=head1 NAME perluniintro - Perl Unicode introduction =head1 DESCRIPTION This document gives a general idea of Unicode and how to use Unicode in Perl. =head2 Unicode Unicode is a character set standard with plans to cover all of the writing systems of the world, plus many other symbols. Unicode and ISO/IEC 10646 are coordinated standards that provide code points for the characters in almost all modern character set standards, covering more than 30 writing systems and hundreds of languages, including all commercially important modern languages. All characters in the largest Chinese, Japanese, and Korean dictionaries are also encoded. The standards will eventually cover almost all characters in more than 250 writing systems and thousands of languages. A Unicode I is an abstract entity. It is not bound to any particular integer width, and especially not to the C language C. Unicode is language neutral and display neutral: it doesn't encode the language of the text, and it doesn't define fonts or other graphical layout details. Unicode operates on characters and on text built from those characters. Unicode defines characters like C or C, and then unique numbers for those, hexadecimal 0x0041 or 0x03B1 for those particular characters. Such unique numbers are called I. The Unicode standard prefers using hexadecimal notation for the code points. (In case this notation, numbers like 0x0041, is unfamiliar to you, take a peek at a later section, L.) The Unicode standard uses the notation C, which gives the hexadecimal code point, and the normative name of the character. Unicode also defines various I for the characters, like "uppercase" or "lowercase", "decimal digit", or "punctuation": these properties are independent of the names of the characters. Furthermore, various operations on the characters like uppercasing, lowercasing, and collating (sorting), are defined. A Unicode character consists either of a single code point, or a I (like C), followed by one or more I (like C). This sequence of a base character and modifiers is called a I. Whether to call these combining character sequences, as a whole, "characters" depends on your point of view. If you are a programmer, you probably would tend towards seeing each element in the sequences as one unit, one "character", but from the user viewpoint, the sequence as a whole is probably considered one "character", since that's probably what it looks like in the context of the user's language. With this "as a whole" view of characters, the number of characters is open-ended. But in the programmer's "one unit is one character" point of view, the concept of "characters" is more deterministic, and so we take that point of view in this document: one "character" is one Unicode code point, be it a base character or a combining character. For some of the combinations there are I characters, for example C is defined as a single code point. These precomposed characters are, however, often available only for some combinations, and mainly they are meant to support round-trip conversions between Unicode and legacy standards (like the ISO 8859), and in general case the composing method is more extensible. To support conversion between the different compositions of the characters, various I are also defined. Because of backward compatibility with legacy encodings, the "a unique number for every character" breaks down a bit: "at least one number for every character" is closer to truth. (This happens when the same character has been encoded in several legacy encodings.) The converse is also not true: not every code point has an assigned character. Firstly, there are unallocated code points within otherwise used blocks. Secondly, there are special Unicode control characters that do not represent true characters. A common myth about Unicode is that it would be "16-bit", that is, 0x10000 (or 65536) characters from 0x0000 to 0xFFFF. B Since Unicode 2.0 Unicode has been defined all the way up to 21 bits (0x10FFFF), and since 3.1 characters have been defined beyond 0xFFFF. The first 0x10000 characters are called the I, or the I (BMP). With the Unicode 3.1, 17 planes in all are defined (but nowhere near full of defined characters yet). Another myth is that the 256-character blocks have something to do with languages: a block per language. B The division into the blocks exists but it is almost completely accidental, an artifact of how the characters have been historically allocated. Instead, there is a concept called I, which may be more useful: there is C script, C script, and so on. Scripts usually span several parts of several blocks. For further information see L. The Unicode code points are just abstract numbers. To input and output these abstract numbers, the numbers must be I somehow. Unicode defines several I, of which I is perhaps the most popular. UTF-8 is a variable length encoding that encodes Unicode characters as 1 to 6 bytes (only 4 with the currently defined characters). Other encodings are UTF-16 and UTF-32 and their big and little endian variants (UTF-8 is byteorder independent). The ISO/IEC 10646 defines the UCS-2 and UCS-4 encoding forms. For more information about encodings, for example to learn what I and I (BOMs) are, see L. =head2 Perl's Unicode Support Starting from Perl 5.6.0, Perl has had the capability of handling Unicode natively. The first recommended release for serious Unicode work is Perl 5.8.0, however. The maintenance release 5.6.1 fixed many of the problems of the initial implementation of Unicode, but for example regular expressions didn't really work with Unicode. B is no longer necessary.> In earlier releases the C pragma was used to declare that operations in the current block or file would be Unicode-aware. This model was found to be wrong, or at least clumsy: the Unicodeness is now carried with the data, not attached to the operations. (There is one remaining case where an explicit C is needed: if your Perl script is in UTF-8, you can use UTF-8 in your variable and subroutine names, and in your string and regular expression literals, by saying C. This is not the default because that would break existing scripts having legacy 8-bit data in them.) =head2 Perl's Unicode Model Perl supports both the old, pre-5.6, model of strings of eight-bit native bytes, and strings of Unicode characters. The principle is that Perl tries to keep its data as eight-bit bytes for as long as possible, but as soon as Unicodeness cannot be avoided, the data is transparently upgraded to Unicode. The internal encoding of Unicode in Perl is UTF-8. The internal encoding is normally hidden, however, and one need not and should not worry about the internal encoding at all: it is all just characters. Perl 5.8.0 will also support Unicode on EBCDIC platforms. There the support is somewhat harder to implement since additional conversions are needed at every step. Because of these difficulties the Unicode support won't be quite as full as in other, mainly ASCII-based, platforms (the Unicode support will be better than in the 5.6 series, which didn't work much at all for EBCDIC platform). On EBCDIC platforms the internal encoding form used is UTF-EBCDIC. =head2 Creating Unicode To create Unicode literals, use the C<\x{...}> notation in doublequoted strings: my $smiley = "\x{263a}"; Similarly for regular expression literals $smiley =~ /\x{263a}/; At run-time you can use C: my $hebrew_alef = chr(0x05d0); (See L for how to find all these numeric codes.) Naturally, C will do the reverse: turn a character to a code point. Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}> and C for arguments less than 0x100 (decimal 256) will generate an eight-bit character for backward compatibility with older Perls. For arguments of 0x100 or more, Unicode will always be produced. If you want UTF-8 always, use C instead of C<\x..>, C<\x{...}>, or C. You can also use the C pragma to invoke characters by name in doublequoted strings: use charnames ':full'; my $arabic_alef = "\N{ARABIC LETTER ALEF}"; And, as mentioned above, you can also C numbers into Unicode characters: my $georgian_an = pack("U", 0x10a0); Note that both C<\x{...}> and C<\N{...}> are compile-time string constants: you cannot use variables in them. if you want similar run-time functionality, use C and C. =head2 Handling Unicode Handling Unicode is for the most part transparent: just use the strings as usual. Functions like C, C, and C will work on the Unicode characters; regular expressions will work on the Unicode characters (see L and L). Note that Perl does B consider combining character sequences to be characters, such for example use charnames ':full'; print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; will print 2, not 1. The only exception is that regular expressions have C<\X> for matching a combining character sequence. When life is not quite so transparent is working with legacy encodings, and I/O, and certain special cases. =head2 Legacy Encodings When you combine legacy data and Unicode the legacy data needs to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if applicable) is assumed. You can override this assumption by using the C pragma, for example use encoding 'latin2'; # ISO 8859-2 in which case literals (string or regular expression) and chr/ord in your whole script are assumed to produce Unicode characters from ISO 8859-2 code points. Note that the matching for the encoding names is forgiving: instead of C you could have said C, or C, and so forth. With just use encoding; first the environment variable C will be consulted, and if that doesn't exist, ISO 8859-1 (Latin 1) will be assumed. The C module knows about many encodings and it has interfaces for doing conversions between those encodings: use Encode 'from_to'; from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 =head2 Unicode I/O Normally writing out Unicode data print FH chr(0x100), "\n"; will print out the raw UTF-8 bytes, but you will get a warning out of that if you use C<-w> or C. To avoid the warning open the stream explicitly in UTF-8: open FH, ">:utf8", "file"; and on already open streams use C: binmode(STDOUT, ":utf8"); Reading in correctly formed UTF-8 data will not magically turn the data into Unicode in Perl's eyes. You can use either the C<':utf8'> I/O discipline when opening files open(my $fh,'<:utf8', 'anything'); my $line_of_utf8 = <$fh>; The I/O disciplines can also be specified more flexibly with the C pragma; see L: use open ':utf8'; # input and output default discipline will be UTF-8 open X, ">file"; print X chr(0x100), "\n"; close X; open Y, "); # this should print 0x100 close Y; With the C pragma you can use the C<:locale> discipline $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R'; # the :locale will probe the locale environment variables like LC_ALL use open OUT => ':locale'; # russki parusski open(O, ">koi8"); print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 close O; open(I, "), "\n"; # this should print 0xc1 close I; or you can also use the C<':encoding(...)'> discipline open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); my $line_of_iliad = <$epic>; Both of these methods install a transparent filter on the I/O stream that will convert data from the specified encoding when it is read in from the stream. In the first example the F file is assumed to be UTF-8 encoded Unicode, in the second example the F file is assumed to be ISO-8858-7 encoded Greek, but the lines read in will be in both cases Unicode. The L pragma affects all the C calls after the pragma by setting default disciplines. If you want to affect only certain streams, use explicit disciplines directly in the C call. You can switch encodings on an already opened stream by using C, see L. The C<:locale> does not currently (as of Perl 5.8.0) work with C and C, only with the C pragma. The C<:utf8> and C<:encoding(...)> do work with all of C, C, and the C pragma. Similarly, you may use these I/O disciplines on input streams to automatically convert data from the specified encoding when it is written to the stream. open(my $unicode, '<:utf8', 'japanese.uni'); open(my $nihongo, '>:encoding(iso2022-jp)', 'japanese.jp'); while (<$unicode>) { print $nihongo } The naming of encodings, both by the C and by the C pragma, is similarly understanding as with the C pragma: C and C will both be understood. Common encodings recognized by ISO, MIME, IANA, and various other standardisation organisations are recognised, for a more detailed list see L. C reads characters and returns the number of characters. C and C operate on byte counts, as do C and C. Notice that because of the default behaviour "input is not UTF-8" it is easy to mistakenly write code that keeps on expanding a file by repeatedly encoding it in UTF-8: # BAD CODE WARNING open F, "file"; local $/; # read in the whole file $t = ; close F; open F, ">:utf8", "file"; print F $t; close F; If you run this code twice, the contents of the F will be twice UTF-8 encoded. A C would have avoided the bug, or explicitly opening also the F for input as UTF-8. B: the C<:utf8> and C<:encoding> features work only if your Perl has been built with the new "perlio" feature. Almost all Perl 5.8 platforms do use "perlio", though: you can see whether yours is by running "perl -V" and looking for C. =head2 Displaying Unicode As Text Sometimes you might want to display Perl scalars containing Unicode as simple ASCII (or EBCDIC) text. The following subroutine will convert its argument so that Unicode characters with code points greater than 255 are displayed as "\x{...}", control characters (like "\n") are displayed as "\x..", and the rest of the characters as themselves. sub nice_string { join("", map { $_ > 255 ? # if wide character... sprintf("\\x{%x}", $_) : # \x{...} chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... sprintf("\\x%02x", $_) : # \x.. chr($_) } # else as themselves unpack("U*", $_[0])); # unpack Unicode characters } For example, C will return C<"foo\x{100}bar\x0a">. =head2 Special Cases =over 4 =item * Bit Complement Operator ~ And vec() The bit complement operator C<~> will produce surprising results if used on strings containing Unicode characters. The results are consistent with the internal UTF-8 encoding of the characters, but not with much else. So don't do that. Similarly for vec(): you will be operating on the UTF-8 bit patterns of the Unicode characters, not on the bytes, which is very probably not what you want. =item * Peeking At UTF-8 One way of peeking inside the internal encoding of Unicode characters is to use C to get the bytes, or C to display the bytes: # this will print c4 80 for the UTF-8 bytes 0xc4 0x80 print join(" ", unpack("H*", pack("U", 0x100))), "\n"; Yet another way would be to use the Devel::Peek module: perl -MDevel::Peek -e 'Dump(chr(0x100))' That will show the UTF8 flag in FLAGS and both the UTF-8 bytes and Unicode characters in PV. See also later in this document the discussion about the C function of the C module. =back =head2 Advanced Topics =over 4 =item * String Equivalence The question of string equivalence turns somewhat complicated in Unicode: what do you mean by equal? (Is C equal to C?) The short answer is that by default Perl compares equivalence (C, C) based only on code points of the characters. In the above case, no (because 0x00C1 != 0x0041). But sometimes any CAPITAL LETTER As being considered equal, or even any As of any case, would be desirable. The long answer is that you need to consider character normalization and casing issues: see L, and Unicode Technical Reports #15 and #21, I and I, http://www.unicode.org/unicode/reports/tr15/ http://www.unicode.org/unicode/reports/tr21/ As of Perl 5.8.0, the's regular expression case-ignoring matching implements only 1:1 semantics: one character matches one character. In I both 1:N and N:1 matches are defined. =item * String Collation People like to see their strings nicely sorted, or as Unicode parlance goes, collated. But again, what do you mean by collate? (Does C come before or after C?) The short answer is that by default Perl compares strings (C, C, C, C, C) based only on the code points of the characters. In the above case, after, since 0x00C1 > 0x00C0. The long answer is that "it depends", and a good answer cannot be given without knowing (at the very least) the language context. See L, and I http://www.unicode.org/unicode/reports/tr10/ =back =head2 Miscellaneous =over 4 =item * Character Ranges Character ranges in regular expression character classes (C) and in the C (also known as C) operator are not magically Unicode-aware. What this means that C<[a-z]> will not magically start to mean "all alphabetic letters" (not that it does mean that even for 8-bit characters, you should be using C for that). For specifying things like that in regular expressions you can use the various Unicode properties, C<\pL> in this particular case. You can use Unicode code points as the end points of character ranges, but that means that particular code point range, nothing more. For further information, see L. =item * String-To-Number Conversions Unicode does define several other decimal (and numeric) characters than just the familiar 0 to 9, such as the Arabic and Indic digits. Perl does not support string-to-number conversion for digits other than the 0 to 9 (and a to f for hexadecimal). =back =head2 Questions With Answers =over 4 =item Will My Old Scripts Break? Very probably not. Unless you are generating Unicode characters somehow, any old behaviour should be preserved. About the only behaviour that has changed and which could start generating Unicode is the old behaviour of C where supplying an argument more than 255 produced a character modulo 255 (for example, C was equal to C). =item How Do I Make My Scripts Work With Unicode? Very little work should be needed since nothing changes until you somehow generate Unicode data. The greatest trick will be getting input as Unicode, and for that see the earlier I/O discussion. =item How Do I Know Whether My String Is In Unicode? You shouldn't care. No, you really shouldn't. If you have to care (beyond the cases described above), it means that we didn't get the transparency of Unicode quite right. Okay, if you insist: use Encode 'is_utf8'; print is_utf8($string) ? 1 : 0, "\n"; But note that this doesn't mean that any of the characters in the string are necessary UTF-8 encoded, or that any of the characters have code points greater than 0xFF (255) or even 0x80 (128), or that the string has any characters at all. All the C does is to return the value of the internal "utf8ness" flag attached to the $string. If the flag is on, characters added to that string will be automatically upgraded to UTF-8 (and even then only if they really need to be upgraded, that is, if their code point is greater than 0xFF). Sometimes you might really need to know the byte length of a string instead of the character length. For that use the C pragma and its only defined function C: my $unicode = chr(0x100); print length($unicode), "\n"; # will print 1 use bytes; print length($unicode), "\n"; # will print 2 (the 0xC4 0x80 of the UTF-8) =item How Do I Detect Invalid UTF-8? Either use Encode 'encode_utf8'; if (encode_utf8($string)) { # valid } else { # invalid } or use warnings; @chars = unpack("U0U*", "\xFF"); # will warn The warning will be C. The "U0" means "expect strictly UTF-8 encoded Unicode". Without that the C would accept also data like C). =item How Do I Convert Data Into UTF-8? Or Vice Versa? This probably isn't as useful (or simple) as you might think. Also, normally you shouldn't need to. In one sense what you are asking doesn't make much sense: UTF-8 is (intended as an) Unicode encoding, so converting "data" into UTF-8 isn't meaningful unless you know in what character set and encoding the binary data is in, and in this case you can use C. use Encode 'from_to'; from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 If you have ASCII (really 7-bit US-ASCII), you already have valid UTF-8, the lowest 128 characters of UTF-8 encoded Unicode and US-ASCII are equivalent. If you have Latin-1 (or want Latin-1), you can just use pack/unpack: $latin1 = pack("C*", unpack("U*", $utf8)); $utf8 = pack("U*", unpack("C*", $latin1)); (The same works for EBCDIC.) If you have a sequence of bytes you B is valid UTF-8, but Perl doesn't know it yet, you can make Perl a believer, too: use Encode 'decode_utf8'; $utf8 = decode_utf8($bytes); You can convert well-formed UTF-8 to a sequence of bytes, but if you just want to convert random binary data into UTF-8, you can't. Any random collection of bytes isn't well-formed UTF-8. You can use C for the former, and you can create well-formed Unicode/UTF-8 data by C. =item How Do I Display Unicode? How Do I Input Unicode? See http://www.hclrss.demon.co.uk/unicode/ and http://www.cl.cam.ac.uk/~mgk25/unicode.html =item How Does Unicode Work With Traditional Locales? In Perl, not very well. Avoid using locales through the C pragma. Use only one or the other. =back =head2 Hexadecimal Notation The Unicode standard prefers using hexadecimal notation because that shows better the division of Unicode into blocks of 256 characters. Hexadecimal is also simply shorter than decimal. You can use decimal notation, too, but learning to use hexadecimal just makes life easier with the Unicode standard. The C<0x> prefix means a hexadecimal number, the digits are 0-9 I a-f (or A-F, case doesn't matter). Each hexadecimal digit represents four bits, or half a byte. C will show a hexadecimal number in decimal, and C will show a decimal number in hexadecimal. If you have just the "hexdigits" of a hexadecimal number, you can use the C function. print 0x0009, "\n"; # 9 print 0x000a, "\n"; # 10 print 0x000f, "\n"; # 15 print 0x0010, "\n"; # 16 print 0x0011, "\n"; # 17 print 0x0100, "\n"; # 256 print 0x0041, "\n"; # 65 printf "%x\n", 65; # 41 printf "%#x\n", 65; # 0x41 print hex("41"), "\n"; # 65 =head2 Further Resources =over 4 =item * Unicode Consortium http://www.unicode.org/ =item * Unicode FAQ http://www.unicode.org/unicode/faq/ =item * Unicode Glossary http://www.unicode.org/glossary/ =item * Unicode Useful Resources http://www.unicode.org/unicode/onlinedat/resources.html =item * Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications http://www.hclrss.demon.co.uk/unicode/ =item * UTF-8 and Unicode FAQ for Unix/Linux http://www.cl.cam.ac.uk/~mgk25/unicode.html =item * Legacy Character Sets http://www.czyborra.com/ http://www.eki.ee/letter/ =item * The Unicode support files live within the Perl installation in the directory $Config{installprivlib}/unicore in Perl 5.8.0 or newer, and $Config{installprivlib}/unicode in the Perl 5.6 series. (The renaming to F was done to avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) The main Unicode data file is F (or F in Perl 5.6.1.) You can find the C<$Config{installprivlib}> by perl "-V:installprivlib" Note that some of the files have been renamed from the Unicode standard since the Perl installation tries to live by the "8.3" filenaming restrictions. The renamings are shown in the accompanying F file. You can explore various information from the Unicode data files using the C module. =back =head1 UNICODE IN OLDER PERLS If you cannot upgrade your Perl to 5.8.0 or later, you can still do some Unicode processing by using the modules C, C, and C, available from CPAN. If you have the GNU recode installed, you can also use the Perl frontend C for character conversions. =head1 SEE ALSO L, L, L, L, L, L, L, L, L, L =head1 ACKNOWLEDGEMENTS Thanks to the kind readers of the perl5-porters@perl.org, perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org mailing lists for their valuable feedback. =head1 AUTHOR, COPYRIGHT, AND LICENSE Copyright 2001 Jarkko Hietaniemi This document may be distributed under the same terms as Perl itself.