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1 nigel 79 .TH PCREBUILD 3
2 nigel 63 .SH NAME
3     PCRE - Perl-compatible regular expressions
5 nigel 63 .rs
6     .sp
7     This document describes the optional features of PCRE that can be selected when
8 ph10 260 the library is compiled. It assumes use of the \fBconfigure\fP script, where
9     the optional features are selected or deselected by providing options to
10     \fBconfigure\fP before running the \fBmake\fP command. However, the same
11     options can be selected in both Unix-like and non-Unix-like environments using
12     the GUI facility of \fBCMakeSetup\fP if you are using \fBCMake\fP instead of
13     \fBconfigure\fP to build PCRE.
14     .P
15     The complete list of options for \fBconfigure\fP (which includes the standard
16     ones such as the selection of the installation directory) can be obtained by
17     running
18 nigel 75 .sp
19 nigel 63 ./configure --help
20 nigel 75 .sp
21 ph10 128 The following sections include descriptions of options whose names begin with
22     --enable or --disable. These settings specify changes to the defaults for the
23 nigel 75 \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
24 nigel 63 --enable and --disable always come in pairs, so the complementary option always
25     exists as well, but as it specifies the default, it is not described.
26 nigel 75 .
27 nigel 83 .SH "C++ SUPPORT"
28     .rs
29     .sp
30     By default, the \fBconfigure\fP script will search for a C++ compiler and C++
31     header files. If it finds them, it automatically builds the C++ wrapper library
32     for PCRE. You can disable this by adding
33     .sp
34     --disable-cpp
35     .sp
36     to the \fBconfigure\fP command.
37     .
38 nigel 75 .SH "UTF-8 SUPPORT"
39 nigel 63 .rs
40     .sp
41     To build PCRE with support for UTF-8 character strings, add
42 nigel 75 .sp
43 nigel 63 --enable-utf8
44 nigel 75 .sp
45     to the \fBconfigure\fP command. Of itself, this does not make PCRE treat
46 nigel 63 strings as UTF-8. As well as compiling PCRE with this option, you also have
47 nigel 75 have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
48 nigel 63 function.
49 nigel 75 .
51 nigel 63 .rs
52     .sp
53 nigel 75 UTF-8 support allows PCRE to process character values greater than 255 in the
54     strings that it handles. On its own, however, it does not provide any
55     facilities for accessing the properties of such characters. If you want to be
56     able to use the pattern escapes \eP, \ep, and \eX, which refer to Unicode
57     character properties, you must add
58     .sp
59     --enable-unicode-properties
60     .sp
61     to the \fBconfigure\fP command. This implies UTF-8 support, even if you have
62     not explicitly requested it.
63     .P
64 ph10 128 Including Unicode property support adds around 30K of tables to the PCRE
65     library. Only the general category properties such as \fILu\fP and \fINd\fP are
66     supported. Details are given in the
67 nigel 75 .\" HREF
68     \fBpcrepattern\fP
69     .\"
70     documentation.
71     .
73     .rs
74     .sp
75 nigel 91 By default, PCRE interprets character 10 (linefeed, LF) as indicating the end
76     of a line. This is the normal newline character on Unix-like systems. You can
77     compile PCRE to use character 13 (carriage return, CR) instead, by adding
78 nigel 75 .sp
79 nigel 63 --enable-newline-is-cr
80 nigel 75 .sp
81 nigel 91 to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
82     which explicitly specifies linefeed as the newline character.
83     .sp
84     Alternatively, you can specify that line endings are to be indicated by the two
85     character sequence CRLF. If you want this, add
86     .sp
87     --enable-newline-is-crlf
88     .sp
89 nigel 93 to the \fBconfigure\fP command. There is a fourth option, specified by
90     .sp
91 ph10 149 --enable-newline-is-anycrlf
92     .sp
93     which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as
94     indicating a line ending. Finally, a fifth option, specified by
95     .sp
96 nigel 93 --enable-newline-is-any
97     .sp
98 ph10 149 causes PCRE to recognize any Unicode newline sequence.
99 nigel 93 .P
100     Whatever line ending convention is selected when PCRE is built can be
101     overridden when the library functions are called. At build time it is
102     conventional to use the standard for your operating system.
103 nigel 75 .
104 ph10 231 .SH "WHAT \eR MATCHES"
105     .rs
106     .sp
107     By default, the sequence \eR in a pattern matches any Unicode newline sequence,
108     whatever has been selected as the line ending sequence. If you specify
109     .sp
110     --enable-bsr-anycrlf
111     .sp
112     the default is changed so that \eR matches only CR, LF, or CRLF. Whatever is
113     selected when PCRE is built can be overridden when the library functions are
114     called.
115     .
117 nigel 63 .rs
118     .sp
119 nigel 75 The PCRE building process uses \fBlibtool\fP to build both shared and static
120 nigel 63 Unix libraries by default. You can suppress one of these by adding one of
121 nigel 75 .sp
122 nigel 63 --disable-shared
123     --disable-static
124 nigel 75 .sp
125     to the \fBconfigure\fP command, as required.
126     .
128 nigel 63 .rs
129     .sp
130 nigel 75 When PCRE is called through the POSIX interface (see the
131     .\" HREF
132     \fBpcreposix\fP
133     .\"
134 nigel 63 documentation), additional working storage is required for holding the pointers
135 nigel 75 to capturing substrings, because PCRE requires three integers per substring,
136 nigel 63 whereas the POSIX interface provides only two. If the number of expected
137     substrings is small, the wrapper function uses space on the stack, because this
138 nigel 75 is faster than using \fBmalloc()\fP for each call. The default threshold above
139 nigel 63 which the stack is no longer used is 10; it can be changed by adding a setting
140     such as
141 nigel 75 .sp
142 nigel 63 --with-posix-malloc-threshold=20
143 nigel 75 .sp
144     to the \fBconfigure\fP command.
145     .
147 nigel 63 .rs
148     .sp
149     Within a compiled pattern, offset values are used to point from one part to
150     another (for example, from an opening parenthesis to an alternation
151 nigel 75 metacharacter). By default, two-byte values are used for these offsets, leading
152 nigel 63 to a maximum size for a compiled pattern of around 64K. This is sufficient to
153     handle all but the most gigantic patterns. Nevertheless, some people do want to
154     process enormous patterns, so it is possible to compile PCRE to use three-byte
155     or four-byte offsets by adding a setting such as
156 nigel 75 .sp
157 nigel 63 --with-link-size=3
158 nigel 75 .sp
159     to the \fBconfigure\fP command. The value given must be 2, 3, or 4. Using
160 nigel 63 longer offsets slows down the operation of PCRE because it has to load
161     additional bytes when handling them.
162 nigel 75 .
164 nigel 73 .rs
165     .sp
166 nigel 77 When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
167     by making recursive calls to an internal function called \fBmatch()\fP. In
168     environments where the size of the stack is limited, this can severely limit
169     PCRE's operation. (The Unix environment does not usually suffer from this
170 nigel 91 problem, but it may sometimes be necessary to increase the maximum stack size.
171     There is a discussion in the
172     .\" HREF
173     \fBpcrestack\fP
174     .\"
175     documentation.) An alternative approach to recursion that uses memory from the
176     heap to remember data, instead of using recursive function calls, has been
177     implemented to work round the problem of limited stack size. If you want to
178     build a version of PCRE that works this way, add
179 nigel 75 .sp
180 nigel 73 --disable-stack-for-recursion
181 nigel 75 .sp
182     to the \fBconfigure\fP command. With this configuration, PCRE will use the
183     \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
184 ph10 174 management functions. By default these point to \fBmalloc()\fP and
185     \fBfree()\fP, but you can replace the pointers so that your own functions are
186 ph10 182 used.
187 ph10 174 .P
188     Separate functions are provided rather than using \fBpcre_malloc\fP and
189     \fBpcre_free\fP because the usage is very predictable: the block sizes
190     requested are always the same, and the blocks are always freed in reverse
191     order. A calling program might be able to implement optimized functions that
192     perform better than \fBmalloc()\fP and \fBfree()\fP. PCRE runs noticeably more
193     slowly when built in this way. This option affects only the \fBpcre_exec()\fP
194     function; it is not relevant for the the \fBpcre_dfa_exec()\fP function.
195 nigel 75 .
197     .rs
198     .sp
199     Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
200     (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
201     function. By controlling the maximum number of times this function may be
202     called during a single matching operation, a limit can be placed on the
203     resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
204     at run time, as described in the
205     .\" HREF
206     \fBpcreapi\fP
207     .\"
208     documentation. The default is 10 million, but this can be changed by adding a
209     setting such as
210     .sp
211     --with-match-limit=500000
212     .sp
213     to the \fBconfigure\fP command. This setting has no effect on the
214     \fBpcre_dfa_exec()\fP matching function.
215     .P
216     In some environments it is desirable to limit the depth of recursive calls of
217     \fBmatch()\fP more strictly than the total number of calls, in order to
218     restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
219     is specified) that is used. A second limit controls this; it defaults to the
220     value that is set for --with-match-limit, which imposes no additional
221     constraints. However, you can set a lower limit by adding, for example,
222     .sp
223     --with-match-limit-recursion=10000
224     .sp
225     to the \fBconfigure\fP command. This value can also be overridden at run time.
226     .
228     .rs
229     .sp
230     PCRE uses fixed tables for processing characters whose code values are less
231     than 256. By default, PCRE is built with a set of tables that are distributed
232     in the file \fIpcre_chartables.c.dist\fP. These tables are for ASCII codes
233     only. If you add
234     .sp
235     --enable-rebuild-chartables
236     .sp
237     to the \fBconfigure\fP command, the distributed tables are no longer used.
238     Instead, a program called \fBdftables\fP is compiled and run. This outputs the
239     source for new set of tables, created in the default locale of your C runtime
240     system. (This method of replacing the tables does not work if you are cross
241     compiling, because \fBdftables\fP is run on the local host. If you need to
242     create alternative tables when cross compiling, you will have to do so "by
243     hand".)
244     .
245 nigel 75 .SH "USING EBCDIC CODE"
246 nigel 73 .rs
247     .sp
248     PCRE assumes by default that it will run in an environment where the character
249 ph10 195 code is ASCII (or Unicode, which is a superset of ASCII). This is the case for
250     most computer operating systems. PCRE can, however, be compiled to run in an
251     EBCDIC environment by adding
252 nigel 75 .sp
253 nigel 73 --enable-ebcdic
254 nigel 75 .sp
255 ph10 128 to the \fBconfigure\fP command. This setting implies
256 ph10 197 --enable-rebuild-chartables. You should only use it if you know that you are in
257 ph10 195 an EBCDIC environment (for example, an IBM mainframe operating system).
258 nigel 93 .
260     .rs
261     .sp
262     By default, \fBpcregrep\fP reads all files as plain text. You can build it so
263     that it recognizes files whose names end in \fB.gz\fP or \fB.bz2\fP, and reads
264     them with \fBlibz\fP or \fBlibbz2\fP, respectively, by adding one or both of
265     .sp
266     --enable-pcregrep-libz
267     --enable-pcregrep-libbz2
268     .sp
269     to the \fBconfigure\fP command. These options naturally require that the
270     relevant libraries are installed on your system. Configuration will fail if
271     they are not.
272 nigel 93 .
273 ph10 286 .
274 nigel 93 .SH "SEE ALSO"
275     .rs
276     .sp
277     \fBpcreapi\fP(3), \fBpcre_config\fP(3).
278 ph10 99 .
279     .
280     .SH AUTHOR
281     .rs
282     .sp
283     .nf
284     Philip Hazel
285     University Computing Service
286     Cambridge CB2 3QH, England.
287     .fi
288     .
289     .
290     .SH REVISION
291     .rs
292     .sp
293     .nf
294 ph10 286 Last updated: 17 December 2007
295 ph10 99 Copyright (c) 1997-2007 University of Cambridge.
296     .fi


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