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3 PCRE - Perl-compatible regular expressions
4 .
5 .
7 .rs
8 .sp
9 This document describes the optional features of PCRE that can be selected when
10 the library is compiled. It assumes use of the \fBconfigure\fP script, where
11 the optional features are selected or deselected by providing options to
12 \fBconfigure\fP before running the \fBmake\fP command. However, the same
13 options can be selected in both Unix-like and non-Unix-like environments using
14 the GUI facility of \fBcmake-gui\fP if you are using \fBCMake\fP instead of
15 \fBconfigure\fP to build PCRE.
16 .P
17 There is a lot more information about building PCRE in non-Unix-like
18 environments in the file called \fINON_UNIX_USE\fP, which is part of the PCRE
19 distribution. You should consult this file as well as the \fIREADME\fP file if
20 you are building in a non-Unix-like environment.
21 .P
22 The complete list of options for \fBconfigure\fP (which includes the standard
23 ones such as the selection of the installation directory) can be obtained by
24 running
25 .sp
26 ./configure --help
27 .sp
28 The following sections include descriptions of options whose names begin with
29 --enable or --disable. These settings specify changes to the defaults for the
30 \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
31 --enable and --disable always come in pairs, so the complementary option always
32 exists as well, but as it specifies the default, it is not described.
33 .
34 .
36 .rs
37 .sp
38 By default, a library called \fBlibpcre\fP is built, containing functions that
39 take string arguments contained in vectors of bytes, either as single-byte
40 characters, or interpreted as UTF-8 strings. You can also build a separate
41 library, called \fBlibpcre16\fP, in which strings are contained in vectors of
42 16-bit data units and interpreted either as single-unit characters or UTF-16
43 strings, by adding
44 .sp
45 --enable-pcre16
46 .sp
47 to the \fBconfigure\fP command. If you do not want the 8-bit library, add
48 .sp
49 --disable-pcre8
50 .sp
51 as well. At least one of the two libraries must be built. Note that the C++ and
52 POSIX wrappers are for the 8-bit library only, and that \fBpcregrep\fP is an
53 8-bit program. None of these are built if you select only the 16-bit library.
54 .
55 .
57 .rs
58 .sp
59 The PCRE building process uses \fBlibtool\fP to build both shared and static
60 Unix libraries by default. You can suppress one of these by adding one of
61 .sp
62 --disable-shared
63 --disable-static
64 .sp
65 to the \fBconfigure\fP command, as required.
66 .
67 .
68 .SH "C++ SUPPORT"
69 .rs
70 .sp
71 By default, if the 8-bit library is being built, the \fBconfigure\fP script
72 will search for a C++ compiler and C++ header files. If it finds them, it
73 automatically builds the C++ wrapper library (which supports only 8-bit
74 strings). You can disable this by adding
75 .sp
76 --disable-cpp
77 .sp
78 to the \fBconfigure\fP command.
79 .
80 .
81 .SH "UTF-8 and UTF-16 SUPPORT"
82 .rs
83 .sp
84 To build PCRE with support for UTF Unicode character strings, add
85 .sp
86 --enable-utf
87 .sp
88 to the \fBconfigure\fP command. This setting applies to both libraries, adding
89 support for UTF-8 to the 8-bit library and support for UTF-16 to the 16-bit
90 library. There are no separate options for enabling UTF-8 and UTF-16
91 independently because that would allow ridiculous settings such as requesting
92 UTF-16 support while building only the 8-bit library. It is not possible to
93 build one library with UTF support and the other without in the same
94 configuration. (For backwards compatibility, --enable-utf8 is a synonym of
95 --enable-utf.)
96 .P
97 Of itself, this setting does not make PCRE treat strings as UTF-8 or UTF-16. As
98 well as compiling PCRE with this option, you also have have to set the
99 PCRE_UTF8 or PCRE_UTF16 option when you call one of the pattern compiling
100 functions.
101 .P
102 If you set --enable-utf when compiling in an EBCDIC environment, PCRE expects
103 its input to be either ASCII or UTF-8 (depending on the runtime option). It is
104 not possible to support both EBCDIC and UTF-8 codes in the same version of the
105 library. Consequently, --enable-utf and --enable-ebcdic are mutually
106 exclusive.
107 .
108 .
110 .rs
111 .sp
112 UTF support allows the libraries to process character codepoints up to 0x10ffff
113 in the strings that they handle. On its own, however, it does not provide any
114 facilities for accessing the properties of such characters. If you want to be
115 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
116 character properties, you must add
117 .sp
118 --enable-unicode-properties
119 .sp
120 to the \fBconfigure\fP command. This implies UTF support, even if you have
121 not explicitly requested it.
122 .P
123 Including Unicode property support adds around 30K of tables to the PCRE
124 library. Only the general category properties such as \fILu\fP and \fINd\fP are
125 supported. Details are given in the
126 .\" HREF
127 \fBpcrepattern\fP
128 .\"
129 documentation.
130 .
131 .
133 .rs
134 .sp
135 Just-in-time compiler support is included in the build by specifying
136 .sp
137 --enable-jit
138 .sp
139 This support is available only for certain hardware architectures. If this
140 option is set for an unsupported architecture, a compile time error occurs.
141 See the
142 .\" HREF
143 \fBpcrejit\fP
144 .\"
145 documentation for a discussion of JIT usage. When JIT support is enabled,
146 pcregrep automatically makes use of it, unless you add
147 .sp
148 --disable-pcregrep-jit
149 .sp
150 to the "configure" command.
151 .
152 .
154 .rs
155 .sp
156 By default, PCRE interprets the linefeed (LF) character as indicating the end
157 of a line. This is the normal newline character on Unix-like systems. You can
158 compile PCRE to use carriage return (CR) instead, by adding
159 .sp
160 --enable-newline-is-cr
161 .sp
162 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
163 which explicitly specifies linefeed as the newline character.
164 .sp
165 Alternatively, you can specify that line endings are to be indicated by the two
166 character sequence CRLF. If you want this, add
167 .sp
168 --enable-newline-is-crlf
169 .sp
170 to the \fBconfigure\fP command. There is a fourth option, specified by
171 .sp
172 --enable-newline-is-anycrlf
173 .sp
174 which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
175 indicating a line ending. Finally, a fifth option, specified by
176 .sp
177 --enable-newline-is-any
178 .sp
179 causes PCRE to recognize any Unicode newline sequence.
180 .P
181 Whatever line ending convention is selected when PCRE is built can be
182 overridden when the library functions are called. At build time it is
183 conventional to use the standard for your operating system.
184 .
185 .
187 .rs
188 .sp
189 By default, the sequence \eR in a pattern matches any Unicode newline sequence,
190 whatever has been selected as the line ending sequence. If you specify
191 .sp
192 --enable-bsr-anycrlf
193 .sp
194 the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
195 selected when PCRE is built can be overridden when the library functions are
196 called.
197 .
198 .
200 .rs
201 .sp
202 When the 8-bit library is called through the POSIX interface (see the
203 .\" HREF
204 \fBpcreposix\fP
205 .\"
206 documentation), additional working storage is required for holding the pointers
207 to capturing substrings, because PCRE requires three integers per substring,
208 whereas the POSIX interface provides only two. If the number of expected
209 substrings is small, the wrapper function uses space on the stack, because this
210 is faster than using \fBmalloc()\fP for each call. The default threshold above
211 which the stack is no longer used is 10; it can be changed by adding a setting
212 such as
213 .sp
214 --with-posix-malloc-threshold=20
215 .sp
216 to the \fBconfigure\fP command.
217 .
218 .
220 .rs
221 .sp
222 Within a compiled pattern, offset values are used to point from one part to
223 another (for example, from an opening parenthesis to an alternation
224 metacharacter). By default, two-byte values are used for these offsets, leading
225 to a maximum size for a compiled pattern of around 64K. This is sufficient to
226 handle all but the most gigantic patterns. Nevertheless, some people do want to
227 process truly enormous patterns, so it is possible to compile PCRE to use
228 three-byte or four-byte offsets by adding a setting such as
229 .sp
230 --with-link-size=3
231 .sp
232 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. For the
233 16-bit library, a value of 3 is rounded up to 4. Using longer offsets slows
234 down the operation of PCRE because it has to load additional data when handling
235 them.
236 .
237 .
239 .rs
240 .sp
241 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
242 by making recursive calls to an internal function called \fBmatch()\fP. In
243 environments where the size of the stack is limited, this can severely limit
244 PCRE's operation. (The Unix environment does not usually suffer from this
245 problem, but it may sometimes be necessary to increase the maximum stack size.
246 There is a discussion in the
247 .\" HREF
248 \fBpcrestack\fP
249 .\"
250 documentation.) An alternative approach to recursion that uses memory from the
251 heap to remember data, instead of using recursive function calls, has been
252 implemented to work round the problem of limited stack size. If you want to
253 build a version of PCRE that works this way, add
254 .sp
255 --disable-stack-for-recursion
256 .sp
257 to the \fBconfigure\fP command. With this configuration, PCRE will use the
258 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
259 management functions. By default these point to \fBmalloc()\fP and
260 \fBfree()\fP, but you can replace the pointers so that your own functions are
261 used instead.
262 .P
263 Separate functions are provided rather than using \fBpcre_malloc\fP and
264 \fBpcre_free\fP because the usage is very predictable: the block sizes
265 requested are always the same, and the blocks are always freed in reverse
266 order. A calling program might be able to implement optimized functions that
267 perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
268 slowly when built in this way. This option affects only the \fBpcre_exec()\fP
269 function; it is not relevant for \fBpcre_dfa_exec()\fP.
270 .
271 .
273 .rs
274 .sp
275 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
276 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
277 function. By controlling the maximum number of times this function may be
278 called during a single matching operation, a limit can be placed on the
279 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
280 at run time, as described in the
281 .\" HREF
282 \fBpcreapi\fP
283 .\"
284 documentation. The default is 10 million, but this can be changed by adding a
285 setting such as
286 .sp
287 --with-match-limit=500000
288 .sp
289 to the \fBconfigure\fP command. This setting has no effect on the
290 \fBpcre_dfa_exec()\fP matching function.
291 .P
292 In some environments it is desirable to limit the depth of recursive calls of
293 \fBmatch()\fP more strictly than the total number of calls, in order to
294 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
295 is specified) that is used. A second limit controls this; it defaults to the
296 value that is set for --with-match-limit, which imposes no additional
297 constraints. However, you can set a lower limit by adding, for example,
298 .sp
299 --with-match-limit-recursion=10000
300 .sp
301 to the \fBconfigure\fP command. This value can also be overridden at run time.
302 .
303 .
305 .rs
306 .sp
307 PCRE uses fixed tables for processing characters whose code values are less
308 than 256. By default, PCRE is built with a set of tables that are distributed
309 in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
310 only. If you add
311 .sp
312 --enable-rebuild-chartables
313 .sp
314 to the \fBconfigure\fP command, the distributed tables are no longer used.
315 Instead, a program called \fBdftables\fP is compiled and run. This outputs the
316 source for new set of tables, created in the default locale of your C runtime
317 system. (This method of replacing the tables does not work if you are cross
318 compiling, because \fBdftables\fP is run on the local host. If you need to
319 create alternative tables when cross compiling, you will have to do so "by
320 hand".)
321 .
322 .
324 .rs
325 .sp
326 PCRE assumes by default that it will run in an environment where the character
327 code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
328 most computer operating systems. PCRE can, however, be compiled to run in an
329 EBCDIC environment by adding
330 .sp
331 --enable-ebcdic
332 .sp
333 to the \fBconfigure\fP command. This setting implies
334 --enable-rebuild-chartables. You should only use it if you know that you are in
335 an EBCDIC environment (for example, an IBM mainframe operating system). The
336 --enable-ebcdic option is incompatible with --enable-utf.
337 .
338 .
340 .rs
341 .sp
342 By default, \fBpcregrep\fP reads all files as plain text. You can build it so
343 that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
344 them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
345 .sp
346 --enable-pcregrep-libz
347 --enable-pcregrep-libbz2
348 .sp
349 to the \fBconfigure\fP command. These options naturally require that the
350 relevant libraries are installed on your system. Configuration will fail if
351 they are not.
352 .
353 .
355 .rs
356 .sp
357 \fBpcregrep\fP uses an internal buffer to hold a "window" on the file it is
358 scanning, in order to be able to output "before" and "after" lines when it
359 finds a match. The size of the buffer is controlled by a parameter whose
360 default value is 20K. The buffer itself is three times this size, but because
361 of the way it is used for holding "before" lines, the longest line that is
362 guaranteed to be processable is the parameter size. You can change the default
363 parameter value by adding, for example,
364 .sp
365 --with-pcregrep-bufsize=50K
366 .sp
367 to the \fBconfigure\fP command. The caller of \fPpcregrep\fP can, however,
368 override this value by specifying a run-time option.
369 .
370 .
372 .rs
373 .sp
374 If you add
375 .sp
376 --enable-pcretest-libreadline
377 .sp
378 to the \fBconfigure\fP command, \fBpcretest\fP is linked with the
379 \fBlibreadline\fP library, and when its input is from a terminal, it reads it
380 using the \fBreadline()\fP function. This provides line-editing and history
381 facilities. Note that \fBlibreadline\fP is GPL-licensed, so if you distribute a
382 binary of \fBpcretest\fP linked in this way, there may be licensing issues.
383 .P
384 Setting this option causes the \fB-lreadline\fP option to be added to the
385 \fBpcretest\fP build. In many operating environments with a sytem-installed
386 \fBlibreadline\fP this is sufficient. However, in some environments (e.g.
387 if an unmodified distribution version of readline is in use), some extra
388 configuration may be necessary. The INSTALL file for \fBlibreadline\fP says
389 this:
390 .sp
391 "Readline uses the termcap functions, but does not link with the
392 termcap or curses library itself, allowing applications which link
393 with readline the to choose an appropriate library."
394 .sp
395 If your environment has not been set up so that an appropriate library is
396 automatically included, you may need to add something like
397 .sp
398 LIBS="-ncurses"
399 .sp
400 immediately before the \fBconfigure\fP command.
401 .
402 .
403 .SH "SEE ALSO"
404 .rs
405 .sp
406 \fBpcreapi\fP(3), \fBpcre16\fP, \fBpcre_config\fP(3).
407 .
408 .
410 .rs
411 .sp
412 .nf
413 Philip Hazel
414 University Computing Service
415 Cambridge CB2 3QH, England.
416 .fi
417 .
418 .
420 .rs
421 .sp
422 .nf
423 Last updated: 07 January 2012
424 Copyright (c) 1997-2012 University of Cambridge.
425 .fi


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