trunk/doc/pcrebuild.3

.TH PCRE 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 "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 treats character 10 (linefeed) as the newline character. This
is the normal newline character on Unix-like systems. You can compile PCRE to
use character 13 (carriage return) instead by adding
.sp
  --enable-newline-is-cr
.sp
to the \fBconfigure\fP command. For completeness there is also a
--enable-newline-is-lf option, which explicitly specifies linefeed as the
newline character.
.
.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 "LIMITING PCRE RESOURCE USAGE"
.rs
.sp
Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
(possibly recursively) when matching a pattern. 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.
.
.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
PCRE implements backtracking while matching 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.) An alternative approach
that uses memory from the heap to remember data, instead of using recursive
function calls, has been implemented to work round this problem. 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.
.
.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.
.P
.in 0
Last updated: 09 September 2004
.br
Copyright (c) 1997-2004 University of Cambridge.
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.