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Revision 231 - (show annotations)
Tue Sep 11 11:15:33 2007 UTC (13 years, 2 months ago) by ph10
File size: 10121 byte(s)
Add facility to make \R match only CR, LF, or CRLF.
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. They are all selected, or deselected, by providing
9 options to the \fBconfigure\fP script that is run before the \fBmake\fP
10 command. The complete list of options for \fBconfigure\fP (which includes the
11 standard ones such as the selection of the installation directory) can be
12 obtained by running
13 .sp
14 ./configure --help
15 .sp
16 The following sections include descriptions of options whose names begin with
17 --enable or --disable. These settings specify changes to the defaults for the
18 \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
19 --enable and --disable always come in pairs, so the complementary option always
20 exists as well, but as it specifies the default, it is not described.
21 .
22 .SH "C++ SUPPORT"
23 .rs
24 .sp
25 By default, the \fBconfigure\fP script will search for a C++ compiler and C++
26 header files. If it finds them, it automatically builds the C++ wrapper library
27 for PCRE. You can disable this by adding
28 .sp
29 --disable-cpp
30 .sp
31 to the \fBconfigure\fP command.
32 .
34 .rs
35 .sp
36 To build PCRE with support for UTF-8 character strings, add
37 .sp
38 --enable-utf8
39 .sp
40 to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
41 strings as UTF-8. As well as compiling PCRE with this option, you also have
42 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43 function.
44 .
46 .rs
47 .sp
48 UTF-8 support allows PCRE to process character values greater than 255 in the
49 strings that it handles. On its own, however, it does not provide any
50 facilities for accessing the properties of such characters. If you want to be
51 able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
52 character properties, you must add
53 .sp
54 --enable-unicode-properties
55 .sp
56 to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
57 not explicitly requested it.
58 .P
59 Including Unicode property support adds around 30K of tables to the PCRE
60 library. Only the general category properties such as \fILu\fP and \fINd\fP are
61 supported. Details are given in the
62 .\" HREF
63 \fBpcrepattern\fP
64 .\"
65 documentation.
66 .
68 .rs
69 .sp
70 By default, PCRE interprets character 10 (linefeed, LF) as indicating the end
71 of a line. This is the normal newline character on Unix-like systems. You can
72 compile PCRE to use character 13 (carriage return, CR) instead, by adding
73 .sp
74 --enable-newline-is-cr
75 .sp
76 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
77 which explicitly specifies linefeed as the newline character.
78 .sp
79 Alternatively, you can specify that line endings are to be indicated by the two
80 character sequence CRLF. If you want this, add
81 .sp
82 --enable-newline-is-crlf
83 .sp
84 to the \fBconfigure\fP command. There is a fourth option, specified by
85 .sp
86 --enable-newline-is-anycrlf
87 .sp
88 which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
89 indicating a line ending. Finally, a fifth option, specified by
90 .sp
91 --enable-newline-is-any
92 .sp
93 causes PCRE to recognize any Unicode newline sequence.
94 .P
95 Whatever line ending convention is selected when PCRE is built can be
96 overridden when the library functions are called. At build time it is
97 conventional to use the standard for your operating system.
98 .
100 .rs
101 .sp
102 By default, the sequence \eR in a pattern matches any Unicode newline sequence,
103 whatever has been selected as the line ending sequence. If you specify
104 .sp
105 --enable-bsr-anycrlf
106 .sp
107 the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
108 selected when PCRE is built can be overridden when the library functions are
109 called.
110 .
112 .rs
113 .sp
114 The PCRE building process uses \fBlibtool\fP to build both shared and static
115 Unix libraries by default. You can suppress one of these by adding one of
116 .sp
117 --disable-shared
118 --disable-static
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120 to the \fBconfigure\fP command, as required.
121 .
123 .rs
124 .sp
125 When PCRE is called through the POSIX interface (see the
126 .\" HREF
127 \fBpcreposix\fP
128 .\"
129 documentation), additional working storage is required for holding the pointers
130 to capturing substrings, because PCRE requires three integers per substring,
131 whereas the POSIX interface provides only two. If the number of expected
132 substrings is small, the wrapper function uses space on the stack, because this
133 is faster than using \fBmalloc()\fP for each call. The default threshold above
134 which the stack is no longer used is 10; it can be changed by adding a setting
135 such as
136 .sp
137 --with-posix-malloc-threshold=20
138 .sp
139 to the \fBconfigure\fP command.
140 .
142 .rs
143 .sp
144 Within a compiled pattern, offset values are used to point from one part to
145 another (for example, from an opening parenthesis to an alternation
146 metacharacter). By default, two-byte values are used for these offsets, leading
147 to a maximum size for a compiled pattern of around 64K. This is sufficient to
148 handle all but the most gigantic patterns. Nevertheless, some people do want to
149 process enormous patterns, so it is possible to compile PCRE to use three-byte
150 or four-byte offsets by adding a setting such as
151 .sp
152 --with-link-size=3
153 .sp
154 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
155 longer offsets slows down the operation of PCRE because it has to load
156 additional bytes when handling them.
157 .
159 .rs
160 .sp
161 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
162 by making recursive calls to an internal function called \fBmatch()\fP. In
163 environments where the size of the stack is limited, this can severely limit
164 PCRE's operation. (The Unix environment does not usually suffer from this
165 problem, but it may sometimes be necessary to increase the maximum stack size.
166 There is a discussion in the
167 .\" HREF
168 \fBpcrestack\fP
169 .\"
170 documentation.) An alternative approach to recursion that uses memory from the
171 heap to remember data, instead of using recursive function calls, has been
172 implemented to work round the problem of limited stack size. If you want to
173 build a version of PCRE that works this way, add
174 .sp
175 --disable-stack-for-recursion
176 .sp
177 to the \fBconfigure\fP command. With this configuration, PCRE will use the
178 \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
179 management functions. By default these point to \fBmalloc()\fP and
180 \fBfree()\fP, but you can replace the pointers so that your own functions are
181 used.
182 .P
183 Separate functions are provided rather than using \fBpcre_malloc\fP and
184 \fBpcre_free\fP because the usage is very predictable: the block sizes
185 requested are always the same, and the blocks are always freed in reverse
186 order. A calling program might be able to implement optimized functions that
187 perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
188 slowly when built in this way. This option affects only the \fBpcre_exec()\fP
189 function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.
190 .
192 .rs
193 .sp
194 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
195 (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
196 function. By controlling the maximum number of times this function may be
197 called during a single matching operation, a limit can be placed on the
198 resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
199 at run time, as described in the
200 .\" HREF
201 \fBpcreapi\fP
202 .\"
203 documentation. The default is 10 million, but this can be changed by adding a
204 setting such as
205 .sp
206 --with-match-limit=500000
207 .sp
208 to the \fBconfigure\fP command. This setting has no effect on the
209 \fBpcre_dfa_exec()\fP matching function.
210 .P
211 In some environments it is desirable to limit the depth of recursive calls of
212 \fBmatch()\fP more strictly than the total number of calls, in order to
213 restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
214 is specified) that is used. A second limit controls this; it defaults to the
215 value that is set for --with-match-limit, which imposes no additional
216 constraints. However, you can set a lower limit by adding, for example,
217 .sp
218 --with-match-limit-recursion=10000
219 .sp
220 to the \fBconfigure\fP command. This value can also be overridden at run time.
221 .
223 .rs
224 .sp
225 PCRE uses fixed tables for processing characters whose code values are less
226 than 256. By default, PCRE is built with a set of tables that are distributed
227 in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
228 only. If you add
229 .sp
230 --enable-rebuild-chartables
231 .sp
232 to the \fBconfigure\fP command, the distributed tables are no longer used.
233 Instead, a program called \fBdftables\fP is compiled and run. This outputs the
234 source for new set of tables, created in the default locale of your C runtime
235 system. (This method of replacing the tables does not work if you are cross
236 compiling, because \fBdftables\fP is run on the local host. If you need to
237 create alternative tables when cross compiling, you will have to do so "by
238 hand".)
239 .
241 .rs
242 .sp
243 PCRE assumes by default that it will run in an environment where the character
244 code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
245 most computer operating systems. PCRE can, however, be compiled to run in an
246 EBCDIC environment by adding
247 .sp
248 --enable-ebcdic
249 .sp
250 to the \fBconfigure\fP command. This setting implies
251 --enable-rebuild-chartables. You should only use it if you know that you are in
252 an EBCDIC environment (for example, an IBM mainframe operating system).
253 .
254 .
255 .SH "SEE ALSO"
256 .rs
257 .sp
258 \fBpcreapi\fP(3), \fBpcre_config\fP(3).
259 .
260 .
262 .rs
263 .sp
264 .nf
265 Philip Hazel
266 University Computing Service
267 Cambridge CB2 3QH, England.
268 .fi
269 .
270 .
272 .rs
273 .sp
274 .nf
275 Last updated: 11 September 2007
276 Copyright (c) 1997-2007 University of Cambridge.
277 .fi


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