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 249If you want to force the result to Unicode characters, use the special 250C<"U0"> prefix. It consumes no arguments but forces the result to be 251in Unicode characters, instead of bytes. 252 253 my $chars = pack("U0C*", 0x80, 0x42); 254 255Likewise, you can force the result to be bytes by using the special 256C<"C0"> prefix. 257 258=head2 Handling Unicode 259 260Handling Unicode is for the most part transparent: just use the 261strings as usual. Functions like C<index()>, C<length()>, and 262C<substr()> will work on the Unicode characters; regular expressions 263will work on the Unicode characters (see L<perlunicode> and L<perlretut>). 264 265Note that Perl considers combining character sequences to be 266separate characters, so for example 267 268 use charnames ':full'; 269 print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n"; 270 271will print 2, not 1. The only exception is that regular expressions 272have C<\X> for matching a combining character sequence. 273 274Life is not quite so transparent, however, when working with legacy 275encodings, I/O, and certain special cases: 276 277=head2 Legacy Encodings 278 279When you combine legacy data and Unicode the legacy data needs 280to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if 281applicable) is assumed. You can override this assumption by 282using the C<encoding> pragma, for example 283 284 use encoding 'latin2'; # ISO 8859-2 285 286in which case literals (string or regular expressions), C<chr()>, 287and C<ord()> in your whole script are assumed to produce Unicode 288characters from ISO 8859-2 code points. Note that the matching for 289encoding names is forgiving: instead of C<latin2> you could have 290said C<Latin 2>, or C<iso8859-2>, or other variations. With just 291 292 use encoding; 293 294the environment variable C<PERL_ENCODING> will be consulted. 295If that variable isn't set, the encoding pragma will fail. 296 297The C<Encode> module knows about many encodings and has interfaces 298for doing conversions between those encodings: 299 300 use Encode 'decode'; 301 $data = decode("iso-8859-3", $data); # convert from legacy to utf-8 302 303=head2 Unicode I/O 304 305Normally, writing out Unicode data 306 307 print FH $some_string_with_unicode, "\n"; 308 309produces raw bytes that Perl happens to use to internally encode the 310Unicode string. Perl's internal encoding depends on the system as 311well as what characters happen to be in the string at the time. If 312any of the characters are at code points C<0x100> or above, you will get 313a warning. To ensure that the output is explicitly rendered in the 314encoding you desire--and to avoid the warning--open the stream with 315the desired encoding. Some examples: 316 317 open FH, ">:utf8", "file"; 318 319 open FH, ">:encoding(ucs2)", "file"; 320 open FH, ">:encoding(UTF-8)", "file"; 321 open FH, ">:encoding(shift_jis)", "file"; 322 323and on already open streams, use C<binmode()>: 324 325 binmode(STDOUT, ":utf8"); 326 327 binmode(STDOUT, ":encoding(ucs2)"); 328 binmode(STDOUT, ":encoding(UTF-8)"); 329 binmode(STDOUT, ":encoding(shift_jis)"); 330 331The matching of encoding names is loose: case does not matter, and 332many encodings have several aliases. Note that the C<:utf8> layer 333must always be specified exactly like that; it is I<not> subject to 334the loose matching of encoding names. 335 336See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and 337L<Encode::PerlIO> for the C<:encoding()> layer, and 338L<Encode::Supported> for many encodings supported by the C<Encode> 339module. 340 341Reading in a file that you know happens to be encoded in one of the 342Unicode or legacy encodings does not magically turn the data into 343Unicode in Perl's eyes. To do that, specify the appropriate 344layer when opening files 345 346 open(my $fh,'<:utf8', 'anything'); 347 my $line_of_unicode = <$fh>; 348 349 open(my $fh,'<:encoding(Big5)', 'anything'); 350 my $line_of_unicode = <$fh>; 351 352The I/O layers can also be specified more flexibly with 353the C<open> pragma. See L<open>, or look at the following example. 354 355 use open ':utf8'; # input and output default layer will be UTF-8 356 open X, ">file"; 357 print X chr(0x100), "\n"; 358 close X; 359 open Y, "<file"; 360 printf "%#x\n", ord(<Y>); # this should print 0x100 361 close Y; 362 363With the C<open> pragma you can use the C<:locale> layer 364 365 BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' } 366 # the :locale will probe the locale environment variables like LC_ALL 367 use open OUT => ':locale'; # russki parusski 368 open(O, ">koi8"); 369 print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1 370 close O; 371 open(I, "<koi8"); 372 printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1 373 close I; 374 375or you can also use the C<':encoding(...)'> layer 376 377 open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); 378 my $line_of_unicode = <$epic>; 379 380These methods install a transparent filter on the I/O stream that 381converts data from the specified encoding when it is read in from the 382stream. The result is always Unicode. 383 384The L<open> pragma affects all the C<open()> calls after the pragma by 385setting default layers. If you want to affect only certain 386streams, use explicit layers directly in the C<open()> call. 387 388You can switch encodings on an already opened stream by using 389C<binmode()>; see L<perlfunc/binmode>. 390 391The C<:locale> does not currently (as of Perl 5.8.0) work with 392C<open()> and C<binmode()>, only with the C<open> pragma. The 393C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>, 394C<binmode()>, and the C<open> pragma. 395 396Similarly, you may use these I/O layers on output streams to 397automatically convert Unicode to the specified encoding when it is 398written to the stream. For example, the following snippet copies the 399contents of the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to 400the file "text.utf8", encoded as UTF-8: 401 402 open(my $nihongo, '<:encoding(iso-2022-jp)', 'text.jis'); 403 open(my $unicode, '>:utf8', 'text.utf8'); 404 while (<$nihongo>) { print $unicode $_ } 405 406The naming of encodings, both by the C<open()> and by the C<open> 407pragma, is similar to the C<encoding> pragma in that it allows for 408flexible names: C<koi8-r> and C<KOI8R> will both be understood. 409 410Common encodings recognized by ISO, MIME, IANA, and various other 411standardisation organisations are recognised; for a more detailed 412list see L<Encode::Supported>. 413 414C<read()> reads characters and returns the number of characters. 415C<seek()> and C<tell()> operate on byte counts, as do C<sysread()> 416and C<sysseek()>. 417 418Notice that because of the default behaviour of not doing any 419conversion upon input if there is no default layer, 420it is easy to mistakenly write code that keeps on expanding a file 421by repeatedly encoding the data: 422 423 # BAD CODE WARNING 424 open F, "file"; 425 local $/; ## read in the whole file of 8-bit characters 426 $t = <F>; 427 close F; 428 open F, ">:utf8", "file"; 429 print F $t; ## convert to UTF-8 on output 430 close F; 431 432If you run this code twice, the contents of the F<file> will be twice 433UTF-8 encoded. A C<use open ':utf8'> would have avoided the bug, or 434explicitly opening also the F<file> for input as UTF-8. 435 436B<NOTE>: the C<:utf8> and C<:encoding> features work only if your 437Perl has been built with the new PerlIO feature (which is the default 438on most systems). 439 440=head2 Displaying Unicode As Text 441 442Sometimes you might want to display Perl scalars containing Unicode as 443simple ASCII (or EBCDIC) text. The following subroutine converts 444its argument so that Unicode characters with code points greater than 445255 are displayed as C<\x{...}>, control characters (like C<\n>) are 446displayed as C<\x..>, and the rest of the characters as themselves: 447 448 sub nice_string { 449 join("", 450 map { $_ > 255 ? # if wide character... 451 sprintf("\\x{%04X}", $_) : # \x{...} 452 chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... 453 sprintf("\\x%02X", $_) : # \x.. 454 quotemeta(chr($_)) # else quoted or as themselves 455 } unpack("U*", $_[0])); # unpack Unicode characters 456 } 457 458For example, 459 460 nice_string("foo\x{100}bar\n") 461 462returns the string 463 464 'foo\x{0100}bar\x0A' 465 466which is ready to be printed. 467 468=head2 Special Cases 469 470=over 4 471 472=item * 473 474Bit Complement Operator ~ And vec() 475 476The bit complement operator C<~> may produce surprising results if 477used on strings containing characters with ordinal values above 478255. In such a case, the results are consistent with the internal 479encoding of the characters, but not with much else. So don't do 480that. Similarly for C<vec()>: you will be operating on the 481internally-encoded bit patterns of the Unicode characters, not on 482the code point values, which is very probably not what you want. 483 484=item * 485 486Peeking At Perl's Internal Encoding 487 488Normal users of Perl should never care how Perl encodes any particular 489Unicode string (because the normal ways to get at the contents of a 490string with Unicode--via input and output--should always be via 491explicitly-defined I/O layers). But if you must, there are two 492ways of looking behind the scenes. 493 494One way of peeking inside the internal encoding of Unicode characters 495is to use C<unpack("C*", ...> to get the bytes or C<unpack("H*", ...)> 496to display the bytes: 497 498 # this prints c4 80 for the UTF-8 bytes 0xc4 0x80 499 print join(" ", unpack("H*", pack("U", 0x100))), "\n"; 500 501Yet another way would be to use the Devel::Peek module: 502 503 perl -MDevel::Peek -e 'Dump(chr(0x100))' 504 505That shows the C<UTF8> flag in FLAGS and both the UTF-8 bytes 506and Unicode characters in C<PV>. See also later in this document 507the discussion about the C<utf8::is_utf8()> function. 508 509=back 510 511=head2 Advanced Topics 512 513=over 4 514 515=item * 516 517String Equivalence 518 519The question of string equivalence turns somewhat complicated 520in Unicode: what do you mean by "equal"? 521 522(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to 523C<LATIN CAPITAL LETTER A>?) 524 525The short answer is that by default Perl compares equivalence (C<eq>, 526C<ne>) based only on code points of the characters. In the above 527case, the answer is no (because 0x00C1 != 0x0041). But sometimes, any 528CAPITAL LETTER As should be considered equal, or even As of any case. 529 530The long answer is that you need to consider character normalization 531and casing issues: see L<Unicode::Normalize>, Unicode Technical 532Reports #15 and #21, I<Unicode Normalization Forms> and I<Case 533Mappings>, http://www.unicode.org/unicode/reports/tr15/ and 534http://www.unicode.org/unicode/reports/tr21/ 535 536As of Perl 5.8.0, the "Full" case-folding of I<Case 537Mappings/SpecialCasing> is implemented. 538 539=item * 540 541String Collation 542 543People like to see their strings nicely sorted--or as Unicode 544parlance goes, collated. But again, what do you mean by collate? 545 546(Does C<LATIN CAPITAL LETTER A WITH ACUTE> come before or after 547C<LATIN CAPITAL LETTER A WITH GRAVE>?) 548 549The short answer is that by default, Perl compares strings (C<lt>, 550C<le>, C<cmp>, C<ge>, C<gt>) based only on the code points of the 551characters. In the above case, the answer is "after", since 552C<0x00C1> > C<0x00C0>. 553 554The long answer is that "it depends", and a good answer cannot be 555given without knowing (at the very least) the language context. 556See L<Unicode::Collate>, and I<Unicode Collation Algorithm> 557http://www.unicode.org/unicode/reports/tr10/ 558 559=back 560 561=head2 Miscellaneous 562 563=over 4 564 565=item * 566 567Character Ranges and Classes 568 569Character ranges in regular expression character classes (C</[a-z]/>) 570and in the C<tr///> (also known as C<y///>) operator are not magically 571Unicode-aware. What this means that C<[A-Za-z]> will not magically start 572to mean "all alphabetic letters"; not that it does mean that even for 5738-bit characters, you should be using C</[[:alpha:]]/> in that case. 574 575For specifying character classes like that in regular expressions, 576you can use the various Unicode properties--C<\pL>, or perhaps 577C<\p{Alphabetic}>, in this particular case. You can use Unicode 578code points as the end points of character ranges, but there is no 579magic associated with specifying a certain range. For further 580information--there are dozens of Unicode character classes--see 581L<perlunicode>. 582 583=item * 584 585String-To-Number Conversions 586 587Unicode does define several other decimal--and numeric--characters 588besides the familiar 0 to 9, such as the Arabic and Indic digits. 589Perl does not support string-to-number conversion for digits other 590than ASCII 0 to 9 (and ASCII a to f for hexadecimal). 591 592=back 593 594=head2 Questions With Answers 595 596=over 4 597 598=item * 599 600Will My Old Scripts Break? 601 602Very probably not. Unless you are generating Unicode characters 603somehow, old behaviour should be preserved. About the only behaviour 604that has changed and which could start generating Unicode is the old 605behaviour of C<chr()> where supplying an argument more than 255 606produced a character modulo 255. C<chr(300)>, for example, was equal 607to C<chr(45)> or "-" (in ASCII), now it is LATIN CAPITAL LETTER I WITH 608BREVE. 609 610=item * 611 612How Do I Make My Scripts Work With Unicode? 613 614Very little work should be needed since nothing changes until you 615generate Unicode data. The most important thing is getting input as 616Unicode; for that, see the earlier I/O discussion. 617 618=item * 619 620How Do I Know Whether My String Is In Unicode? 621 622You shouldn't care. No, you really shouldn't. No, really. If you 623have to care--beyond the cases described above--it means that we 624didn't get the transparency of Unicode quite right. 625 626Okay, if you insist: 627 628 print utf8::is_utf8($string) ? 1 : 0, "\n"; 629 630But note that this doesn't mean that any of the characters in the 631string are necessary UTF-8 encoded, or that any of the characters have 632code points greater than 0xFF (255) or even 0x80 (128), or that the 633string has any characters at all. All the C<is_utf8()> does is to 634return the value of the internal "utf8ness" flag attached to the 635C<$string>. If the flag is off, the bytes in the scalar are interpreted 636as a single byte encoding. If the flag is on, the bytes in the scalar 637are interpreted as the (multi-byte, variable-length) UTF-8 encoded code 638points of the characters. Bytes added to an UTF-8 encoded string are 639automatically upgraded to UTF-8. If mixed non-UTF-8 and UTF-8 scalars 640are merged (double-quoted interpolation, explicit concatenation, and 641printf/sprintf parameter substitution), the result will be UTF-8 encoded 642as if copies of the byte strings were upgraded to UTF-8: for example, 643 644 $a = "ab\x80c"; 645 $b = "\x{100}"; 646 print "$a = $b\n"; 647 648the output string will be UTF-8-encoded C<ab\x80c = \x{100}\n>, but 649C<$a> will stay byte-encoded. 650 651Sometimes you might really need to know the byte length of a string 652instead of the character length. For that use either the 653C<Encode::encode_utf8()> function or the C<bytes> pragma and its only 654defined function C<length()>: 655 656 my $unicode = chr(0x100); 657 print length($unicode), "\n"; # will print 1 658 require Encode; 659 print length(Encode::encode_utf8($unicode)), "\n"; # will print 2 660 use bytes; 661 print length($unicode), "\n"; # will also print 2 662 # (the 0xC4 0x80 of the UTF-8) 663 664=item * 665 666How Do I Detect Data That's Not Valid In a Particular Encoding? 667 668Use the C<Encode> package to try converting it. 669For example, 670 671 use Encode 'encode_utf8'; 672 if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { 673 # valid 674 } else { 675 # invalid 676 } 677 678For UTF-8 only, you can use: 679 680 use warnings; 681 @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); 682 683If invalid, a C<Malformed UTF-8 character (byte 0x##) in unpack> 684warning is produced. The "U0" means "expect strictly UTF-8 encoded 685Unicode". Without that the C<unpack("U*", ...)> would accept also 686data like C<chr(0xFF>), similarly to the C<pack> as we saw earlier. 687 688=item * 689 690How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? 691 692This probably isn't as useful as you might think. 693Normally, you shouldn't need to. 694 695In one sense, what you are asking doesn't make much sense: encodings 696are for characters, and binary data are not "characters", so converting 697"data" into some encoding isn't meaningful unless you know in what 698character set and encoding the binary data is in, in which case it's 699not just binary data, now is it? 700 701If you have a raw sequence of bytes that you know should be 702interpreted via a particular encoding, you can use C<Encode>: 703 704 use Encode 'from_to'; 705 from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8 706 707The call to C<from_to()> changes the bytes in C<$data>, but nothing 708material about the nature of the string has changed as far as Perl is 709concerned. Both before and after the call, the string C<$data> 710contains just a bunch of 8-bit bytes. As far as Perl is concerned, 711the encoding of the string remains as "system-native 8-bit bytes". 712 713You might relate this to a fictional 'Translate' module: 714 715 use Translate; 716 my $phrase = "Yes"; 717 Translate::from_to($phrase, 'english', 'deutsch'); 718 ## phrase now contains "Ja" 719 720The contents of the string changes, but not the nature of the string. 721Perl doesn't know any more after the call than before that the 722contents of the string indicates the affirmative. 723 724Back to converting data. If you have (or want) data in your system's 725native 8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use 726pack/unpack to convert to/from Unicode. 727 728 $native_string = pack("C*", unpack("U*", $Unicode_string)); 729 $Unicode_string = pack("U*", unpack("C*", $native_string)); 730 731If you have a sequence of bytes you B<know> is valid UTF-8, 732but Perl doesn't know it yet, you can make Perl a believer, too: 733 734 use Encode 'decode_utf8'; 735 $Unicode = decode_utf8($bytes); 736 737You can convert well-formed UTF-8 to a sequence of bytes, but if 738you just want to convert random binary data into UTF-8, you can't. 739B<Any random collection of bytes isn't well-formed UTF-8>. You can 740use C<unpack("C*", $string)> for the former, and you can create 741well-formed Unicode data by C<pack("U*", 0xff, ...)>. 742 743=item * 744 745How Do I Display Unicode? How Do I Input Unicode? 746 747See http://www.alanwood.net/unicode/ and 748http://www.cl.cam.ac.uk/~mgk25/unicode.html 749 750=item * 751 752How Does Unicode Work With Traditional Locales? 753 754In Perl, not very well. Avoid using locales through the C<locale> 755pragma. Use only one or the other. But see L<perlrun> for the 756description of the C<-C> switch and its environment counterpart, 757C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features, 758for example by using locale settings. 759 760=back 761 762=head2 Hexadecimal Notation 763 764The Unicode standard prefers using hexadecimal notation because 765that more clearly shows the division of Unicode into blocks of 256 characters. 766Hexadecimal is also simply shorter than decimal. You can use decimal 767notation, too, but learning to use hexadecimal just makes life easier 768with the Unicode standard. The C<U+HHHH> notation uses hexadecimal, 769for example. 770 771The C<0x> prefix means a hexadecimal number, the digits are 0-9 I<and> 772a-f (or A-F, case doesn't matter). Each hexadecimal digit represents 773four bits, or half a byte. C<print 0x..., "\n"> will show a 774hexadecimal number in decimal, and C<printf "%x\n", $decimal> will 775show a decimal number in hexadecimal. If you have just the 776"hex digits" of a hexadecimal number, you can use the C<hex()> function. 777 778 print 0x0009, "\n"; # 9 779 print 0x000a, "\n"; # 10 780 print 0x000f, "\n"; # 15 781 print 0x0010, "\n"; # 16 782 print 0x0011, "\n"; # 17 783 print 0x0100, "\n"; # 256 784 785 print 0x0041, "\n"; # 65 786 787 printf "%x\n", 65; # 41 788 printf "%#x\n", 65; # 0x41 789 790 print hex("41"), "\n"; # 65 791 792=head2 Further Resources 793 794=over 4 795 796=item * 797 798Unicode Consortium 799 800 http://www.unicode.org/ 801 802=item * 803 804Unicode FAQ 805 806 http://www.unicode.org/unicode/faq/ 807 808=item * 809 810Unicode Glossary 811 812 http://www.unicode.org/glossary/ 813 814=item * 815 816Unicode Useful Resources 817 818 http://www.unicode.org/unicode/onlinedat/resources.html 819 820=item * 821 822Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications 823 824 http://www.alanwood.net/unicode/ 825 826=item * 827 828UTF-8 and Unicode FAQ for Unix/Linux 829 830 http://www.cl.cam.ac.uk/~mgk25/unicode.html 831 832=item * 833 834Legacy Character Sets 835 836 http://www.czyborra.com/ 837 http://www.eki.ee/letter/ 838 839=item * 840 841The Unicode support files live within the Perl installation in the 842directory 843 844 $Config{installprivlib}/unicore 845 846in Perl 5.8.0 or newer, and 847 848 $Config{installprivlib}/unicode 849 850in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to 851avoid naming conflicts with lib/Unicode in case-insensitive filesystems.) 852The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in 853Perl 5.6.1.) You can find the C<$Config{installprivlib}> by 854 855 perl "-V:installprivlib" 856 857You can explore various information from the Unicode data files using 858the C<Unicode::UCD> module. 859 860=back 861 862=head1 UNICODE IN OLDER PERLS 863 864If you cannot upgrade your Perl to 5.8.0 or later, you can still 865do some Unicode processing by using the modules C<Unicode::String>, 866C<Unicode::Map8>, and C<Unicode::Map>, available from CPAN. 867If you have the GNU recode installed, you can also use the 868Perl front-end C<Convert::Recode> for character conversions. 869 870The following are fast conversions from ISO 8859-1 (Latin-1) bytes 871to UTF-8 bytes and back, the code works even with older Perl 5 versions. 872 873 # ISO 8859-1 to UTF-8 874 s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg; 875 876 # UTF-8 to ISO 8859-1 877 s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg; 878 879=head1 SEE ALSO 880 881L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>, 882L<perlretut>, L<perlrun>, L<Unicode::Collate>, L<Unicode::Normalize>, 883L<Unicode::UCD> 884 885=head1 ACKNOWLEDGMENTS 886 887Thanks to the kind readers of the perl5-porters@perl.org, 888perl-unicode@perl.org, linux-utf8@nl.linux.org, and unicore@unicode.org 889mailing lists for their valuable feedback. 890 891=head1 AUTHOR, COPYRIGHT, AND LICENSE 892 893Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt> 894 895This document may be distributed under the same terms as Perl itself. 896