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1 nigel 63 .TH PCRE 3
2     .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     .SH "UTF-8 SUPPORT"
23 nigel 63 .rs
24     .sp
25     To build PCRE with support for UTF-8 character strings, add
26 nigel 75 .sp
27 nigel 63 --enable-utf8
28 nigel 75 .sp
29     to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
30 nigel 63 strings as UTF-8. As well as compiling PCRE with this option, you also have
31 nigel 75 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
32 nigel 63 function.
33 nigel 75 .
34     .SH "UNICODE CHARACTER PROPERTY SUPPORT"
35 nigel 63 .rs
36     .sp
37 nigel 75 UTF-8 support allows PCRE to process character values greater than 255 in the
38     strings that it handles. On its own, however, it does not provide any
39     facilities for accessing the properties of such characters. If you want to be
40     able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
41     character properties, you must add
42     .sp
43     --enable-unicode-properties
44     .sp
45     to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
46     not explicitly requested it.
47     .P
48     Including Unicode property support adds around 90K of tables to the PCRE
49     library, approximately doubling its size. Only the general category properties
50     such as \fILu\fP and \fINd\fP are supported. Details are given in the
51     .\" HREF
52     \fBpcrepattern\fP
53     .\"
54     documentation.
55     .
56     .SH "CODE VALUE OF NEWLINE"
57     .rs
58     .sp
59 nigel 63 By default, PCRE treats character 10 (linefeed) as the newline character. This
60     is the normal newline character on Unix-like systems. You can compile PCRE to
61     use character 13 (carriage return) instead by adding
62 nigel 75 .sp
63 nigel 63 --enable-newline-is-cr
64 nigel 75 .sp
65     to the \fBconfigure\fP command. For completeness there is also a
66 nigel 63 --enable-newline-is-lf option, which explicitly specifies linefeed as the
67     newline character.
68 nigel 75 .
69     .SH "BUILDING SHARED AND STATIC LIBRARIES"
70 nigel 63 .rs
71     .sp
72 nigel 75 The PCRE building process uses \fBlibtool\fP to build both shared and static
73 nigel 63 Unix libraries by default. You can suppress one of these by adding one of
74 nigel 75 .sp
75 nigel 63 --disable-shared
76     --disable-static
77 nigel 75 .sp
78     to the \fBconfigure\fP command, as required.
79     .
80     .SH "POSIX MALLOC USAGE"
81 nigel 63 .rs
82     .sp
83 nigel 75 When PCRE is called through the POSIX interface (see the
84     .\" HREF
85     \fBpcreposix\fP
86     .\"
87 nigel 63 documentation), additional working storage is required for holding the pointers
88 nigel 75 to capturing substrings, because PCRE requires three integers per substring,
89 nigel 63 whereas the POSIX interface provides only two. If the number of expected
90     substrings is small, the wrapper function uses space on the stack, because this
91 nigel 75 is faster than using \fBmalloc()\fP for each call. The default threshold above
92 nigel 63 which the stack is no longer used is 10; it can be changed by adding a setting
93     such as
94 nigel 75 .sp
95 nigel 63 --with-posix-malloc-threshold=20
96 nigel 75 .sp
97     to the \fBconfigure\fP command.
98     .
99     .SH "LIMITING PCRE RESOURCE USAGE"
100 nigel 63 .rs
101     .sp
102 nigel 75 Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
103     (possibly recursively) when matching a pattern. By controlling the maximum
104     number of times this function may be called during a single matching operation,
105     a limit can be placed on the resources used by a single call to
106     \fBpcre_exec()\fP. The limit can be changed at run time, as described in the
107     .\" HREF
108     \fBpcreapi\fP
109     .\"
110     documentation. The default is 10 million, but this can be changed by adding a
111     setting such as
112     .sp
113 nigel 63 --with-match-limit=500000
114 nigel 75 .sp
115     to the \fBconfigure\fP command.
116     .
117     .SH "HANDLING VERY LARGE PATTERNS"
118 nigel 63 .rs
119     .sp
120     Within a compiled pattern, offset values are used to point from one part to
121     another (for example, from an opening parenthesis to an alternation
122 nigel 75 metacharacter). By default, two-byte values are used for these offsets, leading
123 nigel 63 to a maximum size for a compiled pattern of around 64K. This is sufficient to
124     handle all but the most gigantic patterns. Nevertheless, some people do want to
125     process enormous patterns, so it is possible to compile PCRE to use three-byte
126     or four-byte offsets by adding a setting such as
127 nigel 75 .sp
128 nigel 63 --with-link-size=3
129 nigel 75 .sp
130     to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
131 nigel 63 longer offsets slows down the operation of PCRE because it has to load
132     additional bytes when handling them.
133 nigel 75 .P
134 nigel 63 If you build PCRE with an increased link size, test 2 (and test 5 if you are
135     using UTF-8) will fail. Part of the output of these tests is a representation
136     of the compiled pattern, and this changes with the link size.
137 nigel 75 .
138     .SH "AVOIDING EXCESSIVE STACK USAGE"
139 nigel 73 .rs
140     .sp
141     PCRE implements backtracking while matching by making recursive calls to an
142 nigel 75 internal function called \fBmatch()\fP. In environments where the size of the
143 nigel 73 stack is limited, this can severely limit PCRE's operation. (The Unix
144     environment does not usually suffer from this problem.) An alternative approach
145     that uses memory from the heap to remember data, instead of using recursive
146     function calls, has been implemented to work round this problem. If you want to
147     build a version of PCRE that works this way, add
148 nigel 75 .sp
149 nigel 73 --disable-stack-for-recursion
150 nigel 75 .sp
151     to the \fBconfigure\fP command. With this configuration, PCRE will use the
152     \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
153 nigel 73 management functions. Separate functions are provided because the usage is very
154     predictable: the block sizes requested are always the same, and the blocks are
155     always freed in reverse order. A calling program might be able to implement
156 nigel 75 optimized functions that perform better than the standard \fBmalloc()\fP and
157     \fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
158 nigel 73 way.
159 nigel 75 .
160     .SH "USING EBCDIC CODE"
161 nigel 73 .rs
162     .sp
163     PCRE assumes by default that it will run in an environment where the character
164 nigel 75 code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
165 nigel 73 compiled to run in an EBCDIC environment by adding
166 nigel 75 .sp
167 nigel 73 --enable-ebcdic
168 nigel 75 .sp
169     to the \fBconfigure\fP command.
170     .P
171 nigel 63 .in 0
172 nigel 75 Last updated: 09 September 2004
173 nigel 63 .br
174 nigel 75 Copyright (c) 1997-2004 University of Cambridge.

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