for an error message. If
437 studying succeeds (even if no data is returned), the variable it points to is
438 set to NULL. Otherwise it points to a textual error message. You should
439 therefore test the error pointer for NULL after calling \fBpcre_study()\fR, to
440 be sure that it has run successfully.
441
442 This is a typical call to \fBpcre_study\fR():
443
444 pcre_extra *pe;
445 pe = pcre_study(
446 re, /* result of pcre_compile() */
447 0, /* no options exist */
448 &error); /* set to NULL or points to a message */
449
450 At present, studying a pattern is useful only for non-anchored patterns that do
451 not have a single fixed starting character. A bitmap of possible starting
452 characters is created.
453
454 .\" HTML <a name="localesupport"></a>
455 .SH LOCALE SUPPORT
456 .rs
457 .sp
458 PCRE handles caseless matching, and determines whether characters are letters,
459 digits, or whatever, by reference to a set of tables. When running in UTF-8
460 mode, this applies only to characters with codes less than 256. The library
461 contains a default set of tables that is created in the default C locale when
462 PCRE is compiled. This is used when the final argument of \fBpcre_compile()\fR
463 is NULL, and is sufficient for many applications.
464
465 An alternative set of tables can, however, be supplied. Such tables are built
466 by calling the \fBpcre_maketables()\fR function, which has no arguments, in the
467 relevant locale. The result can then be passed to \fBpcre_compile()\fR as often
468 as necessary. For example, to build and use tables that are appropriate for the
469 French locale (where accented characters with codes greater than 128 are
470 treated as letters), the following code could be used:
471
472 setlocale(LC_CTYPE, "fr");
473 tables = pcre_maketables();
474 re = pcre_compile(..., tables);
475
476 The tables are built in memory that is obtained via \fBpcre_malloc\fR. The
477 pointer that is passed to \fBpcre_compile\fR is saved with the compiled
478 pattern, and the same tables are used via this pointer by \fBpcre_study()\fR
479 and \fBpcre_exec()\fR. Thus, for any single pattern, compilation, studying and
480 matching all happen in the same locale, but different patterns can be compiled
481 in different locales. It is the caller's responsibility to ensure that the
482 memory containing the tables remains available for as long as it is needed.
483
484 .SH INFORMATION ABOUT A PATTERN
485 .rs
486 .sp
487 .B int pcre_fullinfo(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
488 .ti +5n
489 .B int \fIwhat\fR, void *\fIwhere\fR);
490 .PP
491 The \fBpcre_fullinfo()\fR function returns information about a compiled
492 pattern. It replaces the obsolete \fBpcre_info()\fR function, which is
493 nevertheless retained for backwards compability (and is documented below).
494
495 The first argument for \fBpcre_fullinfo()\fR is a pointer to the compiled
496 pattern. The second argument is the result of \fBpcre_study()\fR, or NULL if
497 the pattern was not studied. The third argument specifies which piece of
498 information is required, and the fourth argument is a pointer to a variable
499 to receive the data. The yield of the function is zero for success, or one of
500 the following negative numbers:
501
502 PCRE_ERROR_NULL the argument \fIcode\fR was NULL
503 the argument \fIwhere\fR was NULL
504 PCRE_ERROR_BADMAGIC the "magic number" was not found
505 PCRE_ERROR_BADOPTION the value of \fIwhat\fR was invalid
506
507 Here is a typical call of \fBpcre_fullinfo()\fR, to obtain the length of the
508 compiled pattern:
509
510 int rc;
511 unsigned long int length;
512 rc = pcre_fullinfo(
513 re, /* result of pcre_compile() */
514 pe, /* result of pcre_study(), or NULL */
515 PCRE_INFO_SIZE, /* what is required */
516 &length); /* where to put the data */
517
518 The possible values for the third argument are defined in \fBpcre.h\fR, and are
519 as follows:
520
521 PCRE_INFO_BACKREFMAX
522
523 Return the number of the highest back reference in the pattern. The fourth
524 argument should point to an \fBint\fR variable. Zero is returned if there are
525 no back references.
526
527 PCRE_INFO_CAPTURECOUNT
528
529 Return the number of capturing subpatterns in the pattern. The fourth argument
530 should point to an \fbint\fR variable.
531
532 PCRE_INFO_FIRSTBYTE
533
534 Return information about the first byte of any matched string, for a
535 non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
536 old name is still recognized for backwards compatibility.)
537
538 If there is a fixed first byte, e.g. from a pattern such as (cat|cow|coyote),
539 it is returned in the integer pointed to by \fIwhere\fR. Otherwise, if either
540
541 (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
542 starts with "^", or
543
544 (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
545 (if it were set, the pattern would be anchored),
546
547 -1 is returned, indicating that the pattern matches only at the start of a
548 subject string or after any newline within the string. Otherwise -2 is
549 returned. For anchored patterns, -2 is returned.
550
551 PCRE_INFO_FIRSTTABLE
552
553 If the pattern was studied, and this resulted in the construction of a 256-bit
554 table indicating a fixed set of bytes for the first byte in any matching
555 string, a pointer to the table is returned. Otherwise NULL is returned. The
556 fourth argument should point to an \fBunsigned char *\fR variable.
557
558 PCRE_INFO_LASTLITERAL
559
560 Return the value of the rightmost literal byte that must exist in any matched
561 string, other than at its start, if such a byte has been recorded. The fourth
562 argument should point to an \fBint\fR variable. If there is no such byte, -1 is
563 returned. For anchored patterns, a last literal byte is recorded only if it
564 follows something of variable length. For example, for the pattern
565 /^a\\d+z\\d+/ the returned value is "z", but for /^a\\dz\\d/ the returned value
566 is -1.
567
568 PCRE_INFO_NAMECOUNT
569 PCRE_INFO_NAMEENTRYSIZE
570 PCRE_INFO_NAMETABLE
571
572 PCRE supports the use of named as well as numbered capturing parentheses. The
573 names are just an additional way of identifying the parentheses, which still
574 acquire a number. A caller that wants to extract data from a named subpattern
575 must convert the name to a number in order to access the correct pointers in
576 the output vector (described with \fBpcre_exec()\fR below). In order to do
577 this, it must first use these three values to obtain the name-to-number mapping
578 table for the pattern.
579
580 The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
581 the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
582 entry; both of these return an \fBint\fR value. The entry size depends on the
583 length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
584 entry of the table (a pointer to \fBchar\fR). The first two bytes of each entry
585 are the number of the capturing parenthesis, most significant byte first. The
586 rest of the entry is the corresponding name, zero terminated. The names are in
587 alphabetical order. For example, consider the following pattern (assume
588 PCRE_EXTENDED is set, so white space - including newlines - is ignored):
589
590 (?P<date> (?P<year>(\\d\\d)?\\d\\d) -
591 (?P<month>\\d\\d) - (?P<day>\\d\\d) )
592
593 There are four named subpatterns, so the table has four entries, and each entry
594 in the table is eight bytes long. The table is as follows, with non-printing
595 bytes shows in hex, and undefined bytes shown as ??:
596
597 00 01 d a t e 00 ??
598 00 05 d a y 00 ?? ??
599 00 04 m o n t h 00
600 00 02 y e a r 00 ??
601
602 When writing code to extract data from named subpatterns, remember that the
603 length of each entry may be different for each compiled pattern.
604
605 PCRE_INFO_OPTIONS
606
607 Return a copy of the options with which the pattern was compiled. The fourth
608 argument should point to an \fBunsigned long int\fR variable. These option bits
609 are those specified in the call to \fBpcre_compile()\fR, modified by any
610 top-level option settings within the pattern itself.
611
612 A pattern is automatically anchored by PCRE if all of its top-level
613 alternatives begin with one of the following:
614
615 ^ unless PCRE_MULTILINE is set
616 \\A always
617 \\G always
618 .* if PCRE_DOTALL is set and there are no back
619 references to the subpattern in which .* appears
620
621 For such patterns, the PCRE_ANCHORED bit is set in the options returned by
622 \fBpcre_fullinfo()\fR.
623
624 PCRE_INFO_SIZE
625
626 Return the size of the compiled pattern, that is, the value that was passed as
627 the argument to \fBpcre_malloc()\fR when PCRE was getting memory in which to
628 place the compiled data. The fourth argument should point to a \fBsize_t\fR
629 variable.
630
631 PCRE_INFO_STUDYSIZE
632
633 Returns the size of the data block pointed to by the \fIstudy_data\fR field in
634 a \fBpcre_extra\fR block. That is, it is the value that was passed to
635 \fBpcre_malloc()\fR when PCRE was getting memory into which to place the data
636 created by \fBpcre_study()\fR. The fourth argument should point to a
637 \fBsize_t\fR variable.
638
639 .SH OBSOLETE INFO FUNCTION
640 .rs
641 .sp
642 .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
643 .B *\fIfirstcharptr\fR);
644 .PP
645 The \fBpcre_info()\fR function is now obsolete because its interface is too
646 restrictive to return all the available data about a compiled pattern. New
647 programs should use \fBpcre_fullinfo()\fR instead. The yield of
648 \fBpcre_info()\fR is the number of capturing subpatterns, or one of the
649 following negative numbers:
650
651 PCRE_ERROR_NULL the argument \fIcode\fR was NULL
652 PCRE_ERROR_BADMAGIC the "magic number" was not found
653
654 If the \fIoptptr\fR argument is not NULL, a copy of the options with which the
655 pattern was compiled is placed in the integer it points to (see
656 PCRE_INFO_OPTIONS above).
657
658 If the pattern is not anchored and the \fIfirstcharptr\fR argument is not NULL,
659 it is used to pass back information about the first character of any matched
660 string (see PCRE_INFO_FIRSTBYTE above).
661
662 .SH MATCHING A PATTERN
663 .rs
664 .sp
665 .B int pcre_exec(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
666 .ti +5n
667 .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIstartoffset\fR,
668 .ti +5n
669 .B int \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
670 .PP
671 The function \fBpcre_exec()\fR is called to match a subject string against a
672 pre-compiled pattern, which is passed in the \fIcode\fR argument. If the
673 pattern has been studied, the result of the study should be passed in the
674 \fIextra\fR argument.
675
676 Here is an example of a simple call to \fBpcre_exec()\fR:
677
678 int rc;
679 int ovector[30];
680 rc = pcre_exec(
681 re, /* result of pcre_compile() */
682 NULL, /* we didn't study the pattern */
683 "some string", /* the subject string */
684 11, /* the length of the subject string */
685 0, /* start at offset 0 in the subject */
686 0, /* default options */
687 ovector, /* vector for substring information */
688 30); /* number of elements in the vector */
689
690 If the \fIextra\fR argument is not NULL, it must point to a \fBpcre_extra\fR
691 data block. The \fBpcre_study()\fR function returns such a block (when it
692 doesn't return NULL), but you can also create one for yourself, and pass
693 additional information in it. The fields in the block are as follows:
694
695 unsigned long int \fIflags\fR;
696 void *\fIstudy_data\fR;
697 unsigned long int \fImatch_limit\fR;
698 void *\fIcallout_data\fR;
699
700 The \fIflags\fR field is a bitmap that specifies which of the other fields
701 are set. The flag bits are:
702
703 PCRE_EXTRA_STUDY_DATA
704 PCRE_EXTRA_MATCH_LIMIT
705 PCRE_EXTRA_CALLOUT_DATA
706
707 Other flag bits should be set to zero. The \fIstudy_data\fR field is set in the
708 \fBpcre_extra\fR block that is returned by \fBpcre_study()\fR, together with
709 the appropriate flag bit. You should not set this yourself, but you can add to
710 the block by setting the other fields.
711
712 The \fImatch_limit\fR field provides a means of preventing PCRE from using up a
713 vast amount of resources when running patterns that are not going to match,
714 but which have a very large number of possibilities in their search trees. The
715 classic example is the use of nested unlimited repeats. Internally, PCRE uses a
716 function called \fBmatch()\fR which it calls repeatedly (sometimes
717 recursively). The limit is imposed on the number of times this function is
718 called during a match, which has the effect of limiting the amount of recursion
719 and backtracking that can take place. For patterns that are not anchored, the
720 count starts from zero for each position in the subject string.
721
722 The default limit for the library can be set when PCRE is built; the default
723 default is 10 million, which handles all but the most extreme cases. You can
724 reduce the default by suppling \fBpcre_exec()\fR with a \fRpcre_extra\fR block
725 in which \fImatch_limit\fR is set to a smaller value, and
726 PCRE_EXTRA_MATCH_LIMIT is set in the \fIflags\fR field. If the limit is
727 exceeded, \fBpcre_exec()\fR returns PCRE_ERROR_MATCHLIMIT.
728
729 The \fIpcre_callout\fR field is used in conjunction with the "callout" feature,
730 which is described in the \fBpcrecallout\fR documentation.
731
732 The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose
733 unused bits must be zero. This limits \fBpcre_exec()\fR to matching at the
734 first matching position. However, if a pattern was compiled with PCRE_ANCHORED,
735 or turned out to be anchored by virtue of its contents, it cannot be made
736 unachored at matching time.
737
738 When PCRE_UTF8 was set at compile time, the validity of the subject as a UTF-8
739 string is automatically checked, and the value of \fIstartoffset\fR is also
740 checked to ensure that it points to the start of a UTF-8 character. If an
741 invalid UTF-8 sequence of bytes is found, \fBpcre_exec()\fR returns the error
742 PCRE_ERROR_BADUTF8. If \fIstartoffset\fR contains an invalid value,
743 PCRE_ERROR_BADUTF8_OFFSET is returned.
744
745 If you already know that your subject is valid, and you want to skip these
746 checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
747 calling \fBpcre_exec()\fR. You might want to do this for the second and
748 subsequent calls to \fBpcre_exec()\fR if you are making repeated calls to find
749 all the matches in a single subject string. However, you should be sure that
750 the value of \fIstartoffset\fR points to the start of a UTF-8 character. When
751 PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
752 subject, or a value of \fIstartoffset\fR that does not point to the start of a
753 UTF-8 character, is undefined. Your program may crash.
754
755 There are also three further options that can be set only at matching time:
756
757 PCRE_NOTBOL
758
759 The first character of the string is not the beginning of a line, so the
760 circumflex metacharacter should not match before it. Setting this without
761 PCRE_MULTILINE (at compile time) causes circumflex never to match.
762
763 PCRE_NOTEOL
764
765 The end of the string is not the end of a line, so the dollar metacharacter
766 should not match it nor (except in multiline mode) a newline immediately before
767 it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
768 to match.
769
770 PCRE_NOTEMPTY
771
772 An empty string is not considered to be a valid match if this option is set. If
773 there are alternatives in the pattern, they are tried. If all the alternatives
774 match the empty string, the entire match fails. For example, if the pattern
775
776 a?b?
777
778 is applied to a string not beginning with "a" or "b", it matches the empty
779 string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
780 valid, so PCRE searches further into the string for occurrences of "a" or "b".
781
782 Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
783 of a pattern match of the empty string within its \fBsplit()\fR function, and
784 when using the /g modifier. It is possible to emulate Perl's behaviour after
785 matching a null string by first trying the match again at the same offset with
786 PCRE_NOTEMPTY set, and then if that fails by advancing the starting offset (see
787 below) and trying an ordinary match again.
788
789 The subject string is passed to \fBpcre_exec()\fR as a pointer in
790 \fIsubject\fR, a length in \fIlength\fR, and a starting byte offset in
791 \fIstartoffset\fR. Unlike the pattern string, the subject may contain binary
792 zero bytes. When the starting offset is zero, the search for a match starts at
793 the beginning of the subject, and this is by far the most common case.
794
795 If the pattern was compiled with the PCRE_UTF8 option, the subject must be a
796 sequence of bytes that is a valid UTF-8 string, and the starting offset must
797 point to the beginning of a UTF-8 character. If an invalid UTF-8 string or
798 offset is passed, an error (either PCRE_ERROR_BADUTF8 or
799 PCRE_ERROR_BADUTF8_OFFSET) is returned, unless the option PCRE_NO_UTF8_CHECK is
800 set, in which case PCRE's behaviour is not defined.
801
802 A non-zero starting offset is useful when searching for another match in the
803 same subject by calling \fBpcre_exec()\fR again after a previous success.
804 Setting \fIstartoffset\fR differs from just passing over a shortened string and
805 setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
806 lookbehind. For example, consider the pattern
807
808 \\Biss\\B
809
810 which finds occurrences of "iss" in the middle of words. (\\B matches only if
811 the current position in the subject is not a word boundary.) When applied to
812 the string "Mississipi" the first call to \fBpcre_exec()\fR finds the first
813 occurrence. If \fBpcre_exec()\fR is called again with just the remainder of the
814 subject, namely "issipi", it does not match, because \\B is always false at the
815 start of the subject, which is deemed to be a word boundary. However, if
816 \fBpcre_exec()\fR is passed the entire string again, but with \fIstartoffset\fR
817 set to 4, it finds the second occurrence of "iss" because it is able to look
818 behind the starting point to discover that it is preceded by a letter.
819
820 If a non-zero starting offset is passed when the pattern is anchored, one
821 attempt to match at the given offset is tried. This can only succeed if the
822 pattern does not require the match to be at the start of the subject.
823
824 In general, a pattern matches a certain portion of the subject, and in
825 addition, further substrings from the subject may be picked out by parts of the
826 pattern. Following the usage in Jeffrey Friedl's book, this is called
827 "capturing" in what follows, and the phrase "capturing subpattern" is used for
828 a fragment of a pattern that picks out a substring. PCRE supports several other
829 kinds of parenthesized subpattern that do not cause substrings to be captured.
830
831 Captured substrings are returned to the caller via a vector of integer offsets
832 whose address is passed in \fIovector\fR. The number of elements in the vector
833 is passed in \fIovecsize\fR. The first two-thirds of the vector is used to pass
834 back captured substrings, each substring using a pair of integers. The
835 remaining third of the vector is used as workspace by \fBpcre_exec()\fR while
836 matching capturing subpatterns, and is not available for passing back
837 information. The length passed in \fIovecsize\fR should always be a multiple of
838 three. If it is not, it is rounded down.
839
840 When a match has been successful, information about captured substrings is
841 returned in pairs of integers, starting at the beginning of \fIovector\fR, and
842 continuing up to two-thirds of its length at the most. The first element of a
843 pair is set to the offset of the first character in a substring, and the second
844 is set to the offset of the first character after the end of a substring. The
845 first pair, \fIovector[0]\fR and \fIovector[1]\fR, identify the portion of the
846 subject string matched by the entire pattern. The next pair is used for the
847 first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fR
848 is the number of pairs that have been set. If there are no capturing
849 subpatterns, the return value from a successful match is 1, indicating that
850 just the first pair of offsets has been set.
851
852 Some convenience functions are provided for extracting the captured substrings
853 as separate strings. These are described in the following section.
854
855 It is possible for an capturing subpattern number \fIn+1\fR to match some
856 part of the subject when subpattern \fIn\fR has not been used at all. For
857 example, if the string "abc" is matched against the pattern (a|(z))(bc)
858 subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
859 values corresponding to the unused subpattern are set to -1.
860
861 If a capturing subpattern is matched repeatedly, it is the last portion of the
862 string that it matched that gets returned.
863
864 If the vector is too small to hold all the captured substrings, it is used as
865 far as possible (up to two-thirds of its length), and the function returns a
866 value of zero. In particular, if the substring offsets are not of interest,
867 \fBpcre_exec()\fR may be called with \fIovector\fR passed as NULL and
868 \fIovecsize\fR as zero. However, if the pattern contains back references and
869 the \fIovector\fR isn't big enough to remember the related substrings, PCRE has
870 to get additional memory for use during matching. Thus it is usually advisable
871 to supply an \fIovector\fR.
872
873 Note that \fBpcre_info()\fR can be used to find out how many capturing
874 subpatterns there are in a compiled pattern. The smallest size for
875 \fIovector\fR that will allow for \fIn\fR captured substrings, in addition to
876 the offsets of the substring matched by the whole pattern, is (\fIn\fR+1)*3.
877
878 If \fBpcre_exec()\fR fails, it returns a negative number. The following are
879 defined in the header file:
880
881 PCRE_ERROR_NOMATCH (-1)
882
883 The subject string did not match the pattern.
884
885 PCRE_ERROR_NULL (-2)
886
887 Either \fIcode\fR or \fIsubject\fR was passed as NULL, or \fIovector\fR was
888 NULL and \fIovecsize\fR was not zero.
889
890 PCRE_ERROR_BADOPTION (-3)
891
892 An unrecognized bit was set in the \fIoptions\fR argument.
893
894 PCRE_ERROR_BADMAGIC (-4)
895
896 PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
897 the case when it is passed a junk pointer. This is the error it gives when the
898 magic number isn't present.
899
900 PCRE_ERROR_UNKNOWN_NODE (-5)
901
902 While running the pattern match, an unknown item was encountered in the
903 compiled pattern. This error could be caused by a bug in PCRE or by overwriting
904 of the compiled pattern.
905
906 PCRE_ERROR_NOMEMORY (-6)
907
908 If a pattern contains back references, but the \fIovector\fR that is passed to
909 \fBpcre_exec()\fR is not big enough to remember the referenced substrings, PCRE
910 gets a block of memory at the start of matching to use for this purpose. If the
911 call via \fBpcre_malloc()\fR fails, this error is given. The memory is freed at
912 the end of matching.
913
914 PCRE_ERROR_NOSUBSTRING (-7)
915
916 This error is used by the \fBpcre_copy_substring()\fR,
917 \fBpcre_get_substring()\fR, and \fBpcre_get_substring_list()\fR functions (see
918 below). It is never returned by \fBpcre_exec()\fR.
919
920 PCRE_ERROR_MATCHLIMIT (-8)
921
922 The recursion and backtracking limit, as specified by the \fImatch_limit\fR
923 field in a \fBpcre_extra\fR structure (or defaulted) was reached. See the
924 description above.
925
926 PCRE_ERROR_CALLOUT (-9)
927
928 This error is never generated by \fBpcre_exec()\fR itself. It is provided for
929 use by callout functions that want to yield a distinctive error code. See the
930 \fBpcrecallout\fR documentation for details.
931
932 PCRE_ERROR_BADUTF8 (-10)
933
934 A string that contains an invalid UTF-8 byte sequence was passed as a subject.
935
936 PCRE_ERROR_BADUTF8_OFFSET (-11)
937
938 The UTF-8 byte sequence that was passed as a subject was valid, but the value
939 of \fIstartoffset\fR did not point to the beginning of a UTF-8 character.
940
941 .SH EXTRACTING CAPTURED SUBSTRINGS BY NUMBER
942 .rs
943 .sp
944 .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
945 .ti +5n
946 .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
947 .ti +5n
948 .B int \fIbuffersize\fR);
949 .PP
950 .br
951 .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
952 .ti +5n
953 .B int \fIstringcount\fR, int \fIstringnumber\fR,
954 .ti +5n
955 .B const char **\fIstringptr\fR);
956 .PP
957 .br
958 .B int pcre_get_substring_list(const char *\fIsubject\fR,
959 .ti +5n
960 .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
961 .PP
962 Captured substrings can be accessed directly by using the offsets returned by
963 \fBpcre_exec()\fR in \fIovector\fR. For convenience, the functions
964 \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
965 \fBpcre_get_substring_list()\fR are provided for extracting captured substrings
966 as new, separate, zero-terminated strings. These functions identify substrings
967 by number. The next section describes functions for extracting named
968 substrings. A substring that contains a binary zero is correctly extracted and
969 has a further zero added on the end, but the result is not, of course,
970 a C string.
971
972 The first three arguments are the same for all three of these functions:
973 \fIsubject\fR is the subject string which has just been successfully matched,
974 \fIovector\fR is a pointer to the vector of integer offsets that was passed to
975 \fBpcre_exec()\fR, and \fIstringcount\fR is the number of substrings that were
976 captured by the match, including the substring that matched the entire regular
977 expression. This is the value returned by \fBpcre_exec\fR if it is greater than
978 zero. If \fBpcre_exec()\fR returned zero, indicating that it ran out of space
979 in \fIovector\fR, the value passed as \fIstringcount\fR should be the size of
980 the vector divided by three.
981
982 The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR
983 extract a single substring, whose number is given as \fIstringnumber\fR. A
984 value of zero extracts the substring that matched the entire pattern, while
985 higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,
986 the string is placed in \fIbuffer\fR, whose length is given by
987 \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of memory is
988 obtained via \fBpcre_malloc\fR, and its address is returned via
989 \fIstringptr\fR. The yield of the function is the length of the string, not
990 including the terminating zero, or one of
991
992 PCRE_ERROR_NOMEMORY (-6)
993
994 The buffer was too small for \fBpcre_copy_substring()\fR, or the attempt to get
995 memory failed for \fBpcre_get_substring()\fR.
996
997 PCRE_ERROR_NOSUBSTRING (-7)
998
999 There is no substring whose number is \fIstringnumber\fR.
1000
1001 The \fBpcre_get_substring_list()\fR function extracts all available substrings
1002 and builds a list of pointers to them. All this is done in a single block of
1003 memory which is obtained via \fBpcre_malloc\fR. The address of the memory block
1004 is returned via \fIlistptr\fR, which is also the start of the list of string
1005 pointers. The end of the list is marked by a NULL pointer. The yield of the
1006 function is zero if all went well, or
1007
1008 PCRE_ERROR_NOMEMORY (-6)
1009
1010 if the attempt to get the memory block failed.
1011
1012 When any of these functions encounter a substring that is unset, which can
1013 happen when capturing subpattern number \fIn+1\fR matches some part of the
1014 subject, but subpattern \fIn\fR has not been used at all, they return an empty
1015 string. This can be distinguished from a genuine zero-length substring by
1016 inspecting the appropriate offset in \fIovector\fR, which is negative for unset
1017 substrings.
1018
1019 The two convenience functions \fBpcre_free_substring()\fR and
1020 \fBpcre_free_substring_list()\fR can be used to free the memory returned by
1021 a previous call of \fBpcre_get_substring()\fR or
1022 \fBpcre_get_substring_list()\fR, respectively. They do nothing more than call
1023 the function pointed to by \fBpcre_free\fR, which of course could be called
1024 directly from a C program. However, PCRE is used in some situations where it is
1025 linked via a special interface to another programming language which cannot use
1026 \fBpcre_free\fR directly; it is for these cases that the functions are
1027 provided.
1028
1029 .SH EXTRACTING CAPTURED SUBSTRINGS BY NAME
1030 .rs
1031 .sp
1032 .B int pcre_copy_named_substring(const pcre *\fIcode\fR,
1033 .ti +5n
1034 .B const char *\fIsubject\fR, int *\fIovector\fR,
1035 .ti +5n
1036 .B int \fIstringcount\fR, const char *\fIstringname\fR,
1037 .ti +5n
1038 .B char *\fIbuffer\fR, int \fIbuffersize\fR);
1039 .PP
1040 .br
1041 .B int pcre_get_stringnumber(const pcre *\fIcode\fR,
1042 .ti +5n
1043 .B const char *\fIname\fR);
1044 .PP
1045 .br
1046 .B int pcre_get_named_substring(const pcre *\fIcode\fR,
1047 .ti +5n
1048 .B const char *\fIsubject\fR, int *\fIovector\fR,
1049 .ti +5n
1050 .B int \fIstringcount\fR, const char *\fIstringname\fR,
1051 .ti +5n
1052 .B const char **\fIstringptr\fR);
1053 .PP
1054 To extract a substring by name, you first have to find associated number. This
1055 can be done by calling \fBpcre_get_stringnumber()\fR. The first argument is the
1056 compiled pattern, and the second is the name. For example, for this pattern
1057
1058 ab(?<xxx>\\d+)...
1059
1060 the number of the subpattern called "xxx" is 1. Given the number, you can then
1061 extract the substring directly, or use one of the functions described in the
1062 previous section. For convenience, there are also two functions that do the
1063 whole job.
1064
1065 Most of the arguments of \fIpcre_copy_named_substring()\fR and
1066 \fIpcre_get_named_substring()\fR are the same as those for the functions that
1067 extract by number, and so are not re-described here. There are just two
1068 differences.
1069
1070 First, instead of a substring number, a substring name is given. Second, there
1071 is an extra argument, given at the start, which is a pointer to the compiled
1072 pattern. This is needed in order to gain access to the name-to-number
1073 translation table.
1074
1075 These functions call \fBpcre_get_stringnumber()\fR, and if it succeeds, they
1076 then call \fIpcre_copy_substring()\fR or \fIpcre_get_substring()\fR, as
1077 appropriate.
1078
1079 .in 0
1080 Last updated: 09 December 2003
1081 .br
1082 Copyright (c) 1997-2003 University of Cambridge.

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