=head2 Important Caveats
-WARNING: While the implementation of Unicode support in Perl is now
-fairly complete it is still evolving to some extent.
-
-In particular the way Unicode is handled on EBCDIC platforms is still
-rather experimental. On such a platform references to UTF-8 encoding
-in this document and elsewhere should be read as meaning UTF-EBCDIC as
-specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
-are specifically discussed. There is no C<utfebcdic> pragma or
-":utfebcdic" layer, rather "utf8" and ":utf8" are re-used to mean
-platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic> for
-more discussion of the issues.
-
-The following areas are still under development.
+Unicode support is an extensive requirement. While perl does not
+implement the Unicode standard or the accompanying technical reports
+from cover to cover, Perl does support many Unicode features.
=over 4
A filehandle can be marked as containing perl's internal Unicode
encoding (UTF-8 or UTF-EBCDIC) by opening it with the ":utf8" layer.
Other encodings can be converted to perl's encoding on input, or from
-perl's encoding on output by use of the ":encoding()" layer. There is
-not yet a clean way to mark the Perl source itself as being in an
-particular encoding.
+perl's encoding on output by use of the ":encoding(...)" layer.
+See L<open>.
+
+To mark the Perl source itself as being in a particular encoding,
+see L<encoding>.
=item Regular Expressions
-The regular expression compiler does now attempt to produce
-polymorphic opcodes. That is the pattern should now adapt to the data
-and automatically switch to the Unicode character scheme when
-presented with Unicode data, or a traditional byte scheme when
-presented with byte data. The implementation is still new and
-(particularly on EBCDIC platforms) may need further work.
+The regular expression compiler produces polymorphic opcodes. That is,
+the pattern adapts to the data and automatically switch to the Unicode
+character scheme when presented with Unicode data, or a traditional
+byte scheme when presented with byte data.
=item C<use utf8> still needed to enable UTF-8/UTF-EBCDIC in scripts
The C<utf8> pragma implements the tables used for Unicode support.
-These tables are automatically loaded on demand, so the C<utf8> pragma
-need not normally be used.
+However, these tables are automatically loaded on demand, so the
+C<utf8> pragma should not normally be used.
-However, as a compatibility measure, this pragma must be explicitly
-used to enable recognition of UTF-8 in the Perl scripts themselves on
-ASCII based machines or recognize UTF-EBCDIC on EBCDIC based machines.
-B<NOTE: this should be the only place where an explicit C<use utf8> is
-needed>.
+As a compatibility measure, this pragma must be explicitly used to
+enable recognition of UTF-8 in the Perl scripts themselves on ASCII
+based machines or recognize UTF-EBCDIC on EBCDIC based machines.
+B<NOTE: this should be the only place where an explicit C<use utf8>
+is needed>.
You can also use the C<encoding> pragma to change the default encoding
of the data in your script; see L<encoding>.
external programs, from information provided by the system (such as %ENV),
or from literals and constants in the source text.
-If the C<-C> command line switch is used, (or the
+On Windows platforms, if the C<-C> command line switch is used, (or the
${^WIDE_SYSTEM_CALLS} global flag is set to C<1>), all system calls
will use the corresponding wide character APIs. Note that this is
-currently only implemented on Windows since other platforms API
-standard on this area.
+currently only implemented on Windows since other platforms lack an
+API standard on this area.
Regardless of the above, the C<bytes> pragma can always be used to
force byte semantics in a particular lexical scope. See L<bytes>.
=item *
-Named Unicode properties and block ranges make be used as character
+Named Unicode properties and block ranges may be used as character
classes via the new C<\p{}> (matches property) and C<\P{}> (doesn't
match property) constructs. For instance, C<\p{Lu}> matches any
character with the Unicode uppercase property, while C<\p{M}> matches
The C<\p{Is...}> test for "general properties" such as "letter",
"digit", while the C<\p{In...}> test for Unicode scripts and blocks.
-The official Unicode script and block names have spaces and dashes and
+The official Unicode script and block names have spaces and dashes as
separators, but for convenience you can have dashes, spaces, and
underbars at every word division, and you need not care about correct
casing. It is recommended, however, that for consistency you use the
For example C<"\x{AC00}" =~ \p{HangulSyllable}> will test true.
(Handling of surrogates is not implemented yet, because Perl
-uses UTF-8 and not UTF-16 internally to represent Unicode.)
+uses UTF-8 and not UTF-16 internally to represent Unicode.
+So you really can't use the "Cs" category.)
Additionally, because scripts differ in their directionality
(for example Hebrew is written right to left), all characters
BidiWS Whitespace
BidiON Other Neutrals
+=back
+
=head2 Scripts
The scripts available for C<\p{In...}> and C<\P{In...}>, for example
-\p{InCyrillic>, are as follows, for example C<\p{InLatin}> or C<\P{InHan}>:
+C<\p{InLatin}> or \p{InCyrillic>, are as follows:
Arabic
Armenian
concept is more an artificial grouping based on groups of 256 Unicode
characters. For example, the C<Latin> script contains letters from
many blocks. On the other hand, the C<Latin> script does not contain
-all the characters from those blocks, it does not for example contain
+all the characters from those blocks. It does not, for example, contain
digits because digits are shared across many scripts. Digits and
other similar groups, like punctuation, are in a category called
C<Common>.
-For more about scripts see the UTR #24:
-http://www.unicode.org/unicode/reports/tr24/
-For more about blocks see
-http://www.unicode.org/Public/UNIDATA/Blocks.txt
+For more about scripts, see the UTR #24:
+
+ http://www.unicode.org/unicode/reports/tr24/
+
+For more about blocks, see:
+
+ http://www.unicode.org/Public/UNIDATA/Blocks.txt
Because there are overlaps in naming (there are, for example, both
a script called C<Katakana> and a block called C<Katakana>, the block
Yi Radicals
Yi Syllables
+=over 4
+
=item *
The special pattern C<\X> match matches any extended Unicode sequence
=back
-What doesn't yet work are the followng cases:
+What doesn't yet work are the following cases:
=over 8
2.2 Categories - done [3][4]
2.3 Subtraction - MISSING [5][6]
2.4 Simple Word Boundaries - done [7]
- 2.5 Simple Loose Matches - MISSING [8]
+ 2.5 Simple Loose Matches - done [8]
2.6 End of Line - MISSING [9][10]
[ 1] \x{...}
[ 2] \N{...}
[ 3] . \p{Is...} \P{Is...}
- [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
+ [ 4] now scripts (see UTR#24 Script Names) in addition to blocks
[ 5] have negation
- [ 6] can use look-ahead to emulate subtracion
+ [ 6] can use look-ahead to emulate subtraction (*)
[ 7] include Letters in word characters
- [ 8] see UTR#21 Case Mappings
+ [ 8] see UTR#21 Case Mappings: Perl implements 1:1 mappings
[ 9] see UTR#13 Unicode Newline Guidelines
- [10] should do ^ and $ also on \x{2028} and \x{2029}
+ [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029})
+ (should also affect <>, $., and script line numbers)
+
+(*) You can mimic class subtraction using lookahead.
+For example, what TR18 might write as
+
+ [{Greek}-[{UNASSIGNED}]]
+
+in Perl can be written as:
+
+ (?!\p{UNASSIGNED})\p{GreekBlock}
+ (?=\p{ASSIGNED})\p{GreekBlock}
+
+But in this particular example, you probably really want
+
+ \p{Greek}
+
+which will match assigned characters known to be part of the Greek script.
+
+In other words: the matched character must not be a non-assigned
+character, but it must be in the block of modern Greek characters.
=item *
=back
+=head2 Unicode Encodings
+
+Unicode characters are assigned to I<code points> which are abstract
+numbers. To use these numbers various encodings are needed.
+
+=over 4
+
+=item UTF-8
+
+UTF-8 is the encoding used internally by Perl. UTF-8 is a variable
+length (1 to 6 bytes, current character allocations require 4 bytes),
+byteorder independent encoding. For ASCII, UTF-8 is transparent
+(and we really do mean 7-bit ASCII, not any 8-bit encoding).
+
+The following table is from Unicode 3.1.
+
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+
+ U+0000..U+007F 00..7F
+ U+0080..U+07FF C2..DF 80..BF
+ U+0800..U+0FFF E0 A0..BF 80..BF
+ U+1000..U+FFFF E1..EF 80..BF 80..BF
+ U+10000..U+3FFFF F0 90..BF 80..BF 80..BF
+ U+40000..U+FFFFF F1..F3 80..BF 80..BF 80..BF
+ U+100000..U+10FFFF F4 80..8F 80..BF 80..BF
+
+Or, another way to look at it, as bits:
+
+ Code Points 1st Byte 2nd Byte 3rd Byte 4th Byte
+
+ 0aaaaaaa 0aaaaaaa
+ 00000bbbbbaaaaaa 110bbbbb 10aaaaaa
+ ccccbbbbbbaaaaaa 1110cccc 10bbbbbb 10aaaaaa
+ 00000dddccccccbbbbbbaaaaaa 11110ddd 10cccccc 10bbbbbb 10aaaaaa
+
+As you can see, the continuation bytes all begin with C<10>, and the
+leading bits of the start byte tells how many bytes the are in the
+encoded character.
+
+=item UTF-EBDIC
+
+Like UTF-8, but EBDCIC-safe, as UTF-8 is ASCII-safe.
+
+=item UTF-16, UTF-16BE, UTF16-LE, Surrogates, and BOMs (Byte Order Marks)
+
+(The followings items are mostly for reference, Perl doesn't
+use them internally.)
+
+UTF-16 is a 2 or 4 byte encoding. The Unicode code points
+0x0000..0xFFFF are stored in two 16-bit units, and the code points
+0x010000..0x10FFFF in two 16-bit units. The latter case is
+using I<surrogates>, the first 16-bit unit being the I<high
+surrogate>, and the second being the I<low surrogate>.
+
+Surrogates are code points set aside to encode the 0x01000..0x10FFFF
+range of Unicode code points in pairs of 16-bit units. The I<high
+surrogates> are the range 0xD800..0xDBFF, and the I<low surrogates>
+are the range 0xDC00..0xDFFFF. The surrogate encoding is
+
+ $hi = ($uni - 0x10000) / 0x400 + 0xD800;
+ $lo = ($uni - 0x10000) % 0x400 + 0xDC00;
+
+and the decoding is
+
+ $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00);
+
+If you try to generate surrogates (for example by using chr()), you
+will get an error because firstly a surrogate on its own is meaningless,
+and secondly because Perl encodes its Unicode characters in UTF-8
+(not 16-bit numbers), which makes the encoded character doubly illegal.
+
+Because of the 16-bitness, UTF-16 is byteorder dependent. UTF-16
+itself can be used for in-memory computations, but if storage or
+transfer is required, either UTF-16BE (Big Endian) or UTF-16LE
+(Little Endian) must be chosen.
+
+This introduces another problem: what if you just know that your data
+is UTF-16, but you don't know which endianness? Byte Order Marks
+(BOMs) are a solution to this. A special character has been reserved
+in Unicode to function as a byte order marker: the character with the
+code point 0xFEFF is the BOM.
+
+The trick is that if you read a BOM, you will know the byte order,
+since if it was written on a big endian platform, you will read the
+bytes 0xFE 0xFF, but if it was written on a little endian platform,
+you will read the bytes 0xFF 0xFE. (And if the originating platform
+was writing in UTF-8, you will read the bytes 0xEF 0xBB 0xBF.)
+
+The way this trick works is that the character with the code point
+0xFFFE is guaranteed not to be a valid Unicode character, so the
+sequence of bytes 0xFF 0xFE is unambiguously "BOM, represented in
+little-endian format" and cannot be "0xFFFE, represented in big-endian
+format".
+
+=item UTF-32, UTF-32BE, UTF32-LE
+
+The UTF-32 family is pretty much like the UTF-16 family, expect that
+the units are 32-bit, and therefore the surrogate scheme is not
+needed. The BOM signatures will be 0x00 0x00 0xFE 0xFF for BE and
+0xFF 0xFE 0x00 0x00 for LE.
+
+=item UCS-2, UCS-4
+
+Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit
+encoding, UCS-4 is a 32-bit encoding. Unlike UTF-16, UCS-2
+is not extensible beyond 0xFFFF, because it does not use surrogates.
+
+=item UTF-7
+
+A seven-bit safe (non-eight-bit) encoding, useful if the
+transport/storage is not eight-bit safe. Defined by RFC 2152.
+
+=back
+
+=head2 Security Implications of Malformed UTF-8
+
+Unfortunately, the specification of UTF-8 leaves some room for
+interpretation of how many bytes of encoded output one should generate
+from one input Unicode character. Strictly speaking, one is supposed
+to always generate the shortest possible sequence of UTF-8 bytes,
+because otherwise there is potential for input buffer overflow at the
+receiving end of a UTF-8 connection. Perl always generates the shortest
+length UTF-8, and with warnings on (C<-w> or C<use warnings;>) Perl will
+warn about non-shortest length UTF-8 (and other malformations, too,
+such as the surrogates, which are not real character code points.)
+
+=head2 Unicode in Perl on EBCDIC
+
+The way Unicode is handled on EBCDIC platforms is still rather
+experimental. On such a platform, references to UTF-8 encoding in this
+document and elsewhere should be read as meaning UTF-EBCDIC as
+specified in Unicode Technical Report 16 unless ASCII vs EBCDIC issues
+are specifically discussed. There is no C<utfebcdic> pragma or
+":utfebcdic" layer, rather, "utf8" and ":utf8" are re-used to mean
+the platform's "natural" 8-bit encoding of Unicode. See L<perlebcdic>
+for more discussion of the issues.
+
+=head2 Using Unicode in XS
+
+If you want to handle Perl Unicode in XS extensions, you may find
+the following C APIs useful:
+
+=over 4
+
+=item *
+
+DO_UTF8(sv) returns true if the UTF8 flag is on and the bytes
+pragma is not in effect. SvUTF8(sv) returns true is the UTF8
+flag is on, the bytes pragma is ignored. Remember that UTF8
+flag being on does not mean that there would be any characters
+of code points greater than 255 or 127 in the scalar, or that
+there even are any characters in the scalar. The UTF8 flag
+means that any characters added to the string will be encoded
+in UTF8 if the code points of the characters are greater than
+255. Not "if greater than 127", since Perl's Unicode model
+is not to use UTF-8 until it's really necessary.
+
+=item *
+
+uvuni_to_utf8(buf, chr) writes a Unicode character code point into a
+buffer encoding the code point as UTF-8, and returns a pointer
+pointing after the UTF-8 bytes.
+
+=item *
+
+utf8_to_uvuni(buf, lenp) reads UTF-8 encoded bytes from a buffer and
+returns the Unicode character code point (and optionally the length of
+the UTF-8 byte sequence).
+
+=item *
+
+utf8_length(s, len) returns the length of the UTF-8 encoded buffer in
+characters. sv_len_utf8(sv) returns the length of the UTF-8 encoded
+scalar.
+
+=item *
+
+sv_utf8_upgrade(sv) converts the string of the scalar to its UTF-8
+encoded form. sv_utf8_downgrade(sv) does the opposite (if possible).
+sv_utf8_encode(sv) is like sv_utf8_upgrade but the UTF8 flag does not
+get turned on. sv_utf8_decode() does the opposite of sv_utf8_encode().
+
+=item *
+
+is_utf8_char(buf) returns true if the buffer points to valid UTF-8.
+
+=item *
+
+is_utf8_string(buf, len) returns true if the len bytes of the buffer
+are valid UTF-8.
+
+=item *
+
+UTF8SKIP(buf) will return the number of bytes in the UTF-8 encoded
+character in the buffer. UNISKIP(chr) will return the number of bytes
+required to UTF-8-encode the Unicode character code point.
+
+=item *
+
+utf8_distance(a, b) will tell the distance in characters between the
+two pointers pointing to the same UTF-8 encoded buffer.
+
+=item *
+
+utf8_hop(s, off) will return a pointer to an UTF-8 encoded buffer that
+is C<off> (positive or negative) Unicode characters displaced from the
+UTF-8 buffer C<s>.
+
+=item *
+
+pv_uni_display(dsv, spv, len, pvlim, flags) and sv_uni_display(dsv,
+ssv, pvlim, flags) are useful for debug output of Unicode strings and
+scalars (only for debug: they display B<all> characters as hexadecimal
+code points).
+
+=item *
+
+ibcmp_utf8(s1, u1, len1, s2, u2, len2) can be used to compare two
+strings case-insensitively in Unicode. (For case-sensitive
+comparisons you can just use memEQ() and memNE() as usual.)
+
+=back
+
+For more information, see L<perlapi>, and F<utf8.c> and F<utf8.h>
+in the Perl source code distribution.
+
=head1 SEE ALSO
-L<bytes>, L<utf8>, L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
+L<perluniintro>, L<encoding>, L<Encode>, L<open>, L<utf8>, L<bytes>,
+L<perlretut>, L<perlvar/"${^WIDE_SYSTEM_CALLS}">
=cut
projects / p5sagit/p5-mst-13.2.git / blobdiff