PCREUNICODE(3)            OpenBSD Programmer's Manual           PCREUNICODE(3)



NAME
       PCRE - Perl-compatible regular expressions

UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT

       As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30)
       and UTF-32 (from release 8.32), by means of two additional libraries.
       They can be built as well as, or instead of, the 8-bit library.

UTF-8 SUPPORT

       In order process UTF-8 strings, you must build PCRE's 8-bit library
       with UTF support, and, in addition, you must call pcre_compile() with
       the PCRE_UTF8 option flag, or the pattern must start with the sequence
       (*UTF8) or (*UTF). 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 strings of individual 1-byte characters.

UTF-16 AND UTF-32 SUPPORT

       In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit
       or 32-bit library with UTF support, and, in addition, you must call
       pcre16_compile() or pcre32_compile() with the PCRE_UTF16 or PCRE_UTF32
       option flag, as appropriate. Alternatively, the pattern must start with
       the sequence (*UTF16), (*UTF32), as appropriate, or (*UTF), which can
       be used with either library. When UTF mode is set, both the pattern and
       any subject strings that are matched against it are treated as UTF-16
       or UTF-32 strings instead of strings of individual 16-bit or 32-bit
       characters.

UTF SUPPORT OVERHEAD

       If you compile PCRE with UTF 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_UTF[8|16|32] flag occasionally, so
       should not be very big.

UNICODE PROPERTY SUPPORT

       If PCRE is built with Unicode character property support (which implies
       UTF support), the escape sequences \p{..}, \P{..}, and \X can be used.
       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&. Full lists is given in the pcrepattern
       and pcresyntax 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.

   Validity of UTF-8 strings

       When you set the PCRE_UTF8 flag, the byte strings passed as patterns
       and subjects are (by default) checked for validity on entry to the
       relevant functions. The entire string is checked before any other
       processing takes place. 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 the surrogate area. (From release 8.33 the so-
       called "non-character" code points are no longer excluded because
       Unicode corrigendum #9 makes it clear that they should not be.)

       Characters in the "Surrogate Area" of Unicode are reserved for use by
       UTF-16, where they are used in pairs to encode codepoints with values
       greater than 0xFFFF. The code points that are encoded by UTF-16 pairs
       are available independently in the UTF-8 and UTF-32 encodings. (In
       other words, the whole surrogate thing is a fudge for UTF-16 which
       unfortunately messes up UTF-8 and UTF-32.)

       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 run-time functions pcre_exec()
       and pcre_dfa_exec() also pass back this information, as well as a more
       detailed reason code if the caller has provided memory in which to do
       this.

       In some situations, you may already know that your strings are valid,
       and therefore want to skip these checks in order to improve
       performance, for example in the case of a long subject string that is
       being scanned repeatedly.  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.

       Note that passing PCRE_NO_UTF8_CHECK to pcre_compile() just disables
       the check for the pattern; it does not also apply to subject strings.
       If you want to disable the check for a subject string you must pass
       this option to pcre_exec() or pcre_dfa_exec().

       If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the
       result is undefined and your program may crash.

   Validity of UTF-16 strings

       When you set the PCRE_UTF16 flag, the strings of 16-bit data units that
       are passed as patterns and subjects are (by default) checked for
       validity on entry to the relevant functions. Values other than those in
       the surrogate range U+D800 to U+DFFF are independent code points.
       Values in the surrogate range must be used in pairs in the correct
       manner.

       If an invalid UTF-16 string is passed to PCRE, an error return is
       given. At compile time, the only additional information is the offset
       to the first data unit of the failing character. The run-time functions
       pcre16_exec() and pcre16_dfa_exec() also pass back this information, as
       well as a more detailed reason code if the caller has provided memory
       in which to do this.

       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_UTF16_CHECK flag at compile time or
       at run time, PCRE assumes that the pattern or subject it is given
       (respectively) contains only valid UTF-16 sequences. In this case, it
       does not diagnose an invalid UTF-16 string.  However, if an invalid
       string is passed, the result is undefined.

   Validity of UTF-32 strings

       When you set the PCRE_UTF32 flag, the strings of 32-bit data units that
       are passed as patterns and subjects are (by default) checked for
       validity on entry to the relevant functions.  This check allows only
       values in the range U+0 to U+10FFFF, excluding the surrogate area
       U+D800 to U+DFFF.

       If an invalid UTF-32 string is passed to PCRE, an error return is
       given. At compile time, the only additional information is the offset
       to the first data unit of the failing character. The run-time functions
       pcre32_exec() and pcre32_dfa_exec() also pass back this information, as
       well as a more detailed reason code if the caller has provided memory
       in which to do this.

       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_UTF32_CHECK flag at compile time or
       at run time, PCRE assumes that the pattern or subject it is given
       (respectively) contains only valid UTF-32 sequences. In this case, it
       does not diagnose an invalid UTF-32 string.  However, if an invalid
       string is passed, the result is undefined.

   General comments about UTF modes

       1. Codepoints less than 256 can be specified in patterns by either
       braced or unbraced hexadecimal escape sequences (for example, \x{b3} or
       \xb3). Larger values have to use braced sequences.

       2. Octal numbers up to \777 are recognized, and in UTF-8 mode they
       match two-byte characters for values greater than \177.

       3. Repeat quantifiers apply to complete UTF characters, not to
       individual data units, for example: \x{100}{3}.

       4. The dot metacharacter matches one UTF character instead of a single
       data unit.

       5. The escape sequence \C can be used to match a single byte in UTF-8
       mode, or a single 16-bit data unit in UTF-16 mode, or a single 32-bit
       data unit in UTF-32 mode, but its use can lead to some strange effects
       because it breaks up multi-unit characters (see the description of \C
       in the pcrepattern documentation). The use of \C is not supported in
       the alternative matching function pcre[16|32]_dfa_exec(), nor is it
       supported in UTF mode by the JIT optimization of pcre[16|32]_exec(). If
       JIT optimization is requested for a UTF pattern that contains \C, it
       will not succeed, and so the matching will be carried out by the normal
       interpretive function.

       6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
       test characters of any code value, but, by default, the characters that
       PCRE recognizes as digits, spaces, or word characters remain the same
       set as in non-UTF mode, all with values less than 256. This remains
       true even when PCRE is built to include Unicode property support,
       because to do otherwise would slow down PCRE in many common cases. Note
       in particular that this applies to \b and \B, because they are defined
       in terms of \w and \W. If you really want to test for a wider sense of,
       say, "digit", you can use explicit Unicode property tests such as
       \p{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 generic character types in the pcrepattern documentation.

       7. Similarly, characters that match the POSIX named character classes
       are all low-valued characters, unless the PCRE_UCP option is set.

       8. However, the horizontal and vertical white space matching escapes
       (\h, \H, \v, and \V) do match all the appropriate Unicode characters,
       whether or not PCRE_UCP is set.

       9. Case-insensitive matching applies only to characters whose values
       are less than 128, unless PCRE is built with Unicode property support.
       A few Unicode characters such as Greek sigma have more than two
       codepoints that are case-equivalent. Up to and including PCRE release
       8.31, only one-to-one case mappings were supported, but later releases
       (with Unicode property support) do treat as case-equivalent all
       versions of characters such as Greek sigma.

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION

       Last updated: 27 February 2013
       Copyright (c) 1997-2013 University of Cambridge.



PCRE 8.33                      27 February 2013                 PCREUNICODE(3)
