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1  .TH PCRE 3  .TH PCRE 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 "UTF-8 SUPPORT"
23  .rs  .rs
24  .sp  .sp
25  To build PCRE with support for UTF-8 character strings, add  To build PCRE with support for UTF-8 character strings, add
26    .sp
27    --enable-utf8    --enable-utf8
28    .sp
29  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
30  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
31  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
32  function.  function.
33    .
34  .SH CODE VALUE OF NEWLINE  .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  .rs
58  .sp  .sp
59  By default, PCRE treats character 10 (linefeed) as the newline character. This  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  is the normal newline character on Unix-like systems. You can compile PCRE to
61  use character 13 (carriage return) instead by adding  use character 13 (carriage return) instead by adding
62    .sp
63    --enable-newline-is-cr    --enable-newline-is-cr
64    .sp
65  to the \fBconfigure\fR command. For completeness there is also a  to the \fBconfigure\fP command. For completeness there is also a
66  --enable-newline-is-lf option, which explicitly specifies linefeed as the  --enable-newline-is-lf option, which explicitly specifies linefeed as the
67  newline character.  newline character.
68    .
69  .SH BUILDING SHARED AND STATIC LIBRARIES  .SH "BUILDING SHARED AND STATIC LIBRARIES"
70  .rs  .rs
71  .sp  .sp
72  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
73  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
74    .sp
75    --disable-shared    --disable-shared
76    --disable-static    --disable-static
77    .sp
78  to the \fBconfigure\fR command, as required.  to the \fBconfigure\fP command, as required.
79    .
80  .SH POSIX MALLOC USAGE  .SH "POSIX MALLOC USAGE"
81  .rs  .rs
82  .sp  .sp
83  When PCRE is called through the POSIX interface (see the \fBpcreposix\fR  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  documentation), additional working storage is required for holding the pointers
88  to capturing substrings because PCRE requires three integers per substring,  to capturing substrings, because PCRE requires three integers per substring,
89  whereas the POSIX interface provides only two. If the number of expected  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  substrings is small, the wrapper function uses space on the stack, because this
91  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
92  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
93  such as  such as
94    .sp
95    --with-posix-malloc-threshold=20    --with-posix-malloc-threshold=20
   
 to the \fBconfigure\fR command.  
   
 .SH LIMITING PCRE RESOURCE USAGE  
 .rs  
96  .sp  .sp
97  Internally, PCRE has a function called \fBmatch()\fR which it calls repeatedly  to the \fBconfigure\fP command.
98  (possibly recursively) when performing a matching operation. By limiting the  .
99  number of times this function may be called, a limit can be placed on the  .SH "LIMITING PCRE RESOURCE USAGE"
100  resources used by a single call to \fBpcre_exec()\fR. The limit can be changed  .rs
101  at run time, as described in the \fBpcreapi\fR documentation. The default is 10  .sp
102  million, but this can be changed by adding a setting such as  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    --with-match-limit=500000
115    .sp
116  to the \fBconfigure\fR command.  to the \fBconfigure\fP command. This setting has no effect on the
117    \fBpcre_dfa_exec()\fP matching function.
118  .SH HANDLING VERY LARGE PATTERNS  .
119    .SH "HANDLING VERY LARGE PATTERNS"
120  .rs  .rs
121  .sp  .sp
122  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
123  another (for example, from an opening parenthesis to an alternation  another (for example, from an opening parenthesis to an alternation
124  metacharacter). By default two-byte values are used for these offsets, leading  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  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  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  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  or four-byte offsets by adding a setting such as
129    .sp
130    --with-link-size=3    --with-link-size=3
131    .sp
132  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
133  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
134  additional bytes when handling them.  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  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  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.  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  .in 0
176  Last updated: 21 January 2003  Last updated: 28 February 2005
177  .br  .br
178  Copyright (c) 1997-2003 University of Cambridge.  Copyright (c) 1997-2005 University of Cambridge.
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