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8.33

    1: .TH PCREUNICODE 3 "27 February 2013" "PCRE 8.33"
    2: .SH NAME
    3: PCRE - Perl-compatible regular expressions
    4: .SH "UTF-8, UTF-16, UTF-32, AND UNICODE PROPERTY SUPPORT"
    5: .rs
    6: .sp
    7: As well as UTF-8 support, PCRE also supports UTF-16 (from release 8.30) and
    8: UTF-32 (from release 8.32), by means of two additional libraries. They can be
    9: built as well as, or instead of, the 8-bit library.
   10: .
   11: .
   12: .SH "UTF-8 SUPPORT"
   13: .rs
   14: .sp
   15: In order process UTF-8 strings, you must build PCRE's 8-bit library with UTF
   16: support, and, in addition, you must call
   17: .\" HREF
   18: \fBpcre_compile()\fP
   19: .\"
   20: with the PCRE_UTF8 option flag, or the pattern must start with the sequence
   21: (*UTF8) or (*UTF). When either of these is the case, both the pattern and any
   22: subject strings that are matched against it are treated as UTF-8 strings
   23: instead of strings of individual 1-byte characters.
   24: .
   25: .
   26: .SH "UTF-16 AND UTF-32 SUPPORT"
   27: .rs
   28: .sp
   29: In order process UTF-16 or UTF-32 strings, you must build PCRE's 16-bit or
   30: 32-bit library with UTF support, and, in addition, you must call
   31: .\" HREF
   32: \fBpcre16_compile()\fP
   33: .\"
   34: or
   35: .\" HREF
   36: \fBpcre32_compile()\fP
   37: .\"
   38: with the PCRE_UTF16 or PCRE_UTF32 option flag, as appropriate. Alternatively,
   39: the pattern must start with the sequence (*UTF16), (*UTF32), as appropriate, or
   40: (*UTF), which can be used with either library. When UTF mode is set, both the
   41: pattern and any subject strings that are matched against it are treated as
   42: UTF-16 or UTF-32 strings instead of strings of individual 16-bit or 32-bit
   43: characters.
   44: .
   45: .
   46: .SH "UTF SUPPORT OVERHEAD"
   47: .rs
   48: .sp
   49: If you compile PCRE with UTF support, but do not use it at run time, the
   50: library will be a bit bigger, but the additional run time overhead is limited
   51: to testing the PCRE_UTF[8|16|32] flag occasionally, so should not be very big.
   52: .
   53: .
   54: .SH "UNICODE PROPERTY SUPPORT"
   55: .rs
   56: .sp
   57: If PCRE is built with Unicode character property support (which implies UTF
   58: support), the escape sequences \ep{..}, \eP{..}, and \eX can be used.
   59: The available properties that can be tested are limited to the general
   60: category properties such as Lu for an upper case letter or Nd for a decimal
   61: number, the Unicode script names such as Arabic or Han, and the derived
   62: properties Any and L&. Full lists is given in the
   63: .\" HREF
   64: \fBpcrepattern\fP
   65: .\"
   66: and
   67: .\" HREF
   68: \fBpcresyntax\fP
   69: .\"
   70: documentation. Only the short names for properties are supported. For example,
   71: \ep{L} matches a letter. Its Perl synonym, \ep{Letter}, is not supported.
   72: Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
   73: compatibility with Perl 5.6. PCRE does not support this.
   74: .
   75: .
   76: .\" HTML <a name="utf8strings"></a>
   77: .SS "Validity of UTF-8 strings"
   78: .rs
   79: .sp
   80: When you set the PCRE_UTF8 flag, the byte strings passed as patterns and
   81: subjects are (by default) checked for validity on entry to the relevant
   82: functions. The entire string is checked before any other processing takes
   83: place. From release 7.3 of PCRE, the check is according the rules of RFC 3629,
   84: which are themselves derived from the Unicode specification. Earlier releases
   85: of PCRE followed the rules of RFC 2279, which allows the full range of 31-bit
   86: values (0 to 0x7FFFFFFF). The current check allows only values in the range U+0
   87: to U+10FFFF, excluding the surrogate area. (From release 8.33 the so-called
   88: "non-character" code points are no longer excluded because Unicode corrigendum
   89: #9 makes it clear that they should not be.)
   90: .P
   91: Characters in the "Surrogate Area" of Unicode are reserved for use by UTF-16,
   92: where they are used in pairs to encode codepoints with values greater than
   93: 0xFFFF. The code points that are encoded by UTF-16 pairs are available
   94: independently in the UTF-8 and UTF-32 encodings. (In other words, the whole
   95: surrogate thing is a fudge for UTF-16 which unfortunately messes up UTF-8 and
   96: UTF-32.)
   97: .P
   98: If an invalid UTF-8 string is passed to PCRE, an error return is given. At
   99: compile time, the only additional information is the offset to the first byte
  100: of the failing character. The run-time functions \fBpcre_exec()\fP and
  101: \fBpcre_dfa_exec()\fP also pass back this information, as well as a more
  102: detailed reason code if the caller has provided memory in which to do this.
  103: .P
  104: In some situations, you may already know that your strings are valid, and
  105: therefore want to skip these checks in order to improve performance, for
  106: example in the case of a long subject string that is being scanned repeatedly.
  107: If you set the PCRE_NO_UTF8_CHECK flag at compile time or at run time, PCRE
  108: assumes that the pattern or subject it is given (respectively) contains only
  109: valid UTF-8 codes. In this case, it does not diagnose an invalid UTF-8 string.
  110: .P
  111: Note that passing PCRE_NO_UTF8_CHECK to \fBpcre_compile()\fP just disables the
  112: check for the pattern; it does not also apply to subject strings. If you want
  113: to disable the check for a subject string you must pass this option to
  114: \fBpcre_exec()\fP or \fBpcre_dfa_exec()\fP.
  115: .P
  116: If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, the result
  117: is undefined and your program may crash.
  118: .
  119: .
  120: .\" HTML <a name="utf16strings"></a>
  121: .SS "Validity of UTF-16 strings"
  122: .rs
  123: .sp
  124: When you set the PCRE_UTF16 flag, the strings of 16-bit data units that are
  125: passed as patterns and subjects are (by default) checked for validity on entry
  126: to the relevant functions. Values other than those in the surrogate range
  127: U+D800 to U+DFFF are independent code points. Values in the surrogate range
  128: must be used in pairs in the correct manner.
  129: .P
  130: If an invalid UTF-16 string is passed to PCRE, an error return is given. At
  131: compile time, the only additional information is the offset to the first data
  132: unit of the failing character. The run-time functions \fBpcre16_exec()\fP and
  133: \fBpcre16_dfa_exec()\fP also pass back this information, as well as a more
  134: detailed reason code if the caller has provided memory in which to do this.
  135: .P
  136: In some situations, you may already know that your strings are valid, and
  137: therefore want to skip these checks in order to improve performance. If you set
  138: the PCRE_NO_UTF16_CHECK flag at compile time or at run time, PCRE assumes that
  139: the pattern or subject it is given (respectively) contains only valid UTF-16
  140: sequences. In this case, it does not diagnose an invalid UTF-16 string.
  141: However, if an invalid string is passed, the result is undefined.
  142: .
  143: .
  144: .\" HTML <a name="utf32strings"></a>
  145: .SS "Validity of UTF-32 strings"
  146: .rs
  147: .sp
  148: When you set the PCRE_UTF32 flag, the strings of 32-bit data units that are
  149: passed as patterns and subjects are (by default) checked for validity on entry
  150: to the relevant functions.  This check allows only values in the range U+0
  151: to U+10FFFF, excluding the surrogate area U+D800 to U+DFFF.
  152: .P
  153: If an invalid UTF-32 string is passed to PCRE, an error return is given. At
  154: compile time, the only additional information is the offset to the first data
  155: unit of the failing character. The run-time functions \fBpcre32_exec()\fP and
  156: \fBpcre32_dfa_exec()\fP also pass back this information, as well as a more
  157: detailed reason code if the caller has provided memory in which to do this.
  158: .P
  159: In some situations, you may already know that your strings are valid, and
  160: therefore want to skip these checks in order to improve performance. If you set
  161: the PCRE_NO_UTF32_CHECK flag at compile time or at run time, PCRE assumes that
  162: the pattern or subject it is given (respectively) contains only valid UTF-32
  163: sequences. In this case, it does not diagnose an invalid UTF-32 string.
  164: However, if an invalid string is passed, the result is undefined.
  165: .
  166: .
  167: .SS "General comments about UTF modes"
  168: .rs
  169: .sp
  170: 1. Codepoints less than 256 can be specified in patterns by either braced or
  171: unbraced hexadecimal escape sequences (for example, \ex{b3} or \exb3). Larger
  172: values have to use braced sequences.
  173: .P
  174: 2. Octal numbers up to \e777 are recognized, and in UTF-8 mode they match
  175: two-byte characters for values greater than \e177.
  176: .P
  177: 3. Repeat quantifiers apply to complete UTF characters, not to individual
  178: data units, for example: \ex{100}{3}.
  179: .P
  180: 4. The dot metacharacter matches one UTF character instead of a single data
  181: unit.
  182: .P
  183: 5. The escape sequence \eC can be used to match a single byte in UTF-8 mode, or
  184: a single 16-bit data unit in UTF-16 mode, or a single 32-bit data unit in
  185: UTF-32 mode, but its use can lead to some strange effects because it breaks up
  186: multi-unit characters (see the description of \eC in the
  187: .\" HREF
  188: \fBpcrepattern\fP
  189: .\"
  190: documentation). The use of \eC is not supported in the alternative matching
  191: function \fBpcre[16|32]_dfa_exec()\fP, nor is it supported in UTF mode by the
  192: JIT optimization of \fBpcre[16|32]_exec()\fP. If JIT optimization is requested
  193: for a UTF pattern that contains \eC, it will not succeed, and so the matching
  194: will be carried out by the normal interpretive function.
  195: .P
  196: 6. The character escapes \eb, \eB, \ed, \eD, \es, \eS, \ew, and \eW correctly
  197: test characters of any code value, but, by default, the characters that PCRE
  198: recognizes as digits, spaces, or word characters remain the same set as in
  199: non-UTF mode, all with values less than 256. This remains true even when PCRE
  200: is built to include Unicode property support, because to do otherwise would
  201: slow down PCRE in many common cases. Note in particular that this applies to
  202: \eb and \eB, because they are defined in terms of \ew and \eW. If you really
  203: want to test for a wider sense of, say, "digit", you can use explicit Unicode
  204: property tests such as \ep{Nd}. Alternatively, if you set the PCRE_UCP option,
  205: the way that the character escapes work is changed so that Unicode properties
  206: are used to determine which characters match. There are more details in the
  207: section on
  208: .\" HTML <a href="pcrepattern.html#genericchartypes">
  209: .\" </a>
  210: generic character types
  211: .\"
  212: in the
  213: .\" HREF
  214: \fBpcrepattern\fP
  215: .\"
  216: documentation.
  217: .P
  218: 7. Similarly, characters that match the POSIX named character classes are all
  219: low-valued characters, unless the PCRE_UCP option is set.
  220: .P
  221: 8. However, the horizontal and vertical white space matching escapes (\eh, \eH,
  222: \ev, and \eV) do match all the appropriate Unicode characters, whether or not
  223: PCRE_UCP is set.
  224: .P
  225: 9. Case-insensitive matching applies only to characters whose values are less
  226: than 128, unless PCRE is built with Unicode property support. A few Unicode
  227: characters such as Greek sigma have more than two codepoints that are
  228: case-equivalent. Up to and including PCRE release 8.31, only one-to-one case
  229: mappings were supported, but later releases (with Unicode property support) do
  230: treat as case-equivalent all versions of characters such as Greek sigma.
  231: .
  232: .
  233: .SH AUTHOR
  234: .rs
  235: .sp
  236: .nf
  237: Philip Hazel
  238: University Computing Service
  239: Cambridge CB2 3QH, England.
  240: .fi
  241: .
  242: .
  243: .SH REVISION
  244: .rs
  245: .sp
  246: .nf
  247: Last updated: 27 February 2013
  248: Copyright (c) 1997-2013 University of Cambridge.
  249: .fi