Unicode defines several I<character encoding forms>, of which I<UTF-8>
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.
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<use utf8> 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<use utf8>. This is not the default because that would
break existing scripts having legacy 8-bit data in them.)
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}/;
Naturally, C<ord()> 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<chr(...)> for arguments less than 0x100 (decimal 256) will
+Note that C<\x..> (no C<{}> and only two hexadecimal digits), C<\x{...}>,
+and C<chr(...)> 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<pack("U", ...)> instead of
-C<\x..>, C<\x{...}>, or C<chr()>.
+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<pack("U", ...)> instead of C<\x..>,
+C<\x{...}>, or C<chr()>.
You can also use the C<charnames> pragma to invoke characters
by name in doublequoted strings:
=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<use warnings>. 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<use
+warnings>. 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()>:
+ 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<Encode> 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<open> pragma; see L<open>:
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<anything> file is assumed to be UTF-8
-encoded Unicode, in the second example the F<iliad.greek> 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<open> pragma affects all the C<open()> calls after the pragma by
setting default disciplines. If you want to affect only certain
streams, use explicit disciplines directly in the C<open()> call.
You can switch encodings on an already opened stream by using
-C<binmode()>, see L<perlfunc/binmode>.
+C<binmode()>; see L<perlfunc/binmode>.
The C<:locale> does not currently (as of Perl 5.8.0) work with
C<open()> and C<binmode()>, only with the C<open> pragma. The
-C<:utf8> and C<:encoding(...)> do work with all of C<open()>,
+C<:utf8> and C<:encoding(...)> methods do work with all of C<open()>,
C<binmode()>, and the C<open> 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<open()> and by the C<open>
pragma, is similarly understanding as with the C<encoding> pragma:
C<koi8-r> and C<KOI8R> 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<Encode>.
C<read()> reads characters and returns the number of characters.
C<seek()> and C<tell()> operate on byte counts, as do C<sysread()>
and C<sysseek()>.
-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 = <F>;
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<file> will be twice
=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
}
nice_string("foo\x{100}bar\n")
-will return:
+returns:
- "foo\x{100}bar\x0a"
+ "foo\x{0100}bar\x0A"
=head2 Special Cases
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<unpack("C*", ...> to get the bytes, or C<unpack("H*", ...)>
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<is_utf8> function of the C<Encode> module.
=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.
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<Encode> 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*", $string_of_bytes_that_I_think_is_utf8);
-The warning will be C<Malformed UTF-8 character (byte 0xff) in
-unpack>. The "U0" means "expect strictly UTF-8 encoded Unicode".
-Without that the C<unpack("U*", ...)> would accept also data like
-C<chr(0xFF>).
+If invalid, a C<Malformed UTF-8 character (byte 0x##) in
+unpack> is produced. The "U0" means "expect strictly UTF-8
+encoded Unicode". Without that the C<unpack("U*", ...)>
+would accept also data like C<chr(0xFF>).
-=item How Do I Convert Data Into UTF-8? Or Vice Versa?
+=item How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
-This probably isn't as useful (or simple) as you might think.
-Also, normally you shouldn't need to.
+This probably isn't as useful as you might think.
+Normally, you shouldn't need to.
-In one sense what you are asking doesn't make much sense: UTF-8 is
-(intended as an) Unicode encoding, so converting "data" into UTF-8
-isn't meaningful unless you know in what character set and encoding
-the binary data is in, and in this case you can use C<Encode>.
+In one sense, what you are asking doesn't make much sense: Encodings are
+for characters, and binary data is not "characters", so converting "data"
+into some encoding isn't meaningful unless you know in what character set
+and encoding the binary data is in, in which case it's not binary data, now
+is it?
+
+If you have a raw sequence of bytes that you know should be interpreted via
+a particular encoding, you can use C<Encode>:
use Encode 'from_to';
from_to($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<know> 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<unpack("C*", $string)> for the former, and you can create
-well-formed Unicode/UTF-8 data by C<pack("U*", 0xff, ...)>.
+well-formed Unicode data by C<pack("U*", 0xff, ...)>.
=item How Do I Display Unicode? How Do I Input Unicode?
projects / p5sagit/p5-mst-13.2.git / commitdiff