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1  .TH PCRE 3  .TH PCREBUILD 3
2  .SH NAME  .SH NAME
3  PCRE - Perl-compatible regular expressions  PCRE - Perl-compatible regular expressions
4  .SH PCRE BUILD-TIME OPTIONS  .SH "PCRE BUILD-TIME OPTIONS"
5  .rs  .rs
6  .sp  .sp
7  This document describes the optional features of PCRE that can be selected when  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  the library is compiled. They are all selected, or deselected, by providing
9  options to the \fBconfigure\fR script which is run before the \fBmake\fR  options to the \fBconfigure\fP script that is run before the \fBmake\fP
10  command. The complete list of options for \fBconfigure\fR (which includes the  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  standard ones such as the selection of the installation directory) can be
12  obtained by running  obtained by running
13    .sp
14    ./configure --help    ./configure --help
15    .sp
16  The following sections describe certain options whose names begin with --enable  The following sections include descriptions of options whose names begin with
17  or --disable. These settings specify changes to the defaults for the  --enable or --disable. These settings specify changes to the defaults for the
18  \fBconfigure\fR command. Because of the way that \fBconfigure\fR works,  \fBconfigure\fP command. Because of the way that \fBconfigure\fP works,
19  --enable and --disable always come in pairs, so the complementary option always  --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.  exists as well, but as it specifies the default, it is not described.
21    .
22  .SH UTF-8 SUPPORT  .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  .rs
35  .sp  .sp
36  To build PCRE with support for UTF-8 character strings, add  To build PCRE with support for UTF-8 character strings, add
37    .sp
38    --enable-utf8    --enable-utf8
39    .sp
40  to the \fBconfigure\fR command. Of itself, this does not make PCRE treat  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  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()\fR  have to set the PCRE_UTF8 option when you call the \fBpcre_compile()\fP
43  function.  function.
44    .
45  .SH CODE VALUE OF NEWLINE  .SH "UNICODE CHARACTER PROPERTY SUPPORT"
46  .rs  .rs
47  .sp  .sp
48  By default, PCRE treats character 10 (linefeed) as the newline character. This  UTF-8 support allows PCRE to process character values greater than 255 in the
49  is the normal newline character on Unix-like systems. You can compile PCRE to  strings that it handles. On its own, however, it does not provide any
50  use character 13 (carriage return) instead by adding  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    --enable-newline-is-cr
75    .sp
76  to the \fBconfigure\fR command. For completeness there is also a  to the \fBconfigure\fP command. There is also a --enable-newline-is-lf option,
77  --enable-newline-is-lf option, which explicitly specifies linefeed as the  which explicitly specifies linefeed as the newline character.
78  newline character.  .sp
79    Alternatively, you can specify that line endings are to be indicated by the two
80  .SH BUILDING SHARED AND STATIC LIBRARIES  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  .rs
101  .sp  .sp
102  The PCRE building process uses \fBlibtool\fR to build both shared and static  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  Unix libraries by default. You can suppress one of these by adding one of
104    .sp
105    --disable-shared    --disable-shared
106    --disable-static    --disable-static
107    .sp
108  to the \fBconfigure\fR command, as required.  to the \fBconfigure\fP command, as required.
109    .
110  .SH POSIX MALLOC USAGE  .SH "POSIX MALLOC USAGE"
111  .rs  .rs
112  .sp  .sp
113  When PCRE is called through the POSIX interface (see the \fBpcreposix\fR  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  documentation), additional working storage is required for holding the pointers
118  to capturing substrings because PCRE requires three integers per substring,  to capturing substrings, because PCRE requires three integers per substring,
119  whereas the POSIX interface provides only two. If the number of expected  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  substrings is small, the wrapper function uses space on the stack, because this
121  is faster than using \fBmalloc()\fR for each call. The default threshold above  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  which the stack is no longer used is 10; it can be changed by adding a setting
123  such as  such as
124    .sp
125    --with-posix-malloc-threshold=20    --with-posix-malloc-threshold=20
   
 to the \fBconfigure\fR command.  
   
 .SH LIMITING PCRE RESOURCE USAGE  
 .rs  
126  .sp  .sp
127  Internally, PCRE has a function called \fBmatch()\fR which it calls repeatedly  to the \fBconfigure\fP command.
128  (possibly recursively) when performing a matching operation. By limiting the  .
129  number of times this function may be called, a limit can be placed on the  .SH "HANDLING VERY LARGE PATTERNS"
 resources used by a single call to \fBpcre_exec()\fR. The limit can be changed  
 at run time, as described in the \fBpcreapi\fR documentation. The default is 10  
 million, but this can be changed by adding a setting such as  
   
   --with-match-limit=500000  
   
 to the \fBconfigure\fR command.  
   
 .SH HANDLING VERY LARGE PATTERNS  
130  .rs  .rs
131  .sp  .sp
132  Within a compiled pattern, offset values are used to point from one part to  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  another (for example, from an opening parenthesis to an alternation
134  metacharacter). By default two-byte values are used for these offsets, leading  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  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  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  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  or four-byte offsets by adding a setting such as
139    .sp
140    --with-link-size=3    --with-link-size=3
141    .sp
142  to the \fBconfigure\fR command. The value given must be 2, 3, or 4. Using  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  longer offsets slows down the operation of PCRE because it has to load
144  additional bytes when handling them.  additional bytes when handling them.
145    .
146  If you build PCRE with an increased link size, test 2 (and test 5 if you are  .SH "AVOIDING EXCESSIVE STACK USAGE"
147  using UTF-8) will fail. Part of the output of these tests is a representation  .rs
148  of the compiled pattern, and this changes with the link size.  .sp
149    When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
150  .in 0  by making recursive calls to an internal function called \fBmatch()\fP. In
151  Last updated: 21 January 2003  environments where the size of the stack is limited, this can severely limit
152  .br  PCRE's operation. (The Unix environment does not usually suffer from this
153  Copyright (c) 1997-2003 University of Cambridge.  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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