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Updated PCRE source to version 8.32 (bug 5593).

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Nicholas Hastings
2013-03-17 11:32:03 -04:00
parent ed6d8521e6
commit 6ce00034a2
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@@ -14,41 +14,69 @@ man page, in case the conversion went wrong.
<br>
<ul>
<li><a name="TOC1" href="#SEC1">INTRODUCTION</a>
<li><a name="TOC2" href="#SEC2">USER DOCUMENTATION</a>
<li><a name="TOC3" href="#SEC3">LIMITATIONS</a>
<li><a name="TOC4" href="#SEC4">UTF-8 AND UNICODE PROPERTY SUPPORT</a>
<li><a name="TOC5" href="#SEC5">AUTHOR</a>
<li><a name="TOC6" href="#SEC6">REVISION</a>
<li><a name="TOC2" href="#SEC2">SECURITY CONSIDERATIONS</a>
<li><a name="TOC3" href="#SEC3">USER DOCUMENTATION</a>
<li><a name="TOC4" href="#SEC4">AUTHOR</a>
<li><a name="TOC5" href="#SEC5">REVISION</a>
</ul>
<br><a name="SEC1" href="#TOC1">INTRODUCTION</a><br>
<P>
The PCRE library is a set of functions that implement regular expression
pattern matching using the same syntax and semantics as Perl, with just a few
differences. Certain features that appeared in Python and PCRE before they
appeared in Perl are also available using the Python syntax. There is also some
support for certain .NET and Oniguruma syntax items, and there is an option for
requesting some minor changes that give better JavaScript compatibility.
differences. Some features that appeared in Python and PCRE before they
appeared in Perl are also available using the Python syntax, there is some
support for one or two .NET and Oniguruma syntax items, and there is an option
for requesting some minor changes that give better JavaScript compatibility.
</P>
<P>
The current implementation of PCRE (release 7.x) corresponds approximately with
Perl 5.10, including support for UTF-8 encoded strings and Unicode general
category properties. However, UTF-8 and Unicode support has to be explicitly
Starting with release 8.30, it is possible to compile two separate PCRE
libraries: the original, which supports 8-bit character strings (including
UTF-8 strings), and a second library that supports 16-bit character strings
(including UTF-16 strings). The build process allows either one or both to be
built. The majority of the work to make this possible was done by Zoltan
Herczeg.
</P>
<P>
Starting with release 8.32 it is possible to compile a third separate PCRE
library, which supports 32-bit character strings (including
UTF-32 strings). The build process allows any set of the 8-, 16- and 32-bit
libraries. The work to make this possible was done by Christian Persch.
</P>
<P>
The three libraries contain identical sets of functions, except that the names
in the 16-bit library start with <b>pcre16_</b> instead of <b>pcre_</b>, and the
names in the 32-bit library start with <b>pcre32_</b> instead of <b>pcre_</b>. To
avoid over-complication and reduce the documentation maintenance load, most of
the documentation describes the 8-bit library, with the differences for the
16-bit and 32-bit libraries described separately in the
<a href="pcre16.html"><b>pcre16</b></a>
and
<a href="pcre32.html"><b>pcre32</b></a>
pages. References to functions or structures of the form <i>pcre[16|32]_xxx</i>
should be read as meaning "<i>pcre_xxx</i> when using the 8-bit library,
<i>pcre16_xxx</i> when using the 16-bit library, or <i>pcre32_xxx</i> when using
the 32-bit library".
</P>
<P>
The current implementation of PCRE corresponds approximately with Perl 5.12,
including support for UTF-8/16/32 encoded strings and Unicode general category
properties. However, UTF-8/16/32 and Unicode support has to be explicitly
enabled; it is not the default. The Unicode tables correspond to Unicode
release 5.1.
release 6.2.0.
</P>
<P>
In addition to the Perl-compatible matching function, PCRE contains an
alternative matching function that matches the same compiled patterns in a
different way. In certain circumstances, the alternative function has some
advantages. For a discussion of the two matching algorithms, see the
alternative function that matches the same compiled patterns in a different
way. In certain circumstances, the alternative function has some advantages.
For a discussion of the two matching algorithms, see the
<a href="pcrematching.html"><b>pcrematching</b></a>
page.
</P>
<P>
PCRE is written in C and released as a C library. A number of people have
written wrappers and interfaces of various kinds. In particular, Google Inc.
have provided a comprehensive C++ wrapper. This is now included as part of the
PCRE distribution. The
have provided a comprehensive C++ wrapper for the 8-bit library. This is now
included as part of the PCRE distribution. The
<a href="pcrecpp.html"><b>pcrecpp</b></a>
page has details of this interface. Other people's contributions can be found
in the <i>Contrib</i> directory at the primary FTP site, which is:
@@ -72,216 +100,86 @@ function makes it possible for a client to discover which features are
available. The features themselves are described in the
<a href="pcrebuild.html"><b>pcrebuild</b></a>
page. Documentation about building PCRE for various operating systems can be
found in the <b>README</b> file in the source distribution.
found in the <b>README</b> and <b>NON-AUTOTOOLS_BUILD</b> files in the source
distribution.
</P>
<P>
The library contains a number of undocumented internal functions and data
The libraries contains a number of undocumented internal functions and data
tables that are used by more than one of the exported external functions, but
which are not intended for use by external callers. Their names all begin with
"_pcre_", which hopefully will not provoke any name clashes. In some
environments, it is possible to control which external symbols are exported
when a shared library is built, and in these cases the undocumented symbols are
not exported.
"_pcre_" or "_pcre16_" or "_pcre32_", which hopefully will not provoke any name
clashes. In some environments, it is possible to control which external symbols
are exported when a shared library is built, and in these cases the
undocumented symbols are not exported.
</P>
<br><a name="SEC2" href="#TOC1">USER DOCUMENTATION</a><br>
<br><a name="SEC2" href="#TOC1">SECURITY CONSIDERATIONS</a><br>
<P>
If you are using PCRE in a non-UTF application that permits users to supply
arbitrary patterns for compilation, you should be aware of a feature that
allows users to turn on UTF support from within a pattern, provided that PCRE
was built with UTF support. For example, an 8-bit pattern that begins with
"(*UTF8)" or "(*UTF)" turns on UTF-8 mode, which interprets patterns and
subjects as strings of UTF-8 characters instead of individual 8-bit characters.
This causes both the pattern and any data against which it is matched to be
checked for UTF-8 validity. If the data string is very long, such a check might
use sufficiently many resources as to cause your application to lose
performance.
</P>
<P>
The best way of guarding against this possibility is to use the
<b>pcre_fullinfo()</b> function to check the compiled pattern's options for UTF.
</P>
<P>
If your application is one that supports UTF, be aware that validity checking
can take time. If the same data string is to be matched many times, you can use
the PCRE_NO_UTF[8|16|32]_CHECK option for the second and subsequent matches to
save redundant checks.
</P>
<P>
Another way that performance can be hit is by running a pattern that has a very
large search tree against a string that will never match. Nested unlimited
repeats in a pattern are a common example. PCRE provides some protection
against this: see the PCRE_EXTRA_MATCH_LIMIT feature in the
<a href="pcreapi.html"><b>pcreapi</b></a>
page.
</P>
<br><a name="SEC3" href="#TOC1">USER DOCUMENTATION</a><br>
<P>
The user documentation for PCRE comprises a number of different sections. In
the "man" format, each of these is a separate "man page". In the HTML format,
each is a separate page, linked from the index page. In the plain text format,
all the sections are concatenated, for ease of searching. The sections are as
follows:
all the sections, except the <b>pcredemo</b> section, are concatenated, for ease
of searching. The sections are as follows:
<pre>
pcre this document
pcre16 details of the 16-bit library
pcre32 details of the 32-bit library
pcre-config show PCRE installation configuration information
pcreapi details of PCRE's native C API
pcrebuild options for building PCRE
pcrecallout details of the callout feature
pcrecompat discussion of Perl compatibility
pcrecpp details of the C++ wrapper
pcregrep description of the <b>pcregrep</b> command
pcrecpp details of the C++ wrapper for the 8-bit library
pcredemo a demonstration C program that uses PCRE
pcregrep description of the <b>pcregrep</b> command (8-bit only)
pcrejit discussion of the just-in-time optimization support
pcrelimits details of size and other limits
pcrematching discussion of the two matching algorithms
pcrepartial details of the partial matching facility
pcrepattern syntax and semantics of supported regular expressions
pcresyntax quick syntax reference
pcreperform discussion of performance issues
pcreposix the POSIX-compatible C API
pcreposix the POSIX-compatible C API for the 8-bit library
pcreprecompile details of saving and re-using precompiled patterns
pcresample discussion of the sample program
pcresample discussion of the pcredemo program
pcrestack discussion of stack usage
pcresyntax quick syntax reference
pcretest description of the <b>pcretest</b> testing command
pcreunicode discussion of Unicode and UTF-8/16/32 support
</pre>
In addition, in the "man" and HTML formats, there is a short page for each
C library function, listing its arguments and results.
</P>
<br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
<P>
There are some size limitations in PCRE but it is hoped that they will never in
practice be relevant.
</P>
<P>
The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
compiled with the default internal linkage size of 2. If you want to process
regular expressions that are truly enormous, you can compile PCRE with an
internal linkage size of 3 or 4 (see the <b>README</b> file in the source
distribution and the
<a href="pcrebuild.html"><b>pcrebuild</b></a>
documentation for details). In these cases the limit is substantially larger.
However, the speed of execution is slower.
</P>
<P>
All values in repeating quantifiers must be less than 65536.
</P>
<P>
There is no limit to the number of parenthesized subpatterns, but there can be
no more than 65535 capturing subpatterns.
</P>
<P>
The maximum length of name for a named subpattern is 32 characters, and the
maximum number of named subpatterns is 10000.
</P>
<P>
The maximum length of a subject string is the largest positive number that an
integer variable can hold. However, when using the traditional matching
function, PCRE uses recursion to handle subpatterns and indefinite repetition.
This means that the available stack space may limit the size of a subject
string that can be processed by certain patterns. For a discussion of stack
issues, see the
<a href="pcrestack.html"><b>pcrestack</b></a>
documentation.
<a name="utf8support"></a></P>
<br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>
<P>
From release 3.3, PCRE has had some support for character strings encoded in
the UTF-8 format. For release 4.0 this was greatly extended to cover most
common requirements, and in release 5.0 additional support for Unicode general
category properties was added.
</P>
<P>
In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
the code, and, in addition, you must call
<a href="pcre_compile.html"><b>pcre_compile()</b></a>
with the PCRE_UTF8 option flag, or the pattern must start with the sequence
(*UTF8). When either of these is the case, both the pattern and any subject
strings that are matched against it are treated as UTF-8 strings instead of
just strings of bytes.
</P>
<P>
If you compile PCRE with UTF-8 support, but do not use it at run time, the
library will be a bit bigger, but the additional run time overhead is limited
to testing the PCRE_UTF8 flag occasionally, so should not be very big.
</P>
<P>
If PCRE is built with Unicode character property support (which implies UTF-8
support), the escape sequences \p{..}, \P{..}, and \X are supported.
The available properties that can be tested are limited to the general
category properties such as Lu for an upper case letter or Nd for a decimal
number, the Unicode script names such as Arabic or Han, and the derived
properties Any and L&. A full list is given in the
<a href="pcrepattern.html"><b>pcrepattern</b></a>
documentation. Only the short names for properties are supported. For example,
\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
compatibility with Perl 5.6. PCRE does not support this.
<a name="utf8strings"></a></P>
<br><b>
Validity of UTF-8 strings
</b><br>
<P>
When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
are (by default) checked for validity on entry to the relevant functions. From
release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
themselves derived from the Unicode specification. Earlier releases of PCRE
followed the rules of RFC 2279, which allows the full range of 31-bit values (0
to 0x7FFFFFFF). The current check allows only values in the range U+0 to
U+10FFFF, excluding U+D800 to U+DFFF.
</P>
<P>
The excluded code points are the "Low Surrogate Area" of Unicode, of which the
Unicode Standard says this: "The Low Surrogate Area does not contain any
character assignments, consequently no character code charts or namelists are
provided for this area. Surrogates are reserved for use with UTF-16 and then
must be used in pairs." The code points that are encoded by UTF-16 pairs are
available as independent code points in the UTF-8 encoding. (In other words,
the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
UTF-8.)
</P>
<P>
If an invalid UTF-8 string is passed to PCRE, an error return
(PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
your strings are valid, and therefore want to skip these checks in order to
improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
at run time, PCRE assumes that the pattern or subject it is given
(respectively) contains only valid UTF-8 codes. In this case, it does not
diagnose an invalid UTF-8 string.
</P>
<P>
If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
happens depends on why the string is invalid. If the string conforms to the
"old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
rules of RFC 2279. However, if the string does not even conform to RFC 2279,
the result is undefined. Your program may crash.
</P>
<P>
If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
encoded in a UTF-8-like manner as per the old RFC, you can set
PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
situation, you will have to apply your own validity check.
</P>
<br><b>
General comments about UTF-8 mode
</b><br>
<P>
1. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte
UTF-8 character if the value is greater than 127.
</P>
<P>
2. Octal numbers up to \777 are recognized, and match two-byte UTF-8
characters for values greater than \177.
</P>
<P>
3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
bytes, for example: \x{100}{3}.
</P>
<P>
4. The dot metacharacter matches one UTF-8 character instead of a single byte.
</P>
<P>
5. The escape sequence \C can be used to match a single byte in UTF-8 mode,
but its use can lead to some strange effects. This facility is not available in
the alternative matching function, <b>pcre_dfa_exec()</b>.
</P>
<P>
6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
test characters of any code value, but the characters that PCRE recognizes as
digits, spaces, or word characters remain the same set as before, all with
values less than 256. This remains true even when PCRE includes Unicode
property support, because to do otherwise would slow down PCRE in many common
cases. If you really want to test for a wider sense of, say, "digit", you
must use Unicode property tests such as \p{Nd}. Note that this also applies to
\b, because it is defined in terms of \w and \W.
</P>
<P>
7. Similarly, characters that match the POSIX named character classes are all
low-valued characters.
</P>
<P>
8. However, the Perl 5.10 horizontal and vertical whitespace matching escapes
(\h, \H, \v, and \V) do match all the appropriate Unicode characters.
</P>
<P>
9. Case-insensitive matching applies only to characters whose values are less
than 128, unless PCRE is built with Unicode property support. Even when Unicode
property support is available, PCRE still uses its own character tables when
checking the case of low-valued characters, so as not to degrade performance.
The Unicode property information is used only for characters with higher
values. Even when Unicode property support is available, PCRE supports
case-insensitive matching only when there is a one-to-one mapping between a
letter's cases. There are a small number of many-to-one mappings in Unicode;
these are not supported by PCRE.
</P>
<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
<br><a name="SEC4" href="#TOC1">AUTHOR</a><br>
<P>
Philip Hazel
<br>
@@ -295,11 +193,11 @@ Putting an actual email address here seems to have been a spam magnet, so I've
taken it away. If you want to email me, use my two initials, followed by the
two digits 10, at the domain cam.ac.uk.
</P>
<br><a name="SEC6" href="#TOC1">REVISION</a><br>
<br><a name="SEC5" href="#TOC1">REVISION</a><br>
<P>
Last updated: 11 April 2009
Last updated: 11 November 2012
<br>
Copyright &copy; 1997-2009 University of Cambridge.
Copyright &copy; 1997-2012 University of Cambridge.
<br>
<p>
Return to the <a href="index.html">PCRE index page</a>.