1PCREBUILD(3) Library Functions Manual PCREBUILD(3)
2
6 PCRE - Perl-compatible regular expressions
7
9 This document describes the optional features of PCRE that can be
11 selected when the library is compiled. It assumes use of the configure
12 script, where the optional features are selected or deselected by pro‐
13 viding options to configure before running the make command. However,
14 the same options can be selected in both Unix-like and non-Unix-like
15 environments using the GUI facility of CMakeSetup if you are using
16 CMake instead of configure to build PCRE.
17 The complete list of options for configure (which includes the standard
19 ones such as the selection of the installation directory) can be
20 obtained by running
21 ./configure --help
23 The following sections include descriptions of options whose names
25 begin with --enable or --disable. These settings specify changes to the
26 defaults for the configure command. Because of the way that configure
27 works, --enable and --disable always come in pairs, so the complemen‐
28 tary option always exists as well, but as it specifies the default, it
29 is not described.
30
32 By default, the configure script will search for a C++ compiler and C++
34 header files. If it finds them, it automatically builds the C++ wrapper
35 library for PCRE. You can disable this by adding
36 --disable-cpp
38 to the configure command.
40
42 To build PCRE with support for UTF-8 character strings, add
44 --enable-utf8
46 to the configure command. Of itself, this does not make PCRE treat
48 strings as UTF-8. As well as compiling PCRE with this option, you also
49 have have to set the PCRE_UTF8 option when you call the pcre_compile()
50 function.
51
53 UTF-8 support allows PCRE to process character values greater than 255
55 in the strings that it handles. On its own, however, it does not pro‐
56 vide any facilities for accessing the properties of such characters. If
57 you want to be able to use the pattern escapes \P, \p, and \X, which
58 refer to Unicode character properties, you must add
59 --enable-unicode-properties
61 to the configure command. This implies UTF-8 support, even if you have
63 not explicitly requested it.
64 Including Unicode property support adds around 30K of tables to the
66 PCRE library. Only the general category properties such as Lu and Nd
67 are supported. Details are given in the pcrepattern documentation.
68
70 By default, PCRE interprets character 10 (linefeed, LF) as indicating
72 the end of a line. This is the normal newline character on Unix-like
73 systems. You can compile PCRE to use character 13 (carriage return, CR)
74 instead, by adding
75 --enable-newline-is-cr
77 to the configure command. There is also a --enable-newline-is-lf
79 option, which explicitly specifies linefeed as the newline character.
80 Alternatively, you can specify that line endings are to be indicated by
82 the two character sequence CRLF. If you want this, add
83 --enable-newline-is-crlf
85 to the configure command. There is a fourth option, specified by
87 --enable-newline-is-anycrlf
89 which causes PCRE to recognize any of the three sequences CR, LF, or
91 CRLF as indicating a line ending. Finally, a fifth option, specified by
92 --enable-newline-is-any
94 causes PCRE to recognize any Unicode newline sequence.
96 Whatever line ending convention is selected when PCRE is built can be
98 overridden when the library functions are called. At build time it is
99 conventional to use the standard for your operating system.
100
102 By default, the sequence \R in a pattern matches any Unicode newline
104 sequence, whatever has been selected as the line ending sequence. If
105 you specify
106 --enable-bsr-anycrlf
108 the default is changed so that \R matches only CR, LF, or CRLF. What‐
110 ever is selected when PCRE is built can be overridden when the library
111 functions are called.
112
114 The PCRE building process uses libtool to build both shared and static
116 Unix libraries by default. You can suppress one of these by adding one
117 of
118 --disable-shared
120 --disable-static
121 to the configure command, as required.
123
125 When PCRE is called through the POSIX interface (see the pcreposix doc‐
127 umentation), additional working storage is required for holding the
128 pointers to capturing substrings, because PCRE requires three integers
129 per substring, whereas the POSIX interface provides only two. If the
130 number of expected substrings is small, the wrapper function uses space
131 on the stack, because this is faster than using malloc() for each call.
132 The default threshold above which the stack is no longer used is 10; it
133 can be changed by adding a setting such as
134 --with-posix-malloc-threshold=20
136 to the configure command.
138
140 Within a compiled pattern, offset values are used to point from one
142 part to another (for example, from an opening parenthesis to an alter‐
143 nation metacharacter). By default, two-byte values are used for these
144 offsets, leading to a maximum size for a compiled pattern of around
145 64K. This is sufficient to handle all but the most gigantic patterns.
146 Nevertheless, some people do want to process enormous patterns, so it
147 is possible to compile PCRE to use three-byte or four-byte offsets by
148 adding a setting such as
149 --with-link-size=3
151 to the configure command. The value given must be 2, 3, or 4. Using
153 longer offsets slows down the operation of PCRE because it has to load
154 additional bytes when handling them.
155
157 When matching with the pcre_exec() function, PCRE implements backtrack‐
159 ing by making recursive calls to an internal function called match().
160 In environments where the size of the stack is limited, this can se‐
161 verely limit PCRE's operation. (The Unix environment does not usually
162 suffer from this problem, but it may sometimes be necessary to increase
163 the maximum stack size. There is a discussion in the pcrestack docu‐
164 mentation.) An alternative approach to recursion that uses memory from
165 the heap to remember data, instead of using recursive function calls,
166 has been implemented to work round the problem of limited stack size.
167 If you want to build a version of PCRE that works this way, add
168 --disable-stack-for-recursion
170 to the configure command. With this configuration, PCRE will use the
172 pcre_stack_malloc and pcre_stack_free variables to call memory manage‐
173 ment functions. By default these point to malloc() and free(), but you
174 can replace the pointers so that your own functions are used.
175 Separate functions are provided rather than using pcre_malloc and
177 pcre_free because the usage is very predictable: the block sizes
178 requested are always the same, and the blocks are always freed in
179 reverse order. A calling program might be able to implement optimized
180 functions that perform better than malloc() and free(). PCRE runs
181 noticeably more slowly when built in this way. This option affects only
182 the pcre_exec() function; it is not relevant for the the
183 pcre_dfa_exec() function.
184
186 Internally, PCRE has a function called match(), which it calls repeat‐
188 edly (sometimes recursively) when matching a pattern with the
189 pcre_exec() function. By controlling the maximum number of times this
190 function may be called during a single matching operation, a limit can
191 be placed on the resources used by a single call to pcre_exec(). The
192 limit can be changed at run time, as described in the pcreapi documen‐
193 tation. The default is 10 million, but this can be changed by adding a
194 setting such as
195 --with-match-limit=500000
197 to the configure command. This setting has no effect on the
199 pcre_dfa_exec() matching function.
200 In some environments it is desirable to limit the depth of recursive
202 calls of match() more strictly than the total number of calls, in order
203 to restrict the maximum amount of stack (or heap, if --disable-stack-
204 for-recursion is specified) that is used. A second limit controls this;
205 it defaults to the value that is set for --with-match-limit, which
206 imposes no additional constraints. However, you can set a lower limit
207 by adding, for example,
208 --with-match-limit-recursion=10000
210 to the configure command. This value can also be overridden at run
212 time.
213
215 PCRE uses fixed tables for processing characters whose code values are
217 less than 256. By default, PCRE is built with a set of tables that are
218 distributed in the file pcre_chartables.c.dist. These tables are for
219 ASCII codes only. If you add
220 --enable-rebuild-chartables
222 to the configure command, the distributed tables are no longer used.
224 Instead, a program called dftables is compiled and run. This outputs
225 the source for new set of tables, created in the default locale of your
226 C run-time system. (This method of replacing the tables does not work
227 if you are cross compiling, because dftables is run on the local host.
228 If you need to create alternative tables when cross compiling, you will
229 have to do so "by hand".)
230
232 PCRE assumes by default that it will run in an environment where the
234 character code is ASCII (or Unicode, which is a superset of ASCII).
235 This is the case for most computer operating systems. PCRE can, how‐
236 ever, be compiled to run in an EBCDIC environment by adding
237 --enable-ebcdic
239 to the configure command. This setting implies --enable-rebuild-charta‐
241 bles. You should only use it if you know that you are in an EBCDIC
242 environment (for example, an IBM mainframe operating system).
243
245 By default, pcregrep reads all files as plain text. You can build it so
247 that it recognizes files whose names end in .gz or .bz2, and reads them
248 with libz or libbz2, respectively, by adding one or both of
249 --enable-pcregrep-libz
251 --enable-pcregrep-libbz2
252 to the configure command. These options naturally require that the rel‐
254 evant libraries are installed on your system. Configuration will fail
255 if they are not.
256
258 If you add
260 --enable-pcretest-libreadline
262 to the configure command, pcretest is linked with the libreadline
264 library, and when its input is from a terminal, it reads it using the
265 readline() function. This provides line-editing and history facilities.
266 Note that libreadline is GPL-licenced, so if you distribute a binary of
267 pcretest linked in this way, there may be licensing issues.
268 Setting this option causes the -lreadline option to be added to the
270 pcretest build. In many operating environments with a sytem-installed
271 libreadline this is sufficient. However, in some environments (e.g. if
272 an unmodified distribution version of readline is in use), some extra
273 configuration may be necessary. The INSTALL file for libreadline says
274 this:
275 "Readline uses the termcap functions, but does not link with the
277 termcap or curses library itself, allowing applications which link
278 with readline the to choose an appropriate library."
279 If your environment has not been set up so that an appropriate library
281 is automatically included, you may need to add something like
282 LIBS="-ncurses"
284 immediately before the configure command.
286
288 pcreapi(3), pcre_config(3).
290
292 Philip Hazel
294 University Computing Service
295 Cambridge CB2 3QH, England.
296
298 Last updated: 13 April 2008
300 Copyright (c) 1997-2008 University of Cambridge.
301 PCREBUILD(3)