freeswitch/libs/pcre/doc/pcrebuild.3

.TH PCREBUILD 3
.SH NAME
PCRE - Perl-compatible regular expressions
.SH "PCRE BUILD-TIME OPTIONS"
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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 describe certain 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"
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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
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  --disable-cpp
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to the \fBconfigure\fP command.
.
.SH "UTF-8 SUPPORT"
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To build PCRE with support for UTF-8 character strings, add
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  --enable-utf8
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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"
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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
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  --enable-unicode-properties
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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 90K of tables to the PCRE
library, approximately doubling its size. 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"
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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
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  --enable-newline-is-cr
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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
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  --enable-newline-is-crlf
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to the \fBconfigure\fP command. 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 "BUILDING SHARED AND STATIC LIBRARIES"
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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
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  --disable-shared
  --disable-static
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to the \fBconfigure\fP command, as required.
.
.SH "POSIX MALLOC USAGE"
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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
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  --with-posix-malloc-threshold=20
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to the \fBconfigure\fP command.
.
.SH "HANDLING VERY LARGE PATTERNS"
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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
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  --with-link-size=3
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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.
.P
If you build PCRE with an increased link size, test 2 (and test 5 if you are
using UTF-8) will fail. Part of the output of these tests is a representation
of the compiled pattern, and this changes with the link size.
.
.SH "AVOIDING EXCESSIVE STACK USAGE"
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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
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  --disable-stack-for-recursion
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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. Separate functions are provided 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 the standard \fBmalloc()\fP and
\fBfree()\fP functions. 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.
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.SH "LIMITING PCRE RESOURCE USAGE"
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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
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  --with-match-limit=500000
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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
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to the \fBconfigure\fP command. This value can also be overridden at run time.
.
.SH "USING EBCDIC CODE"
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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). PCRE can, however, be
compiled to run in an EBCDIC environment by adding
.sp
  --enable-ebcdic
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to the \fBconfigure\fP command.
.P
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Last updated: 06 June 2006
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Copyright (c) 1997-2006 University of Cambridge.