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 include descriptions of 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 30K of tables to the PCRE
library. 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-anycrlf
.sp
which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
indicating a line ending. Finally, a fifth option, specified by
.sp
  --enable-newline-is-any
.sp
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.
.
.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 "CREATING CHARACTER TABLES AT BUILD TIME"
.rs
.sp
PCRE uses fixed tables for processing characters whose code values are less
than 256. By default, PCRE is built with a set of tables that are distributed
in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
only. If you add
.sp
  --enable-rebuild-chartables
.sp
to the \fBconfigure\fP command, the distributed tables are no longer used.
Instead, a program called \fBdftables\fP is compiled and run. This outputs the
source for new set of tables, created in the default locale of your C runtime
system. (This method of replacing the tables does not work if you are cross
compiling, because \fBdftables\fP is run on the local host. If you need to
create alternative tables when cross compiling, you will have to do so "by
hand".)
.
.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. This setting implies
--enable-rebuild-chartables.
.
.
.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: 16 April 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 include descriptions of options whose names begin with
17	--enable 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 30K of tables to the PCRE
60	library. Only the general category properties such as \fILu\fP and \fINd\fP are
61	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-anycrlf
87	.sp
88	which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
89	indicating a line ending. Finally, a fifth option, specified by
90	.sp
91	--enable-newline-is-any
92	.sp
93	causes PCRE to recognize any Unicode newline sequence.
94	.P
95	Whatever line ending convention is selected when PCRE is built can be
96	overridden when the library functions are called. At build time it is
97	conventional to use the standard for your operating system.
98	.
99	.SH "BUILDING SHARED AND STATIC LIBRARIES"
100	.rs
101	.sp
102	The PCRE building process uses \fBlibtool\fP to build both shared and static
103	Unix libraries by default. You can suppress one of these by adding one of
104	.sp
105	--disable-shared
106	--disable-static
107	.sp
108	to the \fBconfigure\fP command, as required.
109	.
110	.SH "POSIX MALLOC USAGE"
111	.rs
112	.sp
113	When PCRE is called through the POSIX interface (see the
114	.\" HREF
115	\fBpcreposix\fP
116	.\"
117	documentation), additional working storage is required for holding the pointers
118	to capturing substrings, because PCRE requires three integers per substring,
119	whereas the POSIX interface provides only two. If the number of expected
120	substrings is small, the wrapper function uses space on the stack, because this
121	is faster than using \fBmalloc()\fP for each call. The default threshold above
122	which the stack is no longer used is 10; it can be changed by adding a setting
123	such as
124	.sp
125	--with-posix-malloc-threshold=20
126	.sp
127	to the \fBconfigure\fP command.
128	.
129	.SH "HANDLING VERY LARGE PATTERNS"
130	.rs
131	.sp
132	Within a compiled pattern, offset values are used to point from one part to
133	another (for example, from an opening parenthesis to an alternation
134	metacharacter). By default, two-byte values are used for these offsets, leading
135	to a maximum size for a compiled pattern of around 64K. This is sufficient to
136	handle all but the most gigantic patterns. Nevertheless, some people do want to
137	process enormous patterns, so it is possible to compile PCRE to use three-byte
138	or four-byte offsets by adding a setting such as
139	.sp
140	--with-link-size=3
141	.sp
142	to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
143	longer offsets slows down the operation of PCRE because it has to load
144	additional bytes when handling them.
145	.
146	.SH "AVOIDING EXCESSIVE STACK USAGE"
147	.rs
148	.sp
149	When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
150	by making recursive calls to an internal function called \fBmatch()\fP. In
151	environments where the size of the stack is limited, this can severely limit
152	PCRE's operation. (The Unix environment does not usually suffer from this
153	problem, but it may sometimes be necessary to increase the maximum stack size.
154	There is a discussion in the
155	.\" HREF
156	\fBpcrestack\fP
157	.\"
158	documentation.) An alternative approach to recursion that uses memory from the
159	heap to remember data, instead of using recursive function calls, has been
160	implemented to work round the problem of limited stack size. If you want to
161	build a version of PCRE that works this way, add
162	.sp
163	--disable-stack-for-recursion
164	.sp
165	to the \fBconfigure\fP command. With this configuration, PCRE will use the
166	\fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
167	management functions. Separate functions are provided because the usage is very
168	predictable: the block sizes requested are always the same, and the blocks are
169	always freed in reverse order. A calling program might be able to implement
170	optimized functions that perform better than the standard \fBmalloc()\fP and
171	\fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
172	way. This option affects only the \fBpcre_exec()\fP function; it is not
173	relevant for the the \fBpcre_dfa_exec()\fP function.
174	.
175	.SH "LIMITING PCRE RESOURCE USAGE"
176	.rs
177	.sp
178	Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
179	(sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
180	function. By controlling the maximum number of times this function may be
181	called during a single matching operation, a limit can be placed on the
182	resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
183	at run time, as described in the
184	.\" HREF
185	\fBpcreapi\fP
186	.\"
187	documentation. The default is 10 million, but this can be changed by adding a
188	setting such as
189	.sp
190	--with-match-limit=500000
191	.sp
192	to the \fBconfigure\fP command. This setting has no effect on the
193	\fBpcre_dfa_exec()\fP matching function.
194	.P
195	In some environments it is desirable to limit the depth of recursive calls of
196	\fBmatch()\fP more strictly than the total number of calls, in order to
197	restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
198	is specified) that is used. A second limit controls this; it defaults to the
199	value that is set for --with-match-limit, which imposes no additional
200	constraints. However, you can set a lower limit by adding, for example,
201	.sp
202	--with-match-limit-recursion=10000
203	.sp
204	to the \fBconfigure\fP command. This value can also be overridden at run time.
205	.
206	.SH "CREATING CHARACTER TABLES AT BUILD TIME"
207	.rs
208	.sp
209	PCRE uses fixed tables for processing characters whose code values are less
210	than 256. By default, PCRE is built with a set of tables that are distributed
211	in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
212	only. If you add
213	.sp
214	--enable-rebuild-chartables
215	.sp
216	to the \fBconfigure\fP command, the distributed tables are no longer used.
217	Instead, a program called \fBdftables\fP is compiled and run. This outputs the
218	source for new set of tables, created in the default locale of your C runtime
219	system. (This method of replacing the tables does not work if you are cross
220	compiling, because \fBdftables\fP is run on the local host. If you need to
221	create alternative tables when cross compiling, you will have to do so "by
222	hand".)
223	.
224	.SH "USING EBCDIC CODE"
225	.rs
226	.sp
227	PCRE assumes by default that it will run in an environment where the character
228	code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
229	compiled to run in an EBCDIC environment by adding
230	.sp
231	--enable-ebcdic
232	.sp
233	to the \fBconfigure\fP command. This setting implies
234	--enable-rebuild-chartables.
235	.
236	.
237	.SH "SEE ALSO"
238	.rs
239	.sp
240	\fBpcreapi\fP(3), \fBpcre_config\fP(3).
241	.
242	.
243	.SH AUTHOR
244	.rs
245	.sp
246	.nf
247	Philip Hazel
248	University Computing Service
249	Cambridge CB2 3QH, England.
250	.fi
251	.
252	.
253	.SH REVISION
254	.rs
255	.sp
256	.nf
257	Last updated: 16 April 2007
258	Copyright (c) 1997-2007 University of Cambridge.
259	.fi
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