1PCREBUILD(3) Library Functions Manual PCREBUILD(3)
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6 PCRE - Perl-compatible regular expressions
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9 This document describes the optional features of PCRE that can be
11 selected when the library is compiled. They are all selected, or dese‐
12 lected, by providing options to the configure script that is run before
13 the make command. The complete list of options for configure (which
14 includes the standard ones such as the selection of the installation
15 directory) can be obtained by running
16 ./configure --help
18 The following sections include descriptions of options whose names
20 begin with --enable or --disable. These settings specify changes to the
21 defaults for the configure command. Because of the way that configure
22 works, --enable and --disable always come in pairs, so the complemen‐
23 tary option always exists as well, but as it specifies the default, it
24 is not described.
25
27 By default, the configure script will search for a C++ compiler and C++
29 header files. If it finds them, it automatically builds the C++ wrapper
30 library for PCRE. You can disable this by adding
31 --disable-cpp
33 to the configure command.
35
37 To build PCRE with support for UTF-8 character strings, add
39 --enable-utf8
41 to the configure command. Of itself, this does not make PCRE treat
43 strings as UTF-8. As well as compiling PCRE with this option, you also
44 have have to set the PCRE_UTF8 option when you call the pcre_compile()
45 function.
46
48 UTF-8 support allows PCRE to process character values greater than 255
50 in the strings that it handles. On its own, however, it does not pro‐
51 vide any facilities for accessing the properties of such characters. If
52 you want to be able to use the pattern escapes \P, \p, and \X, which
53 refer to Unicode character properties, you must add
54 --enable-unicode-properties
56 to the configure command. This implies UTF-8 support, even if you have
58 not explicitly requested it.
59 Including Unicode property support adds around 30K of tables to the
61 PCRE library. Only the general category properties such as Lu and Nd
62 are supported. Details are given in the pcrepattern documentation.
63
65 By default, PCRE interprets character 10 (linefeed, LF) as indicating
67 the end of a line. This is the normal newline character on Unix-like
68 systems. You can compile PCRE to use character 13 (carriage return, CR)
69 instead, by adding
70 --enable-newline-is-cr
72 to the configure command. There is also a --enable-newline-is-lf
74 option, which explicitly specifies linefeed as the newline character.
75 Alternatively, you can specify that line endings are to be indicated by
77 the two character sequence CRLF. If you want this, add
78 --enable-newline-is-crlf
80 to the configure command. There is a fourth option, specified by
82 --enable-newline-is-anycrlf
84 which causes PCRE to recognize any of the three sequences CR, LF, or
86 CRLF as indicating a line ending. Finally, a fifth option, specified by
87 --enable-newline-is-any
89 causes PCRE to recognize any Unicode newline sequence.
91 Whatever line ending convention is selected when PCRE is built can be
93 overridden when the library functions are called. At build time it is
94 conventional to use the standard for your operating system.
95
97 The PCRE building process uses libtool to build both shared and static
99 Unix libraries by default. You can suppress one of these by adding one
100 of
101 --disable-shared
103 --disable-static
104 to the configure command, as required.
106
108 When PCRE is called through the POSIX interface (see the pcreposix doc‐
110 umentation), additional working storage is required for holding the
111 pointers to capturing substrings, because PCRE requires three integers
112 per substring, whereas the POSIX interface provides only two. If the
113 number of expected substrings is small, the wrapper function uses space
114 on the stack, because this is faster than using malloc() for each call.
115 The default threshold above which the stack is no longer used is 10; it
116 can be changed by adding a setting such as
117 --with-posix-malloc-threshold=20
119 to the configure command.
121
123 Within a compiled pattern, offset values are used to point from one
125 part to another (for example, from an opening parenthesis to an alter‐
126 nation metacharacter). By default, two-byte values are used for these
127 offsets, leading to a maximum size for a compiled pattern of around
128 64K. This is sufficient to handle all but the most gigantic patterns.
129 Nevertheless, some people do want to process enormous patterns, so it
130 is possible to compile PCRE to use three-byte or four-byte offsets by
131 adding a setting such as
132 --with-link-size=3
134 to the configure command. The value given must be 2, 3, or 4. Using
136 longer offsets slows down the operation of PCRE because it has to load
137 additional bytes when handling them.
138
140 When matching with the pcre_exec() function, PCRE implements backtrack‐
142 ing by making recursive calls to an internal function called match().
143 In environments where the size of the stack is limited, this can se‐
144 verely limit PCRE's operation. (The Unix environment does not usually
145 suffer from this problem, but it may sometimes be necessary to increase
146 the maximum stack size. There is a discussion in the pcrestack docu‐
147 mentation.) An alternative approach to recursion that uses memory from
148 the heap to remember data, instead of using recursive function calls,
149 has been implemented to work round the problem of limited stack size.
150 If you want to build a version of PCRE that works this way, add
151 --disable-stack-for-recursion
153 to the configure command. With this configuration, PCRE will use the
155 pcre_stack_malloc and pcre_stack_free variables to call memory manage‐
156 ment functions. By default these point to malloc() and free(), but you
157 can replace the pointers so that your own functions are used.
158 Separate functions are provided rather than using pcre_malloc and
160 pcre_free because the usage is very predictable: the block sizes
161 requested are always the same, and the blocks are always freed in
162 reverse order. A calling program might be able to implement optimized
163 functions that perform better than malloc() and free(). PCRE runs
164 noticeably more slowly when built in this way. This option affects only
165 the pcre_exec() function; it is not relevant for the the
166 pcre_dfa_exec() function.
167
169 Internally, PCRE has a function called match(), which it calls repeat‐
171 edly (sometimes recursively) when matching a pattern with the
172 pcre_exec() function. By controlling the maximum number of times this
173 function may be called during a single matching operation, a limit can
174 be placed on the resources used by a single call to pcre_exec(). The
175 limit can be changed at run time, as described in the pcreapi documen‐
176 tation. The default is 10 million, but this can be changed by adding a
177 setting such as
178 --with-match-limit=500000
180 to the configure command. This setting has no effect on the
182 pcre_dfa_exec() matching function.
183 In some environments it is desirable to limit the depth of recursive
185 calls of match() more strictly than the total number of calls, in order
186 to restrict the maximum amount of stack (or heap, if --disable-stack-
187 for-recursion is specified) that is used. A second limit controls this;
188 it defaults to the value that is set for --with-match-limit, which
189 imposes no additional constraints. However, you can set a lower limit
190 by adding, for example,
191 --with-match-limit-recursion=10000
193 to the configure command. This value can also be overridden at run
195 time.
196
198 PCRE uses fixed tables for processing characters whose code values are
200 less than 256. By default, PCRE is built with a set of tables that are
201 distributed in the file pcre_chartables.c.dist. These tables are for
202 ASCII codes only. If you add
203 --enable-rebuild-chartables
205 to the configure command, the distributed tables are no longer used.
207 Instead, a program called dftables is compiled and run. This outputs
208 the source for new set of tables, created in the default locale of your
209 C runtime system. (This method of replacing the tables does not work if
210 you are cross compiling, because dftables is run on the local host. If
211 you need to create alternative tables when cross compiling, you will
212 have to do so "by hand".)
213
215 PCRE assumes by default that it will run in an environment where the
217 character code is ASCII (or Unicode, which is a superset of ASCII).
218 This is the case for most computer operating systems. PCRE can, how‐
219 ever, be compiled to run in an EBCDIC environment by adding
220 --enable-ebcdic
222 to the configure command. This setting implies --enable-rebuild-charta‐
224 bles. You should only use it if you know that you are in an EBCDIC
225 environment (for example, an IBM mainframe operating system).
226
228 pcreapi(3), pcre_config(3).
230
232 Philip Hazel
234 University Computing Service
235 Cambridge CB2 3QH, England.
236
238 Last updated: 30 July 2007
240 Copyright (c) 1997-2007 University of Cambridge.
241 PCREBUILD(3)