From: Jeffrey Friedl Date: Tue, 18 Dec 2001 20:27:42 +0000 (-0800) Subject: pod/perluniintro.pod (removes unnecessary UTF-8 references) X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=commitdiff_plain;h=8baee56661ac73a9765e39a1fe4554b8456a582d;p=p5sagit%2Fp5-mst-13.2.git pod/perluniintro.pod (removes unnecessary UTF-8 references) Message-Id: <200112190427.fBJ4RgP53458@ventrue.corp.yahoo.com> p4raw-id: //depot/perl@13787 --- diff --git a/pod/perluniintro.pod b/pod/perluniintro.pod index c89fef3..1d4162b 100644 --- a/pod/perluniintro.pod +++ b/pod/perluniintro.pod @@ -105,7 +105,7 @@ 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 +defined characters). Other encodings include 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. @@ -126,7 +126,7 @@ 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 +Perl script itself is encoded 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.) @@ -166,24 +166,24 @@ To output UTF-8 always, use the ":utf8" output discipline. Prepending to this sample program ensures the output is completely UTF-8, and of course, removes the warning. -Perl 5.8.0 will also support Unicode on EBCDIC platforms. There the +Perl 5.8.0 also supports 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, +are needed at every step. Because of these difficulties, the Unicode +support isn't quite as full as in other, mainly ASCII-based, +platforms (the Unicode support is 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 instead +platforms, the internal Unicode encoding form is UTF-EBCDIC instead of UTF-8 (the difference is that as UTF-8 is "ASCII-safe" in that ASCII characters encode to UTF-8 as-is, UTF-EBCDIC is "EBCDIC-safe"). =head2 Creating Unicode -To create Unicode literals for code points above 0xFF, use the +To create Unicode characters in literals for code points above 0xFF, use the C<\x{...}> notation in doublequoted strings: my $smiley = "\x{263a}"; -Similarly for regular expression literals +Similarly in regular expression literals $smiley =~ /\x{263a}/; @@ -195,12 +195,13 @@ At run-time you can use C: 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 +Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>, +and C for arguments less than 0x100 (decimal 256) 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. +Perls. For arguments of 0x100 or more, Unicode characters are always +produced. If you want to force the production of Unicode characters +regardless of the numeric value, 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: @@ -264,27 +265,39 @@ for doing conversions between those encodings: =head2 Unicode I/O -Normally writing out Unicode data +Normally, writing out Unicode data - print FH chr(0x100), "\n"; + print FH $some_string_with_unicode, "\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: +produces raw bytes that Perl happens to use to internally encode the +Unicode string (which depends on the system, as well as what characters +happen to be in the string at the time). If any of the characters are at +code points 0x100 or above, you will get a warning if you use C<-w> or C. To ensure that the output is explicitly rendered in the encoding +you desire (and to avoid the warning), open the stream with the desired +encoding. Some examples: - open FH, ">:utf8", "file"; + open FH, ">:ucs2", "file" + open FH, ">:utf8", "file"; + open FH, ">:Shift-JIS", "file"; and on already open streams use C: + binmode(STDOUT, ":ucs2"); binmode(STDOUT, ":utf8"); + binmode(STDOUT, ":Shift-JIS"); -Reading in correctly formed UTF-8 data will not magically turn -the data into Unicode in Perl's eyes. +See documentation for the C module for many supported encodings. -You can use either the C<':utf8'> I/O discipline when opening files +Reading in a file that you know happens to be encoded in one of the Unicode +encodings does not magically turn the data into Unicode in Perl's eyes. +To do that, specify the appropriate discipline when opening files open(my $fh,'<:utf8', 'anything'); - my $line_of_utf8 = <$fh>; + my $line_of_unicode = <$fh>; + + open(my $fh,'<:Big5', 'anything'); + my $line_of_unicode = <$fh>; The I/O disciplines can also be specified more flexibly with the C pragma; see L: @@ -312,58 +325,58 @@ With the C pragma you can use the C<:locale> discipline or you can also use the C<':encoding(...)'> discipline open(my $epic,'<:encoding(iso-8859-7)','iliad.greek'); - my $line_of_iliad = <$epic>; + my $line_of_unicode = <$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. +These methods install a transparent filter on the I/O stream that +converts data from the specified encoding when it is read in from the +stream. The result is always 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. +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<:utf8> and C<:encoding(...)> methods 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. +Similarly, you may use these I/O disciplines on output streams to +automatically convert Unicode to the specified encoding when it is written +to the stream. For example, the following snippet copies the contents of +the file "text.jis" (encoded as ISO-2022-JP, aka JIS) to the file +"text.utf8", encoded as UTF-8: - open(my $unicode, '<:utf8', 'japanese.uni'); - open(my $nihongo, '>:encoding(iso2022-jp)', 'japanese.jp'); - while (<$unicode>) { print $nihongo } + open(my $nihongo, '<:encoding(iso2022-jp)', 'text.jis'); + open(my $unicode, '>:utf8', 'text.utf8'); + while (<$nihongo>) { print $unicode } 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 +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" +Notice that because of the default behaviour of not doing any +conversion upon input if there is no default discipline, it is easy to mistakenly write code that keeps on expanding a file -by repeatedly encoding it in UTF-8: +by repeatedly encoding: # BAD CODE WARNING open F, "file"; - local $/; # read in the whole file + local $/; ## read in the whole file of 8-bit characters $t = ; close F; open F, ">:utf8", "file"; - print F $t; + print F $t; ## convert to UTF-8 on output close F; If you run this code twice, the contents of the F will be twice @@ -378,17 +391,17 @@ 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 +simple ASCII (or EBCDIC) text. The following subroutine converts 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. +displayed as "\x..", and the rest of the characters as themselves: sub nice_string { join("", map { $_ > 255 ? # if wide character... - sprintf("\\x{%x}", $_) : # \x{...} + sprintf("\\x{%04X}", $_) : # \x{...} chr($_) =~ /[[:cntrl:]]/ ? # else if control character ... - sprintf("\\x%02x", $_) : # \x.. + sprintf("\\x%02X", $_) : # \x.. chr($_) # else as themselves } unpack("U*", $_[0])); # unpack Unicode characters } @@ -397,9 +410,9 @@ For example, nice_string("foo\x{100}bar\n") -will return: +returns: - "foo\x{100}bar\x0a" + "foo\x{0100}bar\x0A" =head2 Special Cases @@ -409,29 +422,35 @@ will return: Bit Complement Operator ~ And vec() -The bit complement operator C<~> will produce surprising results if +The bit complement operator C<~> may 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 +consistent with the internal 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. +operating on the internally encoded bit patterns of the Unicode characters, not on +the code point values, which is very probably not what you want. =item * -Peeking At UTF-8 +Peeking At Perl's Internal Encoding + +Normal users of Perl should never care how Perl encodes any particular +Unicode string (because the normal ways to get at the contents of a string +with Unicode -- via input and output -- should always be via +explicitly-defined I/O disciplines). But if you must, there are two ways of +looking behind the scenes. 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 + # this prints 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 +That shows 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. @@ -540,6 +559,26 @@ input as Unicode, and for that see the earlier I/O discussion. =item How Do I Know Whether My String Is In Unicode? + @@| Note to P5P -- I see two problems with this section. One is + @@| that Encode::is_utf8() really should be named + @@| Encode::is_Unicode(), since that's what it's telling you, + @@| isn't it? This + @@| Encode::is_utf8(pack("U"), 0xDF) + @@| returns true, even though the string being checked is + @@| internally kept in the native 8-bit encoding, but flagged as + @@| Unicode. + @@| + @@| Another problem is that yeah, I can see situations where + @@| someone wants to know if a string is Unicode, or if it's + @@| still in the native 8-bit encoding. What's wrong with that? + @@| Perhaps when this section was added, it was with the that + @@| that users don't need to care the particular encoding used + @@| internally, and that's still the case (except for efficiency + @@| issues -- reading utf8 is likely much faster than reading, + @@| say, Shift-JIS). + @@| + @@| Can is_utf8 be renamed to is_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. @@ -567,62 +606,80 @@ and its only defined function C: use bytes; print length($unicode), "\n"; # will print 2 (the 0xC4 0x80 of the UTF-8) -=item How Do I Detect Invalid UTF-8? +=item How Do I Detect Data That's Not Valid In a Particular Encoding -Either +Use the C package to try converting it. +For example, use Encode 'encode_utf8'; - if (encode_utf8($string)) { + if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) { # valid } else { # invalid } -or +For UTF-8 only, you can use: use warnings; - @chars = unpack("U0U*", "\xFF"); # will warn + @chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8); -The warning will be C. The "U0" means "expect strictly UTF-8 encoded Unicode". -Without that the C would accept also data like -C). +If invalid, a C is produced. The "U0" means "expect strictly UTF-8 +encoded Unicode". Without that the C +would accept also data like C). -=item How Do I Convert Data Into UTF-8? Or Vice Versa? +=item How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa? -This probably isn't as useful (or simple) as you might think. -Also, normally you shouldn't need to. +This probably isn't as useful as you might think. +Normally, you shouldn't need to. -In one sense what you are asking doesn't make much sense: UTF-8 is -(intended as an) Unicode encoding, so converting "data" into UTF-8 -isn't meaningful unless you know in what character set and encoding -the binary data is in, and in this case you can use C. +In one sense, what you are asking doesn't make much sense: Encodings are +for characters, and binary data is not "characters", so converting "data" +into some encoding isn't meaningful unless you know in what character set +and encoding the binary data is in, in which case it's not binary data, now +is it? + +If you have a raw sequence of bytes that you know should be interpreted via +a particular encoding, you can use C: use Encode 'from_to'; from_to($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. +The call to from_to() changes the bytes in $data, but nothing material +about the nature of the string has changed as far as Perl is concerned. +Both before and after the call, the string $data contains just a bunch of +8-bit bytes. As far as Perl is concerned, the encoding of the string (as +Perl sees it) remains as "system-native 8-bit bytes". + +You might relate this to a fictional 'Translate' module: + + use Translate; + my $phrase = "Yes"; + Translate::from_to($phrase, 'english', 'deutsch'); + ## phrase now contains "Ja" -If you have Latin-1 (or want Latin-1), you can just use pack/unpack: +The contents of the string changes, but not the nature of the string. +Perl doesn't know any more after the call than before that the contents +of the string indicates the affirmative. - $latin1 = pack("C*", unpack("U*", $utf8)); - $utf8 = pack("U*", unpack("C*", $latin1)); +Back to converting data, if you have (or want) data in your system's native +8-bit encoding (e.g. Latin-1, EBCDIC, etc.), you can use pack/unpack to +convert to/from Unicode. -(The same works for EBCDIC.) + $native_string = pack("C*", unpack("U*", $Unicode_string)); + $Unicode_string = pack("U*", unpack("C*", $native_string)); 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); + $Unicode = decode_utf8($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. +well-formed Unicode data by C. =item How Do I Display Unicode? How Do I Input Unicode?