=head3 Unicode
B<Unicode> is a character set with room for lots of characters. The ordinal
-value of a character is called a B<code point>.
+value of a character is called a B<code point>. (But in practice, the
+distinction between code point and character is blurred, so the terms often
+are used interchangeably.)
-There are many, many code points, but computers work with bytes, and a byte can
-have only 256 values. Unicode has many more characters, so you need a method
-to make these accessible.
+There are many, many code points, but computers work with bytes, and a byte has
+room for only 256 values. Unicode has many more characters than that,
+so you need a method to make these accessible.
Unicode is encoded using several competing encodings, of which UTF-8 is the
most used. In a Unicode encoding, multiple subsequent bytes can be used to
"Content-Type: text/plain; charset=UTF-8",
"Content-Length: $byte_count"
-=head2 Q and A
-
-=head3 This isn't really a Unicode tutorial, is it?
-
-No, Perl has an abstracted interface for all supported character encodings, so
-this is actually a generic C<Encode> tutorial. But many people think that
-Unicode is special and magical, and I didn't want to disappoint them, so I
-decided to call this document a Unicode tutorial.
-
-=head3 What about binary data, like images?
-
-Well, apart from a bare C<binmode $fh>, you shouldn't treat them specially.
-(The binmode is needed because otherwise Perl may convert line endings on Win32
-systems.)
-
-Be careful, though, to never combine text strings with binary strings. If you
-need text in a binary stream, encode your text strings first using the
-appropriate encoding, then join them with binary strings. See also: "What if I
-don't encode?".
-
-=head3 What about the UTF-8 flag?
-
-Please, unless you're hacking the internals, or debugging weirdness, don't
-think about the UTF-8 flag at all. That means that you very probably shouldn't
-use C<is_utf8>, C<_utf8_on> or C<_utf8_off> at all.
-
-Perl's internal format happens to be UTF-8. Unfortunately, Perl can't keep a
-secret, so everyone knows about this. That is the source of much confusion.
-It's better to pretend that the internal format is some unknown encoding,
-and that you always have to encode and decode explicitly.
-
-=head3 When should I decode or encode?
-
-Whenever you're communicating with anything that is external to your perl
-process, like a database, a text file, a socket, or another program. Even if
-the thing you're communicating with is also written in Perl.
-
-=head3 What if I don't decode?
-
-Whenever your encoded, binary string is used together with a text string, Perl
-will assume that your binary string was encoded with ISO-8859-1, also known as
-latin-1. If it wasn't latin-1, then your data is unpleasantly converted. For
-example, if it was UTF-8, the individual bytes of multibyte characters are seen
-as separate characters, and then again converted to UTF-8. Such double encoding
-can be compared to double HTML encoding (C<&gt;>), or double URI encoding
-(C<%253E>).
-
-This silent implicit decoding is known as "upgrading". That may sound
-positive, but it's best to avoid it.
-
-=head3 What if I don't encode?
-
-Your text string will be sent using the bytes in Perl's internal format. In
-some cases, Perl will warn you that you're doing something wrong, with a
-friendly warning:
-
- Wide character in print at example.pl line 2.
-
-Because the internal format is often UTF-8, these bugs are hard to spot,
-because UTF-8 is usually the encoding you wanted! But don't be lazy, and don't
-use the fact that Perl's internal format is UTF-8 to your advantage. Encode
-explicitly to avoid weird bugs, and to show to maintenance programmers that you
-thought this through.
-
-=head3 Is there a way to automatically decode or encode?
-
-If all data that comes from a certain handle is encoded in exactly the same
-way, you can tell the PerlIO system to automatically decode everything, with
-the C<encoding> layer. If you do this, you can't accidentally forget to decode
-or encode anymore, on things that use the layered handle.
-
-You can provide this layer when C<open>ing the file:
-
- open my $fh, '>:encoding(UTF-8)', $filename; # auto encoding on write
- open my $fh, '<:encoding(UTF-8)', $filename; # auto decoding on read
-
-Or if you already have an open filehandle:
-
- binmode $fh, ':encoding(UTF-8)';
-
-Some database drivers for DBI can also automatically encode and decode, but
-that is typically limited to the UTF-8 encoding, because they cheat.
-
-=head3 Cheat?! Tell me, how can I cheat?
-
-Well, because Perl's internal format is UTF-8, you can just skip the encoding
-or decoding step, and manipulate the UTF-8 flag directly.
-
-Instead of C<:encoding(UTF-8)>, you can simply use C<:utf8>. This is widely
-accepted as good behavior.
-
-Instead of C<decode> and C<encode>, you could use C<_utf8_on> and C<_utf8_off>.
-But this is, contrary to C<:utf8>, considered bad style.
-
-There are some shortcuts for oneliners; see C<-C> in L<perlrun>.
-
-=head3 What if I don't know which encoding was used?
-
-Do whatever you can to find out, and if you have to: guess. (Don't forget to
-document your guess with a comment.)
-
-You could open the document in a web browser, and change the character set or
-character encoding until you can visually confirm that all characters look the
-way they should.
-
-There is no way to reliably detect the encoding automatically, so if people
-keep sending you data without charset indication, you may have to educate them.
-
-=head3 Can I use Unicode in my Perl sources?
-
-Yes, you can! If your sources are UTF-8 encoded, you can indicate that with the
-C<use utf8> pragma.
-
- use utf8;
-
-This doesn't do anything to your input, or to your output. It only influences
-the way your sources are read. You can use Unicode in string literals, in
-identifiers (but they still have to be "word characters" according to C<\w>),
-and even in custom delimiters.
-
-=head3 Data::Dumper doesn't restore the UTF-8 flag; is it broken?
-
-No, Data::Dumper's Unicode abilities are as they should be. There have been
-some complaints that it should restore the UTF-8 flag when the data is read
-again with C<eval>. However, you should really not look at the flag, and
-nothing indicates that Data::Dumper should break this rule.
-
-Here's what happens: when Perl reads in a string literal, it sticks to 8 bit
-encoding as long as it can. (But perhaps originally it was internally encoded
-as UTF-8, when you dumped it.) When it has to give that up because other
-characters are added to the text string, it silently upgrades the string to
-UTF-8.
-
-If you properly encode your strings for output, none of this is of your
-concern, and you can just C<eval> dumped data as always.
-
-=head3 How can I determine if a string is a text string or a binary string?
-
-You can't. Some use the UTF-8 flag for this, but that's misuse, and makes well
-behaved modules like Data::Dumper look bad. The flag is useless for this
-purpose, because it's off when an 8 bit encoding (by default ISO-8859-1) is
-used to store the string.
-
-This is something you, the programmer, has to keep track of; sorry. You could
-consider adopting a kind of "Hungarian notation" to help with this.
-
-=head3 How do I convert from encoding FOO to encoding BAR?
-
-By first converting the FOO-encoded byte string to a text string, and then the
-text string to a BAR-encoded byte string:
-
- my $text_string = decode('FOO', $foo_string);
- my $bar_string = encode('BAR', $text_string);
-
-or by skipping the text string part, and going directly from one binary
-encoding to the other:
-
- use Encode qw(from_to);
- from_to($string, 'FOO', 'BAR'); # changes contents of $string
-
-or by letting automatic decoding and encoding do all the work:
-
- open my $foofh, '<:encoding(FOO)', 'example.foo.txt';
- open my $barfh, '>:encoding(BAR)', 'example.bar.txt';
- print { $barfh } $_ while <$foofh>;
-
-=head3 What about the C<use bytes> pragma?
-
-Don't use it. It makes no sense to deal with bytes in a text string, and it
-makes no sense to deal with characters in a byte string. Do the proper
-conversions (by decoding/encoding), and things will work out well: you get
-character counts for decoded data, and byte counts for encoded data.
-
-C<use bytes> is usually a failed attempt to do something useful. Just forget
-about it.
-
-=head3 What are C<decode_utf8> and C<encode_utf8>?
-
-These are alternate syntaxes for C<decode('utf8', ...)> and C<encode('utf8',
-...)>.
-
-=head3 What's the difference between C<UTF-8> and C<utf8>?
-
-C<UTF-8> is the official standard. C<utf8> is Perl's way of being liberal in
-what it accepts. If you have to communicate with things that aren't so liberal,
-you may want to consider using C<UTF-8>. If you have to communicate with things
-that are too liberal, you may have to use C<utf8>. The full explanation is in
-L<Encode>.
-
-C<UTF-8> is internally known as C<utf-8-strict>. This tutorial uses UTF-8
-consistently, even where utf8 is actually used internally, because the
-distinction can be hard to make, and is mostly irrelevant.
-
-Okay, if you insist: the "internal format" is utf8, not UTF-8. (When it's not
-some other encoding.)
-
-=head3 I lost track; what encoding is the internal format really?
-
-It's good that you lost track, because you shouldn't depend on the internal
-format being any specific encoding. But since you asked: by default, the
-internal format is either ISO-8859-1 (latin-1), or utf8, depending on the
-history of the string.
-
-Perl knows how it stored the string internally, and will use that knowledge
-when you C<encode>. In other words: don't try to find out what the internal
-encoding for a certain string is, but instead just encode it into the encoding
-that you want.
-
-=head3 What character encodings does Perl support?
-
-To find out which character encodings your Perl supports, run:
-
- perl -MEncode -le "print for Encode->encodings(':all')"
-
-=head3 Which version of perl should I use?
-
-Well, if you can, upgrade to the most recent, but certainly C<5.8.1> or newer.
-This tutorial is based on the status quo as of C<5.8.7>.
-
-You should also check your modules, and upgrade them if necessary. For example,
-HTML::Entities requires version >= 1.32 to function correctly, even though the
-changelog is silent about this.
-
=head1 SUMMARY
Decode everything you receive, encode everything you send out. (If it's text
data.)
+=head1 Q and A (or FAQ)
+
+After reading this document, you ought to read L<perlunifaq> too.
+
=head1 ACKNOWLEDGEMENTS
Thanks to Johan Vromans from Squirrel Consultancy. His UTF-8 rants during the
=head1 AUTHOR
-Juerd Waalboer <juerd@cpan.org>
+Juerd Waalboer <#####@juerd.nl>
=head1 SEE ALSO
-L<perlunicode>, L<perluniintro>, L<Encode>
+L<perluni
faq>, L<perlunicode>, L<perluniintro>, L<Encode>
https://perl5.git.perl.org / perl5.git / blobdiff