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 "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 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.
.
.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.) 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. This option affects only the \fBpcre_exec()\fP function; it is not
relevant for the the \fBpcre_dfa_exec()\fP function.
.
.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: 28 February 2005
.br
Copyright (c) 1997-2005 University of Cambridge.
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 "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 with the \fBpcre_exec()\fP
104	function. By controlling the maximum number of times this function may be
105	called during a single matching operation, a limit can be placed on the
106	resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
107	at run time, as described in the
108	.\" HREF
109	\fBpcreapi\fP
110	.\"
111	documentation. The default is 10 million, but this can be changed by adding a
112	setting such as
113	.sp
114	--with-match-limit=500000
115	.sp
116	to the \fBconfigure\fP command. This setting has no effect on the
117	\fBpcre_dfa_exec()\fP matching function.
118	.
119	.SH "HANDLING VERY LARGE PATTERNS"
120	.rs
121	.sp
122	Within a compiled pattern, offset values are used to point from one part to
123	another (for example, from an opening parenthesis to an alternation
124	metacharacter). By default, two-byte values are used for these offsets, leading
125	to a maximum size for a compiled pattern of around 64K. This is sufficient to
126	handle all but the most gigantic patterns. Nevertheless, some people do want to
127	process enormous patterns, so it is possible to compile PCRE to use three-byte
128	or four-byte offsets by adding a setting such as
129	.sp
130	--with-link-size=3
131	.sp
132	to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
133	longer offsets slows down the operation of PCRE because it has to load
134	additional bytes when handling them.
135	.P
136	If you build PCRE with an increased link size, test 2 (and test 5 if you are
137	using UTF-8) will fail. Part of the output of these tests is a representation
138	of the compiled pattern, and this changes with the link size.
139	.
140	.SH "AVOIDING EXCESSIVE STACK USAGE"
141	.rs
142	.sp
143	When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
144	by making recursive calls to an internal function called \fBmatch()\fP. In
145	environments where the size of the stack is limited, this can severely limit
146	PCRE's operation. (The Unix environment does not usually suffer from this
147	problem.) An alternative approach that uses memory from the heap to remember
148	data, instead of using recursive function calls, has been implemented to work
149	round this problem. If you want to build a version of PCRE that works this way,
150	add
151	.sp
152	--disable-stack-for-recursion
153	.sp
154	to the \fBconfigure\fP command. With this configuration, PCRE will use the
155	\fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
156	management functions. Separate functions are provided because the usage is very
157	predictable: the block sizes requested are always the same, and the blocks are
158	always freed in reverse order. A calling program might be able to implement
159	optimized functions that perform better than the standard \fBmalloc()\fP and
160	\fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
161	way. This option affects only the \fBpcre_exec()\fP function; it is not
162	relevant for the the \fBpcre_dfa_exec()\fP function.
163	.
164	.SH "USING EBCDIC CODE"
165	.rs
166	.sp
167	PCRE assumes by default that it will run in an environment where the character
168	code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
169	compiled to run in an EBCDIC environment by adding
170	.sp
171	--enable-ebcdic
172	.sp
173	to the \fBconfigure\fP command.
174	.P
175	.in 0
176	Last updated: 28 February 2005
177	.br
178	Copyright (c) 1997-2005 University of Cambridge.