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1 nigel 79 .TH PCREBUILD 3
2 nigel 63 .SH NAME
3     PCRE - Perl-compatible regular expressions
4 nigel 75 .SH "PCRE BUILD-TIME OPTIONS"
5 nigel 63 .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 nigel 75 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 nigel 63 standard ones such as the selection of the installation directory) can be
12     obtained by running
13 nigel 75 .sp
14 nigel 63 ./configure --help
15 nigel 75 .sp
16 nigel 63 The following sections describe certain options whose names begin with --enable
17     or --disable. These settings specify changes to the defaults for the
18 nigel 75 \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
19 nigel 63 --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 nigel 75 .
22 nigel 83 .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     .
33 nigel 75 .SH "UTF-8 SUPPORT"
34 nigel 63 .rs
35     .sp
36     To build PCRE with support for UTF-8 character strings, add
37 nigel 75 .sp
38 nigel 63 --enable-utf8
39 nigel 75 .sp
40     to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
41 nigel 63 strings as UTF-8. As well as compiling PCRE with this option, you also have
42 nigel 75 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43 nigel 63 function.
44 nigel 75 .
45     .SH "UNICODE CHARACTER PROPERTY SUPPORT"
46 nigel 63 .rs
47     .sp
48 nigel 75 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 90K of tables to the PCRE
60     library, approximately doubling its size. Only the general category properties
61     such as \fILu\fP and \fINd\fP are supported. Details are given in the
62     .\" HREF
63     \fBpcrepattern\fP
64     .\"
65     documentation.
66     .
67     .SH "CODE VALUE OF NEWLINE"
68     .rs
69     .sp
70 nigel 91 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 nigel 75 .sp
74 nigel 63 --enable-newline-is-cr
75 nigel 75 .sp
76 nigel 91 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 nigel 93 to the \fBconfigure\fP command. There is a fourth option, specified by
85     .sp
86     --enable-newline-is-any
87     .sp
88     which causes PCRE to recognize any Unicode newline sequence.
89     .P
90     Whatever line ending convention is selected when PCRE is built can be
91     overridden when the library functions are called. At build time it is
92     conventional to use the standard for your operating system.
93 nigel 75 .
94     .SH "BUILDING SHARED AND STATIC LIBRARIES"
95 nigel 63 .rs
96     .sp
97 nigel 75 The PCRE building process uses \fBlibtool\fP to build both shared and static
98 nigel 63 Unix libraries by default. You can suppress one of these by adding one of
99 nigel 75 .sp
100 nigel 63 --disable-shared
101     --disable-static
102 nigel 75 .sp
103     to the \fBconfigure\fP command, as required.
104     .
105     .SH "POSIX MALLOC USAGE"
106 nigel 63 .rs
107     .sp
108 nigel 75 When PCRE is called through the POSIX interface (see the
109     .\" HREF
110     \fBpcreposix\fP
111     .\"
112 nigel 63 documentation), additional working storage is required for holding the pointers
113 nigel 75 to capturing substrings, because PCRE requires three integers per substring,
114 nigel 63 whereas the POSIX interface provides only two. If the number of expected
115     substrings is small, the wrapper function uses space on the stack, because this
116 nigel 75 is faster than using \fBmalloc()\fP for each call. The default threshold above
117 nigel 63 which the stack is no longer used is 10; it can be changed by adding a setting
118     such as
119 nigel 75 .sp
120 nigel 63 --with-posix-malloc-threshold=20
121 nigel 75 .sp
122     to the \fBconfigure\fP command.
123     .
124     .SH "HANDLING VERY LARGE PATTERNS"
125 nigel 63 .rs
126     .sp
127     Within a compiled pattern, offset values are used to point from one part to
128     another (for example, from an opening parenthesis to an alternation
129 nigel 75 metacharacter). By default, two-byte values are used for these offsets, leading
130 nigel 63 to a maximum size for a compiled pattern of around 64K. This is sufficient to
131     handle all but the most gigantic patterns. Nevertheless, some people do want to
132     process enormous patterns, so it is possible to compile PCRE to use three-byte
133     or four-byte offsets by adding a setting such as
134 nigel 75 .sp
135 nigel 63 --with-link-size=3
136 nigel 75 .sp
137     to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
138 nigel 63 longer offsets slows down the operation of PCRE because it has to load
139     additional bytes when handling them.
140 nigel 75 .P
141 nigel 63 If you build PCRE with an increased link size, test 2 (and test 5 if you are
142     using UTF-8) will fail. Part of the output of these tests is a representation
143     of the compiled pattern, and this changes with the link size.
144 nigel 75 .
145     .SH "AVOIDING EXCESSIVE STACK USAGE"
146 nigel 73 .rs
147     .sp
148 nigel 77 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
149     by making recursive calls to an internal function called \fBmatch()\fP. In
150     environments where the size of the stack is limited, this can severely limit
151     PCRE's operation. (The Unix environment does not usually suffer from this
152 nigel 91 problem, but it may sometimes be necessary to increase the maximum stack size.
153     There is a discussion in the
154     .\" HREF
155     \fBpcrestack\fP
156     .\"
157     documentation.) An alternative approach to recursion that uses memory from the
158     heap to remember data, instead of using recursive function calls, has been
159     implemented to work round the problem of limited stack size. If you want to
160     build a version of PCRE that works this way, add
161 nigel 75 .sp
162 nigel 73 --disable-stack-for-recursion
163 nigel 75 .sp
164     to the \fBconfigure\fP command. With this configuration, PCRE will use the
165     \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
166 nigel 73 management functions. Separate functions are provided because the usage is very
167     predictable: the block sizes requested are always the same, and the blocks are
168     always freed in reverse order. A calling program might be able to implement
169 nigel 75 optimized functions that perform better than the standard \fBmalloc()\fP and
170     \fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
171 nigel 77 way. This option affects only the \fBpcre_exec()\fP function; it is not
172     relevant for the the \fBpcre_dfa_exec()\fP function.
173 nigel 75 .
174 nigel 91 .SH "LIMITING PCRE RESOURCE USAGE"
175     .rs
176     .sp
177     Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
178     (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
179     function. By controlling the maximum number of times this function may be
180     called during a single matching operation, a limit can be placed on the
181     resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
182     at run time, as described in the
183     .\" HREF
184     \fBpcreapi\fP
185     .\"
186     documentation. The default is 10 million, but this can be changed by adding a
187     setting such as
188     .sp
189     --with-match-limit=500000
190     .sp
191     to the \fBconfigure\fP command. This setting has no effect on the
192     \fBpcre_dfa_exec()\fP matching function.
193     .P
194     In some environments it is desirable to limit the depth of recursive calls of
195     \fBmatch()\fP more strictly than the total number of calls, in order to
196     restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
197     is specified) that is used. A second limit controls this; it defaults to the
198     value that is set for --with-match-limit, which imposes no additional
199     constraints. However, you can set a lower limit by adding, for example,
200     .sp
201     --with-match-limit-recursion=10000
202     .sp
203     to the \fBconfigure\fP command. This value can also be overridden at run time.
204     .
205 nigel 75 .SH "USING EBCDIC CODE"
206 nigel 73 .rs
207     .sp
208     PCRE assumes by default that it will run in an environment where the character
209 nigel 75 code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
210 nigel 73 compiled to run in an EBCDIC environment by adding
211 nigel 75 .sp
212 nigel 73 --enable-ebcdic
213 nigel 75 .sp
214     to the \fBconfigure\fP command.
215 nigel 93 .
216     .
217     .SH "SEE ALSO"
218     .rs
219     .sp
220     \fBpcreapi\fP(3), \fBpcre_config\fP(3).
221 nigel 75 .P
222 nigel 63 .in 0
223 nigel 93 Last updated: 30 November 2006
224 nigel 63 .br
225 nigel 91 Copyright (c) 1997-2006 University of Cambridge.

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