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1 .TH PCRE 3
2 .SH NAME
3 PCRE - Perl-compatible regular expressions
4 .SH "PCRE BUILD-TIME OPTIONS"
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 describe certain options whose names begin with --enable
17 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 "UTF-8 SUPPORT"
23 .rs
24 .sp
25 To build PCRE with support for UTF-8 character strings, add
26 .sp
27 --enable-utf8
28 .sp
29 to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
30 strings as UTF-8. As well as compiling PCRE with this option, you also have
31 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
32 function.
33 .
34 .SH "UNICODE CHARACTER PROPERTY SUPPORT"
35 .rs
36 .sp
37 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 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 .sp
63 --enable-newline-is-cr
64 .sp
65 to the \fBconfigure\fP command. For completeness there is also a
66 --enable-newline-is-lf option, which explicitly specifies linefeed as the
67 newline character.
68 .
69 .SH "BUILDING SHARED AND STATIC LIBRARIES"
70 .rs
71 .sp
72 The PCRE building process uses \fBlibtool\fP to build both shared and static
73 Unix libraries by default. You can suppress one of these by adding one of
74 .sp
75 --disable-shared
76 --disable-static
77 .sp
78 to the \fBconfigure\fP command, as required.
79 .
80 .SH "POSIX MALLOC USAGE"
81 .rs
82 .sp
83 When PCRE is called through the POSIX interface (see the
84 .\" HREF
85 \fBpcreposix\fP
86 .\"
87 documentation), additional working storage is required for holding the pointers
88 to capturing substrings, because PCRE requires three integers per substring,
89 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 is faster than using \fBmalloc()\fP for each call. The default threshold above
92 which the stack is no longer used is 10; it can be changed by adding a setting
93 such as
94 .sp
95 --with-posix-malloc-threshold=20
96 .sp
97 to the \fBconfigure\fP command.
98 .
99 .SH "LIMITING PCRE RESOURCE USAGE"
100 .rs
101 .sp
102 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 --with-match-limit=500000
114 .sp
115 to the \fBconfigure\fP command.
116 .
117 .SH "HANDLING VERY LARGE PATTERNS"
118 .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 metacharacter). By default, two-byte values are used for these offsets, leading
123 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 .sp
128 --with-link-size=3
129 .sp
130 to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
131 longer offsets slows down the operation of PCRE because it has to load
132 additional bytes when handling them.
133 .P
134 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 .
138 .SH "AVOIDING EXCESSIVE STACK USAGE"
139 .rs
140 .sp
141 PCRE implements backtracking while matching by making recursive calls to an
142 internal function called \fBmatch()\fP. In environments where the size of the
143 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 .sp
149 --disable-stack-for-recursion
150 .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 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 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 way.
159 .
160 .SH "USING EBCDIC CODE"
161 .rs
162 .sp
163 PCRE assumes by default that it will run in an environment where the character
164 code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
165 compiled to run in an EBCDIC environment by adding
166 .sp
167 --enable-ebcdic
168 .sp
169 to the \fBconfigure\fP command.
170 .P
171 .in 0
172 Last updated: 09 September 2004
173 .br
174 Copyright (c) 1997-2004 University of Cambridge.

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