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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 describe certain options whose names begin with --enable
17  or --disable. These settings specify changes to the defaults for the  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 90K of tables to the PCRE
60    library, approximately doubling its size. Only the general category properties
61    such as \fILu\fP and \fINd\fP are 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. Whatever line ending convention is selected
85    when PCRE is built can be overridden when the library functions are called. At
86    build time it is conventional to use the standard for your operating system.
87    .
88    .SH "BUILDING SHARED AND STATIC LIBRARIES"
89  .rs  .rs
90  .sp  .sp
91  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
92  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
93    .sp
94    --disable-shared    --disable-shared
95    --disable-static    --disable-static
96    .sp
97  to the \fBconfigure\fR command, as required.  to the \fBconfigure\fP command, as required.
98    .
99  .SH POSIX MALLOC USAGE  .SH "POSIX MALLOC USAGE"
100  .rs  .rs
101  .sp  .sp
102  When PCRE is called through the POSIX interface (see the \fBpcreposix\fR  When PCRE is called through the POSIX interface (see the
103    .\" HREF
104    \fBpcreposix\fP
105    .\"
106  documentation), additional working storage is required for holding the pointers  documentation), additional working storage is required for holding the pointers
107  to capturing substrings because PCRE requires three integers per substring,  to capturing substrings, because PCRE requires three integers per substring,
108  whereas the POSIX interface provides only two. If the number of expected  whereas the POSIX interface provides only two. If the number of expected
109  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
110  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
111  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
112  such as  such as
113    .sp
114    --with-posix-malloc-threshold=20    --with-posix-malloc-threshold=20
   
 to the \fBconfigure\fR command.  
   
 .SH LIMITING PCRE RESOURCE USAGE  
 .rs  
115  .sp  .sp
116  Internally, PCRE has a function called \fBmatch()\fR which it calls repeatedly  to the \fBconfigure\fP command.
117  (possibly recursively) when performing a matching operation. By limiting the  .
118  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  
119  .rs  .rs
120  .sp  .sp
121  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
122  another (for example, from an opening parenthesis to an alternation  another (for example, from an opening parenthesis to an alternation
123  metacharacter). By default two-byte values are used for these offsets, leading  metacharacter). By default, two-byte values are used for these offsets, leading
124  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
125  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
126  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
127  or four-byte offsets by adding a setting such as  or four-byte offsets by adding a setting such as
128    .sp
129    --with-link-size=3    --with-link-size=3
130    .sp
131  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
132  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
133  additional bytes when handling them.  additional bytes when handling them.
134    .P
135  If you build PCRE with an increased link size, test 2 (and test 5 if you are  If you build PCRE with an increased link size, test 2 (and test 5 if you are
136  using UTF-8) will fail. Part of the output of these tests is a representation  using UTF-8) will fail. Part of the output of these tests is a representation
137  of the compiled pattern, and this changes with the link size.  of the compiled pattern, and this changes with the link size.
138    .
139    .SH "AVOIDING EXCESSIVE STACK USAGE"
140    .rs
141    .sp
142    When matching with the \fBpcre_exec()\fP function, PCRE implements backtracking
143    by making recursive calls to an internal function called \fBmatch()\fP. In
144    environments where the size of the stack is limited, this can severely limit
145    PCRE's operation. (The Unix environment does not usually suffer from this
146    problem, but it may sometimes be necessary to increase the maximum stack size.
147    There is a discussion in the
148    .\" HREF
149    \fBpcrestack\fP
150    .\"
151    documentation.) An alternative approach to recursion that uses memory from the
152    heap to remember data, instead of using recursive function calls, has been
153    implemented to work round the problem of limited stack size. If you want to
154    build a version of PCRE that works this way, add
155    .sp
156      --disable-stack-for-recursion
157    .sp
158    to the \fBconfigure\fP command. With this configuration, PCRE will use the
159    \fBpcre_stack_malloc\fP and \fBpcre_stack_free\fP variables to call memory
160    management functions. Separate functions are provided because the usage is very
161    predictable: the block sizes requested are always the same, and the blocks are
162    always freed in reverse order. A calling program might be able to implement
163    optimized functions that perform better than the standard \fBmalloc()\fP and
164    \fBfree()\fP functions. PCRE runs noticeably more slowly when built in this
165    way. This option affects only the \fBpcre_exec()\fP function; it is not
166    relevant for the the \fBpcre_dfa_exec()\fP function.
167    .
168    .SH "LIMITING PCRE RESOURCE USAGE"
169    .rs
170    .sp
171    Internally, PCRE has a function called \fBmatch()\fP, which it calls repeatedly
172    (sometimes recursively) when matching a pattern with the \fBpcre_exec()\fP
173    function. By controlling the maximum number of times this function may be
174    called during a single matching operation, a limit can be placed on the
175    resources used by a single call to \fBpcre_exec()\fP. The limit can be changed
176    at run time, as described in the
177    .\" HREF
178    \fBpcreapi\fP
179    .\"
180    documentation. The default is 10 million, but this can be changed by adding a
181    setting such as
182    .sp
183      --with-match-limit=500000
184    .sp
185    to the \fBconfigure\fP command. This setting has no effect on the
186    \fBpcre_dfa_exec()\fP matching function.
187    .P
188    In some environments it is desirable to limit the depth of recursive calls of
189    \fBmatch()\fP more strictly than the total number of calls, in order to
190    restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion
191    is specified) that is used. A second limit controls this; it defaults to the
192    value that is set for --with-match-limit, which imposes no additional
193    constraints. However, you can set a lower limit by adding, for example,
194    .sp
195      --with-match-limit-recursion=10000
196    .sp
197    to the \fBconfigure\fP command. This value can also be overridden at run time.
198    .
199    .SH "USING EBCDIC CODE"
200    .rs
201    .sp
202    PCRE assumes by default that it will run in an environment where the character
203    code is ASCII (or Unicode, which is a superset of ASCII). PCRE can, however, be
204    compiled to run in an EBCDIC environment by adding
205    .sp
206      --enable-ebcdic
207    .sp
208    to the \fBconfigure\fP command.
209    .P
210  .in 0  .in 0
211  Last updated: 21 January 2003  Last updated: 06 June 2006
212  .br  .br
213  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2006 University of Cambridge.
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