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 "WHAT \eR MATCHES"
.rs
.sp
By default, the sequence \eR in a pattern matches any Unicode newline sequence,
whatever has been selected as the line ending sequence. If you specify
.sp
  --enable-bsr-anycrlf
.sp
the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
selected when PCRE is built can be overridden when the library functions are
called.
.
.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. By default these point to \fBmalloc()\fP and
\fBfree()\fP, but you can replace the pointers so that your own functions are
used.
.P
Separate functions are provided rather than using \fBpcre_malloc\fP and
\fBpcre_free\fP 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 \fBmalloc()\fP and \fBfree()\fP. 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). This is the case for
most computer operating systems. 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. You should only use it if you know that you are in
an EBCDIC environment (for example, an IBM mainframe operating system).
.
.
.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: 11 September 2007
Copyright (c) 1997-2007 University of Cambridge.
.fi
1	nigel	79	.TH PCREBUILD 3
2	nigel	63	.SH NAME
3			PCRE - Perl-compatible regular expressions
4	nigel	75	.SH "PCRE BUILD-TIME OPTIONS"
5	nigel	63	.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	nigel	75	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	nigel	63	standard ones such as the selection of the installation directory) can be
12			obtained by running
13	nigel	75	.sp
14	nigel	63	./configure --help
15	nigel	75	.sp
16	ph10	128	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	nigel	75	\fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
19	nigel	63	--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	nigel	75	.
22	nigel	83	.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	nigel	75	.SH "UTF-8 SUPPORT"
34	nigel	63	.rs
35			.sp
36			To build PCRE with support for UTF-8 character strings, add
37	nigel	75	.sp
38	nigel	63	--enable-utf8
39	nigel	75	.sp
40			to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
41	nigel	63	strings as UTF-8. As well as compiling PCRE with this option, you also have
42	nigel	75	have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43	nigel	63	function.
44	nigel	75	.
45			.SH "UNICODE CHARACTER PROPERTY SUPPORT"
46	nigel	63	.rs
47			.sp
48	nigel	75	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	ph10	128	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	nigel	75	.\" HREF
63			\fBpcrepattern\fP
64			.\"
65			documentation.
66			.
67			.SH "CODE VALUE OF NEWLINE"
68			.rs
69			.sp
70	nigel	91	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	nigel	75	.sp
74	nigel	63	--enable-newline-is-cr
75	nigel	75	.sp
76	nigel	91	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	nigel	93	to the \fBconfigure\fP command. There is a fourth option, specified by
85			.sp
86	ph10	149	--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	nigel	93	--enable-newline-is-any
92			.sp
93	ph10	149	causes PCRE to recognize any Unicode newline sequence.
94	nigel	93	.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	nigel	75	.
99	ph10	231	.SH "WHAT \eR MATCHES"
100			.rs
101			.sp
102			By default, the sequence \eR in a pattern matches any Unicode newline sequence,
103			whatever has been selected as the line ending sequence. If you specify
104			.sp
105			--enable-bsr-anycrlf
106			.sp
107			the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
108			selected when PCRE is built can be overridden when the library functions are
109			called.
110			.
111	nigel	75	.SH "BUILDING SHARED AND STATIC LIBRARIES"
112	nigel	63	.rs
113			.sp
114	nigel	75	The PCRE building process uses \fBlibtool\fP to build both shared and static
115	nigel	63	Unix libraries by default. You can suppress one of these by adding one of
116	nigel	75	.sp
117	nigel	63	--disable-shared
118			--disable-static
119	nigel	75	.sp
120			to the \fBconfigure\fP command, as required.
121			.
122			.SH "POSIX MALLOC USAGE"
123	nigel	63	.rs
124			.sp
125	nigel	75	When PCRE is called through the POSIX interface (see the
126			.\" HREF
127			\fBpcreposix\fP
128			.\"
129	nigel	63	documentation), additional working storage is required for holding the pointers
130	nigel	75	to capturing substrings, because PCRE requires three integers per substring,
131	nigel	63	whereas the POSIX interface provides only two. If the number of expected
132			substrings is small, the wrapper function uses space on the stack, because this
133	nigel	75	is faster than using \fBmalloc()\fP for each call. The default threshold above
134	nigel	63	which the stack is no longer used is 10; it can be changed by adding a setting
135			such as
136	nigel	75	.sp
137	nigel	63	--with-posix-malloc-threshold=20
138	nigel	75	.sp
139			to the \fBconfigure\fP command.
140			.
141			.SH "HANDLING VERY LARGE PATTERNS"
142	nigel	63	.rs
143			.sp
144			Within a compiled pattern, offset values are used to point from one part to
145			another (for example, from an opening parenthesis to an alternation
146	nigel	75	metacharacter). By default, two-byte values are used for these offsets, leading
147	nigel	63	to a maximum size for a compiled pattern of around 64K. This is sufficient to
148			handle all but the most gigantic patterns. Nevertheless, some people do want to
149			process enormous patterns, so it is possible to compile PCRE to use three-byte
150			or four-byte offsets by adding a setting such as
151	nigel	75	.sp
152	nigel	63	--with-link-size=3
153	nigel	75	.sp
154			to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
155	nigel	63	longer offsets slows down the operation of PCRE because it has to load
156			additional bytes when handling them.
157	nigel	75	.
158			.SH "AVOIDING EXCESSIVE STACK USAGE"
159	nigel	73	.rs
160			.sp
161	nigel	77	When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
162			by making recursive calls to an internal function called \fBmatch()\fP. In
163			environments where the size of the stack is limited, this can severely limit
164			PCRE's operation. (The Unix environment does not usually suffer from this
165	nigel	91	problem, but it may sometimes be necessary to increase the maximum stack size.
166			There is a discussion in the
167			.\" HREF
168			\fBpcrestack\fP
169			.\"
170			documentation.) An alternative approach to recursion that uses memory from the
171			heap to remember data, instead of using recursive function calls, has been
172			implemented to work round the problem of limited stack size. If you want to
173			build a version of PCRE that works this way, add
174	nigel	75	.sp
175	nigel	73	--disable-stack-for-recursion
176	nigel	75	.sp
177			to the \fBconfigure\fP command. With this configuration, PCRE will use the
178			\fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
179	ph10	174	management functions. By default these point to \fBmalloc()\fP and
180			\fBfree()\fP, but you can replace the pointers so that your own functions are
181	ph10	182	used.
182	ph10	174	.P
183			Separate functions are provided rather than using \fBpcre_malloc\fP and
184			\fBpcre_free\fP because the usage is very predictable: the block sizes
185			requested are always the same, and the blocks are always freed in reverse
186			order. A calling program might be able to implement optimized functions that
187			perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
188			slowly when built in this way. This option affects only the \fBpcre_exec()\fP
189			function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.
190	nigel	75	.
191	nigel	91	.SH "LIMITING PCRE RESOURCE USAGE"
192			.rs
193			.sp
194			Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
195			(sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
196			function. By controlling the maximum number of times this function may be
197			called during a single matching operation, a limit can be placed on the
198			resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
199			at run time, as described in the
200			.\" HREF
201			\fBpcreapi\fP
202			.\"
203			documentation. The default is 10 million, but this can be changed by adding a
204			setting such as
205			.sp
206			--with-match-limit=500000
207			.sp
208			to the \fBconfigure\fP command. This setting has no effect on the
209			\fBpcre_dfa_exec()\fP matching function.
210			.P
211			In some environments it is desirable to limit the depth of recursive calls of
212			\fBmatch()\fP more strictly than the total number of calls, in order to
213			restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
214			is specified) that is used. A second limit controls this; it defaults to the
215			value that is set for --with-match-limit, which imposes no additional
216			constraints. However, you can set a lower limit by adding, for example,
217			.sp
218			--with-match-limit-recursion=10000
219			.sp
220			to the \fBconfigure\fP command. This value can also be overridden at run time.
221			.
222	ph10	128	.SH "CREATING CHARACTER TABLES AT BUILD TIME"
223			.rs
224			.sp
225			PCRE uses fixed tables for processing characters whose code values are less
226			than 256. By default, PCRE is built with a set of tables that are distributed
227			in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
228			only. If you add
229			.sp
230			--enable-rebuild-chartables
231			.sp
232			to the \fBconfigure\fP command, the distributed tables are no longer used.
233			Instead, a program called \fBdftables\fP is compiled and run. This outputs the
234			source for new set of tables, created in the default locale of your C runtime
235			system. (This method of replacing the tables does not work if you are cross
236			compiling, because \fBdftables\fP is run on the local host. If you need to
237			create alternative tables when cross compiling, you will have to do so "by
238			hand".)
239			.
240	nigel	75	.SH "USING EBCDIC CODE"
241	nigel	73	.rs
242			.sp
243			PCRE assumes by default that it will run in an environment where the character
244	ph10	195	code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
245			most computer operating systems. PCRE can, however, be compiled to run in an
246			EBCDIC environment by adding
247	nigel	75	.sp
248	nigel	73	--enable-ebcdic
249	nigel	75	.sp
250	ph10	128	to the \fBconfigure\fP command. This setting implies
251	ph10	197	--enable-rebuild-chartables. You should only use it if you know that you are in
252	ph10	195	an EBCDIC environment (for example, an IBM mainframe operating system).
253	nigel	93	.
254			.
255			.SH "SEE ALSO"
256			.rs
257			.sp
258			\fBpcreapi\fP(3), \fBpcre_config\fP(3).
259	ph10	99	.
260			.
261			.SH AUTHOR
262			.rs
263			.sp
264			.nf
265			Philip Hazel
266			University Computing Service
267			Cambridge CB2 3QH, England.
268			.fi
269			.
270			.
271			.SH REVISION
272			.rs
273			.sp
274			.nf
275	ph10	231	Last updated: 11 September 2007
276	ph10	99	Copyright (c) 1997-2007 University of Cambridge.
277			.fi
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