package. The user-defined properties can be used in the regular expression C and C constructs. Note that the effect is compile-time and immutable once defined. The subroutines must return a specially-formatted string, with one or more newline-separated lines. Each line must be one of the following: =over 4 =item * Two hexadecimal numbers separated by horizontal whitespace (space or tabular characters) denoting a range of Unicode code points to include. =item * Something to include, prefixed by "+": a built-in character property (prefixed by "utf8::"), to represent all the characters in that property; two hexadecimal code points for a range; or a single hexadecimal code point. =item * Something to exclude, prefixed by "-": an existing character property (prefixed by "utf8::"), for all the characters in that property; two hexadecimal code points for a range; or a single hexadecimal code point. =item * Something to negate, prefixed "!": an existing character property (prefixed by "utf8::") for all the characters except the characters in the property; two hexadecimal code points for a range; or a single hexadecimal code point. =back For example, to define a property that covers both the Japanese syllabaries (hiragana and katakana), you can define sub InKana { return and C. You could also have used the existing block property names: sub InKana { return package with names like C (for lc() and lcfirst()), C (for the first character in ucfirst()), and C (for uc(), and the rest of the characters in ucfirst()). The string returned by the subroutines needs now to be three hexadecimal numbers separated by tabulators: start of the source range, end of the source range, and start of the destination range. For example: sub ToUpper { return /F. The mapping data is returned as the here-document, and the C<:tospecfoo> are special exception mappings derived from /F. The C and C mappings that one can see in the directory are not directly user-accessible, one can use either the C<:ucd> module, or just match case-insensitively (that's when the C mapping is used). A final note on the user-defined property tests and mappings: they will be used only if the scalar has been marked as having Unicode characters. Old byte-style strings will not be affected. =head2 Character Encodings for Input and Output See L. =head2 Unicode Regular Expression Support Level The following list of Unicode support for regular expressions describes all the features currently supported. The references to "Level N" and the section numbers refer to the Unicode Technical Report 18, "Unicode Regular Expression Guidelines", version 6 (Unicode 3.2.0, Perl 5.8.0). =over 4 =item * Level 1 - Basic Unicode Support 2.1 Hex Notation - done [1] Named Notation - done [2] 2.2 Categories - done [3][4] 2.3 Subtraction - MISSING [5][6] 2.4 Simple Word Boundaries - done [7] 2.5 Simple Loose Matches - done [8] 2.6 End of Line - MISSING [9][10] [ 1] \x{...} [ 2] \N{...} [ 3] . \p{...} \P{...} [ 4] now scripts (see UTR#24 Script Names) in addition to blocks [ 5] have negation [ 6] can use regular expression look-ahead [a] or user-defined character properties [b] to emulate subtraction [ 7] include Letters in word characters [ 8] note that Perl does Full case-folding in matching, not Simple: for example U+1F88 is equivalent with U+1F00 U+03B9, not with 1F80. This difference matters for certain Greek capital letters with certain modifiers: the Full case-folding decomposes the letter, while the Simple case-folding would map it to a single character. [ 9] see UTR #13 Unicode Newline Guidelines [10] should do ^ and $ also on \x{85}, \x{2028} and \x{2029} (should also affect , $., and script line numbers) (the \x{85}, \x{2028} and \x{2029} do match \s) [a] You can mimic class subtraction using lookahead. For example, what UTR #18 might write as [{Greek}-[{UNASSIGNED}]] in Perl can be written as: (?!\p{Unassigned})\p{InGreekAndCoptic} (?=\p{Assigned})\p{InGreekAndCoptic} But in this particular example, you probably really want \p{GreekAndCoptic} which will match assigned characters known to be part of the Greek script. Also see the Unicode::Regex::Set module, it does implement the full UTR #18 grouping, intersection, union, and removal (subtraction) syntax. [b] See L"User-Defined Character Properties">. =item * Level 2 - Extended Unicode Support 3.1 Surrogates - MISSING [11] 3.2 Canonical Equivalents - MISSING [12][13] 3.3 Locale-Independent Graphemes - MISSING [14] 3.4 Locale-Independent Words - MISSING [15] 3.5 Locale-Independent Loose Matches - MISSING [16] [11] Surrogates are solely a UTF-16 concept and Perl's internal representation is UTF-8. The Encode module does UTF-16, though. [12] see UTR#15 Unicode Normalization [13] have Unicode::Normalize but not integrated to regexes [14] have \X but at this level . should equal that [15] need three classes, not just \w and \W [16] see UTR#21 Case Mappings =item * Level 3 - Locale-Sensitive Support 4.1 Locale-Dependent Categories - MISSING 4.2 Locale-Dependent Graphemes - MISSING [16][17] 4.3 Locale-Dependent Words - MISSING 4.4 Locale-Dependent Loose Matches - MISSING 4.5 Locale-Dependent Ranges - MISSING [16] see UTR#10 Unicode Collation Algorithms [17] have Unicode::Collate but not integrated to regexes =back =head2 Unicode Encodings Unicode characters are assigned to I, which are abstract numbers. To use these numbers, various encodings are needed. =over 4 =item * UTF-8 UTF-8 is a variable-length (1 to 6 bytes, current character allocations require 4 bytes), byte-order independent encoding. For ASCII (and we really do mean 7-bit ASCII, not another 8-bit encoding), UTF-8 is transparent. The following table is from Unicode 3.2. 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+CFFF E1..EC 80..BF 80..BF U+D000..U+D7FF ED 80..9F 80..BF U+D800..U+DFFF ******* ill-formed ******* U+E000..U+FFFF EE..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 Note the C in C, the C in C, the CF in C, and the C in C. The "gaps" are caused by legal UTF-8 avoiding non-shortest encodings: it is technically possible to UTF-8-encode a single code point in different ways, but that is explicitly forbidden, and the shortest possible encoding should always be used. So that's what Perl does. Another way to look at it is via 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, and the leading bits of the start byte tell how many bytes the are in the encoded character. =item * UTF-EBCDIC Like UTF-8 but EBCDIC-safe, in the way that UTF-8 is ASCII-safe. =item * UTF-16, UTF-16BE, UTF-16LE, Surrogates, and BOMs (Byte Order Marks) The followings items are mostly for reference and general Unicode knowledge, Perl doesn't use these constructs internally. UTF-16 is a 2 or 4 byte encoding. The Unicode code points C are stored in a single 16-bit unit, and the code points C in two 16-bit units. The latter case is using I, the first 16-bit unit being the I, and the second being the I. Surrogates are code points set aside to encode the C range of Unicode code points in pairs of 16-bit units. The I are the range C, and the I are the range C. The surrogate encoding is $hi = ($uni - 0x10000) / 0x400 + 0xD800; $lo = ($uni - 0x10000) % 0x400 + 0xDC00; and the decoding is $uni = 0x10000 + ($hi - 0xD800) * 0x400 + ($lo - 0xDC00); If you try to generate surrogates (for example by using chr()), you will get a warning if warnings are turned on, because those code points are not valid for a Unicode character. Because of the 16-bitness, UTF-16 is byte-order 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) encodings 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, or 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 C 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 C, but if it was written on a little-endian platform, you will read the bytes C. (And if the originating platform was writing in UTF-8, you will read the bytes C.) The way this trick works is that the character with the code point C is guaranteed not to be a valid Unicode character, so the sequence of bytes C is unambiguously "BOM, represented in little-endian format" and cannot be C, represented in big-endian format". =item * UTF-32, UTF-32BE, UTF-32LE 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 C for BE and C for LE. =item * UCS-2, UCS-4 Encodings defined by the ISO 10646 standard. UCS-2 is a 16-bit encoding. Unlike UTF-16, UCS-2 is not extensible beyond C, because it does not use surrogates. UCS-4 is a 32-bit encoding, functionally identical to UTF-32. =item * UTF-7 A seven-bit safe (non-eight-bit) encoding, which is useful if the transport or storage is not eight-bit safe. Defined by RFC 2152. =back =head2 Security Implications of Unicode =over 4 =item * 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, the shortest possible sequence of UTF-8 bytes should be generated, because otherwise there is potential for an input buffer overflow at the receiving end of a UTF-8 connection. Perl always generates the shortest length UTF-8, and with warnings on Perl will warn about non-shortest length UTF-8 along with other malformations, such as the surrogates, which are not real Unicode code points. =item * Regular expressions behave slightly differently between byte data and character (Unicode) data. For example, the "word character" character class C will work differently depending on if data is eight-bit bytes or Unicode. In the first case, the set of C characters is either small--the default set of alphabetic characters, digits, and the "_"--or, if you are using a locale (see L), the C might contain a few more letters according to your language and country. In the second case, the C set of characters is much, much larger. Most importantly, even in the set of the first 256 characters, it will probably match different characters: unlike most locales, which are specific to a language and country pair, Unicode classifies all the characters that are letters I as C. For example, your locale might not think that LATIN SMALL LETTER ETH is a letter (unless you happen to speak Icelandic), but Unicode does. As discussed elsewhere, Perl has one foot (two hooves?) planted in each of two worlds: the old world of bytes and the new world of characters, upgrading from bytes to characters when necessary. If your legacy code does not explicitly use Unicode, no automatic switch-over to characters should happen. Characters shouldn't get downgraded to bytes, either. It is possible to accidentally mix bytes and characters, however (see L), in which case C in regular expressions might start behaving differently. Review your code. Use warnings and the C pragma. =back =head2 Unicode in Perl on EBCDIC The way Unicode is handled on EBCDIC platforms is still experimental. On such platforms, references to UTF-8 encoding in this document and elsewhere should be read as meaning the UTF-EBCDIC specified in Unicode Technical Report 16, unless ASCII vs. EBCDIC issues are specifically discussed. There is no C pragma or ":utfebcdic" layer; rather, "utf8" and ":utf8" are reused to mean the platform's "natural" 8-bit encoding of Unicode. See L for more discussion of the issues. =head2 Locales Usually locale settings and Unicode do not affect each other, but there are a couple of exceptions: =over 4 =item * You can enable automatic UTF-8-ification of your standard file handles, default C layer, and C by using either the C command line switch or the C environment variable, see L for the documentation of the C switch. =item * Perl tries really hard to work both with Unicode and the old byte-oriented world. Most often this is nice, but sometimes Perl's straddling of the proverbial fence causes problems. =back =head2 When Unicode Does Not Happen While Perl does have extensive ways to input and output in Unicode, and few other 'entry points' like the @ARGV which can be interpreted as Unicode (UTF-8), there still are many places where Unicode (in some encoding or another) could be given as arguments or received as results, or both, but it is not. The following are such interfaces. For all of these Perl currently (as of 5.8.1) simply assumes byte strings both as arguments and results. One reason why Perl does not attempt to resolve the role of Unicode in this cases is that the answers are highly dependent on the operating system and the file system(s). For example, whether filenames can be in Unicode, and in exactly what kind of encoding, is not exactly a portable concept. Similarly for the qx and system: how well will the 'command line interface' (and which of them?) handle Unicode? =over 4 =item * chmod, chmod, chown, chroot, exec, link, mkdir rename, rmdir stat, symlink, truncate, unlink, utime =item * %ENV =item * glob (aka the ) =item * open, opendir, sysopen =item * qx (aka the backtick operator), system =item * readdir, readlink =back =head2 Forcing Unicode in Perl (Or Unforcing Unicode in Perl) Sometimes (see L"When Unicode Does Not Happen">) there are situations where you simply need to force Perl to believe that a byte string is UTF-8, or vice versa. The low-level calls utf8::upgrade($bytestring) and utf8::downgrade($utf8string) are the answers. Do not use them without careful thought, though: Perl may easily get very confused, angry, or even crash, if you suddenly change the 'nature' of scalar like that. Especially careful you have to be if you use the utf8::upgrade(): any random byte string is not valid UTF-8. =head2 Using Unicode in XS If you want to handle Perl Unicode in XS extensions, you may find the following C APIs useful. See also L for an explanation about Unicode at the XS level, and L for the API details. =over 4 =item * C returns true if the C flag is on and the bytes pragma is not in effect. C returns true is the C flag is on; the bytes pragma is ignored. The C flag being on does B mean that there are any characters of code points greater than 255 (or 127) in the scalar or that there are even any characters in the scalar. What the C flag means is that the sequence of octets in the representation of the scalar is the sequence of UTF-8 encoded code points of the characters of a string. The C flag being off means that each octet in this representation encodes a single character with code point 0..255 within the string. Perl's Unicode model is not to use UTF-8 until it is absolutely necessary. =item * C 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 * C 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 * C returns the length of the UTF-8 encoded buffer in characters. C returns the length of the UTF-8 encoded scalar. =item * C converts the string of the scalar to its UTF-8 encoded form. C does the opposite, if possible. C is like sv_utf8_upgrade except that it does not set the C flag. C does the opposite of C. Note that none of these are to be used as general-purpose encoding or decoding interfaces: C for that. C is affected by the encoding pragma but C is not (since the encoding pragma is designed to be a one-way street). =item * C returns true if the pointer points to a valid UTF-8 character. =item * C returns true if C bytes of the buffer are valid UTF-8. =item * C will return the number of bytes in the UTF-8 encoded character in the buffer. C will return the number of bytes required to UTF-8-encode the Unicode character code point. C is useful for example for iterating over the characters of a UTF-8 encoded buffer; C is useful, for example, in computing the size required for a UTF-8 encoded buffer. =item * C will tell the distance in characters between the two pointers pointing to the same UTF-8 encoded buffer. =item * C will return a pointer to an UTF-8 encoded buffer that is C (positive or negative) Unicode characters displaced from the UTF-8 buffer C. Be careful not to overstep the buffer: C will merrily run off the end or the beginning of the buffer if told to do so. =item * C and C are useful for debugging the output of Unicode strings and scalars. By default they are useful only for debugging--they display B characters as hexadecimal code points--but with the flags C, C, and C you can make the output more readable. =item * C can be used to compare two strings case-insensitively in Unicode. For case-sensitive comparisons you can just use C and C as usual. =back For more information, see L, and F and F in the Perl source code distribution. =head1 BUGS =head2 Interaction with Locales Use of locales with Unicode data may lead to odd results. Currently, Perl attempts to attach 8-bit locale info to characters in the range 0..255, but this technique is demonstrably incorrect for locales that use characters above that range when mapped into Unicode. Perl's Unicode support will also tend to run slower. Use of locales with Unicode is discouraged. =head2 Interaction with Extensions When Perl exchanges data with an extension, the extension should be able to understand the UTF-8 flag and act accordingly. If the extension doesn't know about the flag, it's likely that the extension will return incorrectly-flagged data. So if you're working with Unicode data, consult the documentation of every module you're using if there are any issues with Unicode data exchange. If the documentation does not talk about Unicode at all, suspect the worst and probably look at the source to learn how the module is implemented. Modules written completely in Perl shouldn't cause problems. Modules that directly or indirectly access code written in other programming languages are at risk. For affected functions, the simple strategy to avoid data corruption is to always make the encoding of the exchanged data explicit. Choose an encoding that you know the extension can handle. Convert arguments passed to the extensions to that encoding and convert results back from that encoding. Write wrapper functions that do the conversions for you, so you can later change the functions when the extension catches up. To provide an example, let's say the popular Foo::Bar::escape_html function doesn't deal with Unicode data yet. The wrapper function would convert the argument to raw UTF-8 and convert the result back to Perl's internal representation like so: sub my_escape_html ($) { my($what) = shift; return unless defined $what; Encode::decode_utf8(Foo::Bar::escape_html(Encode::encode_utf8($what))); } Sometimes, when the extension does not convert data but just stores and retrieves them, you will be in a position to use the otherwise dangerous Encode::_utf8_on() function. Let's say the popular C<:bar> extension, written in C, provides a C method that lets you store and retrieve data according to these prototypes: $self->param($name, $value); # set a scalar $value = $self->param($name); # retrieve a scalar If it does not yet provide support for any encoding, one could write a derived class with such a C method: sub param { my($self,$name,$value) = @_; utf8::upgrade($name); # make sure it is UTF-8 encoded if (defined $value) utf8::upgrade($value); # make sure it is UTF-8 encoded return $self->SUPER::param($name,$value); } else { my $ret = $self->SUPER::param($name); Encode::_utf8_on($ret); # we know, it is UTF-8 encoded return $ret; } } Some extensions provide filters on data entry/exit points, such as DB_File::filter_store_key and family. Look out for such filters in the documentation of your extensions, they can make the transition to Unicode data much easier. =head2 Speed Some functions are slower when working on UTF-8 encoded strings than on byte encoded strings. All functions that need to hop over characters such as length(), substr() or index(), or matching regular expressions can work B faster when the underlying data are byte-encoded. In Perl 5.8.0 the slowness was often quite spectacular; in Perl 5.8.1 a caching scheme was introduced which will hopefully make the slowness somewhat less spectacular, at least for some operations. In general, operations with UTF-8 encoded strings are still slower. As an example, the Unicode properties (character classes) like C are known to be quite a bit slower (5-20 times) than their simpler counterparts like C (then again, there 268 Unicode characters matching C compared with the 10 ASCII characters matching C). =head2 Porting code from perl-5.6.X Perl 5.8 has a different Unicode model from 5.6. In 5.6 the programmer was required to use the C pragma to declare that a given scope expected to deal with Unicode data and had to make sure that only Unicode data were reaching that scope. If you have code that is working with 5.6, you will need some of the following adjustments to your code. The examples are written such that the code will continue to work under 5.6, so you should be safe to try them out. =over 4 =item * A filehandle that should read or write UTF-8 if ($] > 5.007) { binmode $fh, ":utf8"; } =item * A scalar that is going to be passed to some extension Be it Compress::Zlib, Apache::Request or any extension that has no mention of Unicode in the manpage, you need to make sure that the UTF-8 flag is stripped off. Note that at the time of this writing (October 2002) the mentioned modules are not UTF-8-aware. Please check the documentation to verify if this is still true. if ($] > 5.007) { require Encode; $val = Encode::encode_utf8($val); # make octets } =item * A scalar we got back from an extension If you believe the scalar comes back as UTF-8, you will most likely want the UTF-8 flag restored: if ($] > 5.007) { require Encode; $val = Encode::decode_utf8($val); } =item * Same thing, if you are really sure it is UTF-8 if ($] > 5.007) { require Encode; Encode::_utf8_on($val); } =item * A wrapper for fetchrow_array and fetchrow_hashref When the database contains only UTF-8, a wrapper function or method is a convenient way to replace all your fetchrow_array and fetchrow_hashref calls. A wrapper function will also make it easier to adapt to future enhancements in your database driver. Note that at the time of this writing (October 2002), the DBI has no standardized way to deal with UTF-8 data. Please check the documentation to verify if that is still true. sub fetchrow { my($self, $sth, $what) = @_; # $what is one of fetchrow_{array,hashref} if ($] $what; } else { require Encode; if (wantarray) { my @arr = $sth->$what; for (@arr) { defined && /[^\000-\177]/ && Encode::_utf8_on($_); } return @arr; } else { my $ret = $sth->$what; if (ref $ret) { for my $k (keys %$ret) { defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret->{$k}; } return $ret; } else { defined && /[^\000-\177]/ && Encode::_utf8_on($_) for $ret; return $ret; } } } } =item * A large scalar that you know can only contain ASCII Scalars that contain only ASCII and are marked as UTF-8 are sometimes a drag to your program. If you recognize such a situation, just remove the UTF-8 flag: utf8::downgrade($val) if $] > 5.007; =back =head1 SEE ALSO L, L, L, L, L, L, L, L =cut