1 |
.TH PCRE 3
|
2 |
.SH NAME
|
3 |
PCRE - Perl-compatible regular expressions
|
4 |
.SH "PCRE NATIVE API"
|
5 |
.rs
|
6 |
.sp
|
7 |
.B #include <pcre.h>
|
8 |
.PP
|
9 |
.SM
|
10 |
.br
|
11 |
.B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
|
12 |
.ti +5n
|
13 |
.B const char **\fIerrptr\fP, int *\fIerroffset\fP,
|
14 |
.ti +5n
|
15 |
.B const unsigned char *\fItableptr\fP);
|
16 |
.PP
|
17 |
.br
|
18 |
.B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
|
19 |
.ti +5n
|
20 |
.B const char **\fIerrptr\fP);
|
21 |
.PP
|
22 |
.br
|
23 |
.B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
|
24 |
.ti +5n
|
25 |
.B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
|
26 |
.ti +5n
|
27 |
.B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
|
28 |
.PP
|
29 |
.br
|
30 |
.B int pcre_copy_named_substring(const pcre *\fIcode\fP,
|
31 |
.ti +5n
|
32 |
.B const char *\fIsubject\fP, int *\fIovector\fP,
|
33 |
.ti +5n
|
34 |
.B int \fIstringcount\fP, const char *\fIstringname\fP,
|
35 |
.ti +5n
|
36 |
.B char *\fIbuffer\fP, int \fIbuffersize\fP);
|
37 |
.PP
|
38 |
.br
|
39 |
.B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
|
40 |
.ti +5n
|
41 |
.B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
|
42 |
.ti +5n
|
43 |
.B int \fIbuffersize\fP);
|
44 |
.PP
|
45 |
.br
|
46 |
.B int pcre_get_named_substring(const pcre *\fIcode\fP,
|
47 |
.ti +5n
|
48 |
.B const char *\fIsubject\fP, int *\fIovector\fP,
|
49 |
.ti +5n
|
50 |
.B int \fIstringcount\fP, const char *\fIstringname\fP,
|
51 |
.ti +5n
|
52 |
.B const char **\fIstringptr\fP);
|
53 |
.PP
|
54 |
.br
|
55 |
.B int pcre_get_stringnumber(const pcre *\fIcode\fP,
|
56 |
.ti +5n
|
57 |
.B const char *\fIname\fP);
|
58 |
.PP
|
59 |
.br
|
60 |
.B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
|
61 |
.ti +5n
|
62 |
.B int \fIstringcount\fP, int \fIstringnumber\fP,
|
63 |
.ti +5n
|
64 |
.B const char **\fIstringptr\fP);
|
65 |
.PP
|
66 |
.br
|
67 |
.B int pcre_get_substring_list(const char *\fIsubject\fP,
|
68 |
.ti +5n
|
69 |
.B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
|
70 |
.PP
|
71 |
.br
|
72 |
.B void pcre_free_substring(const char *\fIstringptr\fP);
|
73 |
.PP
|
74 |
.br
|
75 |
.B void pcre_free_substring_list(const char **\fIstringptr\fP);
|
76 |
.PP
|
77 |
.br
|
78 |
.B const unsigned char *pcre_maketables(void);
|
79 |
.PP
|
80 |
.br
|
81 |
.B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
|
82 |
.ti +5n
|
83 |
.B int \fIwhat\fP, void *\fIwhere\fP);
|
84 |
.PP
|
85 |
.br
|
86 |
.B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
|
87 |
.B *\fIfirstcharptr\fP);
|
88 |
.PP
|
89 |
.br
|
90 |
.B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
|
91 |
.PP
|
92 |
.br
|
93 |
.B char *pcre_version(void);
|
94 |
.PP
|
95 |
.br
|
96 |
.B void *(*pcre_malloc)(size_t);
|
97 |
.PP
|
98 |
.br
|
99 |
.B void (*pcre_free)(void *);
|
100 |
.PP
|
101 |
.br
|
102 |
.B void *(*pcre_stack_malloc)(size_t);
|
103 |
.PP
|
104 |
.br
|
105 |
.B void (*pcre_stack_free)(void *);
|
106 |
.PP
|
107 |
.br
|
108 |
.B int (*pcre_callout)(pcre_callout_block *);
|
109 |
.
|
110 |
.
|
111 |
.SH "PCRE API OVERVIEW"
|
112 |
.rs
|
113 |
.sp
|
114 |
PCRE has its own native API, which is described in this document. There is also
|
115 |
a set of wrapper functions that correspond to the POSIX regular expression API.
|
116 |
These are described in the
|
117 |
.\" HREF
|
118 |
\fBpcreposix\fP
|
119 |
.\"
|
120 |
documentation.
|
121 |
.P
|
122 |
The native API function prototypes are defined in the header file \fBpcre.h\fP,
|
123 |
and on Unix systems the library itself is called \fBlibpcre\fP. It can
|
124 |
normally be accessed by adding \fB-lpcre\fP to the command for linking an
|
125 |
application that uses PCRE. The header file defines the macros PCRE_MAJOR and
|
126 |
PCRE_MINOR to contain the major and minor release numbers for the library.
|
127 |
Applications can use these to include support for different releases of PCRE.
|
128 |
.P
|
129 |
The functions \fBpcre_compile()\fP, \fBpcre_study()\fP, and \fBpcre_exec()\fP
|
130 |
are used for compiling and matching regular expressions. A sample program that
|
131 |
demonstrates the simplest way of using them is provided in the file called
|
132 |
\fIpcredemo.c\fP in the source distribution. The
|
133 |
.\" HREF
|
134 |
\fBpcresample\fP
|
135 |
.\"
|
136 |
documentation describes how to run it.
|
137 |
.P
|
138 |
In addition to the main compiling and matching functions, there are convenience
|
139 |
functions for extracting captured substrings from a matched subject string.
|
140 |
They are:
|
141 |
.sp
|
142 |
\fBpcre_copy_substring()\fP
|
143 |
\fBpcre_copy_named_substring()\fP
|
144 |
\fBpcre_get_substring()\fP
|
145 |
\fBpcre_get_named_substring()\fP
|
146 |
\fBpcre_get_substring_list()\fP
|
147 |
\fBpcre_get_stringnumber()\fP
|
148 |
.sp
|
149 |
\fBpcre_free_substring()\fP and \fBpcre_free_substring_list()\fP are also
|
150 |
provided, to free the memory used for extracted strings.
|
151 |
.P
|
152 |
The function \fBpcre_maketables()\fP is used to build a set of character tables
|
153 |
in the current locale for passing to \fBpcre_compile()\fP or \fBpcre_exec()\fP.
|
154 |
This is an optional facility that is provided for specialist use. Most
|
155 |
commonly, no special tables are passed, in which case internal tables that are
|
156 |
generated when PCRE is built are used.
|
157 |
.P
|
158 |
The function \fBpcre_fullinfo()\fP is used to find out information about a
|
159 |
compiled pattern; \fBpcre_info()\fP is an obsolete version that returns only
|
160 |
some of the available information, but is retained for backwards compatibility.
|
161 |
The function \fBpcre_version()\fP returns a pointer to a string containing the
|
162 |
version of PCRE and its date of release.
|
163 |
.P
|
164 |
The global variables \fBpcre_malloc\fP and \fBpcre_free\fP initially contain
|
165 |
the entry points of the standard \fBmalloc()\fP and \fBfree()\fP functions,
|
166 |
respectively. PCRE calls the memory management functions via these variables,
|
167 |
so a calling program can replace them if it wishes to intercept the calls. This
|
168 |
should be done before calling any PCRE functions.
|
169 |
.P
|
170 |
The global variables \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are also
|
171 |
indirections to memory management functions. These special functions are used
|
172 |
only when PCRE is compiled to use the heap for remembering data, instead of
|
173 |
recursive function calls. This is a non-standard way of building PCRE, for use
|
174 |
in environments that have limited stacks. Because of the greater use of memory
|
175 |
management, it runs more slowly. Separate functions are provided so that
|
176 |
special-purpose external code can be used for this case. When used, these
|
177 |
functions are always called in a stack-like manner (last obtained, first
|
178 |
freed), and always for memory blocks of the same size.
|
179 |
.P
|
180 |
The global variable \fBpcre_callout\fP initially contains NULL. It can be set
|
181 |
by the caller to a "callout" function, which PCRE will then call at specified
|
182 |
points during a matching operation. Details are given in the
|
183 |
.\" HREF
|
184 |
\fBpcrecallout\fP
|
185 |
.\"
|
186 |
documentation.
|
187 |
.
|
188 |
.
|
189 |
.SH MULTITHREADING
|
190 |
.rs
|
191 |
.sp
|
192 |
The PCRE functions can be used in multi-threading applications, with the
|
193 |
proviso that the memory management functions pointed to by \fBpcre_malloc\fP,
|
194 |
\fBpcre_free\fP, \fBpcre_stack_malloc\fP, and \fBpcre_stack_free\fP, and the
|
195 |
callout function pointed to by \fBpcre_callout\fP, are shared by all threads.
|
196 |
.P
|
197 |
The compiled form of a regular expression is not altered during matching, so
|
198 |
the same compiled pattern can safely be used by several threads at once.
|
199 |
.
|
200 |
.
|
201 |
.SH "SAVING PRECOMPILED PATTERNS FOR LATER USE"
|
202 |
.rs
|
203 |
.sp
|
204 |
The compiled form of a regular expression can be saved and re-used at a later
|
205 |
time, possibly by a different program, and even on a host other than the one on
|
206 |
which it was compiled. Details are given in the
|
207 |
.\" HREF
|
208 |
\fBpcreprecompile\fP
|
209 |
.\"
|
210 |
documentation.
|
211 |
.
|
212 |
.
|
213 |
.SH "CHECKING BUILD-TIME OPTIONS"
|
214 |
.rs
|
215 |
.sp
|
216 |
.B int pcre_config(int \fIwhat\fP, void *\fIwhere\fP);
|
217 |
.PP
|
218 |
The function \fBpcre_config()\fP makes it possible for a PCRE client to
|
219 |
discover which optional features have been compiled into the PCRE library. The
|
220 |
.\" HREF
|
221 |
\fBpcrebuild\fP
|
222 |
.\"
|
223 |
documentation has more details about these optional features.
|
224 |
.P
|
225 |
The first argument for \fBpcre_config()\fP is an integer, specifying which
|
226 |
information is required; the second argument is a pointer to a variable into
|
227 |
which the information is placed. The following information is available:
|
228 |
.sp
|
229 |
PCRE_CONFIG_UTF8
|
230 |
.sp
|
231 |
The output is an integer that is set to one if UTF-8 support is available;
|
232 |
otherwise it is set to zero.
|
233 |
.sp
|
234 |
PCRE_CONFIG_UNICODE_PROPERTIES
|
235 |
.sp
|
236 |
The output is an integer that is set to one if support for Unicode character
|
237 |
properties is available; otherwise it is set to zero.
|
238 |
.sp
|
239 |
PCRE_CONFIG_NEWLINE
|
240 |
.sp
|
241 |
The output is an integer that is set to the value of the code that is used for
|
242 |
the newline character. It is either linefeed (10) or carriage return (13), and
|
243 |
should normally be the standard character for your operating system.
|
244 |
.sp
|
245 |
PCRE_CONFIG_LINK_SIZE
|
246 |
.sp
|
247 |
The output is an integer that contains the number of bytes used for internal
|
248 |
linkage in compiled regular expressions. The value is 2, 3, or 4. Larger values
|
249 |
allow larger regular expressions to be compiled, at the expense of slower
|
250 |
matching. The default value of 2 is sufficient for all but the most massive
|
251 |
patterns, since it allows the compiled pattern to be up to 64K in size.
|
252 |
.sp
|
253 |
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
|
254 |
.sp
|
255 |
The output is an integer that contains the threshold above which the POSIX
|
256 |
interface uses \fBmalloc()\fP for output vectors. Further details are given in
|
257 |
the
|
258 |
.\" HREF
|
259 |
\fBpcreposix\fP
|
260 |
.\"
|
261 |
documentation.
|
262 |
.sp
|
263 |
PCRE_CONFIG_MATCH_LIMIT
|
264 |
.sp
|
265 |
The output is an integer that gives the default limit for the number of
|
266 |
internal matching function calls in a \fBpcre_exec()\fP execution. Further
|
267 |
details are given with \fBpcre_exec()\fP below.
|
268 |
.sp
|
269 |
PCRE_CONFIG_STACKRECURSE
|
270 |
.sp
|
271 |
The output is an integer that is set to one if internal recursion is
|
272 |
implemented by recursive function calls that use the stack to remember their
|
273 |
state. This is the usual way that PCRE is compiled. The output is zero if PCRE
|
274 |
was compiled to use blocks of data on the heap instead of recursive function
|
275 |
calls. In this case, \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP are
|
276 |
called to manage memory blocks on the heap, thus avoiding the use of the stack.
|
277 |
.
|
278 |
.
|
279 |
.SH "COMPILING A PATTERN"
|
280 |
.rs
|
281 |
.sp
|
282 |
.B pcre *pcre_compile(const char *\fIpattern\fP, int \fIoptions\fP,
|
283 |
.ti +5n
|
284 |
.B const char **\fIerrptr\fP, int *\fIerroffset\fP,
|
285 |
.ti +5n
|
286 |
.B const unsigned char *\fItableptr\fP);
|
287 |
.P
|
288 |
The function \fBpcre_compile()\fP is called to compile a pattern into an
|
289 |
internal form. The pattern is a C string terminated by a binary zero, and
|
290 |
is passed in the \fIpattern\fP argument. A pointer to a single block of memory
|
291 |
that is obtained via \fBpcre_malloc\fP is returned. This contains the compiled
|
292 |
code and related data. The \fBpcre\fP type is defined for the returned block;
|
293 |
this is a typedef for a structure whose contents are not externally defined. It
|
294 |
is up to the caller to free the memory when it is no longer required.
|
295 |
.P
|
296 |
Although the compiled code of a PCRE regex is relocatable, that is, it does not
|
297 |
depend on memory location, the complete \fBpcre\fP data block is not
|
298 |
fully relocatable, because it may contain a copy of the \fItableptr\fP
|
299 |
argument, which is an address (see below).
|
300 |
.P
|
301 |
The \fIoptions\fP argument contains independent bits that affect the
|
302 |
compilation. It should be zero if no options are required. The available
|
303 |
options are described below. Some of them, in particular, those that are
|
304 |
compatible with Perl, can also be set and unset from within the pattern (see
|
305 |
the detailed description in the
|
306 |
.\" HREF
|
307 |
\fBpcrepattern\fP
|
308 |
.\"
|
309 |
documentation). For these options, the contents of the \fIoptions\fP argument
|
310 |
specifies their initial settings at the start of compilation and execution. The
|
311 |
PCRE_ANCHORED option can be set at the time of matching as well as at compile
|
312 |
time.
|
313 |
.P
|
314 |
If \fIerrptr\fP is NULL, \fBpcre_compile()\fP returns NULL immediately.
|
315 |
Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fP returns
|
316 |
NULL, and sets the variable pointed to by \fIerrptr\fP to point to a textual
|
317 |
error message. The offset from the start of the pattern to the character where
|
318 |
the error was discovered is placed in the variable pointed to by
|
319 |
\fIerroffset\fP, which must not be NULL. If it is, an immediate error is given.
|
320 |
.P
|
321 |
If the final argument, \fItableptr\fP, is NULL, PCRE uses a default set of
|
322 |
character tables that are built when PCRE is compiled, using the default C
|
323 |
locale. Otherwise, \fItableptr\fP must be an address that is the result of a
|
324 |
call to \fBpcre_maketables()\fP. This value is stored with the compiled
|
325 |
pattern, and used again by \fBpcre_exec()\fP, unless another table pointer is
|
326 |
passed to it. For more discussion, see the section on locale support below.
|
327 |
.P
|
328 |
This code fragment shows a typical straightforward call to \fBpcre_compile()\fP:
|
329 |
.sp
|
330 |
pcre *re;
|
331 |
const char *error;
|
332 |
int erroffset;
|
333 |
re = pcre_compile(
|
334 |
"^A.*Z", /* the pattern */
|
335 |
0, /* default options */
|
336 |
&error, /* for error message */
|
337 |
&erroffset, /* for error offset */
|
338 |
NULL); /* use default character tables */
|
339 |
.sp
|
340 |
The following names for option bits are defined in the \fBpcre.h\fP header
|
341 |
file:
|
342 |
.sp
|
343 |
PCRE_ANCHORED
|
344 |
.sp
|
345 |
If this bit is set, the pattern is forced to be "anchored", that is, it is
|
346 |
constrained to match only at the first matching point in the string that is
|
347 |
being searched (the "subject string"). This effect can also be achieved by
|
348 |
appropriate constructs in the pattern itself, which is the only way to do it in
|
349 |
Perl.
|
350 |
.sp
|
351 |
PCRE_AUTO_CALLOUT
|
352 |
.sp
|
353 |
If this bit is set, \fBpcre_compile()\fP automatically inserts callout items,
|
354 |
all with number 255, before each pattern item. For discussion of the callout
|
355 |
facility, see the
|
356 |
.\" HREF
|
357 |
\fBpcrecallout\fP
|
358 |
.\"
|
359 |
documentation.
|
360 |
.sp
|
361 |
PCRE_CASELESS
|
362 |
.sp
|
363 |
If this bit is set, letters in the pattern match both upper and lower case
|
364 |
letters. It is equivalent to Perl's /i option, and it can be changed within a
|
365 |
pattern by a (?i) option setting. When running in UTF-8 mode, case support for
|
366 |
high-valued characters is available only when PCRE is built with Unicode
|
367 |
character property support.
|
368 |
.sp
|
369 |
PCRE_DOLLAR_ENDONLY
|
370 |
.sp
|
371 |
If this bit is set, a dollar metacharacter in the pattern matches only at the
|
372 |
end of the subject string. Without this option, a dollar also matches
|
373 |
immediately before the final character if it is a newline (but not before any
|
374 |
other newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is
|
375 |
set. There is no equivalent to this option in Perl, and no way to set it within
|
376 |
a pattern.
|
377 |
.sp
|
378 |
PCRE_DOTALL
|
379 |
.sp
|
380 |
If this bit is set, a dot metacharater in the pattern matches all characters,
|
381 |
including newlines. Without it, newlines are excluded. This option is
|
382 |
equivalent to Perl's /s option, and it can be changed within a pattern by a
|
383 |
(?s) option setting. A negative class such as [^a] always matches a newline
|
384 |
character, independent of the setting of this option.
|
385 |
.sp
|
386 |
PCRE_EXTENDED
|
387 |
.sp
|
388 |
If this bit is set, whitespace data characters in the pattern are totally
|
389 |
ignored except when escaped or inside a character class. Whitespace does not
|
390 |
include the VT character (code 11). In addition, characters between an
|
391 |
unescaped # outside a character class and the next newline character,
|
392 |
inclusive, are also ignored. This is equivalent to Perl's /x option, and it can
|
393 |
be changed within a pattern by a (?x) option setting.
|
394 |
.P
|
395 |
This option makes it possible to include comments inside complicated patterns.
|
396 |
Note, however, that this applies only to data characters. Whitespace characters
|
397 |
may never appear within special character sequences in a pattern, for example
|
398 |
within the sequence (?( which introduces a conditional subpattern.
|
399 |
.sp
|
400 |
PCRE_EXTRA
|
401 |
.sp
|
402 |
This option was invented in order to turn on additional functionality of PCRE
|
403 |
that is incompatible with Perl, but it is currently of very little use. When
|
404 |
set, any backslash in a pattern that is followed by a letter that has no
|
405 |
special meaning causes an error, thus reserving these combinations for future
|
406 |
expansion. By default, as in Perl, a backslash followed by a letter with no
|
407 |
special meaning is treated as a literal. There are at present no other features
|
408 |
controlled by this option. It can also be set by a (?X) option setting within a
|
409 |
pattern.
|
410 |
.sp
|
411 |
PCRE_MULTILINE
|
412 |
.sp
|
413 |
By default, PCRE treats the subject string as consisting of a single line of
|
414 |
characters (even if it actually contains newlines). The "start of line"
|
415 |
metacharacter (^) matches only at the start of the string, while the "end of
|
416 |
line" metacharacter ($) matches only at the end of the string, or before a
|
417 |
terminating newline (unless PCRE_DOLLAR_ENDONLY is set). This is the same as
|
418 |
Perl.
|
419 |
.P
|
420 |
When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs
|
421 |
match immediately following or immediately before any newline in the subject
|
422 |
string, respectively, as well as at the very start and end. This is equivalent
|
423 |
to Perl's /m option, and it can be changed within a pattern by a (?m) option
|
424 |
setting. If there are no "\en" characters in a subject string, or no
|
425 |
occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect.
|
426 |
.sp
|
427 |
PCRE_NO_AUTO_CAPTURE
|
428 |
.sp
|
429 |
If this option is set, it disables the use of numbered capturing parentheses in
|
430 |
the pattern. Any opening parenthesis that is not followed by ? behaves as if it
|
431 |
were followed by ?: but named parentheses can still be used for capturing (and
|
432 |
they acquire numbers in the usual way). There is no equivalent of this option
|
433 |
in Perl.
|
434 |
.sp
|
435 |
PCRE_UNGREEDY
|
436 |
.sp
|
437 |
This option inverts the "greediness" of the quantifiers so that they are not
|
438 |
greedy by default, but become greedy if followed by "?". It is not compatible
|
439 |
with Perl. It can also be set by a (?U) option setting within the pattern.
|
440 |
.sp
|
441 |
PCRE_UTF8
|
442 |
.sp
|
443 |
This option causes PCRE to regard both the pattern and the subject as strings
|
444 |
of UTF-8 characters instead of single-byte character strings. However, it is
|
445 |
available only when PCRE is built to include UTF-8 support. If not, the use
|
446 |
of this option provokes an error. Details of how this option changes the
|
447 |
behaviour of PCRE are given in the
|
448 |
.\" HTML <a href="pcre.html#utf8support">
|
449 |
.\" </a>
|
450 |
section on UTF-8 support
|
451 |
.\"
|
452 |
in the main
|
453 |
.\" HREF
|
454 |
\fBpcre\fP
|
455 |
.\"
|
456 |
page.
|
457 |
.sp
|
458 |
PCRE_NO_UTF8_CHECK
|
459 |
.sp
|
460 |
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
|
461 |
automatically checked. If an invalid UTF-8 sequence of bytes is found,
|
462 |
\fBpcre_compile()\fP returns an error. If you already know that your pattern is
|
463 |
valid, and you want to skip this check for performance reasons, you can set the
|
464 |
PCRE_NO_UTF8_CHECK option. When it is set, the effect of passing an invalid
|
465 |
UTF-8 string as a pattern is undefined. It may cause your program to crash.
|
466 |
Note that this option can also be passed to \fBpcre_exec()\fP, to suppress the
|
467 |
UTF-8 validity checking of subject strings.
|
468 |
.
|
469 |
.
|
470 |
.SH "STUDYING A PATTERN"
|
471 |
.rs
|
472 |
.sp
|
473 |
.B pcre_extra *pcre_study(const pcre *\fIcode\fP, int \fIoptions\fP,
|
474 |
.ti +5n
|
475 |
.B const char **\fIerrptr\fP);
|
476 |
.PP
|
477 |
If a compiled pattern is going to be used several times, it is worth spending
|
478 |
more time analyzing it in order to speed up the time taken for matching. The
|
479 |
function \fBpcre_study()\fP takes a pointer to a compiled pattern as its first
|
480 |
argument. If studying the pattern produces additional information that will
|
481 |
help speed up matching, \fBpcre_study()\fP returns a pointer to a
|
482 |
\fBpcre_extra\fP block, in which the \fIstudy_data\fP field points to the
|
483 |
results of the study.
|
484 |
.P
|
485 |
The returned value from \fBpcre_study()\fP can be passed directly to
|
486 |
\fBpcre_exec()\fP. However, a \fBpcre_extra\fP block also contains other
|
487 |
fields that can be set by the caller before the block is passed; these are
|
488 |
described
|
489 |
.\" HTML <a href="#extradata">
|
490 |
.\" </a>
|
491 |
below
|
492 |
.\"
|
493 |
in the section on matching a pattern.
|
494 |
.P
|
495 |
If studying the pattern does not produce any additional information,
|
496 |
\fBpcre_study()\fP returns NULL. In that circumstance, if the calling program
|
497 |
wants to pass any of the other fields to \fBpcre_exec()\fP, it must set up its
|
498 |
own \fBpcre_extra\fP block.
|
499 |
.P
|
500 |
The second argument of \fBpcre_study()\fP contains option bits. At present, no
|
501 |
options are defined, and this argument should always be zero.
|
502 |
.P
|
503 |
The third argument for \fBpcre_study()\fP is a pointer for an error message. If
|
504 |
studying succeeds (even if no data is returned), the variable it points to is
|
505 |
set to NULL. Otherwise it points to a textual error message. You should
|
506 |
therefore test the error pointer for NULL after calling \fBpcre_study()\fP, to
|
507 |
be sure that it has run successfully.
|
508 |
.P
|
509 |
This is a typical call to \fBpcre_study\fP():
|
510 |
.sp
|
511 |
pcre_extra *pe;
|
512 |
pe = pcre_study(
|
513 |
re, /* result of pcre_compile() */
|
514 |
0, /* no options exist */
|
515 |
&error); /* set to NULL or points to a message */
|
516 |
.sp
|
517 |
At present, studying a pattern is useful only for non-anchored patterns that do
|
518 |
not have a single fixed starting character. A bitmap of possible starting
|
519 |
bytes is created.
|
520 |
.
|
521 |
.
|
522 |
.\" HTML <a name="localesupport"></a>
|
523 |
.SH "LOCALE SUPPORT"
|
524 |
.rs
|
525 |
.sp
|
526 |
PCRE handles caseless matching, and determines whether characters are letters,
|
527 |
digits, or whatever, by reference to a set of tables, indexed by character
|
528 |
value. (When running in UTF-8 mode, this applies only to characters with codes
|
529 |
less than 128. Higher-valued codes never match escapes such as \ew or \ed, but
|
530 |
can be tested with \ep if PCRE is built with Unicode character property
|
531 |
support.)
|
532 |
.P
|
533 |
An internal set of tables is created in the default C locale when PCRE is
|
534 |
built. This is used when the final argument of \fBpcre_compile()\fP is NULL,
|
535 |
and is sufficient for many applications. An alternative set of tables can,
|
536 |
however, be supplied. These may be created in a different locale from the
|
537 |
default. As more and more applications change to using Unicode, the need for
|
538 |
this locale support is expected to die away.
|
539 |
.P
|
540 |
External tables are built by calling the \fBpcre_maketables()\fP function,
|
541 |
which has no arguments, in the relevant locale. The result can then be passed
|
542 |
to \fBpcre_compile()\fP or \fBpcre_exec()\fP as often as necessary. For
|
543 |
example, to build and use tables that are appropriate for the French locale
|
544 |
(where accented characters with values greater than 128 are treated as letters),
|
545 |
the following code could be used:
|
546 |
.sp
|
547 |
setlocale(LC_CTYPE, "fr_FR");
|
548 |
tables = pcre_maketables();
|
549 |
re = pcre_compile(..., tables);
|
550 |
.sp
|
551 |
When \fBpcre_maketables()\fP runs, the tables are built in memory that is
|
552 |
obtained via \fBpcre_malloc\fP. It is the caller's responsibility to ensure
|
553 |
that the memory containing the tables remains available for as long as it is
|
554 |
needed.
|
555 |
.P
|
556 |
The pointer that is passed to \fBpcre_compile()\fP is saved with the compiled
|
557 |
pattern, and the same tables are used via this pointer by \fBpcre_study()\fP
|
558 |
and normally also by \fBpcre_exec()\fP. Thus, by default, for any single
|
559 |
pattern, compilation, studying and matching all happen in the same locale, but
|
560 |
different patterns can be compiled in different locales.
|
561 |
.P
|
562 |
It is possible to pass a table pointer or NULL (indicating the use of the
|
563 |
internal tables) to \fBpcre_exec()\fP. Although not intended for this purpose,
|
564 |
this facility could be used to match a pattern in a different locale from the
|
565 |
one in which it was compiled. Passing table pointers at run time is discussed
|
566 |
below in the section on matching a pattern.
|
567 |
.
|
568 |
.
|
569 |
.SH "INFORMATION ABOUT A PATTERN"
|
570 |
.rs
|
571 |
.sp
|
572 |
.B int pcre_fullinfo(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
|
573 |
.ti +5n
|
574 |
.B int \fIwhat\fP, void *\fIwhere\fP);
|
575 |
.PP
|
576 |
The \fBpcre_fullinfo()\fP function returns information about a compiled
|
577 |
pattern. It replaces the obsolete \fBpcre_info()\fP function, which is
|
578 |
nevertheless retained for backwards compability (and is documented below).
|
579 |
.P
|
580 |
The first argument for \fBpcre_fullinfo()\fP is a pointer to the compiled
|
581 |
pattern. The second argument is the result of \fBpcre_study()\fP, or NULL if
|
582 |
the pattern was not studied. The third argument specifies which piece of
|
583 |
information is required, and the fourth argument is a pointer to a variable
|
584 |
to receive the data. The yield of the function is zero for success, or one of
|
585 |
the following negative numbers:
|
586 |
.sp
|
587 |
PCRE_ERROR_NULL the argument \fIcode\fP was NULL
|
588 |
the argument \fIwhere\fP was NULL
|
589 |
PCRE_ERROR_BADMAGIC the "magic number" was not found
|
590 |
PCRE_ERROR_BADOPTION the value of \fIwhat\fP was invalid
|
591 |
.sp
|
592 |
The "magic number" is placed at the start of each compiled pattern as an simple
|
593 |
check against passing an arbitrary memory pointer. Here is a typical call of
|
594 |
\fBpcre_fullinfo()\fP, to obtain the length of the compiled pattern:
|
595 |
.sp
|
596 |
int rc;
|
597 |
unsigned long int length;
|
598 |
rc = pcre_fullinfo(
|
599 |
re, /* result of pcre_compile() */
|
600 |
pe, /* result of pcre_study(), or NULL */
|
601 |
PCRE_INFO_SIZE, /* what is required */
|
602 |
&length); /* where to put the data */
|
603 |
.sp
|
604 |
The possible values for the third argument are defined in \fBpcre.h\fP, and are
|
605 |
as follows:
|
606 |
.sp
|
607 |
PCRE_INFO_BACKREFMAX
|
608 |
.sp
|
609 |
Return the number of the highest back reference in the pattern. The fourth
|
610 |
argument should point to an \fBint\fP variable. Zero is returned if there are
|
611 |
no back references.
|
612 |
.sp
|
613 |
PCRE_INFO_CAPTURECOUNT
|
614 |
.sp
|
615 |
Return the number of capturing subpatterns in the pattern. The fourth argument
|
616 |
should point to an \fBint\fP variable.
|
617 |
.sp
|
618 |
PCRE_INFO_DEFAULTTABLES
|
619 |
.sp
|
620 |
Return a pointer to the internal default character tables within PCRE. The
|
621 |
fourth argument should point to an \fBunsigned char *\fP variable. This
|
622 |
information call is provided for internal use by the \fBpcre_study()\fP
|
623 |
function. External callers can cause PCRE to use its internal tables by passing
|
624 |
a NULL table pointer.
|
625 |
.sp
|
626 |
PCRE_INFO_FIRSTBYTE
|
627 |
.sp
|
628 |
Return information about the first byte of any matched string, for a
|
629 |
non-anchored pattern. (This option used to be called PCRE_INFO_FIRSTCHAR; the
|
630 |
old name is still recognized for backwards compatibility.)
|
631 |
.P
|
632 |
If there is a fixed first byte, for example, from a pattern such as
|
633 |
(cat|cow|coyote), it is returned in the integer pointed to by \fIwhere\fP.
|
634 |
Otherwise, if either
|
635 |
.sp
|
636 |
(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
|
637 |
starts with "^", or
|
638 |
.sp
|
639 |
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
|
640 |
(if it were set, the pattern would be anchored),
|
641 |
.sp
|
642 |
-1 is returned, indicating that the pattern matches only at the start of a
|
643 |
subject string or after any newline within the string. Otherwise -2 is
|
644 |
returned. For anchored patterns, -2 is returned.
|
645 |
.sp
|
646 |
PCRE_INFO_FIRSTTABLE
|
647 |
.sp
|
648 |
If the pattern was studied, and this resulted in the construction of a 256-bit
|
649 |
table indicating a fixed set of bytes for the first byte in any matching
|
650 |
string, a pointer to the table is returned. Otherwise NULL is returned. The
|
651 |
fourth argument should point to an \fBunsigned char *\fP variable.
|
652 |
.sp
|
653 |
PCRE_INFO_LASTLITERAL
|
654 |
.sp
|
655 |
Return the value of the rightmost literal byte that must exist in any matched
|
656 |
string, other than at its start, if such a byte has been recorded. The fourth
|
657 |
argument should point to an \fBint\fP variable. If there is no such byte, -1 is
|
658 |
returned. For anchored patterns, a last literal byte is recorded only if it
|
659 |
follows something of variable length. For example, for the pattern
|
660 |
/^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
|
661 |
is -1.
|
662 |
.sp
|
663 |
PCRE_INFO_NAMECOUNT
|
664 |
PCRE_INFO_NAMEENTRYSIZE
|
665 |
PCRE_INFO_NAMETABLE
|
666 |
.sp
|
667 |
PCRE supports the use of named as well as numbered capturing parentheses. The
|
668 |
names are just an additional way of identifying the parentheses, which still
|
669 |
acquire numbers. A convenience function called \fBpcre_get_named_substring()\fP
|
670 |
is provided for extracting an individual captured substring by name. It is also
|
671 |
possible to extract the data directly, by first converting the name to a number
|
672 |
in order to access the correct pointers in the output vector (described with
|
673 |
\fBpcre_exec()\fP below). To do the conversion, you need to use the
|
674 |
name-to-number map, which is described by these three values.
|
675 |
.P
|
676 |
The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives
|
677 |
the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each
|
678 |
entry; both of these return an \fBint\fP value. The entry size depends on the
|
679 |
length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first
|
680 |
entry of the table (a pointer to \fBchar\fP). The first two bytes of each entry
|
681 |
are the number of the capturing parenthesis, most significant byte first. The
|
682 |
rest of the entry is the corresponding name, zero terminated. The names are in
|
683 |
alphabetical order. For example, consider the following pattern (assume
|
684 |
PCRE_EXTENDED is set, so white space - including newlines - is ignored):
|
685 |
.sp
|
686 |
.\" JOIN
|
687 |
(?P<date> (?P<year>(\ed\ed)?\ed\ed) -
|
688 |
(?P<month>\ed\ed) - (?P<day>\ed\ed) )
|
689 |
.sp
|
690 |
There are four named subpatterns, so the table has four entries, and each entry
|
691 |
in the table is eight bytes long. The table is as follows, with non-printing
|
692 |
bytes shows in hexadecimal, and undefined bytes shown as ??:
|
693 |
.sp
|
694 |
00 01 d a t e 00 ??
|
695 |
00 05 d a y 00 ?? ??
|
696 |
00 04 m o n t h 00
|
697 |
00 02 y e a r 00 ??
|
698 |
.sp
|
699 |
When writing code to extract data from named subpatterns using the
|
700 |
name-to-number map, remember that the length of each entry is likely to be
|
701 |
different for each compiled pattern.
|
702 |
.sp
|
703 |
PCRE_INFO_OPTIONS
|
704 |
.sp
|
705 |
Return a copy of the options with which the pattern was compiled. The fourth
|
706 |
argument should point to an \fBunsigned long int\fP variable. These option bits
|
707 |
are those specified in the call to \fBpcre_compile()\fP, modified by any
|
708 |
top-level option settings within the pattern itself.
|
709 |
.P
|
710 |
A pattern is automatically anchored by PCRE if all of its top-level
|
711 |
alternatives begin with one of the following:
|
712 |
.sp
|
713 |
^ unless PCRE_MULTILINE is set
|
714 |
\eA always
|
715 |
\eG always
|
716 |
.\" JOIN
|
717 |
.* if PCRE_DOTALL is set and there are no back
|
718 |
references to the subpattern in which .* appears
|
719 |
.sp
|
720 |
For such patterns, the PCRE_ANCHORED bit is set in the options returned by
|
721 |
\fBpcre_fullinfo()\fP.
|
722 |
.sp
|
723 |
PCRE_INFO_SIZE
|
724 |
.sp
|
725 |
Return the size of the compiled pattern, that is, the value that was passed as
|
726 |
the argument to \fBpcre_malloc()\fP when PCRE was getting memory in which to
|
727 |
place the compiled data. The fourth argument should point to a \fBsize_t\fP
|
728 |
variable.
|
729 |
.sp
|
730 |
PCRE_INFO_STUDYSIZE
|
731 |
.sp
|
732 |
Return the size of the data block pointed to by the \fIstudy_data\fP field in
|
733 |
a \fBpcre_extra\fP block. That is, it is the value that was passed to
|
734 |
\fBpcre_malloc()\fP when PCRE was getting memory into which to place the data
|
735 |
created by \fBpcre_study()\fP. The fourth argument should point to a
|
736 |
\fBsize_t\fP variable.
|
737 |
.
|
738 |
.
|
739 |
.SH "OBSOLETE INFO FUNCTION"
|
740 |
.rs
|
741 |
.sp
|
742 |
.B int pcre_info(const pcre *\fIcode\fP, int *\fIoptptr\fP, int
|
743 |
.B *\fIfirstcharptr\fP);
|
744 |
.PP
|
745 |
The \fBpcre_info()\fP function is now obsolete because its interface is too
|
746 |
restrictive to return all the available data about a compiled pattern. New
|
747 |
programs should use \fBpcre_fullinfo()\fP instead. The yield of
|
748 |
\fBpcre_info()\fP is the number of capturing subpatterns, or one of the
|
749 |
following negative numbers:
|
750 |
.sp
|
751 |
PCRE_ERROR_NULL the argument \fIcode\fP was NULL
|
752 |
PCRE_ERROR_BADMAGIC the "magic number" was not found
|
753 |
.sp
|
754 |
If the \fIoptptr\fP argument is not NULL, a copy of the options with which the
|
755 |
pattern was compiled is placed in the integer it points to (see
|
756 |
PCRE_INFO_OPTIONS above).
|
757 |
.P
|
758 |
If the pattern is not anchored and the \fIfirstcharptr\fP argument is not NULL,
|
759 |
it is used to pass back information about the first character of any matched
|
760 |
string (see PCRE_INFO_FIRSTBYTE above).
|
761 |
.
|
762 |
.
|
763 |
.SH "MATCHING A PATTERN"
|
764 |
.rs
|
765 |
.sp
|
766 |
.B int pcre_exec(const pcre *\fIcode\fP, "const pcre_extra *\fIextra\fP,"
|
767 |
.ti +5n
|
768 |
.B "const char *\fIsubject\fP," int \fIlength\fP, int \fIstartoffset\fP,
|
769 |
.ti +5n
|
770 |
.B int \fIoptions\fP, int *\fIovector\fP, int \fIovecsize\fP);
|
771 |
.P
|
772 |
The function \fBpcre_exec()\fP is called to match a subject string against a
|
773 |
compiled pattern, which is passed in the \fIcode\fP argument. If the
|
774 |
pattern has been studied, the result of the study should be passed in the
|
775 |
\fIextra\fP argument.
|
776 |
.P
|
777 |
In most applications, the pattern will have been compiled (and optionally
|
778 |
studied) in the same process that calls \fBpcre_exec()\fP. However, it is
|
779 |
possible to save compiled patterns and study data, and then use them later
|
780 |
in different processes, possibly even on different hosts. For a discussion
|
781 |
about this, see the
|
782 |
.\" HREF
|
783 |
\fBpcreprecompile\fP
|
784 |
.\"
|
785 |
documentation.
|
786 |
.P
|
787 |
Here is an example of a simple call to \fBpcre_exec()\fP:
|
788 |
.sp
|
789 |
int rc;
|
790 |
int ovector[30];
|
791 |
rc = pcre_exec(
|
792 |
re, /* result of pcre_compile() */
|
793 |
NULL, /* we didn't study the pattern */
|
794 |
"some string", /* the subject string */
|
795 |
11, /* the length of the subject string */
|
796 |
0, /* start at offset 0 in the subject */
|
797 |
0, /* default options */
|
798 |
ovector, /* vector of integers for substring information */
|
799 |
30); /* number of elements in the vector (NOT size in bytes) */
|
800 |
.
|
801 |
.\" HTML <a name="extradata"></a>
|
802 |
.SS "Extra data for \fBpcre_exec()\fR"
|
803 |
.rs
|
804 |
.sp
|
805 |
If the \fIextra\fP argument is not NULL, it must point to a \fBpcre_extra\fP
|
806 |
data block. The \fBpcre_study()\fP function returns such a block (when it
|
807 |
doesn't return NULL), but you can also create one for yourself, and pass
|
808 |
additional information in it. The fields in a \fBpcre_extra\fP block are as
|
809 |
follows:
|
810 |
.sp
|
811 |
unsigned long int \fIflags\fP;
|
812 |
void *\fIstudy_data\fP;
|
813 |
unsigned long int \fImatch_limit\fP;
|
814 |
void *\fIcallout_data\fP;
|
815 |
const unsigned char *\fItables\fP;
|
816 |
.sp
|
817 |
The \fIflags\fP field is a bitmap that specifies which of the other fields
|
818 |
are set. The flag bits are:
|
819 |
.sp
|
820 |
PCRE_EXTRA_STUDY_DATA
|
821 |
PCRE_EXTRA_MATCH_LIMIT
|
822 |
PCRE_EXTRA_CALLOUT_DATA
|
823 |
PCRE_EXTRA_TABLES
|
824 |
.sp
|
825 |
Other flag bits should be set to zero. The \fIstudy_data\fP field is set in the
|
826 |
\fBpcre_extra\fP block that is returned by \fBpcre_study()\fP, together with
|
827 |
the appropriate flag bit. You should not set this yourself, but you may add to
|
828 |
the block by setting the other fields and their corresponding flag bits.
|
829 |
.P
|
830 |
The \fImatch_limit\fP field provides a means of preventing PCRE from using up a
|
831 |
vast amount of resources when running patterns that are not going to match,
|
832 |
but which have a very large number of possibilities in their search trees. The
|
833 |
classic example is the use of nested unlimited repeats.
|
834 |
.P
|
835 |
Internally, PCRE uses a function called \fBmatch()\fP which it calls repeatedly
|
836 |
(sometimes recursively). The limit is imposed on the number of times this
|
837 |
function is called during a match, which has the effect of limiting the amount
|
838 |
of recursion and backtracking that can take place. For patterns that are not
|
839 |
anchored, the count starts from zero for each position in the subject string.
|
840 |
.P
|
841 |
The default limit for the library can be set when PCRE is built; the default
|
842 |
default is 10 million, which handles all but the most extreme cases. You can
|
843 |
reduce the default by suppling \fBpcre_exec()\fP with a \fBpcre_extra\fP block
|
844 |
in which \fImatch_limit\fP is set to a smaller value, and
|
845 |
PCRE_EXTRA_MATCH_LIMIT is set in the \fIflags\fP field. If the limit is
|
846 |
exceeded, \fBpcre_exec()\fP returns PCRE_ERROR_MATCHLIMIT.
|
847 |
.P
|
848 |
The \fIpcre_callout\fP field is used in conjunction with the "callout" feature,
|
849 |
which is described in the
|
850 |
.\" HREF
|
851 |
\fBpcrecallout\fP
|
852 |
.\"
|
853 |
documentation.
|
854 |
.P
|
855 |
The \fItables\fP field is used to pass a character tables pointer to
|
856 |
\fBpcre_exec()\fP; this overrides the value that is stored with the compiled
|
857 |
pattern. A non-NULL value is stored with the compiled pattern only if custom
|
858 |
tables were supplied to \fBpcre_compile()\fP via its \fItableptr\fP argument.
|
859 |
If NULL is passed to \fBpcre_exec()\fP using this mechanism, it forces PCRE's
|
860 |
internal tables to be used. This facility is helpful when re-using patterns
|
861 |
that have been saved after compiling with an external set of tables, because
|
862 |
the external tables might be at a different address when \fBpcre_exec()\fP is
|
863 |
called. See the
|
864 |
.\" HREF
|
865 |
\fBpcreprecompile\fP
|
866 |
.\"
|
867 |
documentation for a discussion of saving compiled patterns for later use.
|
868 |
.
|
869 |
.SS "Option bits for \fBpcre_exec()\fP"
|
870 |
.rs
|
871 |
.sp
|
872 |
The unused bits of the \fIoptions\fP argument for \fBpcre_exec()\fP must be
|
873 |
zero. The only bits that may be set are PCRE_ANCHORED, PCRE_NOTBOL,
|
874 |
PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NO_UTF8_CHECK and PCRE_PARTIAL.
|
875 |
.sp
|
876 |
PCRE_ANCHORED
|
877 |
.sp
|
878 |
The PCRE_ANCHORED option limits \fBpcre_exec()\fP to matching at the first
|
879 |
matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out
|
880 |
to be anchored by virtue of its contents, it cannot be made unachored at
|
881 |
matching time.
|
882 |
.sp
|
883 |
PCRE_NOTBOL
|
884 |
.sp
|
885 |
This option specifies that first character of the subject string is not the
|
886 |
beginning of a line, so the circumflex metacharacter should not match before
|
887 |
it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex
|
888 |
never to match. This option affects only the behaviour of the circumflex
|
889 |
metacharacter. It does not affect \eA.
|
890 |
.sp
|
891 |
PCRE_NOTEOL
|
892 |
.sp
|
893 |
This option specifies that the end of the subject string is not the end of a
|
894 |
line, so the dollar metacharacter should not match it nor (except in multiline
|
895 |
mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at
|
896 |
compile time) causes dollar never to match. This option affects only the
|
897 |
behaviour of the dollar metacharacter. It does not affect \eZ or \ez.
|
898 |
.sp
|
899 |
PCRE_NOTEMPTY
|
900 |
.sp
|
901 |
An empty string is not considered to be a valid match if this option is set. If
|
902 |
there are alternatives in the pattern, they are tried. If all the alternatives
|
903 |
match the empty string, the entire match fails. For example, if the pattern
|
904 |
.sp
|
905 |
a?b?
|
906 |
.sp
|
907 |
is applied to a string not beginning with "a" or "b", it matches the empty
|
908 |
string at the start of the subject. With PCRE_NOTEMPTY set, this match is not
|
909 |
valid, so PCRE searches further into the string for occurrences of "a" or "b".
|
910 |
.P
|
911 |
Perl has no direct equivalent of PCRE_NOTEMPTY, but it does make a special case
|
912 |
of a pattern match of the empty string within its \fBsplit()\fP function, and
|
913 |
when using the /g modifier. It is possible to emulate Perl's behaviour after
|
914 |
matching a null string by first trying the match again at the same offset with
|
915 |
PCRE_NOTEMPTY and PCRE_ANCHORED, and then if that fails by advancing the
|
916 |
starting offset (see below) and trying an ordinary match again. There is some
|
917 |
code that demonstrates how to do this in the \fIpcredemo.c\fP sample program.
|
918 |
.sp
|
919 |
PCRE_NO_UTF8_CHECK
|
920 |
.sp
|
921 |
When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
|
922 |
string is automatically checked when \fBpcre_exec()\fP is subsequently called.
|
923 |
The value of \fIstartoffset\fP is also checked to ensure that it points to the
|
924 |
start of a UTF-8 character. If an invalid UTF-8 sequence of bytes is found,
|
925 |
\fBpcre_exec()\fP returns the error PCRE_ERROR_BADUTF8. If \fIstartoffset\fP
|
926 |
contains an invalid value, PCRE_ERROR_BADUTF8_OFFSET is returned.
|
927 |
.P
|
928 |
If you already know that your subject is valid, and you want to skip these
|
929 |
checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when
|
930 |
calling \fBpcre_exec()\fP. You might want to do this for the second and
|
931 |
subsequent calls to \fBpcre_exec()\fP if you are making repeated calls to find
|
932 |
all the matches in a single subject string. However, you should be sure that
|
933 |
the value of \fIstartoffset\fP points to the start of a UTF-8 character. When
|
934 |
PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8 string as a
|
935 |
subject, or a value of \fIstartoffset\fP that does not point to the start of a
|
936 |
UTF-8 character, is undefined. Your program may crash.
|
937 |
.sp
|
938 |
PCRE_PARTIAL
|
939 |
.sp
|
940 |
This option turns on the partial matching feature. If the subject string fails
|
941 |
to match the pattern, but at some point during the matching process the end of
|
942 |
the subject was reached (that is, the subject partially matches the pattern and
|
943 |
the failure to match occurred only because there were not enough subject
|
944 |
characters), \fBpcre_exec()\fP returns PCRE_ERROR_PARTIAL instead of
|
945 |
PCRE_ERROR_NOMATCH. When PCRE_PARTIAL is used, there are restrictions on what
|
946 |
may appear in the pattern. These are discussed in the
|
947 |
.\" HREF
|
948 |
\fBpcrepartial\fP
|
949 |
.\"
|
950 |
documentation.
|
951 |
.
|
952 |
.SS "The string to be matched by \fBpcre_exec()\fP"
|
953 |
.rs
|
954 |
.sp
|
955 |
The subject string is passed to \fBpcre_exec()\fP as a pointer in
|
956 |
\fIsubject\fP, a length in \fIlength\fP, and a starting byte offset in
|
957 |
\fIstartoffset\fP. In UTF-8 mode, the byte offset must point to the start of a
|
958 |
UTF-8 character. Unlike the pattern string, the subject may contain binary zero
|
959 |
bytes. When the starting offset is zero, the search for a match starts at the
|
960 |
beginning of the subject, and this is by far the most common case.
|
961 |
.P
|
962 |
A non-zero starting offset is useful when searching for another match in the
|
963 |
same subject by calling \fBpcre_exec()\fP again after a previous success.
|
964 |
Setting \fIstartoffset\fP differs from just passing over a shortened string and
|
965 |
setting PCRE_NOTBOL in the case of a pattern that begins with any kind of
|
966 |
lookbehind. For example, consider the pattern
|
967 |
.sp
|
968 |
\eBiss\eB
|
969 |
.sp
|
970 |
which finds occurrences of "iss" in the middle of words. (\eB matches only if
|
971 |
the current position in the subject is not a word boundary.) When applied to
|
972 |
the string "Mississipi" the first call to \fBpcre_exec()\fP finds the first
|
973 |
occurrence. If \fBpcre_exec()\fP is called again with just the remainder of the
|
974 |
subject, namely "issipi", it does not match, because \eB is always false at the
|
975 |
start of the subject, which is deemed to be a word boundary. However, if
|
976 |
\fBpcre_exec()\fP is passed the entire string again, but with \fIstartoffset\fP
|
977 |
set to 4, it finds the second occurrence of "iss" because it is able to look
|
978 |
behind the starting point to discover that it is preceded by a letter.
|
979 |
.P
|
980 |
If a non-zero starting offset is passed when the pattern is anchored, one
|
981 |
attempt to match at the given offset is made. This can only succeed if the
|
982 |
pattern does not require the match to be at the start of the subject.
|
983 |
.
|
984 |
.SS "How \fBpcre_exec()\fP returns captured substrings"
|
985 |
.rs
|
986 |
.sp
|
987 |
In general, a pattern matches a certain portion of the subject, and in
|
988 |
addition, further substrings from the subject may be picked out by parts of the
|
989 |
pattern. Following the usage in Jeffrey Friedl's book, this is called
|
990 |
"capturing" in what follows, and the phrase "capturing subpattern" is used for
|
991 |
a fragment of a pattern that picks out a substring. PCRE supports several other
|
992 |
kinds of parenthesized subpattern that do not cause substrings to be captured.
|
993 |
.P
|
994 |
Captured substrings are returned to the caller via a vector of integer offsets
|
995 |
whose address is passed in \fIovector\fP. The number of elements in the vector
|
996 |
is passed in \fIovecsize\fP, which must be a non-negative number. \fBNote\fP:
|
997 |
this argument is NOT the size of \fIovector\fP in bytes.
|
998 |
.P
|
999 |
The first two-thirds of the vector is used to pass back captured substrings,
|
1000 |
each substring using a pair of integers. The remaining third of the vector is
|
1001 |
used as workspace by \fBpcre_exec()\fP while matching capturing subpatterns,
|
1002 |
and is not available for passing back information. The length passed in
|
1003 |
\fIovecsize\fP should always be a multiple of three. If it is not, it is
|
1004 |
rounded down.
|
1005 |
.P
|
1006 |
When a match is successful, information about captured substrings is returned
|
1007 |
in pairs of integers, starting at the beginning of \fIovector\fP, and
|
1008 |
continuing up to two-thirds of its length at the most. The first element of a
|
1009 |
pair is set to the offset of the first character in a substring, and the second
|
1010 |
is set to the offset of the first character after the end of a substring. The
|
1011 |
first pair, \fIovector[0]\fP and \fIovector[1]\fP, identify the portion of the
|
1012 |
subject string matched by the entire pattern. The next pair is used for the
|
1013 |
first capturing subpattern, and so on. The value returned by \fBpcre_exec()\fP
|
1014 |
is the number of pairs that have been set. If there are no capturing
|
1015 |
subpatterns, the return value from a successful match is 1, indicating that
|
1016 |
just the first pair of offsets has been set.
|
1017 |
.P
|
1018 |
Some convenience functions are provided for extracting the captured substrings
|
1019 |
as separate strings. These are described in the following section.
|
1020 |
.P
|
1021 |
It is possible for an capturing subpattern number \fIn+1\fP to match some
|
1022 |
part of the subject when subpattern \fIn\fP has not been used at all. For
|
1023 |
example, if the string "abc" is matched against the pattern (a|(z))(bc)
|
1024 |
subpatterns 1 and 3 are matched, but 2 is not. When this happens, both offset
|
1025 |
values corresponding to the unused subpattern are set to -1.
|
1026 |
.P
|
1027 |
If a capturing subpattern is matched repeatedly, it is the last portion of the
|
1028 |
string that it matched that is returned.
|
1029 |
.P
|
1030 |
If the vector is too small to hold all the captured substring offsets, it is
|
1031 |
used as far as possible (up to two-thirds of its length), and the function
|
1032 |
returns a value of zero. In particular, if the substring offsets are not of
|
1033 |
interest, \fBpcre_exec()\fP may be called with \fIovector\fP passed as NULL and
|
1034 |
\fIovecsize\fP as zero. However, if the pattern contains back references and
|
1035 |
the \fIovector\fP is not big enough to remember the related substrings, PCRE
|
1036 |
has to get additional memory for use during matching. Thus it is usually
|
1037 |
advisable to supply an \fIovector\fP.
|
1038 |
.P
|
1039 |
Note that \fBpcre_info()\fP can be used to find out how many capturing
|
1040 |
subpatterns there are in a compiled pattern. The smallest size for
|
1041 |
\fIovector\fP that will allow for \fIn\fP captured substrings, in addition to
|
1042 |
the offsets of the substring matched by the whole pattern, is (\fIn\fP+1)*3.
|
1043 |
.
|
1044 |
.SS "Return values from \fBpcre_exec()\fP"
|
1045 |
.rs
|
1046 |
.sp
|
1047 |
If \fBpcre_exec()\fP fails, it returns a negative number. The following are
|
1048 |
defined in the header file:
|
1049 |
.sp
|
1050 |
PCRE_ERROR_NOMATCH (-1)
|
1051 |
.sp
|
1052 |
The subject string did not match the pattern.
|
1053 |
.sp
|
1054 |
PCRE_ERROR_NULL (-2)
|
1055 |
.sp
|
1056 |
Either \fIcode\fP or \fIsubject\fP was passed as NULL, or \fIovector\fP was
|
1057 |
NULL and \fIovecsize\fP was not zero.
|
1058 |
.sp
|
1059 |
PCRE_ERROR_BADOPTION (-3)
|
1060 |
.sp
|
1061 |
An unrecognized bit was set in the \fIoptions\fP argument.
|
1062 |
.sp
|
1063 |
PCRE_ERROR_BADMAGIC (-4)
|
1064 |
.sp
|
1065 |
PCRE stores a 4-byte "magic number" at the start of the compiled code, to catch
|
1066 |
the case when it is passed a junk pointer and to detect when a pattern that was
|
1067 |
compiled in an environment of one endianness is run in an environment with the
|
1068 |
other endianness. This is the error that PCRE gives when the magic number is
|
1069 |
not present.
|
1070 |
.sp
|
1071 |
PCRE_ERROR_UNKNOWN_NODE (-5)
|
1072 |
.sp
|
1073 |
While running the pattern match, an unknown item was encountered in the
|
1074 |
compiled pattern. This error could be caused by a bug in PCRE or by overwriting
|
1075 |
of the compiled pattern.
|
1076 |
.sp
|
1077 |
PCRE_ERROR_NOMEMORY (-6)
|
1078 |
.sp
|
1079 |
If a pattern contains back references, but the \fIovector\fP that is passed to
|
1080 |
\fBpcre_exec()\fP is not big enough to remember the referenced substrings, PCRE
|
1081 |
gets a block of memory at the start of matching to use for this purpose. If the
|
1082 |
call via \fBpcre_malloc()\fP fails, this error is given. The memory is
|
1083 |
automatically freed at the end of matching.
|
1084 |
.sp
|
1085 |
PCRE_ERROR_NOSUBSTRING (-7)
|
1086 |
.sp
|
1087 |
This error is used by the \fBpcre_copy_substring()\fP,
|
1088 |
\fBpcre_get_substring()\fP, and \fBpcre_get_substring_list()\fP functions (see
|
1089 |
below). It is never returned by \fBpcre_exec()\fP.
|
1090 |
.sp
|
1091 |
PCRE_ERROR_MATCHLIMIT (-8)
|
1092 |
.sp
|
1093 |
The recursion and backtracking limit, as specified by the \fImatch_limit\fP
|
1094 |
field in a \fBpcre_extra\fP structure (or defaulted) was reached. See the
|
1095 |
description above.
|
1096 |
.sp
|
1097 |
PCRE_ERROR_CALLOUT (-9)
|
1098 |
.sp
|
1099 |
This error is never generated by \fBpcre_exec()\fP itself. It is provided for
|
1100 |
use by callout functions that want to yield a distinctive error code. See the
|
1101 |
.\" HREF
|
1102 |
\fBpcrecallout\fP
|
1103 |
.\"
|
1104 |
documentation for details.
|
1105 |
.sp
|
1106 |
PCRE_ERROR_BADUTF8 (-10)
|
1107 |
.sp
|
1108 |
A string that contains an invalid UTF-8 byte sequence was passed as a subject.
|
1109 |
.sp
|
1110 |
PCRE_ERROR_BADUTF8_OFFSET (-11)
|
1111 |
.sp
|
1112 |
The UTF-8 byte sequence that was passed as a subject was valid, but the value
|
1113 |
of \fIstartoffset\fP did not point to the beginning of a UTF-8 character.
|
1114 |
.sp
|
1115 |
PCRE_ERROR_PARTIAL (-12)
|
1116 |
.sp
|
1117 |
The subject string did not match, but it did match partially. See the
|
1118 |
.\" HREF
|
1119 |
\fBpcrepartial\fP
|
1120 |
.\"
|
1121 |
documentation for details of partial matching.
|
1122 |
.sp
|
1123 |
PCRE_ERROR_BAD_PARTIAL (-13)
|
1124 |
.sp
|
1125 |
The PCRE_PARTIAL option was used with a compiled pattern containing items that
|
1126 |
are not supported for partial matching. See the
|
1127 |
.\" HREF
|
1128 |
\fBpcrepartial\fP
|
1129 |
.\"
|
1130 |
documentation for details of partial matching.
|
1131 |
.sp
|
1132 |
PCRE_ERROR_INTERNAL (-14)
|
1133 |
.sp
|
1134 |
An unexpected internal error has occurred. This error could be caused by a bug
|
1135 |
in PCRE or by overwriting of the compiled pattern.
|
1136 |
.sp
|
1137 |
PCRE_ERROR_BADCOUNT (-15)
|
1138 |
.sp
|
1139 |
This error is given if the value of the \fIovecsize\fP argument is negative.
|
1140 |
.
|
1141 |
.
|
1142 |
.SH "EXTRACTING CAPTURED SUBSTRINGS BY NUMBER"
|
1143 |
.rs
|
1144 |
.sp
|
1145 |
.B int pcre_copy_substring(const char *\fIsubject\fP, int *\fIovector\fP,
|
1146 |
.ti +5n
|
1147 |
.B int \fIstringcount\fP, int \fIstringnumber\fP, char *\fIbuffer\fP,
|
1148 |
.ti +5n
|
1149 |
.B int \fIbuffersize\fP);
|
1150 |
.PP
|
1151 |
.br
|
1152 |
.B int pcre_get_substring(const char *\fIsubject\fP, int *\fIovector\fP,
|
1153 |
.ti +5n
|
1154 |
.B int \fIstringcount\fP, int \fIstringnumber\fP,
|
1155 |
.ti +5n
|
1156 |
.B const char **\fIstringptr\fP);
|
1157 |
.PP
|
1158 |
.br
|
1159 |
.B int pcre_get_substring_list(const char *\fIsubject\fP,
|
1160 |
.ti +5n
|
1161 |
.B int *\fIovector\fP, int \fIstringcount\fP, "const char ***\fIlistptr\fP);"
|
1162 |
.PP
|
1163 |
Captured substrings can be accessed directly by using the offsets returned by
|
1164 |
\fBpcre_exec()\fP in \fIovector\fP. For convenience, the functions
|
1165 |
\fBpcre_copy_substring()\fP, \fBpcre_get_substring()\fP, and
|
1166 |
\fBpcre_get_substring_list()\fP are provided for extracting captured substrings
|
1167 |
as new, separate, zero-terminated strings. These functions identify substrings
|
1168 |
by number. The next section describes functions for extracting named
|
1169 |
substrings. A substring that contains a binary zero is correctly extracted and
|
1170 |
has a further zero added on the end, but the result is not, of course,
|
1171 |
a C string.
|
1172 |
.P
|
1173 |
The first three arguments are the same for all three of these functions:
|
1174 |
\fIsubject\fP is the subject string that has just been successfully matched,
|
1175 |
\fIovector\fP is a pointer to the vector of integer offsets that was passed to
|
1176 |
\fBpcre_exec()\fP, and \fIstringcount\fP is the number of substrings that were
|
1177 |
captured by the match, including the substring that matched the entire regular
|
1178 |
expression. This is the value returned by \fBpcre_exec()\fP if it is greater
|
1179 |
than zero. If \fBpcre_exec()\fP returned zero, indicating that it ran out of
|
1180 |
space in \fIovector\fP, the value passed as \fIstringcount\fP should be the
|
1181 |
number of elements in the vector divided by three.
|
1182 |
.P
|
1183 |
The functions \fBpcre_copy_substring()\fP and \fBpcre_get_substring()\fP
|
1184 |
extract a single substring, whose number is given as \fIstringnumber\fP. A
|
1185 |
value of zero extracts the substring that matched the entire pattern, whereas
|
1186 |
higher values extract the captured substrings. For \fBpcre_copy_substring()\fP,
|
1187 |
the string is placed in \fIbuffer\fP, whose length is given by
|
1188 |
\fIbuffersize\fP, while for \fBpcre_get_substring()\fP a new block of memory is
|
1189 |
obtained via \fBpcre_malloc\fP, and its address is returned via
|
1190 |
\fIstringptr\fP. The yield of the function is the length of the string, not
|
1191 |
including the terminating zero, or one of
|
1192 |
.sp
|
1193 |
PCRE_ERROR_NOMEMORY (-6)
|
1194 |
.sp
|
1195 |
The buffer was too small for \fBpcre_copy_substring()\fP, or the attempt to get
|
1196 |
memory failed for \fBpcre_get_substring()\fP.
|
1197 |
.sp
|
1198 |
PCRE_ERROR_NOSUBSTRING (-7)
|
1199 |
.sp
|
1200 |
There is no substring whose number is \fIstringnumber\fP.
|
1201 |
.P
|
1202 |
The \fBpcre_get_substring_list()\fP function extracts all available substrings
|
1203 |
and builds a list of pointers to them. All this is done in a single block of
|
1204 |
memory that is obtained via \fBpcre_malloc\fP. The address of the memory block
|
1205 |
is returned via \fIlistptr\fP, which is also the start of the list of string
|
1206 |
pointers. The end of the list is marked by a NULL pointer. The yield of the
|
1207 |
function is zero if all went well, or
|
1208 |
.sp
|
1209 |
PCRE_ERROR_NOMEMORY (-6)
|
1210 |
.sp
|
1211 |
if the attempt to get the memory block failed.
|
1212 |
.P
|
1213 |
When any of these functions encounter a substring that is unset, which can
|
1214 |
happen when capturing subpattern number \fIn+1\fP matches some part of the
|
1215 |
subject, but subpattern \fIn\fP has not been used at all, they return an empty
|
1216 |
string. This can be distinguished from a genuine zero-length substring by
|
1217 |
inspecting the appropriate offset in \fIovector\fP, which is negative for unset
|
1218 |
substrings.
|
1219 |
.P
|
1220 |
The two convenience functions \fBpcre_free_substring()\fP and
|
1221 |
\fBpcre_free_substring_list()\fP can be used to free the memory returned by
|
1222 |
a previous call of \fBpcre_get_substring()\fP or
|
1223 |
\fBpcre_get_substring_list()\fP, respectively. They do nothing more than call
|
1224 |
the function pointed to by \fBpcre_free\fP, which of course could be called
|
1225 |
directly from a C program. However, PCRE is used in some situations where it is
|
1226 |
linked via a special interface to another programming language which cannot use
|
1227 |
\fBpcre_free\fP directly; it is for these cases that the functions are
|
1228 |
provided.
|
1229 |
.
|
1230 |
.
|
1231 |
.SH "EXTRACTING CAPTURED SUBSTRINGS BY NAME"
|
1232 |
.rs
|
1233 |
.sp
|
1234 |
.B int pcre_get_stringnumber(const pcre *\fIcode\fP,
|
1235 |
.ti +5n
|
1236 |
.B const char *\fIname\fP);
|
1237 |
.PP
|
1238 |
.br
|
1239 |
.B int pcre_copy_named_substring(const pcre *\fIcode\fP,
|
1240 |
.ti +5n
|
1241 |
.B const char *\fIsubject\fP, int *\fIovector\fP,
|
1242 |
.ti +5n
|
1243 |
.B int \fIstringcount\fP, const char *\fIstringname\fP,
|
1244 |
.ti +5n
|
1245 |
.B char *\fIbuffer\fP, int \fIbuffersize\fP);
|
1246 |
.PP
|
1247 |
.br
|
1248 |
.B int pcre_get_named_substring(const pcre *\fIcode\fP,
|
1249 |
.ti +5n
|
1250 |
.B const char *\fIsubject\fP, int *\fIovector\fP,
|
1251 |
.ti +5n
|
1252 |
.B int \fIstringcount\fP, const char *\fIstringname\fP,
|
1253 |
.ti +5n
|
1254 |
.B const char **\fIstringptr\fP);
|
1255 |
.PP
|
1256 |
To extract a substring by name, you first have to find associated number.
|
1257 |
For example, for this pattern
|
1258 |
.sp
|
1259 |
(a+)b(?<xxx>\ed+)...
|
1260 |
.sp
|
1261 |
the number of the subpattern called "xxx" is 2. You can find the number from
|
1262 |
the name by calling \fBpcre_get_stringnumber()\fP. The first argument is the
|
1263 |
compiled pattern, and the second is the name. The yield of the function is the
|
1264 |
subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of
|
1265 |
that name.
|
1266 |
.P
|
1267 |
Given the number, you can extract the substring directly, or use one of the
|
1268 |
functions described in the previous section. For convenience, there are also
|
1269 |
two functions that do the whole job.
|
1270 |
.P
|
1271 |
Most of the arguments of \fIpcre_copy_named_substring()\fP and
|
1272 |
\fIpcre_get_named_substring()\fP are the same as those for the similarly named
|
1273 |
functions that extract by number. As these are described in the previous
|
1274 |
section, they are not re-described here. There are just two differences:
|
1275 |
.P
|
1276 |
First, instead of a substring number, a substring name is given. Second, there
|
1277 |
is an extra argument, given at the start, which is a pointer to the compiled
|
1278 |
pattern. This is needed in order to gain access to the name-to-number
|
1279 |
translation table.
|
1280 |
.P
|
1281 |
These functions call \fBpcre_get_stringnumber()\fP, and if it succeeds, they
|
1282 |
then call \fIpcre_copy_substring()\fP or \fIpcre_get_substring()\fP, as
|
1283 |
appropriate.
|
1284 |
.P
|
1285 |
.in 0
|
1286 |
Last updated: 09 September 2004
|
1287 |
.br
|
1288 |
Copyright (c) 1997-2004 University of Cambridge.
|