trunk/doc/pcrebuild.3

.TH PCREBUILD 3
.SH NAME
PCRE - Perl-compatible regular expressions
.SH "PCRE BUILD-TIME OPTIONS"
.rs
.sp
This document describes the optional features of PCRE that can be selected when
the library is compiled. They are all selected, or deselected, by providing
options to the \fBconfigure\fP script that is run before the \fBmake\fP
command. The complete list of options for \fBconfigure\fP (which includes the
standard ones such as the selection of the installation directory) can be
obtained by running
.sp
  ./configure --help
.sp
The following sections describe certain options whose names begin with --enable
or --disable. These settings specify changes to the defaults for the
\fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
--enable and --disable always come in pairs, so the complementary option always
exists as well, but as it specifies the default, it is not described.
.
.SH "C++ SUPPORT"
.rs
.sp
By default, the \fBconfigure\fP script will search for a C++ compiler and C++
header files. If it finds them, it automatically builds the C++ wrapper library
for PCRE. You can disable this by adding
.sp
  --disable-cpp
.sp
to the \fBconfigure\fP command.
.
.SH "UTF-8 SUPPORT"
.rs
.sp
To build PCRE with support for UTF-8 character strings, add
.sp
  --enable-utf8
.sp
to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
strings as UTF-8. As well as compiling PCRE with this option, you also have
have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
function.
.
.SH "UNICODE CHARACTER PROPERTY SUPPORT"
.rs
.sp
UTF-8 support allows PCRE to process character values greater than 255 in the
strings that it handles. On its own, however, it does not provide any
facilities for accessing the properties of such characters. If you want to be
able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
character properties, you must add
.sp
  --enable-unicode-properties
.sp
to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
not explicitly requested it.
.P
Including Unicode property support adds around 90K of tables to the PCRE
library, approximately doubling its size. Only the general category properties
such as \fILu\fP and \fINd\fP are supported. Details are given in the
.\" HREF
\fBpcrepattern\fP
.\"
documentation.
.
.SH "CODE VALUE OF NEWLINE"
.rs
.sp
By default, PCRE interprets character 10 (linefeed, LF) as indicating the end
of a line. This is the normal newline character on Unix-like systems. You can
compile PCRE to use character 13 (carriage return, CR) instead, by adding
.sp
  --enable-newline-is-cr
.sp
to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
which explicitly specifies linefeed as the newline character.
.sp
Alternatively, you can specify that line endings are to be indicated by the two
character sequence CRLF. If you want this, add
.sp
  --enable-newline-is-crlf
.sp
to the \fBconfigure\fP command. There is a fourth option, specified by
.sp
  --enable-newline-is-any
.sp
which causes PCRE to recognize any Unicode newline sequence.
.P
Whatever line ending convention is selected when PCRE is built can be
overridden when the library functions are called. At build time it is
conventional to use the standard for your operating system.
.
.SH "BUILDING SHARED AND STATIC LIBRARIES"
.rs
.sp
The PCRE building process uses \fBlibtool\fP to build both shared and static
Unix libraries by default. You can suppress one of these by adding one of
.sp
  --disable-shared
  --disable-static
.sp
to the \fBconfigure\fP command, as required.
.
.SH "POSIX MALLOC USAGE"
.rs
.sp
When PCRE is called through the POSIX interface (see the
.\" HREF
\fBpcreposix\fP
.\"
documentation), additional working storage is required for holding the pointers
to capturing substrings, because PCRE requires three integers per substring,
whereas the POSIX interface provides only two. If the number of expected
substrings is small, the wrapper function uses space on the stack, because this
is faster than using \fBmalloc()\fP for each call. The default threshold above
which the stack is no longer used is 10; it can be changed by adding a setting
such as
.sp
  --with-posix-malloc-threshold=20
.sp
to the \fBconfigure\fP command.
.
.SH "HANDLING VERY LARGE PATTERNS"
.rs
.sp
Within a compiled pattern, offset values are used to point from one part to
another (for example, from an opening parenthesis to an alternation
metacharacter). By default, two-byte values are used for these offsets, leading
to a maximum size for a compiled pattern of around 64K. This is sufficient to
handle all but the most gigantic patterns. Nevertheless, some people do want to
process enormous patterns, so it is possible to compile PCRE to use three-byte
or four-byte offsets by adding a setting such as
.sp
  --with-link-size=3
.sp
to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
longer offsets slows down the operation of PCRE because it has to load
additional bytes when handling them.
.P
If you build PCRE with an increased link size, test 2 (and test 5 if you are
using UTF-8) will fail. Part of the output of these tests is a representation
of the compiled pattern, and this changes with the link size.
.
.SH "AVOIDING EXCESSIVE STACK USAGE"
.rs
.sp
When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
by making recursive calls to an internal function called \fBmatch()\fP. In
environments where the size of the stack is limited, this can severely limit
PCRE's operation. (The Unix environment does not usually suffer from this
problem, but it may sometimes be necessary to increase the maximum stack size.
There is a discussion in the
.\" HREF
\fBpcrestack\fP
.\"
documentation.) An alternative approach to recursion that uses memory from the
heap to remember data, instead of using recursive function calls, has been
implemented to work round the problem of limited stack size. If you want to
build a version of PCRE that works this way, add
.sp
  --disable-stack-for-recursion
.sp
to the \fBconfigure\fP command. With this configuration, PCRE will use the
\fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
management functions. Separate functions are provided because the usage is very
predictable: the block sizes requested are always the same, and the blocks are
always freed in reverse order. A calling program might be able to implement
optimized functions that perform better than the standard \fBmalloc()\fP and
\fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
way. This option affects only the \fBpcre_exec()\fP function; it is not
relevant for the the \fBpcre_dfa_exec()\fP function.
.
.SH "LIMITING PCRE RESOURCE USAGE"
.rs
.sp
Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
(sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
function. By controlling the maximum number of times this function may be
called during a single matching operation, a limit can be placed on the
resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
at run time, as described in the
.\" HREF
\fBpcreapi\fP
.\"
documentation. The default is 10 million, but this can be changed by adding a
setting such as
.sp
  --with-match-limit=500000
.sp
to the \fBconfigure\fP command. This setting has no effect on the
\fBpcre_dfa_exec()\fP matching function.
.P
In some environments it is desirable to limit the depth of recursive calls of
\fBmatch()\fP more strictly than the total number of calls, in order to
restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
is specified) that is used. A second limit controls this; it defaults to the
value that is set for --with-match-limit, which imposes no additional
constraints. However, you can set a lower limit by adding, for example,
.sp
  --with-match-limit-recursion=10000
.sp
to the \fBconfigure\fP command. This value can also be overridden at run time.
.
.SH "USING EBCDIC CODE"
.rs
.sp
PCRE assumes by default that it will run in an environment where the character
code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
compiled to run in an EBCDIC environment by adding
.sp
  --enable-ebcdic
.sp
to the \fBconfigure\fP command.
.
.
.SH "SEE ALSO"
.rs
.sp
\fBpcreapi\fP(3), \fBpcre_config\fP(3).
.
.
.SH AUTHOR
.rs
.sp
.nf
Philip Hazel
University Computing Service
Cambridge CB2 3QH, England.
.fi
.
.
.SH REVISION
.rs
.sp
.nf
Last updated: 06 March 2007
Copyright (c) 1997-2007 University of Cambridge.
.fi
1	.TH PCREBUILD 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 "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	.SH "UTF-8 SUPPORT"
34	.rs
35	.sp
36	To build PCRE with support for UTF-8 character strings, add
37	.sp
38	--enable-utf8
39	.sp
40	to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
41	strings as UTF-8. As well as compiling PCRE with this option, you also have
42	have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43	function.
44	.
45	.SH "UNICODE CHARACTER PROPERTY SUPPORT"
46	.rs
47	.sp
48	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	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	.sp
74	--enable-newline-is-cr
75	.sp
76	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	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	.
94	.SH "BUILDING SHARED AND STATIC LIBRARIES"
95	.rs
96	.sp
97	The PCRE building process uses \fBlibtool\fP to build both shared and static
98	Unix libraries by default. You can suppress one of these by adding one of
99	.sp
100	--disable-shared
101	--disable-static
102	.sp
103	to the \fBconfigure\fP command, as required.
104	.
105	.SH "POSIX MALLOC USAGE"
106	.rs
107	.sp
108	When PCRE is called through the POSIX interface (see the
109	.\" HREF
110	\fBpcreposix\fP
111	.\"
112	documentation), additional working storage is required for holding the pointers
113	to capturing substrings, because PCRE requires three integers per substring,
114	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	is faster than using \fBmalloc()\fP for each call. The default threshold above
117	which the stack is no longer used is 10; it can be changed by adding a setting
118	such as
119	.sp
120	--with-posix-malloc-threshold=20
121	.sp
122	to the \fBconfigure\fP command.
123	.
124	.SH "HANDLING VERY LARGE PATTERNS"
125	.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	metacharacter). By default, two-byte values are used for these offsets, leading
130	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	.sp
135	--with-link-size=3
136	.sp
137	to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
138	longer offsets slows down the operation of PCRE because it has to load
139	additional bytes when handling them.
140	.P
141	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	.
145	.SH "AVOIDING EXCESSIVE STACK USAGE"
146	.rs
147	.sp
148	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	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	.sp
162	--disable-stack-for-recursion
163	.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	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	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	way. This option affects only the \fBpcre_exec()\fP function; it is not
172	relevant for the the \fBpcre_dfa_exec()\fP function.
173	.
174	.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	.SH "USING EBCDIC CODE"
206	.rs
207	.sp
208	PCRE assumes by default that it will run in an environment where the character
209	code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
210	compiled to run in an EBCDIC environment by adding
211	.sp
212	--enable-ebcdic
213	.sp
214	to the \fBconfigure\fP command.
215	.
216	.
217	.SH "SEE ALSO"
218	.rs
219	.sp
220	\fBpcreapi\fP(3), \fBpcre_config\fP(3).
221	.
222	.
223	.SH AUTHOR
224	.rs
225	.sp
226	.nf
227	Philip Hazel
228	University Computing Service
229	Cambridge CB2 3QH, England.
230	.fi
231	.
232	.
233	.SH REVISION
234	.rs
235	.sp
236	.nf
237	Last updated: 06 March 2007
238	Copyright (c) 1997-2007 University of Cambridge.
239	.fi
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