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Update after detrailing for a test release.
3 PCRE - Perl-compatible regular expressions
5 .rs
6 .sp
7 This document describes the optional features of PCRE that can be selected when
8 the library is compiled. It assumes use of the \fBconfigure\fP script, where
9 the optional features are selected or deselected by providing options to
10 \fBconfigure\fP before running the \fBmake\fP command. However, the same
11 options can be selected in both Unix-like and non-Unix-like environments using
12 the GUI facility of \fBCMakeSetup\fP if you are using \fBCMake\fP instead of
13 \fBconfigure\fP to build PCRE.
14 .P
15 The complete list of options for \fBconfigure\fP (which includes the standard
16 ones such as the selection of the installation directory) can be obtained by
17 running
18 .sp
19 ./configure --help
20 .sp
21 The following sections include descriptions of options whose names begin with
22 --enable or --disable. These settings specify changes to the defaults for the
23 \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
24 --enable and --disable always come in pairs, so the complementary option always
25 exists as well, but as it specifies the default, it is not described.
26 .
27 .SH "C++ SUPPORT"
28 .rs
29 .sp
30 By default, the \fBconfigure\fP script will search for a C++ compiler and C++
31 header files. If it finds them, it automatically builds the C++ wrapper library
32 for PCRE. You can disable this by adding
33 .sp
34 --disable-cpp
35 .sp
36 to the \fBconfigure\fP command.
37 .
39 .rs
40 .sp
41 To build PCRE with support for UTF-8 Unicode character strings, add
42 .sp
43 --enable-utf8
44 .sp
45 to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
46 strings as UTF-8. As well as compiling PCRE with this option, you also have
47 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
48 function.
49 .P
50 If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE expects
51 its input to be either ASCII or UTF-8 (depending on the runtime option). It is
52 not possible to support both EBCDIC and UTF-8 codes in the same version of the
53 library. Consequently, --enable-utf8 and --enable-ebcdic are mutually
54 exclusive.
55 .
57 .rs
58 .sp
59 UTF-8 support allows PCRE to process character values greater than 255 in the
60 strings that it handles. On its own, however, it does not provide any
61 facilities for accessing the properties of such characters. If you want to be
62 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
63 character properties, you must add
64 .sp
65 --enable-unicode-properties
66 .sp
67 to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
68 not explicitly requested it.
69 .P
70 Including Unicode property support adds around 30K of tables to the PCRE
71 library. Only the general category properties such as \fILu\fP and \fINd\fP are
72 supported. Details are given in the
73 .\" HREF
74 \fBpcrepattern\fP
75 .\"
76 documentation.
77 .
79 .rs
80 .sp
81 By default, PCRE interprets the linefeed (LF) character as indicating the end
82 of a line. This is the normal newline character on Unix-like systems. You can
83 compile PCRE to use carriage return (CR) instead, by adding
84 .sp
85 --enable-newline-is-cr
86 .sp
87 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
88 which explicitly specifies linefeed as the newline character.
89 .sp
90 Alternatively, you can specify that line endings are to be indicated by the two
91 character sequence CRLF. If you want this, add
92 .sp
93 --enable-newline-is-crlf
94 .sp
95 to the \fBconfigure\fP command. There is a fourth option, specified by
96 .sp
97 --enable-newline-is-anycrlf
98 .sp
99 which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
100 indicating a line ending. Finally, a fifth option, specified by
101 .sp
102 --enable-newline-is-any
103 .sp
104 causes PCRE to recognize any Unicode newline sequence.
105 .P
106 Whatever line ending convention is selected when PCRE is built can be
107 overridden when the library functions are called. At build time it is
108 conventional to use the standard for your operating system.
109 .
111 .rs
112 .sp
113 By default, the sequence \eR in a pattern matches any Unicode newline sequence,
114 whatever has been selected as the line ending sequence. If you specify
115 .sp
116 --enable-bsr-anycrlf
117 .sp
118 the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
119 selected when PCRE is built can be overridden when the library functions are
120 called.
121 .
123 .rs
124 .sp
125 The PCRE building process uses \fBlibtool\fP to build both shared and static
126 Unix libraries by default. You can suppress one of these by adding one of
127 .sp
128 --disable-shared
129 --disable-static
130 .sp
131 to the \fBconfigure\fP command, as required.
132 .
134 .rs
135 .sp
136 When PCRE is called through the POSIX interface (see the
137 .\" HREF
138 \fBpcreposix\fP
139 .\"
140 documentation), additional working storage is required for holding the pointers
141 to capturing substrings, because PCRE requires three integers per substring,
142 whereas the POSIX interface provides only two. If the number of expected
143 substrings is small, the wrapper function uses space on the stack, because this
144 is faster than using \fBmalloc()\fP for each call. The default threshold above
145 which the stack is no longer used is 10; it can be changed by adding a setting
146 such as
147 .sp
148 --with-posix-malloc-threshold=20
149 .sp
150 to the \fBconfigure\fP command.
151 .
153 .rs
154 .sp
155 Within a compiled pattern, offset values are used to point from one part to
156 another (for example, from an opening parenthesis to an alternation
157 metacharacter). By default, two-byte values are used for these offsets, leading
158 to a maximum size for a compiled pattern of around 64K. This is sufficient to
159 handle all but the most gigantic patterns. Nevertheless, some people do want to
160 process enormous patterns, so it is possible to compile PCRE to use three-byte
161 or four-byte offsets by adding a setting such as
162 .sp
163 --with-link-size=3
164 .sp
165 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
166 longer offsets slows down the operation of PCRE because it has to load
167 additional bytes when handling them.
168 .
170 .rs
171 .sp
172 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
173 by making recursive calls to an internal function called \fBmatch()\fP. In
174 environments where the size of the stack is limited, this can severely limit
175 PCRE's operation. (The Unix environment does not usually suffer from this
176 problem, but it may sometimes be necessary to increase the maximum stack size.
177 There is a discussion in the
178 .\" HREF
179 \fBpcrestack\fP
180 .\"
181 documentation.) An alternative approach to recursion that uses memory from the
182 heap to remember data, instead of using recursive function calls, has been
183 implemented to work round the problem of limited stack size. If you want to
184 build a version of PCRE that works this way, add
185 .sp
186 --disable-stack-for-recursion
187 .sp
188 to the \fBconfigure\fP command. With this configuration, PCRE will use the
189 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
190 management functions. By default these point to \fBmalloc()\fP and
191 \fBfree()\fP, but you can replace the pointers so that your own functions are
192 used.
193 .P
194 Separate functions are provided rather than using \fBpcre_malloc\fP and
195 \fBpcre_free\fP because the usage is very predictable: the block sizes
196 requested are always the same, and the blocks are always freed in reverse
197 order. A calling program might be able to implement optimized functions that
198 perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
199 slowly when built in this way. This option affects only the \fBpcre_exec()\fP
200 function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.
201 .
203 .rs
204 .sp
205 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
206 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
207 function. By controlling the maximum number of times this function may be
208 called during a single matching operation, a limit can be placed on the
209 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
210 at run time, as described in the
211 .\" HREF
212 \fBpcreapi\fP
213 .\"
214 documentation. The default is 10 million, but this can be changed by adding a
215 setting such as
216 .sp
217 --with-match-limit=500000
218 .sp
219 to the \fBconfigure\fP command. This setting has no effect on the
220 \fBpcre_dfa_exec()\fP matching function.
221 .P
222 In some environments it is desirable to limit the depth of recursive calls of
223 \fBmatch()\fP more strictly than the total number of calls, in order to
224 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
225 is specified) that is used. A second limit controls this; it defaults to the
226 value that is set for --with-match-limit, which imposes no additional
227 constraints. However, you can set a lower limit by adding, for example,
228 .sp
229 --with-match-limit-recursion=10000
230 .sp
231 to the \fBconfigure\fP command. This value can also be overridden at run time.
232 .
234 .rs
235 .sp
236 PCRE uses fixed tables for processing characters whose code values are less
237 than 256. By default, PCRE is built with a set of tables that are distributed
238 in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
239 only. If you add
240 .sp
241 --enable-rebuild-chartables
242 .sp
243 to the \fBconfigure\fP command, the distributed tables are no longer used.
244 Instead, a program called \fBdftables\fP is compiled and run. This outputs the
245 source for new set of tables, created in the default locale of your C runtime
246 system. (This method of replacing the tables does not work if you are cross
247 compiling, because \fBdftables\fP is run on the local host. If you need to
248 create alternative tables when cross compiling, you will have to do so "by
249 hand".)
250 .
252 .rs
253 .sp
254 PCRE assumes by default that it will run in an environment where the character
255 code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
256 most computer operating systems. PCRE can, however, be compiled to run in an
257 EBCDIC environment by adding
258 .sp
259 --enable-ebcdic
260 .sp
261 to the \fBconfigure\fP command. This setting implies
262 --enable-rebuild-chartables. You should only use it if you know that you are in
263 an EBCDIC environment (for example, an IBM mainframe operating system). The
264 --enable-ebcdic option is incompatible with --enable-utf8.
265 .
267 .rs
268 .sp
269 By default, \fBpcregrep\fP reads all files as plain text. You can build it so
270 that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
271 them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
272 .sp
273 --enable-pcregrep-libz
274 --enable-pcregrep-libbz2
275 .sp
276 to the \fBconfigure\fP command. These options naturally require that the
277 relevant libraries are installed on your system. Configuration will fail if
278 they are not.
279 .
281 .rs
282 .sp
283 If you add
284 .sp
285 --enable-pcretest-libreadline
286 .sp
287 to the \fBconfigure\fP command, \fBpcretest\fP is linked with the
288 \fBlibreadline\fP library, and when its input is from a terminal, it reads it
289 using the \fBreadline()\fP function. This provides line-editing and history
290 facilities. Note that \fBlibreadline\fP is GPL-licenced, so if you distribute a
291 binary of \fBpcretest\fP linked in this way, there may be licensing issues.
292 .P
293 Setting this option causes the \fB-lreadline\fP option to be added to the
294 \fBpcretest\fP build. In many operating environments with a sytem-installed
295 \fBlibreadline\fP this is sufficient. However, in some environments (e.g.
296 if an unmodified distribution version of readline is in use), some extra
297 configuration may be necessary. The INSTALL file for \fBlibreadline\fP says
298 this:
299 .sp
300 "Readline uses the termcap functions, but does not link with the
301 termcap or curses library itself, allowing applications which link
302 with readline the to choose an appropriate library."
303 .sp
304 If your environment has not been set up so that an appropriate library is
305 automatically included, you may need to add something like
306 .sp
307 LIBS="-ncurses"
308 .sp
309 immediately before the \fBconfigure\fP command.
310 .
311 .
312 .SH "SEE ALSO"
313 .rs
314 .sp
315 \fBpcreapi\fP(3), \fBpcre_config\fP(3).
316 .
317 .
319 .rs
320 .sp
321 .nf
322 Philip Hazel
323 University Computing Service
324 Cambridge CB2 3QH, England.
325 .fi
326 .
327 .
329 .rs
330 .sp
331 .nf
332 Last updated: 17 March 2009
333 Copyright (c) 1997-2009 University of Cambridge.
334 .fi


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