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of searching. The sections are as follows:
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111
pcre this document
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pcre16 details of the 16-bit library
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113
pcre-config show PCRE installation configuration information
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114
pcreapi details of PCRE's native C API
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115
pcrebuild options for building PCRE
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116
pcrecallout details of the callout feature
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117
pcrecompat discussion of Perl compatibility
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pcrecpp details of the C++ wrapper
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pcrecpp details of the C++ wrapper for the 8-bit library
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pcredemo a demonstration C program that uses PCRE
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pcregrep description of the <b>pcregrep</b> command
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pcregrep description of the <b>pcregrep</b> command (8-bit only)
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pcrejit discussion of the just-in-time optimization support
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pcrelimits details of size and other limits
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pcrematching discussion of the two matching algorithms
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pcrepartial details of the partial matching facility
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pcrepattern syntax and semantics of supported regular expressions
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pcreperform discussion of performance issues
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pcreposix the POSIX-compatible C API
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pcreposix the POSIX-compatible C API for the 8-bit library
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128
pcreprecompile details of saving and re-using precompiled patterns
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129
pcresample discussion of the pcredemo program
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130
pcrestack discussion of stack usage
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pcresyntax quick syntax reference
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pcretest description of the <b>pcretest</b> testing command
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pcreunicode discussion of Unicode and UTF-8/16 support
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In addition, in the "man" and HTML formats, there is a short page for each
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C library function, listing its arguments and results.
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<br><a name="SEC3" href="#TOC1">LIMITATIONS</a><br>
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There are some size limitations in PCRE but it is hoped that they will never in
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practice be relevant.
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The maximum length of a compiled pattern is 65539 (sic) bytes if PCRE is
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compiled with the default internal linkage size of 2. If you want to process
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regular expressions that are truly enormous, you can compile PCRE with an
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internal linkage size of 3 or 4 (see the <b>README</b> file in the source
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<a href="pcrebuild.html"><b>pcrebuild</b></a>
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documentation for details). In these cases the limit is substantially larger.
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However, the speed of execution is slower.
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All values in repeating quantifiers must be less than 65536.
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There is no limit to the number of parenthesized subpatterns, but there can be
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no more than 65535 capturing subpatterns.
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The maximum length of name for a named subpattern is 32 characters, and the
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maximum number of named subpatterns is 10000.
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The maximum length of a subject string is the largest positive number that an
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integer variable can hold. However, when using the traditional matching
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function, PCRE uses recursion to handle subpatterns and indefinite repetition.
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This means that the available stack space may limit the size of a subject
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string that can be processed by certain patterns. For a discussion of stack
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<a href="pcrestack.html"><b>pcrestack</b></a>
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<a name="utf8support"></a></P>
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<br><a name="SEC4" href="#TOC1">UTF-8 AND UNICODE PROPERTY SUPPORT</a><br>
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From release 3.3, PCRE has had some support for character strings encoded in
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the UTF-8 format. For release 4.0 this was greatly extended to cover most
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common requirements, and in release 5.0 additional support for Unicode general
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category properties was added.
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In order process UTF-8 strings, you must build PCRE to include UTF-8 support in
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the code, and, in addition, you must call
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<a href="pcre_compile.html"><b>pcre_compile()</b></a>
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with the PCRE_UTF8 option flag, or the pattern must start with the sequence
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(*UTF8). When either of these is the case, both the pattern and any subject
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strings that are matched against it are treated as UTF-8 strings instead of
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strings of 1-byte characters.
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If you compile PCRE with UTF-8 support, but do not use it at run time, the
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library will be a bit bigger, but the additional run time overhead is limited
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to testing the PCRE_UTF8 flag occasionally, so should not be very big.
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If PCRE is built with Unicode character property support (which implies UTF-8
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support), the escape sequences \p{..}, \P{..}, and \X are supported.
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The available properties that can be tested are limited to the general
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category properties such as Lu for an upper case letter or Nd for a decimal
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number, the Unicode script names such as Arabic or Han, and the derived
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properties Any and L&. A full list is given in the
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<a href="pcrepattern.html"><b>pcrepattern</b></a>
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documentation. Only the short names for properties are supported. For example,
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\p{L} matches a letter. Its Perl synonym, \p{Letter}, is not supported.
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Furthermore, in Perl, many properties may optionally be prefixed by "Is", for
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compatibility with Perl 5.6. PCRE does not support this.
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<a name="utf8strings"></a></P>
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Validity of UTF-8 strings
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When you set the PCRE_UTF8 flag, the strings passed as patterns and subjects
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are (by default) checked for validity on entry to the relevant functions. From
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release 7.3 of PCRE, the check is according the rules of RFC 3629, which are
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themselves derived from the Unicode specification. Earlier releases of PCRE
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followed the rules of RFC 2279, which allows the full range of 31-bit values (0
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to 0x7FFFFFFF). The current check allows only values in the range U+0 to
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U+10FFFF, excluding U+D800 to U+DFFF.
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The excluded code points are the "Low Surrogate Area" of Unicode, of which the
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Unicode Standard says this: "The Low Surrogate Area does not contain any
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character assignments, consequently no character code charts or namelists are
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provided for this area. Surrogates are reserved for use with UTF-16 and then
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must be used in pairs." The code points that are encoded by UTF-16 pairs are
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available as independent code points in the UTF-8 encoding. (In other words,
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the whole surrogate thing is a fudge for UTF-16 which unfortunately messes up
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If an invalid UTF-8 string is passed to PCRE, an error return
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(PCRE_ERROR_BADUTF8) is given. In some situations, you may already know that
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your strings are valid, and therefore want to skip these checks in order to
213
improve performance. If you set the PCRE_NO_UTF8_CHECK flag at compile time or
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at run time, PCRE assumes that the pattern or subject it is given
215
(respectively) contains only valid UTF-8 codes. In this case, it does not
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diagnose an invalid UTF-8 string.
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If you pass an invalid UTF-8 string when PCRE_NO_UTF8_CHECK is set, what
220
happens depends on why the string is invalid. If the string conforms to the
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"old" definition of UTF-8 (RFC 2279), it is processed as a string of characters
222
in the range 0 to 0x7FFFFFFF. In other words, apart from the initial validity
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test, PCRE (when in UTF-8 mode) handles strings according to the more liberal
224
rules of RFC 2279. However, if the string does not even conform to RFC 2279,
225
the result is undefined. Your program may crash.
228
If you want to process strings of values in the full range 0 to 0x7FFFFFFF,
229
encoded in a UTF-8-like manner as per the old RFC, you can set
230
PCRE_NO_UTF8_CHECK to bypass the more restrictive test. However, in this
231
situation, you will have to apply your own validity check.
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General comments about UTF-8 mode
237
1. An unbraced hexadecimal escape sequence (such as \xb3) matches a two-byte
238
UTF-8 character if the value is greater than 127.
241
2. Octal numbers up to \777 are recognized, and match two-byte UTF-8
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characters for values greater than \177.
245
3. Repeat quantifiers apply to complete UTF-8 characters, not to individual
246
bytes, for example: \x{100}{3}.
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4. The dot metacharacter matches one UTF-8 character instead of a single byte.
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5. The escape sequence \C can be used to match a single byte in UTF-8 mode,
253
but its use can lead to some strange effects. This facility is not available in
254
the alternative matching function, <b>pcre_dfa_exec()</b>.
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6. The character escapes \b, \B, \d, \D, \s, \S, \w, and \W correctly
258
test characters of any code value, but, by default, the characters that PCRE
259
recognizes as digits, spaces, or word characters remain the same set as before,
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all with values less than 256. This remains true even when PCRE is built to
261
include Unicode property support, because to do otherwise would slow down PCRE
262
in many common cases. Note in particular that this applies to \b and \B,
263
because they are defined in terms of \w and \W. If you really want to test
264
for a wider sense of, say, "digit", you can use explicit Unicode property tests
265
such as \p{Nd}. Alternatively, if you set the PCRE_UCP option, the way that
266
the character escapes work is changed so that Unicode properties are used to
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determine which characters match. There are more details in the section on
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<a href="pcrepattern.html#genericchartypes">generic character types</a>
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<a href="pcrepattern.html"><b>pcrepattern</b></a>
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7. Similarly, characters that match the POSIX named character classes are all
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low-valued characters, unless the PCRE_UCP option is set.
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8. However, the horizontal and vertical whitespace matching escapes (\h, \H,
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\v, and \V) do match all the appropriate Unicode characters, whether or not
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9. Case-insensitive matching applies only to characters whose values are less
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than 128, unless PCRE is built with Unicode property support. Even when Unicode
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property support is available, PCRE still uses its own character tables when
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checking the case of low-valued characters, so as not to degrade performance.
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The Unicode property information is used only for characters with higher
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values. Furthermore, PCRE supports case-insensitive matching only when there is
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a one-to-one mapping between a letter's cases. There are a small number of
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many-to-one mappings in Unicode; these are not supported by PCRE.
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<br><a name="SEC5" href="#TOC1">AUTHOR</a><br>
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8-bit C library function, listing its arguments and results.
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<br><a name="SEC3" href="#TOC1">AUTHOR</a><br>