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

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