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1 nigel 63 .TH PCRE 3
2     .SH NAME
3     PCRE - Perl-compatible regular expressions
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 *);
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.
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.
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.
123     There are convenience functions for extracting captured substrings from a
124     matched subject string. They are:
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
132     \fBpcre_free_substring()\fR and \fBpcre_free_substring_list()\fR are also
133     provided, to free the memory used for extracted strings.
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.
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.
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.
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.
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.
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.
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.
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:
184     The output is an integer that is set to one if UTF-8 support is available;
185     otherwise it is set to zero.
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.
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.
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.
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.
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
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.
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).
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.
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.
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.
257     This code fragment shows a typical straightforward call to \fBpcre_compile()\fR:
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 */
269     The following option bits are defined:
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.
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.
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.
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.
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.
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.
316     PCRE_EXTRA
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.
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.
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.
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.
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.
357     PCRE_UTF8
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.
375     .rs
376     .sp
377     .B pcre_extra *pcre_study(const pcre *\fIcode\fR, int \fIoptions\fR,
378     .ti +5n
379     .B const char **\fIerrptr\fR);
380     .PP
381     When a pattern is going to be used several times, it is worth spending more
382     time analyzing it in order to speed up the time taken for matching. The
383     function \fBpcre_study()\fR takes a pointer to a compiled pattern as its first
384     argument. If studing the pattern produces additional information that will help
385     speed up matching, \fBpcre_study()\fR returns a pointer to a \fBpcre_extra\fR
386     block, in which the \fIstudy_data\fR field points to the results of the study.
388     The returned value from a \fBpcre_study()\fR can be passed directly to
389     \fBpcre_exec()\fR. However, the \fBpcre_extra\fR block also contains other
390     fields that can be set by the caller before the block is passed; these are
391     described below. If studying the pattern does not produce any additional
392     information, \fBpcre_study()\fR returns NULL. In that circumstance, if the
393     calling program wants to pass some of the other fields to \fBpcre_exec()\fR, it
394     must set up its own \fBpcre_extra\fR block.
396     The second argument contains option bits. At present, no options are defined
397     for \fBpcre_study()\fR, and this argument should always be zero.
399     The third argument for \fBpcre_study()\fR is a pointer for an error message. If
400     studying succeeds (even if no data is returned), the variable it points to is
401     set to NULL. Otherwise it points to a textual error message. You should
402     therefore test the error pointer for NULL after calling \fBpcre_study()\fR, to
403     be sure that it has run successfully.
405     This is a typical call to \fBpcre_study\fR():
407     pcre_extra *pe;
408     pe = pcre_study(
409     re, /* result of pcre_compile() */
410     0, /* no options exist */
411     &error); /* set to NULL or points to a message */
413     At present, studying a pattern is useful only for non-anchored patterns that do
414     not have a single fixed starting character. A bitmap of possible starting
415     characters is created.
417     .\" HTML <a name="localesupport"></a>
419     .rs
420     .sp
421     PCRE handles caseless matching, and determines whether characters are letters,
422     digits, or whatever, by reference to a set of tables. When running in UTF-8
423     mode, this applies only to characters with codes less than 256. The library
424     contains a default set of tables that is created in the default C locale when
425     PCRE is compiled. This is used when the final argument of \fBpcre_compile()\fR
426     is NULL, and is sufficient for many applications.
428     An alternative set of tables can, however, be supplied. Such tables are built
429     by calling the \fBpcre_maketables()\fR function, which has no arguments, in the
430     relevant locale. The result can then be passed to \fBpcre_compile()\fR as often
431     as necessary. For example, to build and use tables that are appropriate for the
432     French locale (where accented characters with codes greater than 128 are
433     treated as letters), the following code could be used:
435     setlocale(LC_CTYPE, "fr");
436     tables = pcre_maketables();
437     re = pcre_compile(..., tables);
439     The tables are built in memory that is obtained via \fBpcre_malloc\fR. The
440     pointer that is passed to \fBpcre_compile\fR is saved with the compiled
441     pattern, and the same tables are used via this pointer by \fBpcre_study()\fR
442     and \fBpcre_exec()\fR. Thus, for any single pattern, compilation, studying and
443     matching all happen in the same locale, but different patterns can be compiled
444     in different locales. It is the caller's responsibility to ensure that the
445     memory containing the tables remains available for as long as it is needed.
448     .rs
449     .sp
450     .B int pcre_fullinfo(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
451     .ti +5n
452     .B int \fIwhat\fR, void *\fIwhere\fR);
453     .PP
454     The \fBpcre_fullinfo()\fR function returns information about a compiled
455     pattern. It replaces the obsolete \fBpcre_info()\fR function, which is
456     nevertheless retained for backwards compability (and is documented below).
458     The first argument for \fBpcre_fullinfo()\fR is a pointer to the compiled
459     pattern. The second argument is the result of \fBpcre_study()\fR, or NULL if
460     the pattern was not studied. The third argument specifies which piece of
461     information is required, and the fourth argument is a pointer to a variable
462     to receive the data. The yield of the function is zero for success, or one of
463     the following negative numbers:
465     PCRE_ERROR_NULL the argument \fIcode\fR was NULL
466     the argument \fIwhere\fR was NULL
467     PCRE_ERROR_BADMAGIC the "magic number" was not found
468     PCRE_ERROR_BADOPTION the value of \fIwhat\fR was invalid
470     Here is a typical call of \fBpcre_fullinfo()\fR, to obtain the length of the
471     compiled pattern:
473     int rc;
474     unsigned long int length;
475     rc = pcre_fullinfo(
476     re, /* result of pcre_compile() */
477     pe, /* result of pcre_study(), or NULL */
478     PCRE_INFO_SIZE, /* what is required */
479     &length); /* where to put the data */
481     The possible values for the third argument are defined in \fBpcre.h\fR, and are
482     as follows:
486     Return the number of the highest back reference in the pattern. The fourth
487     argument should point to an \fBint\fR variable. Zero is returned if there are
488     no back references.
492     Return the number of capturing subpatterns in the pattern. The fourth argument
493     should point to an \fbint\fR variable.
497     Return information about the first byte of any matched string, for a
498     non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
499     old name is still recognized for backwards compatibility.)
501     If there is a fixed first byte, e.g. from a pattern such as (cat|cow|coyote),
502     it is returned in the integer pointed to by \fIwhere\fR. Otherwise, if either
504     (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
505     starts with "^", or
507     (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
508     (if it were set, the pattern would be anchored),
510     -1 is returned, indicating that the pattern matches only at the start of a
511     subject string or after any newline within the string. Otherwise -2 is
512     returned. For anchored patterns, -2 is returned.
516     If the pattern was studied, and this resulted in the construction of a 256-bit
517     table indicating a fixed set of bytes for the first byte in any matching
518     string, a pointer to the table is returned. Otherwise NULL is returned. The
519     fourth argument should point to an \fBunsigned char *\fR variable.
523     For a non-anchored pattern, return the value of the rightmost literal byte
524     which must exist in any matched string, other than at its start. The fourth
525     argument should point to an \fBint\fR variable. If there is no such byte, or if
526     the pattern is anchored, -1 is returned. For example, for the pattern
527     /a\\d+z\\d+/ the returned value is 'z'.
533     PCRE supports the use of named as well as numbered capturing parentheses. The
534     names are just an additional way of identifying the parentheses, which still
535     acquire a number. A caller that wants to extract data from a named subpattern
536     must convert the name to a number in order to access the correct pointers in
537     the output vector (described with \fBpcre_exec()\fR below). In order to do
538     this, it must first use these three values to obtain the name-to-number mapping
539     table for the pattern.
541     The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
542     the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
543     entry; both of these return an \fBint\fR value. The entry size depends on the
544     length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
545     entry of the table (a pointer to \fBchar\fR). The first two bytes of each entry
546     are the number of the capturing parenthesis, most significant byte first. The
547     rest of the entry is the corresponding name, zero terminated. The names are in
548     alphabetical order. For example, consider the following pattern (assume
549     PCRE_EXTENDED is set, so white space - including newlines - is ignored):
551     (?P<date> (?P<year>(\\d\\d)?\\d\\d) -
552     (?P<month>\\d\\d) - (?P<day>\\d\\d) )
554     There are four named subpatterns, so the table has four entries, and each entry
555     in the table is eight bytes long. The table is as follows, with non-printing
556     bytes shows in hex, and undefined bytes shown as ??:
558     00 01 d a t e 00 ??
559     00 05 d a y 00 ?? ??
560     00 04 m o n t h 00
561     00 02 y e a r 00 ??
563     When writing code to extract data from named subpatterns, remember that the
564     length of each entry may be different for each compiled pattern.
568     Return a copy of the options with which the pattern was compiled. The fourth
569     argument should point to an \fBunsigned long int\fR variable. These option bits
570     are those specified in the call to \fBpcre_compile()\fR, modified by any
571     top-level option settings within the pattern itself.
573     A pattern is automatically anchored by PCRE if all of its top-level
574     alternatives begin with one of the following:
576     ^ unless PCRE_MULTILINE is set
577     \\A always
578     \\G always
579     .* if PCRE_DOTALL is set and there are no back
580     references to the subpattern in which .* appears
582     For such patterns, the PCRE_ANCHORED bit is set in the options returned by
583     \fBpcre_fullinfo()\fR.
587     Return the size of the compiled pattern, that is, the value that was passed as
588     the argument to \fBpcre_malloc()\fR when PCRE was getting memory in which to
589     place the compiled data. The fourth argument should point to a \fBsize_t\fR
590     variable.
594     Returns the size of the data block pointed to by the \fIstudy_data\fR field in
595     a \fBpcre_extra\fR block. That is, it is the value that was passed to
596     \fBpcre_malloc()\fR when PCRE was getting memory into which to place the data
597     created by \fBpcre_study()\fR. The fourth argument should point to a
598     \fBsize_t\fR variable.
601     .rs
602     .sp
603     .B int pcre_info(const pcre *\fIcode\fR, int *\fIoptptr\fR, int
604     .B *\fIfirstcharptr\fR);
605     .PP
606     The \fBpcre_info()\fR function is now obsolete because its interface is too
607     restrictive to return all the available data about a compiled pattern. New
608     programs should use \fBpcre_fullinfo()\fR instead. The yield of
609     \fBpcre_info()\fR is the number of capturing subpatterns, or one of the
610     following negative numbers:
612     PCRE_ERROR_NULL the argument \fIcode\fR was NULL
613     PCRE_ERROR_BADMAGIC the "magic number" was not found
615     If the \fIoptptr\fR argument is not NULL, a copy of the options with which the
616     pattern was compiled is placed in the integer it points to (see
617     PCRE_INFO_OPTIONS above).
619     If the pattern is not anchored and the \fIfirstcharptr\fR argument is not NULL,
620     it is used to pass back information about the first character of any matched
621     string (see PCRE_INFO_FIRSTBYTE above).
624     .rs
625     .sp
626     .B int pcre_exec(const pcre *\fIcode\fR, "const pcre_extra *\fIextra\fR,"
627     .ti +5n
628     .B "const char *\fIsubject\fR," int \fIlength\fR, int \fIstartoffset\fR,
629     .ti +5n
630     .B int \fIoptions\fR, int *\fIovector\fR, int \fIovecsize\fR);
631     .PP
632     The function \fBpcre_exec()\fR is called to match a subject string against a
633     pre-compiled pattern, which is passed in the \fIcode\fR argument. If the
634     pattern has been studied, the result of the study should be passed in the
635     \fIextra\fR argument.
637     Here is an example of a simple call to \fBpcre_exec()\fR:
639     int rc;
640     int ovector[30];
641     rc = pcre_exec(
642     re, /* result of pcre_compile() */
643     NULL, /* we didn't study the pattern */
644     "some string", /* the subject string */
645     11, /* the length of the subject string */
646     0, /* start at offset 0 in the subject */
647     0, /* default options */
648     ovector, /* vector for substring information */
649     30); /* number of elements in the vector */
651     If the \fIextra\fR argument is not NULL, it must point to a \fBpcre_extra\fR
652     data block. The \fBpcre_study()\fR function returns such a block (when it
653     doesn't return NULL), but you can also create one for yourself, and pass
654     additional information in it. The fields in the block are as follows:
656     unsigned long int \fIflags\fR;
657     void *\fIstudy_data\fR;
658     unsigned long int \fImatch_limit\fR;
659     void *\fIcallout_data\fR;
661     The \fIflags\fR field is a bitmap that specifies which of the other fields
662     are set. The flag bits are:
668     Other flag bits should be set to zero. The \fIstudy_data\fR field is set in the
669     \fBpcre_extra\fR block that is returned by \fBpcre_study()\fR, together with
670     the appropriate flag bit. You should not set this yourself, but you can add to
671     the block by setting the other fields.
673     The \fImatch_limit\fR field provides a means of preventing PCRE from using up a
674     vast amount of resources when running patterns that are not going to match,
675     but which have a very large number of possibilities in their search trees. The
676     classic example is the use of nested unlimited repeats. Internally, PCRE uses a
677     function called \fBmatch()\fR which it calls repeatedly (sometimes
678     recursively). The limit is imposed on the number of times this function is
679     called during a match, which has the effect of limiting the amount of recursion
680     and backtracking that can take place. For patterns that are not anchored, the
681     count starts from zero for each position in the subject string.
683     The default limit for the library can be set when PCRE is built; the default
684     default is 10 million, which handles all but the most extreme cases. You can
685     reduce the default by suppling \fBpcre_exec()\fR with a \fRpcre_extra\fR block
686     in which \fImatch_limit\fR is set to a smaller value, and
687     PCRE_EXTRA_MATCH_LIMIT is set in the \fIflags\fR field. If the limit is
688     exceeded, \fBpcre_exec()\fR returns PCRE_ERROR_MATCHLIMIT.
690     The \fIpcre_callout\fR field is used in conjunction with the "callout" feature,
691     which is described in the \fBpcrecallout\fR documentation.
693     The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose
694     unused bits must be zero. This limits \fBpcre_exec()\fR to matching at the
695     first matching position. However, if a pattern was compiled with PCRE_ANCHORED,
696     or turned out to be anchored by virtue of its contents, it cannot be made
697     unachored at matching time.
699     There are also three further options that can be set only at matching time:
703     The first character of the string is not the beginning of a line, so the
704     circumflex metacharacter should not match before it. Setting this without
705     PCRE_MULTILINE (at compile time) causes circumflex never to match.
709     The end of the string is not the end of a line, so the dollar metacharacter
710     should not match it nor (except in multiline mode) a newline immediately before
711     it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never
712     to match.
716     An empty string is not considered to be a valid match if this option is set. If
717     there are alternatives in the pattern, they are tried. If all the alternatives
718     match the empty string, the entire match fails. For example, if the pattern
720     a?b?
722     is applied to a string not beginning with "a" or "b", it matches the empty
723     string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
724     valid, so PCRE searches further into the string for occurrences of "a" or "b".
726     Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
727     of a pattern match of the empty string within its \fBsplit()\fR function, and
728     when using the /g modifier. It is possible to emulate Perl's behaviour after
729     matching a null string by first trying the match again at the same offset with
730     PCRE_NOTEMPTY set, and then if that fails by advancing the starting offset (see
731     below) and trying an ordinary match again.
733     The subject string is passed to \fBpcre_exec()\fR as a pointer in
734     \fIsubject\fR, a length in \fIlength\fR, and a starting offset in
735     \fIstartoffset\fR. Unlike the pattern string, the subject may contain binary
736     zero bytes. When the starting offset is zero, the search for a match starts at
737     the beginning of the subject, and this is by far the most common case.
739     If the pattern was compiled with the PCRE_UTF8 option, the subject must be a
740     sequence of bytes that is a valid UTF-8 string. If an invalid UTF-8 string is
741     passed, PCRE's behaviour is not defined.
743     A non-zero starting offset is useful when searching for another match in the
744     same subject by calling \fBpcre_exec()\fR again after a previous success.
745     Setting \fIstartoffset\fR differs from just passing over a shortened string and
746     setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
747     lookbehind. For example, consider the pattern
749     \\Biss\\B
751     which finds occurrences of "iss" in the middle of words. (\\B matches only if
752     the current position in the subject is not a word boundary.) When applied to
753     the string "Mississipi" the first call to \fBpcre_exec()\fR finds the first
754     occurrence. If \fBpcre_exec()\fR is called again with just the remainder of the
755     subject, namely "issipi", it does not match, because \\B is always false at the
756     start of the subject, which is deemed to be a word boundary. However, if
757     \fBpcre_exec()\fR is passed the entire string again, but with \fIstartoffset\fR
758     set to 4, it finds the second occurrence of "iss" because it is able to look
759     behind the starting point to discover that it is preceded by a letter.
761     If a non-zero starting offset is passed when the pattern is anchored, one
762     attempt to match at the given offset is tried. This can only succeed if the
763     pattern does not require the match to be at the start of the subject.
765     In general, a pattern matches a certain portion of the subject, and in
766     addition, further substrings from the subject may be picked out by parts of the
767     pattern. Following the usage in Jeffrey Friedl's book, this is called
768     "capturing" in what follows, and the phrase "capturing subpattern" is used for
769     a fragment of a pattern that picks out a substring. PCRE supports several other
770     kinds of parenthesized subpattern that do not cause substrings to be captured.
772     Captured substrings are returned to the caller via a vector of integer offsets
773     whose address is passed in \fIovector\fR. The number of elements in the vector
774     is passed in \fIovecsize\fR. The first two-thirds of the vector is used to pass
775     back captured substrings, each substring using a pair of integers. The
776     remaining third of the vector is used as workspace by \fBpcre_exec()\fR while
777     matching capturing subpatterns, and is not available for passing back
778     information. The length passed in \fIovecsize\fR should always be a multiple of
779     three. If it is not, it is rounded down.
781     When a match has been successful, information about captured substrings is
782     returned in pairs of integers, starting at the beginning of \fIovector\fR, and
783     continuing up to two-thirds of its length at the most. The first element of a
784     pair is set to the offset of the first character in a substring, and the second
785     is set to the offset of the first character after the end of a substring. The
786     first pair, \fIovector[0]\fR and \fIovector[1]\fR, identify the portion of the
787     subject string matched by the entire pattern. The next pair is used for the
788     first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fR
789     is the number of pairs that have been set. If there are no capturing
790     subpatterns, the return value from a successful match is 1, indicating that
791     just the first pair of offsets has been set.
793     Some convenience functions are provided for extracting the captured substrings
794     as separate strings. These are described in the following section.
796     It is possible for an capturing subpattern number \fIn+1\fR to match some
797     part of the subject when subpattern \fIn\fR has not been used at all. For
798     example, if the string "abc" is matched against the pattern (a|(z))(bc)
799     subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
800     values corresponding to the unused subpattern are set to -1.
802     If a capturing subpattern is matched repeatedly, it is the last portion of the
803     string that it matched that gets returned.
805     If the vector is too small to hold all the captured substrings, it is used as
806     far as possible (up to two-thirds of its length), and the function returns a
807     value of zero. In particular, if the substring offsets are not of interest,
808     \fBpcre_exec()\fR may be called with \fIovector\fR passed as NULL and
809     \fIovecsize\fR as zero. However, if the pattern contains back references and
810     the \fIovector\fR isn't big enough to remember the related substrings, PCRE has
811     to get additional memory for use during matching. Thus it is usually advisable
812     to supply an \fIovector\fR.
814     Note that \fBpcre_info()\fR can be used to find out how many capturing
815     subpatterns there are in a compiled pattern. The smallest size for
816     \fIovector\fR that will allow for \fIn\fR captured substrings, in addition to
817     the offsets of the substring matched by the whole pattern, is (\fIn\fR+1)*3.
819     If \fBpcre_exec()\fR fails, it returns a negative number. The following are
820     defined in the header file:
824     The subject string did not match the pattern.
826     PCRE_ERROR_NULL (-2)
828     Either \fIcode\fR or \fIsubject\fR was passed as NULL, or \fIovector\fR was
829     NULL and \fIovecsize\fR was not zero.
833     An unrecognized bit was set in the \fIoptions\fR argument.
837     PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
838     the case when it is passed a junk pointer. This is the error it gives when the
839     magic number isn't present.
843     While running the pattern match, an unknown item was encountered in the
844     compiled pattern. This error could be caused by a bug in PCRE or by overwriting
845     of the compiled pattern.
849     If a pattern contains back references, but the \fIovector\fR that is passed to
850     \fBpcre_exec()\fR is not big enough to remember the referenced substrings, PCRE
851     gets a block of memory at the start of matching to use for this purpose. If the
852     call via \fBpcre_malloc()\fR fails, this error is given. The memory is freed at
853     the end of matching.
857     This error is used by the \fBpcre_copy_substring()\fR,
858     \fBpcre_get_substring()\fR, and \fBpcre_get_substring_list()\fR functions (see
859     below). It is never returned by \fBpcre_exec()\fR.
863     The recursion and backtracking limit, as specified by the \fImatch_limit\fR
864     field in a \fBpcre_extra\fR structure (or defaulted) was reached. See the
865     description above.
869     This error is never generated by \fBpcre_exec()\fR itself. It is provided for
870     use by callout functions that want to yield a distinctive error code. See the
871     \fBpcrecallout\fR documentation for details.
874     .rs
875     .sp
876     .B int pcre_copy_substring(const char *\fIsubject\fR, int *\fIovector\fR,
877     .ti +5n
878     .B int \fIstringcount\fR, int \fIstringnumber\fR, char *\fIbuffer\fR,
879     .ti +5n
880     .B int \fIbuffersize\fR);
881     .PP
882     .br
883     .B int pcre_get_substring(const char *\fIsubject\fR, int *\fIovector\fR,
884     .ti +5n
885     .B int \fIstringcount\fR, int \fIstringnumber\fR,
886     .ti +5n
887     .B const char **\fIstringptr\fR);
888     .PP
889     .br
890     .B int pcre_get_substring_list(const char *\fIsubject\fR,
891     .ti +5n
892     .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
893     .PP
894     Captured substrings can be accessed directly by using the offsets returned by
895     \fBpcre_exec()\fR in \fIovector\fR. For convenience, the functions
896     \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
897     \fBpcre_get_substring_list()\fR are provided for extracting captured substrings
898     as new, separate, zero-terminated strings. These functions identify substrings
899     by number. The next section describes functions for extracting named
900     substrings. A substring that contains a binary zero is correctly extracted and
901     has a further zero added on the end, but the result is not, of course,
902     a C string.
904     The first three arguments are the same for all three of these functions:
905     \fIsubject\fR is the subject string which has just been successfully matched,
906     \fIovector\fR is a pointer to the vector of integer offsets that was passed to
907     \fBpcre_exec()\fR, and \fIstringcount\fR is the number of substrings that were
908     captured by the match, including the substring that matched the entire regular
909     expression. This is the value returned by \fBpcre_exec\fR if it is greater than
910     zero. If \fBpcre_exec()\fR returned zero, indicating that it ran out of space
911     in \fIovector\fR, the value passed as \fIstringcount\fR should be the size of
912     the vector divided by three.
914     The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR
915     extract a single substring, whose number is given as \fIstringnumber\fR. A
916     value of zero extracts the substring that matched the entire pattern, while
917     higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,
918     the string is placed in \fIbuffer\fR, whose length is given by
919     \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of memory is
920     obtained via \fBpcre_malloc\fR, and its address is returned via
921     \fIstringptr\fR. The yield of the function is the length of the string, not
922     including the terminating zero, or one of
926     The buffer was too small for \fBpcre_copy_substring()\fR, or the attempt to get
927     memory failed for \fBpcre_get_substring()\fR.
931     There is no substring whose number is \fIstringnumber\fR.
933     The \fBpcre_get_substring_list()\fR function extracts all available substrings
934     and builds a list of pointers to them. All this is done in a single block of
935     memory which is obtained via \fBpcre_malloc\fR. The address of the memory block
936     is returned via \fIlistptr\fR, which is also the start of the list of string
937     pointers. The end of the list is marked by a NULL pointer. The yield of the
938     function is zero if all went well, or
942     if the attempt to get the memory block failed.
944     When any of these functions encounter a substring that is unset, which can
945     happen when capturing subpattern number \fIn+1\fR matches some part of the
946     subject, but subpattern \fIn\fR has not been used at all, they return an empty
947     string. This can be distinguished from a genuine zero-length substring by
948     inspecting the appropriate offset in \fIovector\fR, which is negative for unset
949     substrings.
951     The two convenience functions \fBpcre_free_substring()\fR and
952     \fBpcre_free_substring_list()\fR can be used to free the memory returned by
953     a previous call of \fBpcre_get_substring()\fR or
954     \fBpcre_get_substring_list()\fR, respectively. They do nothing more than call
955     the function pointed to by \fBpcre_free\fR, which of course could be called
956     directly from a C program. However, PCRE is used in some situations where it is
957     linked via a special interface to another programming language which cannot use
958     \fBpcre_free\fR directly; it is for these cases that the functions are
959     provided.
962     .rs
963     .sp
964     .B int pcre_copy_named_substring(const pcre *\fIcode\fR,
965     .ti +5n
966     .B const char *\fIsubject\fR, int *\fIovector\fR,
967     .ti +5n
968     .B int \fIstringcount\fR, const char *\fIstringname\fR,
969     .ti +5n
970     .B char *\fIbuffer\fR, int \fIbuffersize\fR);
971     .PP
972     .br
973     .B int pcre_get_stringnumber(const pcre *\fIcode\fR,
974     .ti +5n
975     .B const char *\fIname\fR);
976     .PP
977     .br
978     .B int pcre_get_named_substring(const pcre *\fIcode\fR,
979     .ti +5n
980     .B const char *\fIsubject\fR, int *\fIovector\fR,
981     .ti +5n
982     .B int \fIstringcount\fR, const char *\fIstringname\fR,
983     .ti +5n
984     .B const char **\fIstringptr\fR);
985     .PP
986     To extract a substring by name, you first have to find associated number. This
987     can be done by calling \fBpcre_get_stringnumber()\fR. The first argument is the
988     compiled pattern, and the second is the name. For example, for this pattern
990     ab(?<xxx>\\d+)...
992     the number of the subpattern called "xxx" is 1. Given the number, you can then
993     extract the substring directly, or use one of the functions described in the
994     previous section. For convenience, there are also two functions that do the
995     whole job.
997     Most of the arguments of \fIpcre_copy_named_substring()\fR and
998     \fIpcre_get_named_substring()\fR are the same as those for the functions that
999     extract by number, and so are not re-described here. There are just two
1000     differences.
1002     First, instead of a substring number, a substring name is given. Second, there
1003     is an extra argument, given at the start, which is a pointer to the compiled
1004     pattern. This is needed in order to gain access to the name-to-number
1005     translation table.
1007     These functions call \fBpcre_get_stringnumber()\fR, and if it succeeds, they
1008     then call \fIpcre_copy_substring()\fR or \fIpcre_get_substring()\fR, as
1009     appropriate.
1011     .in 0
1012     Last updated: 03 February 2003
1013     .br
1014     Copyright (c) 1997-2003 University of Cambridge.

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