.TH PCRE 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\fR script which is run before the \fBmake\fR
command. The complete list of options for \fBconfigure\fR (which includes the
standard ones such as the selection of the installation directory) can be
obtained by running

  ./configure --help

The following sections describe certain options whose names begin with --enable
or --disable. These settings specify changes to the defaults for the
\fBconfigure\fR command. Because of the way that \fBconfigure\fR 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 UTF-8 SUPPORT
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To build PCRE with support for UTF-8 character strings, add

  --enable-utf8

to the \fBconfigure\fR 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()\fR
function.

.SH CODE VALUE OF NEWLINE
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By default, PCRE treats character 10 (linefeed) as the newline character. This
is the normal newline character on Unix-like systems. You can compile PCRE to
use character 13 (carriage return) instead by adding

  --enable-newline-is-cr

to the \fBconfigure\fR command. For completeness there is also a
--enable-newline-is-lf option, which explicitly specifies linefeed as the
newline character.

.SH BUILDING SHARED AND STATIC LIBRARIES
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The PCRE building process uses \fBlibtool\fR to build both shared and static
Unix libraries by default. You can suppress one of these by adding one of

  --disable-shared
  --disable-static

to the \fBconfigure\fR command, as required.

.SH POSIX MALLOC USAGE
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When PCRE is called through the POSIX interface (see the \fBpcreposix\fR
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()\fR 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

  --with-posix-malloc-threshold=20

to the \fBconfigure\fR command.

.SH LIMITING PCRE RESOURCE USAGE
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Internally, PCRE has a function called \fBmatch()\fR which it calls repeatedly
(possibly recursively) when performing a matching operation. By limiting the
number of times this function may be called, a limit can be placed on the
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
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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

  --with-link-size=3

to the \fBconfigure\fR 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.

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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PCRE implements backtracking while matching by making recursive calls to an
internal function called \fBmatch()\fR. 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.) An alternative approach
that uses memory from the heap to remember data, instead of using recursive
function calls, has been implemented to work round this problem. If you want to
build a version of PCRE that works this way, add

  --disable-stack-for-recursion

to the \fBconfigure\fR command. With this configuration, PCRE will use the
\fBpcre_stack_malloc\fR and \fBpcre_stack_free\fR 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()\fR and
\fBfree()\fR functions. PCRE runs noticeably more slowly when built in this
way.

.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 UTF-8, which is a superset of ASCII). PCRE can, however, be
compiled to run in an EBCDIC environment by adding

  --enable-ebcdic

to the \fBconfigure\fR command.

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Last updated: 09 December 2003
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Copyright (c) 1997-2003 University of Cambridge.