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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 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 .
51 .rs
52 .sp
53 UTF-8 support allows PCRE to process character values greater than 255 in the
54 strings that it handles. On its own, however, it does not provide any
55 facilities for accessing the properties of such characters. If you want to be
56 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
57 character properties, you must add
58 .sp
59 --enable-unicode-properties
60 .sp
61 to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
62 not explicitly requested it.
63 .P
64 Including Unicode property support adds around 30K of tables to the PCRE
65 library. Only the general category properties such as \fILu\fP and \fINd\fP are
66 supported. Details are given in the
67 .\" HREF
68 \fBpcrepattern\fP
69 .\"
70 documentation.
71 .
73 .rs
74 .sp
75 By default, PCRE interprets character 10 (linefeed, LF) as indicating the end
76 of a line. This is the normal newline character on Unix-like systems. You can
77 compile PCRE to use character 13 (carriage return, CR) instead, by adding
78 .sp
79 --enable-newline-is-cr
80 .sp
81 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
82 which explicitly specifies linefeed as the newline character.
83 .sp
84 Alternatively, you can specify that line endings are to be indicated by the two
85 character sequence CRLF. If you want this, add
86 .sp
87 --enable-newline-is-crlf
88 .sp
89 to the \fBconfigure\fP command. There is a fourth option, specified by
90 .sp
91 --enable-newline-is-anycrlf
92 .sp
93 which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
94 indicating a line ending. Finally, a fifth option, specified by
95 .sp
96 --enable-newline-is-any
97 .sp
98 causes PCRE to recognize any Unicode newline sequence.
99 .P
100 Whatever line ending convention is selected when PCRE is built can be
101 overridden when the library functions are called. At build time it is
102 conventional to use the standard for your operating system.
103 .
105 .rs
106 .sp
107 By default, the sequence \eR in a pattern matches any Unicode newline sequence,
108 whatever has been selected as the line ending sequence. If you specify
109 .sp
110 --enable-bsr-anycrlf
111 .sp
112 the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
113 selected when PCRE is built can be overridden when the library functions are
114 called.
115 .
117 .rs
118 .sp
119 The PCRE building process uses \fBlibtool\fP to build both shared and static
120 Unix libraries by default. You can suppress one of these by adding one of
121 .sp
122 --disable-shared
123 --disable-static
124 .sp
125 to the \fBconfigure\fP command, as required.
126 .
128 .rs
129 .sp
130 When PCRE is called through the POSIX interface (see the
131 .\" HREF
132 \fBpcreposix\fP
133 .\"
134 documentation), additional working storage is required for holding the pointers
135 to capturing substrings, because PCRE requires three integers per substring,
136 whereas the POSIX interface provides only two. If the number of expected
137 substrings is small, the wrapper function uses space on the stack, because this
138 is faster than using \fBmalloc()\fP for each call. The default threshold above
139 which the stack is no longer used is 10; it can be changed by adding a setting
140 such as
141 .sp
142 --with-posix-malloc-threshold=20
143 .sp
144 to the \fBconfigure\fP command.
145 .
147 .rs
148 .sp
149 Within a compiled pattern, offset values are used to point from one part to
150 another (for example, from an opening parenthesis to an alternation
151 metacharacter). By default, two-byte values are used for these offsets, leading
152 to a maximum size for a compiled pattern of around 64K. This is sufficient to
153 handle all but the most gigantic patterns. Nevertheless, some people do want to
154 process enormous patterns, so it is possible to compile PCRE to use three-byte
155 or four-byte offsets by adding a setting such as
156 .sp
157 --with-link-size=3
158 .sp
159 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
160 longer offsets slows down the operation of PCRE because it has to load
161 additional bytes when handling them.
162 .
164 .rs
165 .sp
166 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
167 by making recursive calls to an internal function called \fBmatch()\fP. In
168 environments where the size of the stack is limited, this can severely limit
169 PCRE's operation. (The Unix environment does not usually suffer from this
170 problem, but it may sometimes be necessary to increase the maximum stack size.
171 There is a discussion in the
172 .\" HREF
173 \fBpcrestack\fP
174 .\"
175 documentation.) An alternative approach to recursion that uses memory from the
176 heap to remember data, instead of using recursive function calls, has been
177 implemented to work round the problem of limited stack size. If you want to
178 build a version of PCRE that works this way, add
179 .sp
180 --disable-stack-for-recursion
181 .sp
182 to the \fBconfigure\fP command. With this configuration, PCRE will use the
183 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
184 management functions. By default these point to \fBmalloc()\fP and
185 \fBfree()\fP, but you can replace the pointers so that your own functions are
186 used.
187 .P
188 Separate functions are provided rather than using \fBpcre_malloc\fP and
189 \fBpcre_free\fP because the usage is very predictable: the block sizes
190 requested are always the same, and the blocks are always freed in reverse
191 order. A calling program might be able to implement optimized functions that
192 perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
193 slowly when built in this way. This option affects only the \fBpcre_exec()\fP
194 function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.
195 .
197 .rs
198 .sp
199 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
200 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
201 function. By controlling the maximum number of times this function may be
202 called during a single matching operation, a limit can be placed on the
203 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
204 at run time, as described in the
205 .\" HREF
206 \fBpcreapi\fP
207 .\"
208 documentation. The default is 10 million, but this can be changed by adding a
209 setting such as
210 .sp
211 --with-match-limit=500000
212 .sp
213 to the \fBconfigure\fP command. This setting has no effect on the
214 \fBpcre_dfa_exec()\fP matching function.
215 .P
216 In some environments it is desirable to limit the depth of recursive calls of
217 \fBmatch()\fP more strictly than the total number of calls, in order to
218 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
219 is specified) that is used. A second limit controls this; it defaults to the
220 value that is set for --with-match-limit, which imposes no additional
221 constraints. However, you can set a lower limit by adding, for example,
222 .sp
223 --with-match-limit-recursion=10000
224 .sp
225 to the \fBconfigure\fP command. This value can also be overridden at run time.
226 .
228 .rs
229 .sp
230 PCRE uses fixed tables for processing characters whose code values are less
231 than 256. By default, PCRE is built with a set of tables that are distributed
232 in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
233 only. If you add
234 .sp
235 --enable-rebuild-chartables
236 .sp
237 to the \fBconfigure\fP command, the distributed tables are no longer used.
238 Instead, a program called \fBdftables\fP is compiled and run. This outputs the
239 source for new set of tables, created in the default locale of your C runtime
240 system. (This method of replacing the tables does not work if you are cross
241 compiling, because \fBdftables\fP is run on the local host. If you need to
242 create alternative tables when cross compiling, you will have to do so "by
243 hand".)
244 .
246 .rs
247 .sp
248 PCRE assumes by default that it will run in an environment where the character
249 code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
250 most computer operating systems. PCRE can, however, be compiled to run in an
251 EBCDIC environment by adding
252 .sp
253 --enable-ebcdic
254 .sp
255 to the \fBconfigure\fP command. This setting implies
256 --enable-rebuild-chartables. You should only use it if you know that you are in
257 an EBCDIC environment (for example, an IBM mainframe operating system).
258 .
260 .rs
261 .sp
262 By default, \fBpcregrep\fP reads all files as plain text. You can build it so
263 that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
264 them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
265 .sp
266 --enable-pcregrep-libz
267 --enable-pcregrep-libbz2
268 .sp
269 to the \fBconfigure\fP command. These options naturally require that the
270 relevant libraries are installed on your system. Configuration will fail if
271 they are not.
272 .
274 .rs
275 .sp
276 If you add
277 .sp
278 --enable-pcretest-libreadline
279 .sp
280 to the \fBconfigure\fP command, \fBpcretest\fP is linked with the
281 \fBlibreadline\fP library, and when its input is from a terminal, it reads it
282 using the \fBreadline()\fP function. This provides line-editing and history
283 facilities. Note that \fBlibreadline\fP is GPL-licenced, so if you distribute a
284 binary of \fBpcretest\fP linked in this way, there may be licensing issues.
285 .
286 .
287 .SH "SEE ALSO"
288 .rs
289 .sp
290 \fBpcreapi\fP(3), \fBpcre_config\fP(3).
291 .
292 .
294 .rs
295 .sp
296 .nf
297 Philip Hazel
298 University Computing Service
299 Cambridge CB2 3QH, England.
300 .fi
301 .
302 .
304 .rs
305 .sp
306 .nf
307 Last updated: 18 December 2007
308 Copyright (c) 1997-2007 University of Cambridge.
309 .fi


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