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-revision 93 by nigel,
Sat Feb 24 21:41:42 2007 UTC
+revision 654 by ph10,
Tue Aug  2 11:00:40 2011 UTC
 Line 6 
 PCRE - Perl-compatible regular expressio
  .sp
  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
+ differences. Some features that appeared in Python and PCRE before they
- appeared in Perl are also available using the Python syntax.)
+ appeared in Perl are also available using the Python syntax, there is some
- .P
+ support for one or two .NET and Oniguruma syntax items, and there is an option
- The current implementation of PCRE (release 7.x) corresponds approximately with
+ for requesting some minor changes that give better JavaScript compatibility.
- Perl 5.10, including support for UTF-8 encoded strings and Unicode general
+ .P
- category properties. However, UTF-8 and Unicode support has to be explicitly
+ The current implementation of PCRE corresponds approximately with Perl 5.12,
- enabled; it is not the default. The Unicode tables correspond to Unicode
+ including support for UTF-8 encoded strings and Unicode general category
- release 5.0.0.
+ properties. However, UTF-8 and Unicode support has to be explicitly enabled; it
+ is not the default. The Unicode tables correspond to Unicode release 6.0.0.
  .P
  In addition to the Perl-compatible matching function, PCRE contains an
- alternative matching function that matches the same compiled patterns in a
+ alternative function that matches the same compiled patterns in a different
- different way. In certain circumstances, the alternative function has some
+ way. In certain circumstances, the alternative function has some advantages.
- advantages. For a discussion of the two matching algorithms, see the
+ For a discussion of the two matching algorithms, see the
  .\" HREF
  \fBpcrematching\fP
  .\"
-Line 32 
 PCRE distribution. The
+Line 33 
 PCRE distribution. The
  \fBpcrecpp\fP
  .\"
  page has details of this interface. Other people's contributions can be found
- in the \fIContrib\fR directory at the primary FTP site, which is:
+ in the \fIContrib\fP directory at the primary FTP site, which is:
  .sp
  .\" HTML <a href="ftp://ftp.csx.cam.ac.uk/pub/software/programming/pcre">
  .\" </a>
-Line 41 
 ftp://ftp.csx.cam.ac.uk/pub/software/pro
+Line 42 
 ftp://ftp.csx.cam.ac.uk/pub/software/pro
  Details of exactly which Perl regular expression features are and are not
  supported by PCRE are given in separate documents. See the
  .\" HREF
- \fBpcrepattern\fR
+ \fBpcrepattern\fP
  .\"
  and
  .\" HREF
- \fBpcrecompat\fR
+ \fBpcrecompat\fP
+ .\"
+ pages. There is a syntax summary in the
+ .\" HREF
+ \fBpcresyntax\fP
  .\"
- pages.
+ page.
  .P
  Some features of PCRE can be included, excluded, or changed when the library is
  built. The
  .\" HREF
- \fBpcre_config()\fR
+ \fBpcre_config()\fP
  .\"
  function makes it possible for a client to discover which features are
  available. The features themselves are described in the
-Line 60 
 available. The features themselves are d
+Line 65 
 available. The features themselves are d
  \fBpcrebuild\fP
  .\"
  page. Documentation about building PCRE for various operating systems can be
- found in the \fBREADME\fP file in the source distribution.
+ found in the \fBREADME\fP and \fBNON-UNIX-USE\fP files in the source
+ distribution.
  .P
  The library contains a number of undocumented internal functions and data
  tables that are used by more than one of the exported external functions, but
-Line 77 
 not exported.
+Line 83 
 not exported.
  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
+ all the sections, except the \fBpcredemo\fP section, are concatenated, for ease
- follows:
+ of searching. The sections are as follows:
  .sp
    pcre              this document
+   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
+   pcredemo          a demonstration C program that uses PCRE
    pcregrep          description of the \fBpcregrep\fP command
    pcrematching      discussion of the two matching algorithms
    pcrepartial       details of the partial matching facility
-Line 95 
 follows:
+Line 103 
 follows:
    pcreperform       discussion of performance issues
    pcreposix         the POSIX-compatible C API
    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 \fBpcretest\fP testing command
  .sp
  In addition, in the "man" and HTML formats, there is a short page for each
-Line 120 
 distribution and the
+Line 129 
 distribution and the
  documentation for details). In these cases the limit is substantially larger.
  However, the speed of execution is slower.
  .P
- All values in repeating quantifiers must be less than 65536. The maximum
+ All values in repeating quantifiers must be less than 65536.
- compiled length of subpattern with an explicit repeat count is 30000 bytes. The
- maximum number of capturing subpatterns is 65535.
  .P
  There is no limit to the number of parenthesized subpatterns, but there can be
  no more than 65535 capturing subpatterns.
-Line 140 
 issues, see the
+Line 147 
 issues, see the
  \fBpcrestack\fP
  .\"
  documentation.
- .sp
- .\" HTML <a name="utf8support"></a>
  .
  .
+ .\" HTML <a name="utf8support"></a>
  .SH "UTF-8 AND UNICODE PROPERTY SUPPORT"
  .rs
  .sp
-Line 157 
 the code, and, in addition, you must cal
+Line 163 
 the code, and, in addition, you must cal
  .\" HREF
  \fBpcre_compile()\fP
  .\"
- with the PCRE_UTF8 option flag. When you do this, both the pattern and any
+ with the PCRE_UTF8 option flag, or the pattern must start with the sequence
- subject strings that are matched against it are treated as UTF-8 strings
+ (*UTF8). When either of these is the case, both the pattern and any subject
- instead of just strings of bytes.
+ strings that are matched against it are treated as UTF-8 strings instead of
+ strings of 1-byte characters.
  .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
-Line 178 
 documentation. Only the short names for
+Line 185 
 documentation. Only the short names for
  \ep{L} matches a letter. Its Perl synonym, \ep{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.
- .P
+ .
- The following comments apply when PCRE is running in UTF-8 mode:
+ .
- .P
+ .\" HTML <a name="utf8strings"></a>
-. When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
+ .SS "Validity of UTF-8 strings"
- are checked for validity on entry to the relevant functions. If an invalid
+ .rs
- UTF-8 string is passed, an error return is given. In some situations, you may
+ .sp
- already know that your strings are valid, and therefore want to skip these
+ When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
- checks in order to improve performance. If you set the PCRE_NO_UTF8_CHECK flag
+ are (by default) checked for validity on entry to the relevant functions. From
- at compile time or at run time, PCRE assumes that the pattern or subject it
+ release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
- is given (respectively) contains only valid UTF-8 codes. In this case, it does
+ themselves derived from the Unicode specification. Earlier releases of PCRE
- not diagnose an invalid UTF-8 string. If you pass an invalid UTF-8 string to
+ followed the rules of RFC 2279, which allows the full range of 31-bit values (0
- PCRE when PCRE_NO_UTF8_CHECK is set, the results are undefined. Your program
+ to 0x7FFFFFFF). The current check allows only values in the range U+0 to
- may crash.
+ U+10FFFF, excluding U+D800 to U+DFFF.
  .P
-. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
+ 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
+ If an invalid UTF-8 string is passed to PCRE, an error return is given. At
+ compile time, the only additional information is the offset to the first byte
+ of the failing character. The runtime functions (\fBpcre_exec()\fP and
+ \fBpcre_dfa_exec()\fP), pass back this information as well as a more detailed
+ reason code if the caller has provided memory in which to do this.
+ .P
+ 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
+ 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
+ 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.
+ .
+ .
+ .SS "General comments about UTF-8 mode"
+ .rs
+ .sp
+. An unbraced hexadecimal escape sequence (such as \exb3) matches a two-byte
  UTF-8 character if the value is greater than 127.
  .P
 . Octal numbers up to \e777 are recognized, and match two-byte UTF-8
  characters for values greater than \e177.
  .P
 . Repeat quantifiers apply to complete UTF-8 characters, not to individual
  bytes, for example: \ex{100}{3}.
  .P
 . The dot metacharacter matches one UTF-8 character instead of a single byte.
  .P
 . The escape sequence \eC 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, \fBpcre_dfa_exec()\fP.
  .P
 . The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
- test characters of any code value, but the characters that PCRE recognizes as
+ test characters of any code value, but, by default, the characters that PCRE
- digits, spaces, or word characters remain the same set as before, all with
+ recognizes as digits, spaces, or word characters remain the same set as before,
- values less than 256. This remains true even when PCRE includes Unicode
+ all with values less than 256. This remains true even when PCRE is built to
- property support, because to do otherwise would slow down PCRE in many common
+ include Unicode property support, because to do otherwise would slow down PCRE
- cases. If you really want to test for a wider sense of, say, "digit", you
+ in many common cases. Note in particular that this applies to \eb and \eB,
- must use Unicode property tests such as \ep{Nd}.
+ because they are defined in terms of \ew and \eW. If you really want to test
+ for a wider sense of, say, "digit", you can use explicit Unicode property tests
+ such as \ep{Nd}. Alternatively, if you set the PCRE_UCP option, the way that
+ the character escapes work is changed so that Unicode properties are used to
+ determine which characters match. There are more details in the section on
+ .\" HTML <a href="pcrepattern.html#genericchartypes">
+ .\" </a>
+ generic character types
+ .\"
+ in the
+ .\" HREF
+ \fBpcrepattern\fP
+ .\"
+ documentation.
  .P
 . Similarly, characters that match the POSIX named character classes are all
- low-valued characters.
+ low-valued characters, unless the PCRE_UCP option is set.
+ .P
+. However, the horizontal and vertical whitespace matching escapes (\eh, \eH,
+ \ev, and \eV) do match all the appropriate Unicode characters, whether or not
+ PCRE_UCP is set.
  .P
 . 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
+ values. Furthermore, PCRE supports case-insensitive matching only when there is
- case-insensitive matching only when there is a one-to-one mapping between a
+ a one-to-one mapping between a letter's cases. There are a small number of
- letter's cases. There are a small number of many-to-one mappings in Unicode;
+ many-to-one mappings in Unicode; these are not supported by PCRE.
- these are not supported by PCRE.
+ .
  .
  .SH AUTHOR
  .rs
  .sp
+ .nf
  Philip Hazel
- .br
+ University Computing Service
- University Computing Service,
- .br
  Cambridge CB2 3QH, England.
+ .fi
  .P
  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 initial and surname, separated
+ taken it away. If you want to email me, use my two initials, followed by the
- by a dot, at the domain ucs.cam.ac.uk.
+ two digits 10, at the domain cam.ac.uk.
+ .
+ .
+ .SH REVISION
+ .rs
  .sp
- .in 0
+ .nf
- Last updated: 23 November 2006
+ Last updated: 07 May 2011
- .br
+ Copyright (c) 1997-2011 University of Cambridge.
- Copyright (c) 1997-2006 University of Cambridge.
+ .fi

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