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Documentation update
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 .
35 .SH "C++ SUPPORT"
36 .rs
37 .sp
38 By default, the \fBconfigure\fP script will search for a C++ compiler and C++
39 header files. If it finds them, it automatically builds the C++ wrapper library
40 for PCRE. You can disable this by adding
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42 --disable-cpp
43 .sp
44 to the \fBconfigure\fP command.
45 .
46 .
48 .rs
49 .sp
50 To build PCRE with support for UTF-8 Unicode character strings, add
51 .sp
52 --enable-utf8
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54 to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
55 strings as UTF-8. As well as compiling PCRE with this option, you also have
56 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
57 or \fBpcre_compile2()\fP functions.
58 .P
59 If you set --enable-utf8 when compiling in an EBCDIC environment, PCRE expects
60 its input to be either ASCII or UTF-8 (depending on the runtime option). It is
61 not possible to support both EBCDIC and UTF-8 codes in the same version of the
62 library. Consequently, --enable-utf8 and --enable-ebcdic are mutually
63 exclusive.
64 .
65 .
67 .rs
68 .sp
69 UTF-8 support allows PCRE to process character values greater than 255 in the
70 strings that it handles. On its own, however, it does not provide any
71 facilities for accessing the properties of such characters. If you want to be
72 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
73 character properties, you must add
74 .sp
75 --enable-unicode-properties
76 .sp
77 to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
78 not explicitly requested it.
79 .P
80 Including Unicode property support adds around 30K of tables to the PCRE
81 library. Only the general category properties such as \fILu\fP and \fINd\fP are
82 supported. Details are given in the
83 .\" HREF
84 \fBpcrepattern\fP
85 .\"
86 documentation.
87 .
88 .
90 .rs
91 .sp
92 By default, PCRE interprets the linefeed (LF) character as indicating the end
93 of a line. This is the normal newline character on Unix-like systems. You can
94 compile PCRE to use carriage return (CR) instead, by adding
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96 --enable-newline-is-cr
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98 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
99 which explicitly specifies linefeed as the newline character.
100 .sp
101 Alternatively, you can specify that line endings are to be indicated by the two
102 character sequence CRLF. If you want this, add
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104 --enable-newline-is-crlf
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106 to the \fBconfigure\fP command. There is a fourth option, specified by
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108 --enable-newline-is-anycrlf
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110 which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
111 indicating a line ending. Finally, a fifth option, specified by
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113 --enable-newline-is-any
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115 causes PCRE to recognize any Unicode newline sequence.
116 .P
117 Whatever line ending convention is selected when PCRE is built can be
118 overridden when the library functions are called. At build time it is
119 conventional to use the standard for your operating system.
120 .
121 .
123 .rs
124 .sp
125 By default, the sequence \eR in a pattern matches any Unicode newline sequence,
126 whatever has been selected as the line ending sequence. If you specify
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128 --enable-bsr-anycrlf
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130 the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
131 selected when PCRE is built can be overridden when the library functions are
132 called.
133 .
134 .
136 .rs
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138 The PCRE building process uses \fBlibtool\fP to build both shared and static
139 Unix libraries by default. You can suppress one of these by adding one of
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141 --disable-shared
142 --disable-static
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144 to the \fBconfigure\fP command, as required.
145 .
146 .
148 .rs
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150 When PCRE is called through the POSIX interface (see the
151 .\" HREF
152 \fBpcreposix\fP
153 .\"
154 documentation), additional working storage is required for holding the pointers
155 to capturing substrings, because PCRE requires three integers per substring,
156 whereas the POSIX interface provides only two. If the number of expected
157 substrings is small, the wrapper function uses space on the stack, because this
158 is faster than using \fBmalloc()\fP for each call. The default threshold above
159 which the stack is no longer used is 10; it can be changed by adding a setting
160 such as
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162 --with-posix-malloc-threshold=20
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164 to the \fBconfigure\fP command.
165 .
166 .
168 .rs
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170 Within a compiled pattern, offset values are used to point from one part to
171 another (for example, from an opening parenthesis to an alternation
172 metacharacter). By default, two-byte values are used for these offsets, leading
173 to a maximum size for a compiled pattern of around 64K. This is sufficient to
174 handle all but the most gigantic patterns. Nevertheless, some people do want to
175 process truyl enormous patterns, so it is possible to compile PCRE to use
176 three-byte or four-byte offsets by adding a setting such as
177 .sp
178 --with-link-size=3
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180 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
181 longer offsets slows down the operation of PCRE because it has to load
182 additional bytes when handling them.
183 .
184 .
186 .rs
187 .sp
188 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
189 by making recursive calls to an internal function called \fBmatch()\fP. In
190 environments where the size of the stack is limited, this can severely limit
191 PCRE's operation. (The Unix environment does not usually suffer from this
192 problem, but it may sometimes be necessary to increase the maximum stack size.
193 There is a discussion in the
194 .\" HREF
195 \fBpcrestack\fP
196 .\"
197 documentation.) An alternative approach to recursion that uses memory from the
198 heap to remember data, instead of using recursive function calls, has been
199 implemented to work round the problem of limited stack size. If you want to
200 build a version of PCRE that works this way, add
201 .sp
202 --disable-stack-for-recursion
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204 to the \fBconfigure\fP command. With this configuration, PCRE will use the
205 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
206 management functions. By default these point to \fBmalloc()\fP and
207 \fBfree()\fP, but you can replace the pointers so that your own functions are
208 used instead.
209 .P
210 Separate functions are provided rather than using \fBpcre_malloc\fP and
211 \fBpcre_free\fP because the usage is very predictable: the block sizes
212 requested are always the same, and the blocks are always freed in reverse
213 order. A calling program might be able to implement optimized functions that
214 perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
215 slowly when built in this way. This option affects only the \fBpcre_exec()\fP
216 function; it is not relevant for \fBpcre_dfa_exec()\fP.
217 .
218 .
220 .rs
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222 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
223 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
224 function. By controlling the maximum number of times this function may be
225 called during a single matching operation, a limit can be placed on the
226 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
227 at run time, as described in the
228 .\" HREF
229 \fBpcreapi\fP
230 .\"
231 documentation. The default is 10 million, but this can be changed by adding a
232 setting such as
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234 --with-match-limit=500000
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236 to the \fBconfigure\fP command. This setting has no effect on the
237 \fBpcre_dfa_exec()\fP matching function.
238 .P
239 In some environments it is desirable to limit the depth of recursive calls of
240 \fBmatch()\fP more strictly than the total number of calls, in order to
241 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
242 is specified) that is used. A second limit controls this; it defaults to the
243 value that is set for --with-match-limit, which imposes no additional
244 constraints. However, you can set a lower limit by adding, for example,
245 .sp
246 --with-match-limit-recursion=10000
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248 to the \fBconfigure\fP command. This value can also be overridden at run time.
249 .
250 .
252 .rs
253 .sp
254 PCRE uses fixed tables for processing characters whose code values are less
255 than 256. By default, PCRE is built with a set of tables that are distributed
256 in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
257 only. If you add
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259 --enable-rebuild-chartables
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261 to the \fBconfigure\fP command, the distributed tables are no longer used.
262 Instead, a program called \fBdftables\fP is compiled and run. This outputs the
263 source for new set of tables, created in the default locale of your C runtime
264 system. (This method of replacing the tables does not work if you are cross
265 compiling, because \fBdftables\fP is run on the local host. If you need to
266 create alternative tables when cross compiling, you will have to do so "by
267 hand".)
268 .
269 .
271 .rs
272 .sp
273 PCRE assumes by default that it will run in an environment where the character
274 code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
275 most computer operating systems. PCRE can, however, be compiled to run in an
276 EBCDIC environment by adding
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278 --enable-ebcdic
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280 to the \fBconfigure\fP command. This setting implies
281 --enable-rebuild-chartables. You should only use it if you know that you are in
282 an EBCDIC environment (for example, an IBM mainframe operating system). The
283 --enable-ebcdic option is incompatible with --enable-utf8.
284 .
285 .
287 .rs
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289 By default, \fBpcregrep\fP reads all files as plain text. You can build it so
290 that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
291 them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
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293 --enable-pcregrep-libz
294 --enable-pcregrep-libbz2
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296 to the \fBconfigure\fP command. These options naturally require that the
297 relevant libraries are installed on your system. Configuration will fail if
298 they are not.
299 .
300 .
302 .rs
303 .sp
304 If you add
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306 --enable-pcretest-libreadline
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308 to the \fBconfigure\fP command, \fBpcretest\fP is linked with the
309 \fBlibreadline\fP library, and when its input is from a terminal, it reads it
310 using the \fBreadline()\fP function. This provides line-editing and history
311 facilities. Note that \fBlibreadline\fP is GPL-licensed, so if you distribute a
312 binary of \fBpcretest\fP linked in this way, there may be licensing issues.
313 .P
314 Setting this option causes the \fB-lreadline\fP option to be added to the
315 \fBpcretest\fP build. In many operating environments with a sytem-installed
316 \fBlibreadline\fP this is sufficient. However, in some environments (e.g.
317 if an unmodified distribution version of readline is in use), some extra
318 configuration may be necessary. The INSTALL file for \fBlibreadline\fP says
319 this:
320 .sp
321 "Readline uses the termcap functions, but does not link with the
322 termcap or curses library itself, allowing applications which link
323 with readline the to choose an appropriate library."
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325 If your environment has not been set up so that an appropriate library is
326 automatically included, you may need to add something like
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328 LIBS="-ncurses"
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330 immediately before the \fBconfigure\fP command.
331 .
332 .
333 .SH "SEE ALSO"
334 .rs
335 .sp
336 \fBpcreapi\fP(3), \fBpcre_config\fP(3).
337 .
338 .
340 .rs
341 .sp
342 .nf
343 Philip Hazel
344 University Computing Service
345 Cambridge CB2 3QH, England.
346 .fi
347 .
348 .
350 .rs
351 .sp
352 .nf
353 Last updated: 29 September 2009
354 Copyright (c) 1997-2009 University of Cambridge.
355 .fi


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