1=head1 NAME 2 3perluniintro - Perl Unicode introduction 4 5=head1 DESCRIPTION 6 7This document gives a general idea of Unicode and how to use Unicode 8in Perl. 9 10=head2 Unicode 11 12Unicode is a character set standard which plans to codify all of the 13writing systems of the world, plus many other symbols. 14 15Unicode and ISO/IEC 10646 are coordinated standards that provide code 16points for characters in almost all modern character set standards, 17covering more than 30 writing systems and hundreds of languages, 18including all commercially-important modern languages. All characters 19in the largest Chinese, Japanese, and Korean dictionaries are also 20encoded. The standards will eventually cover almost all characters in 21more than 250 writing systems and thousands of languages. 22Unicode 1.0 was released in October 1991, and 4.0 in April 2003. 23 24A Unicode I<character> is an abstract entity. It is not bound to any 25particular integer width, especially not to the C language C<char>. 26Unicode is language-neutral and display-neutral: it does not encode the 27language of the text and it does not define fonts or other graphical 28layout details. Unicode operates on characters and on text built from 29those characters. 30 31Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK 32SMALL LETTER ALPHA> and unique numbers for the characters, in this 33case 0x0041 and 0x03B1, respectively. These unique numbers are called 34I<code points>. 35 36The Unicode standard prefers using hexadecimal notation for the code 37points. If numbers like C<0x0041> are unfamiliar to you, take a peek 38at a later section, L</"Hexadecimal Notation">. The Unicode standard 39uses the notation C<U+0041 LATIN CAPITAL LETTER A>, to give the 40hexadecimal code point and the normative name of the character. 41 42Unicode also defines various I<properties> for the characters, like 43"uppercase" or "lowercase", "decimal digit", or "punctuation"; 44these properties are independent of the names of the characters. 45Furthermore, various operations on the characters like uppercasing, 46lowercasing, and collating (sorting) are defined. 47 48A Unicode character consists either of a single code point, or a 49I<base character> (like C<LATIN CAPITAL LETTER A>), followed by one or 50more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of 51base character and modifiers is called a I<combining character 52sequence>. 53 54Whether to call these combining character sequences "characters" 55depends on your point of view. If you are a programmer, you probably 56would tend towards seeing each element in the sequences as one unit, 57or "character". The whole sequence could be seen as one "character", 58however, from the user's point of view, since that's probably what it 59looks like in the context of the user's language. 60 61With this "whole sequence" view of characters, the total number of 62characters is open-ended. But in the programmer's "one unit is one 63character" point of view, the concept of "characters" is more 64deterministic. In this document, we take that second point of view: 65one "character" is one Unicode code point, be it a base character or 66a combining character. 67 68For some combinations, there are I<precomposed> characters. 69C<LATIN CAPITAL LETTER A WITH ACUTE>, for example, is defined as 70a single code point. These precomposed characters are, however, 71only available for some combinations, and are mainly 72meant to support round-trip conversions between Unicode and legacy 73standards (like the ISO 8859). In the general case, the composing 74method is more extensible. To support conversion between 75different compositions of the characters, various I<normalization 76forms> to standardize representations are also defined. 77 78Because of backward compatibility with legacy encodings, the "a unique 79number for every character" idea breaks down a bit: instead, there is 80"at least one number for every character". The same character could 81be represented differently in several legacy encodings. The 82converse is also not true: some code points do not have an assigned 83character. Firstly, there are unallocated code points within 84otherwise used blocks. Secondly, there are special Unicode control 85characters that do not represent true characters. 86 87A common myth about Unicode is that it would be "16-bit", that is, 88Unicode is only represented as C<0x10000> (or 65536) characters from 89C<0x0000> to C<0xFFFF>. B<This is untrue.> Since Unicode 2.0 (July 901996), Unicode has been defined all the way up to 21 bits (C<0x10FFFF>), 91and since Unicode 3.1 (March 2001), characters have been defined 92beyond C<0xFFFF>. The first C<0x10000> characters are called the 93I<Plane 0>, or the I<Basic Multilingual Plane> (BMP). With Unicode 943.1, 17 (yes, seventeen) planes in all were defined--but they are 95nowhere near full of defined characters, yet. 96 97Another myth is that the 256-character blocks have something to 98do with languages--that each block would define the characters used 99by a language or a set of languages. B<This is also untrue.> 100The division into blocks exists, but it is almost completely 101accidental--an artifact of how the characters have been and 102still are allocated. Instead, there is a concept called I<scripts>, 103which is more useful: there is C<Latin> script, C<Greek> script, and 104so on. Scripts usually span varied parts of several blocks. 105For further information see L<Unicode::UCD>. 106 107The Unicode code points are just abstract numbers. To input and 108output these abstract numbers, the numbers must be I<encoded> or 109I<serialised> somehow. Unicode defines several I<character encoding 110forms>, of which I<UTF-8> is perhaps the most popular. UTF-8 is a 111variable length encoding that encodes Unicode characters as 1 to 6 112bytes (only 4 with the currently defined characters). Other encodings 113include UTF-16 and UTF-32 and their big- and little-endian variants 114(UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2 115and UCS-4 encoding forms. 116 117For more information about encodings--for instance, to learn what 118I<surrogates> and I<byte order marks> (BOMs) are--see L<perlunicode>. 119 120=head2 Perl's Unicode Support 121 122Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode 123natively. Perl 5.8.0, however, is the first recommended release for 124serious Unicode work. The maintenance release 5.6.1 fixed many of the 125problems of the initial Unicode implementation, but for example 126regular expressions still do not work with Unicode in 5.6.1. 127 128B<Starting from Perl 5.8.0, the use of C<use utf8> is no longer 129necessary.> In earlier releases the C<utf8> pragma was used to declare 130that operations in the current block or file would be Unicode-aware. 131This model was found to be wrong, or at least clumsy: the "Unicodeness" 132is now carried with the data, instead of being attached to the 133operations. Only one case remains where an explicit C<use utf8> is 134needed: if your Perl script itself is encoded in UTF-8, you can use 135UTF-8 in your identifier names, and in string and regular expression 136literals, by saying C<use utf8>. This is not the default because 137scripts with legacy 8-bit data in them would break. See L<utf8>. 138 139=head2 Perl's Unicode Model 140 141Perl supports both pre-5.6 strings of eight-bit native bytes, and 142strings of Unicode characters. The principle is that Perl tries to 143keep its data as eight-bit bytes for as long as possible, but as soon 144as Unicodeness cannot be avoided, the data is transparently upgraded 145to Unicode. 146 147Internally, Perl currently uses either whatever the native eight-bit 148character set of the platform (for example Latin-1) is, defaulting to 149UTF-8, to encode Unicode strings. Specifically, if all code points in 150the string are C<0xFF> or less, Perl uses the native eight-bit 151character set. Otherwise, it uses UTF-8. 152 153A user of Perl does not normally need to know nor care how Perl 154happens to encode its internal strings, but it becomes relevant when 155outputting Unicode strings to a stream without a PerlIO layer -- one with 156the "default" encoding. In such a case, the raw bytes used internally 157(the native character set or UTF-8, as appropriate for each string) 158will be used, and a "Wide character" warning will be issued if those 159strings contain a character beyond 0x00FF. 160 161For example, 162 163 perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"' 164 165produces a fairly useless mixture of native bytes and UTF-8, as well 166as a warning: 167 168 Wide character in print at ... 169 170To output UTF-8, use the C<:utf8> output layer. Prepending 171 172 binmode(STDOUT, ":utf8"); 173 174to this sample program ensures that the output is completely UTF-8, 175and removes the program's warning. 176 177You can enable automatic UTF-8-ification of your standard file 178handles, default C<open()> layer, and C<@ARGV> by using either 179the C<-C> command line switch or the C<PERL_UNICODE> environment 180variable, see L<perlrun> for the documentation of the C<-C> switch. 181 182Note that this means that Perl expects other software to work, too: 183if Perl has been led to believe that STDIN should be UTF-8, but then 184STDIN coming in from another command is not UTF-8, Perl will complain 185about the malformed UTF-8. 186 187All features that combine Unicode and I/O also require using the new 188PerlIO feature. Almost all Perl 5.8 platforms do use PerlIO, though: 189you can see whether yours is by running "perl -V" and looking for 190C<useperlio=define>. 191 192=head2 Unicode and EBCDIC 193 194Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, 195Unicode support is somewhat more complex to implement since 196additional conversions are needed at every step. Some problems 197remain, see L<perlebcdic> for details. 198 199In any case, the Unicode support on EBCDIC platforms is better than 200in the 5.6 series, which didn't work much at all for EBCDIC platform. 201On EBCDIC platforms, the internal Unicode encoding form is UTF-EBCDIC 202instead of UTF-8. The difference is that as UTF-8 is "ASCII-safe" in 203that ASCII characters encode to UTF-8 as-is, while UTF-EBCDIC is 204"EBCDIC-safe". 205 206=head2 Creating Unicode 207 208To create Unicode characters in literals for code points above C<0xFF>, 209use the C<\x{...}> notation in double-quoted strings: 210 211 my $smiley = "\x{263a}"; 212 213Similarly, it can be used in regular expression literals 214 215 $smiley =~ /\x{263a}/; 216 217At run-time you can use C<chr()>: 218 219 my $hebrew_alef = chr(0x05d0); 220 221See L</"Further Resources"> for how to find all these numeric codes. 222 223Naturally, C<ord()> will do the reverse: it turns a character into 224a code point. 225 226Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>, 227and C<chr(...)> for arguments less than C<0x100> (decimal 256) 228generate an eight-bit character for backward compatibility with older 229Perls. For arguments of C<0x100> or more, Unicode characters are 230always produced. If you want to force the production of Unicode 231characters regardless of the numeric value, use C<pack("U", ...)> 232instead of C<\x..>, C<\x{...}>, or C<chr()>. 233 234You can also use the C<charnames> pragma to invoke characters 235by name in double-quoted strings: 236 237 use charnames ':full'; 238 my $arabic_alef = "\N{ARABIC LETTER ALEF}"; 239 240And, as mentioned above, you can also C<pack()> numbers into Unicode 241characters: 242 243 my $georgian_an = pack("U", 0x10a0); 244 245Note that both C<\x{...}> and C<\N{...}> are compile-time string 246constants: you cannot use variables in them. if you want similar 247run-time functionality, use C<chr()> and C<charnames::vianame()>. 248 249Also note that if all the code points for pack "U" are below 0x100, 250bytes will be generated, just like if you were using C<chr()>. 251 252 my $bytes = pack("U*", 0x80, 0xFF); 253 254If you want to force the result to Unicode characters, use the special 255C<"U0"> prefix. It consumes no arguments but forces the result to be 256in Unicode characters, instead of bytes. 257 258 my $chars = pack("U0U*", 0x80, 0xFF); 259 260=head2 Handling Unicode 261 262Handling Unicode is for the most part transparent: just use the 263strings as usual. Functions like C<index()>, C<length()>, and 264C<substr()> will work on the Unicode characters; regular expressions 265will work on the Unicode characters (see L<perlunicode> and L<perlretut>). 266 267Note that Perl considers combining character sequences to be 268characters, so for example 269 270 use charnames ':full'; 271 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; 272 273will print 2, not 1. The only exception is that regular expressions 274have C<\X> for matching a combining character sequence. 275 276Life is not quite so transparent, however, when working with legacy 277encodings, I/O, and certain special cases: 278 279=head2 Legacy Encodings 280 281When you combine legacy data and Unicode the legacy data needs 282to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if 283applicable) is assumed. You can override this assumption by 284using the C<encoding> pragma, for example 285 286 use encoding 'latin2'; # ISO 8859-2 287 288in which case literals (string or regular expressions), C<chr()>, 289and C<ord()> in your whole script are assumed to produce Unicode 290characters from ISO 8859-2 code points. Note that the matching for 291encoding names is forgiving: instead of C<latin2> you could have 292said C<Latin 2>, or C<iso8859-2>, or other variations. With just 293 294 use encoding; 295 296the environment variable C<PERL_ENCODING> will be consulted. 297If that variable isn't set, the encoding pragma will fail. 298 299The C<Encode> module knows about many encodings and has interfaces 300for doing conversions between those encodings: 301 302 use Encode 'from_to'; 303 from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8 304 305=head2 Unicode I/O 306 307Normally, writing out Unicode data 308 309 print FH $some_string_with_unicode, "\n"; 310 311produces raw bytes that Perl happens to use to internally encode the 312Unicode string. Perl's internal encoding depends on the system as 313well as what characters happen to be in the string at the time. If 314any of the characters are at code points C<0x100> or above, you will get 315a warning. To ensure that the output is explicitly rendered in the 316encoding you desire--and to avoid the warning--open the stream with 317the desired encoding. Some examples: 318 319 open FH, ">:utf8", "file"; 320 321 open FH, ">:encoding(ucs2)", "file"; 322 open FH, ">:encoding(UTF-8)", "file"; 323 open FH, ">:encoding(shift_jis)", "file"; 324 325and on already open streams, use C<binmode()>: 326 327 binmode(STDOUT, ":utf8"); 328 329 binmode(STDOUT, ":encoding(ucs2)"); 330 binmode(STDOUT, ":encoding(UTF-8)"); 331 binmode(STDOUT, ":encoding(shift_jis)"); 332 333The matching of encoding names is loose: case does not matter, and 334many encodings have several aliases. Note that the C<:utf8> layer 335must always be specified exactly like that; it is I<not> subject to 336the loose matching of encoding names. 337 338See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and 339L<Encode::PerlIO> for the C<:encoding()> layer, and 340L<Encode::Supported> for many encodings supported by the C<Encode> 341module. 342 343Reading in a file that you know happens to be encoded in one of the 344Unicode or legacy encodings does not magically turn the data into 345Unicode in Perl's eyes. To do that, specify the appropriate 346layer when opening files 347 348 open(my $fh,'<:utf8', 'anything'); 349 my $line_of_unicode = <$fh>; 350 351 open(my $fh,'<:encoding(Big5)', 'anything'); 352 my $line_of_unicode = <$fh>; 353 354The I/O layers can also be specified more flexibly with 355the C<open> pragma. See L<open>, or look at the following example. 356 357 use open ':utf8'; # input and output default layer will be UTF-8 358 open X, ">file"; 359 print X chr(0x100), "\n"; 360 close X; 361 open Y, "<file"; 362 printf "%#x\n", ord(<Y>); # this should print 0x100 363 close Y; 364 365With the C<open> pragma you can use the C<:locale> layer 366 367 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' } 368 # the :locale will probe the locale environment variables like LC_ALL 369 use open OUT => ':locale'; # russki parusski 370 open(O, ">koi8"); 371 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 372 close O; 373 open(I, "<koi8"); 374 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 375 close I; 376 377or you can also use the C<':encoding(...)'> layer 378 379 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); 380 my $line_of_unicode = <$epic>; 381 382These methods install a transparent filter on the I/O stream that 383converts data from the specified encoding when it is read in from the 384stream. The result is always Unicode. 385 386The L<open> pragma affects all the C<open()> calls after the pragma by 387setting default layers. If you want to affect only certain 388streams, use explicit layers directly in the C<open()> call. 389 390You can switch encodings on an already opened stream by using 391C<binmode()>; see L<perlfunc/binmode>. 392 393The C<:locale> does not currently (as of Perl 5.8.0) work with 394C<open()> and C<binmode()>, only with the C<open> pragma. The 395C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, 396C<binmode()>, and the C<open> pragma. 397 398Similarly, you may use these I/O layers on output streams to 399automatically convert Unicode to the specified encoding when it is 400written to the stream. For example, the following snippet copies the 401contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to 402the file "text.utf8", encoded as UTF-8: 403 404 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis'); 405 open(my $unicode, '>:utf8', 'text.utf8'); 406 while (<$nihongo>) { print $unicode $_ } 407 408The naming of encodings, both by the C<open()> and by the C<open> 409pragma, is similar to the C<encoding> pragma in that it allows for 410flexible names: C<koi8-r> and C<KOI8R> will both be understood. 411 412Common encodings recognized by ISO, MIME, IANA, and various other 413standardisation organisations are recognised; for a more detailed 414list see L<Encode::Supported>. 415 416C<read()> reads characters and returns the number of characters. 417C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> 418and C<sysseek()>. 419 420Notice that because of the default behaviour of not doing any 421conversion upon input if there is no default layer, 422it is easy to mistakenly write code that keeps on expanding a file 423by repeatedly encoding the data: 424 425 # BAD CODE WARNING 426 open F, "file"; 427 local $/; ## read in the whole file of 8-bit characters 428 $t = <F>; 429 close F; 430 open F, ">:utf8", "file"; 431 print F $t; ## convert to UTF-8 on output 432 close F; 433 434If you run this code twice, the contents of the F<file> will be twice 435UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or 436explicitly opening also the F<file> for input as UTF-8. 437 438B<NOTE>: the C<:utf8> and C<:encoding> features work only if your 439Perl has been built with the new PerlIO feature (which is the default 440on most systems). 441 442=head2 Displaying Unicode As Text 443 444Sometimes you might want to display Perl scalars containing Unicode as 445simple ASCII (or EBCDIC) text. The following subroutine converts 446its argument so that Unicode characters with code points greater than 447255 are displayed as C<\x{...}>, control characters (like C<\n>) are 448displayed as C<\x..>, and the rest of the characters as themselves: 449 450 sub nice_string { 451 join("", 452 map { $_ > 255 ? # if wide character... 453 sprintf("\\x{%04X}", $_) : # \x{...} 454 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... 455 sprintf("\\x%02X", $_) : # \x.. 456 quotemeta(chr($_)) # else quoted or as themselves 457 } unpack("U*", $_[0])); # unpack Unicode characters 458 } 459 460For example, 461 462 nice_string("foo\x{100}bar\n") 463 464returns the string 465 466 'foo\x{0100}bar\x0A' 467 468which is ready to be printed. 469 470=head2 Special Cases 471 472=over 4 473 474=item * 475 476Bit Complement Operator ~ And vec() 477 478The bit complement operator C<~> may produce surprising results if 479used on strings containing characters with ordinal values above 480255. In such a case, the results are consistent with the internal 481encoding of the characters, but not with much else. So don't do 482that. Similarly for C<vec()>: you will be operating on the 483internally-encoded bit patterns of the Unicode characters, not on 484the code point values, which is very probably not what you want. 485 486=item * 487 488Peeking At Perl's Internal Encoding 489 490Normal users of Perl should never care how Perl encodes any particular 491Unicode string (because the normal ways to get at the contents of a 492string with Unicode--via input and output--should always be via 493explicitly-defined I/O layers). But if you must, there are two 494ways of looking behind the scenes. 495 496One way of peeking inside the internal encoding of Unicode characters 497is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)> 498to display the bytes: 499 500 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 501 print join(" ", unpack("H*", pack("U", 0x100))), "\n"; 502 503Yet another way would be to use the Devel::Peek module: 504 505 perl -MDevel::Peek -e 'Dump(chr(0x100))' 506 507That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes 508and Unicode characters in C<PV>. See also later in this document 509the discussion about the C<utf8::is_utf8()> function. 510 511=back 512 513=head2 Advanced Topics 514 515=over 4 516 517=item * 518 519String Equivalence 520 521The question of string equivalence turns somewhat complicated 522in Unicode: what do you mean by "equal"? 523 524(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to 525C<LATIN CAPITAL LETTER A>?) 526 527The short answer is that by default Perl compares equivalence (C<eq>, 528C<ne>) based only on code points of the characters. In the above 529case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any 530CAPITAL LETTER As should be considered equal, or even As of any case. 531 532The long answer is that you need to consider character normalization 533and casing issues: see L<Unicode::Normalize>, Unicode Technical 534Reports #15 and #21, I<Unicode Normalization Forms> and I<Case 535Mappings>, http://www.unicode.org/unicode/reports/tr15/ and 536http://www.unicode.org/unicode/reports/tr21/ 537 538As of Perl 5.8.0, the "Full" case-folding of I<Case 539Mappings/SpecialCasing> is implemented. 540 541=item * 542 543String Collation 544 545People like to see their strings nicely sorted--or as Unicode 546parlance goes, collated. But again, what do you mean by collate? 547 548(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after 549C<LATIN CAPITAL LETTER A WITH GRAVE>?) 550 551The short answer is that by default, Perl compares strings (C<lt>, 552C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the 553characters. In the above case, the answer is "after", since 554C<0x00C1> > C<0x00C0>. 555 556The long answer is that "it depends", and a good answer cannot be 557given without knowing (at the very least) the language context. 558See L<Unicode::Collate>, and I<Unicode Collation Algorithm> 559http://www.unicode.org/unicode/reports/tr10/ 560 561=back 562 563=head2 Miscellaneous 564 565=over 4 566 567=item * 568 569Character Ranges and Classes 570 571Character ranges in regular expression character classes (C</[a-z]/>) 572and in the C<tr///> (also known as C<y///>) operator are not magically 573Unicode-aware. What this means that C<[A-Za-z]> will not magically start 574to mean "all alphabetic letters"; not that it does mean that even for 5758-bit characters, you should be using C</[[:alpha:]]/> in that case. 576 577For specifying character classes like that in regular expressions, 578you can use the various Unicode properties--C<\pL>, or perhaps 579C<\p{Alphabetic}>, in this particular case. You can use Unicode 580code points as the end points of character ranges, but there is no 581magic associated with specifying a certain range. For further 582information--there are dozens of Unicode character classes--see 583L<perlunicode>. 584 585=item * 586 587String-To-Number Conversions 588 589Unicode does define several other decimal--and numeric--characters 590besides the familiar 0 to 9, such as the Arabic and Indic digits. 591Perl does not support string-to-number conversion for digits other 592than ASCII 0 to 9 (and ASCII a to f for hexadecimal). 593 594=back 595 596=head2 Questions With Answers 597 598=over 4 599 600=item * 601 602Will My Old Scripts Break? 603 604Very probably not. Unless you are generating Unicode characters 605somehow, old behaviour should be preserved. About the only behaviour 606that has changed and which could start generating Unicode is the old 607behaviour of C<chr()> where supplying an argument more than 255 608produced a character modulo 255. C<chr(300)>, for example, was equal 609to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH 610BREVE. 611 612=item * 613 614How Do I Make My Scripts Work With Unicode? 615 616Very little work should be needed since nothing changes until you 617generate Unicode data. The most important thing is getting input as 618Unicode; for that, see the earlier I/O discussion. 619 620=item * 621 622How Do I Know Whether My String Is In Unicode? 623 624You shouldn't care. No, you really shouldn't. No, really. If you 625have to care--beyond the cases described above--it means that we 626didn't get the transparency of Unicode quite right. 627 628Okay, if you insist: 629 630 print utf8::is_utf8($string) ? 1 : 0, "\n"; 631 632But note that this doesn't mean that any of the characters in the 633string are necessary UTF-8 encoded, or that any of the characters have 634code points greater than 0xFF (255) or even 0x80 (128), or that the 635string has any characters at all. All the C<is_utf8()> does is to 636return the value of the internal "utf8ness" flag attached to the 637C<$string>. If the flag is off, the bytes in the scalar are interpreted 638as a single byte encoding. If the flag is on, the bytes in the scalar 639are interpreted as the (multi-byte, variable-length) UTF-8 encoded code 640points of the characters. Bytes added to an UTF-8 encoded string are 641automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars 642are merged (double-quoted interpolation, explicit concatenation, and 643printf/sprintf parameter substitution), the result will be UTF-8 encoded 644as if copies of the byte strings were upgraded to UTF-8: for example, 645 646 $a = "ab\x80c"; 647 $b = "\x{100}"; 648 print "$a = $b\n"; 649 650the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but 651C<$a> will stay byte-encoded. 652 653Sometimes you might really need to know the byte length of a string 654instead of the character length. For that use either the 655C<Encode::encode_utf8()> function or the C<bytes> pragma and its only 656defined function C<length()>: 657 658 my $unicode = chr(0x100); 659 print length($unicode), "\n"; # will print 1 660 require Encode; 661 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 662 use bytes; 663 print length($unicode), "\n"; # will also print 2 664 # (the 0xC4 0x80 of the UTF-8) 665 666=item * 667 668How Do I Detect Data That's Not Valid In a Particular Encoding? 669 670Use the C<Encode> package to try converting it. 671For example, 672 673 use Encode 'encode_utf8'; 674 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { 675 # valid 676 } else { 677 # invalid 678 } 679 680For UTF-8 only, you can use: 681 682 use warnings; 683 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); 684 685If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> 686warning is produced. The "U0" means "expect strictly UTF-8 encoded 687Unicode". Without that the C<unpack("U*", ...)> would accept also 688data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier. 689 690=item * 691 692How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? 693 694This probably isn't as useful as you might think. 695Normally, you shouldn't need to. 696 697In one sense, what you are asking doesn't make much sense: encodings 698are for characters, and binary data are not "characters", so converting 699"data" into some encoding isn't meaningful unless you know in what 700character set and encoding the binary data is in, in which case it's 701not just binary data, now is it? 702 703If you have a raw sequence of bytes that you know should be 704interpreted via a particular encoding, you can use C<Encode>: 705 706 use Encode 'from_to'; 707 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 708 709The call to C<from_to()> changes the bytes in C<$data>, but nothing 710material about the nature of the string has changed as far as Perl is 711concerned. Both before and after the call, the string C<$data> 712contains just a bunch of 8-bit bytes. As far as Perl is concerned, 713the encoding of the string remains as "system-native 8-bit bytes". 714 715You might relate this to a fictional 'Translate' module: 716 717 use Translate; 718 my $phrase = "Yes"; 719 Translate::from_to($phrase, 'english', 'deutsch'); 720 ## phrase now contains "Ja" 721 722The contents of the string changes, but not the nature of the string. 723Perl doesn't know any more after the call than before that the 724contents of the string indicates the affirmative. 725 726Back to converting data. If you have (or want) data in your system's 727native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use 728pack/unpack to convert to/from Unicode. 729 730 $native_string = pack("C*", unpack("U*", $Unicode_string)); 731 $Unicode_string = pack("U*", unpack("C*", $native_string)); 732 733If you have a sequence of bytes you B<know> is valid UTF-8, 734but Perl doesn't know it yet, you can make Perl a believer, too: 735 736 use Encode 'decode_utf8'; 737 $Unicode = decode_utf8($bytes); 738 739You can convert well-formed UTF-8 to a sequence of bytes, but if 740you just want to convert random binary data into UTF-8, you can't. 741B<Any random collection of bytes isn't well-formed UTF-8>. You can 742use C<unpack("C*", $string)> for the former, and you can create 743well-formed Unicode data by C<pack("U*", 0xff, ...)>. 744 745=item * 746 747How Do I Display Unicode? How Do I Input Unicode? 748 749See http://www.alanwood.net/unicode/ and 750http://www.cl.cam.ac.uk/~mgk25/unicode.html 751 752=item * 753 754How Does Unicode Work With Traditional Locales? 755 756In Perl, not very well. Avoid using locales through the C<locale> 757pragma. Use only one or the other. But see L<perlrun> for the 758description of the C<-C> switch and its environment counterpart, 759C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, 760for example by using locale settings. 761 762=back 763 764=head2 Hexadecimal Notation 765 766The Unicode standard prefers using hexadecimal notation because 767that more clearly shows the division of Unicode into blocks of 256 characters. 768Hexadecimal is also simply shorter than decimal. You can use decimal 769notation, too, but learning to use hexadecimal just makes life easier 770with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, 771for example. 772 773The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> 774a-f (or A-F, case doesn't matter). Each hexadecimal digit represents 775four bits, or half a byte. C<print 0x..., "\n"> will show a 776hexadecimal number in decimal, and C<printf "%x\n", $decimal> will 777show a decimal number in hexadecimal. If you have just the 778"hex digits" of a hexadecimal number, you can use the C<hex()> function. 779 780 print 0x0009, "\n"; # 9 781 print 0x000a, "\n"; # 10 782 print 0x000f, "\n"; # 15 783 print 0x0010, "\n"; # 16 784 print 0x0011, "\n"; # 17 785 print 0x0100, "\n"; # 256 786 787 print 0x0041, "\n"; # 65 788 789 printf "%x\n", 65; # 41 790 printf "%#x\n", 65; # 0x41 791 792 print hex("41"), "\n"; # 65 793 794=head2 Further Resources 795 796=over 4 797 798=item * 799 800Unicode Consortium 801 802 http://www.unicode.org/ 803 804=item * 805 806Unicode FAQ 807 808 http://www.unicode.org/unicode/faq/ 809 810=item * 811 812Unicode Glossary 813 814 http://www.unicode.org/glossary/ 815 816=item * 817 818Unicode Useful Resources 819 820 http://www.unicode.org/unicode/onlinedat/resources.html 821 822=item * 823 824Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications 825 826 http://www.alanwood.net/unicode/ 827 828=item * 829 830UTF-8 and Unicode FAQ for Unix/Linux 831 832 http://www.cl.cam.ac.uk/~mgk25/unicode.html 833 834=item * 835 836Legacy Character Sets 837 838 http://www.czyborra.com/ 839 http://www.eki.ee/letter/ 840 841=item * 842 843The Unicode support files live within the Perl installation in the 844directory 845 846 $Config{installprivlib}/unicore 847 848in Perl 5.8.0 or newer, and 849 850 $Config{installprivlib}/unicode 851 852in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to 853avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) 854The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in 855Perl 5.6.1.) You can find the C<$Config{installprivlib}> by 856 857 perl "-V:installprivlib" 858 859You can explore various information from the Unicode data files using 860the C<Unicode::UCD> module. 861 862=back 863 864=head1 UNICODE IN OLDER PERLS 865 866If you cannot upgrade your Perl to 5.8.0 or later, you can still 867do some Unicode processing by using the modules C<Unicode::String>, 868C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. 869If you have the GNU recode installed, you can also use the 870Perl front-end C<Convert::Recode> for character conversions. 871 872The following are fast conversions from ISO 8859-1 (Latin-1) bytes 873to UTF-8 bytes and back, the code works even with older Perl 5 versions. 874 875 # ISO 8859-1 to UTF-8 876 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; 877 878 # UTF-8 to ISO 8859-1 879 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; 880 881=head1 SEE ALSO 882 883L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, 884L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>, 885L<Unicode::UCD> 886 887=head1 ACKNOWLEDGMENTS 888 889Thanks to the kind readers of the perl5-porters@perl.org, 890perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org 891mailing lists for their valuable feedback. 892 893=head1 AUTHOR, COPYRIGHT, AND LICENSE 894 895Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt> 896 897This document may be distributed under the same terms as Perl itself. 898