a base character and modifiers is called a I<combining character
sequence>.
-Whether to call these combining character sequences, as a whole,
-"characters" depends on your point of view. If you are a programmer, you
-probably would tend towards seeing each element in the sequences as one
-unit, one "character", but from the user viewpoint, the sequence as a
-whole is probably considered one "character", since that's probably what
-it looks like in the context of the user's language.
+Whether to call these combining character sequences, as a whole,
+"characters" depends on your point of view. If you are a programmer,
+you probably would tend towards seeing each element in the sequences
+as one unit, one "character", but from the user viewpoint, the
+sequence as a whole is probably considered one "character", since
+that's probably what it looks like in the context of the user's
+language.
With this "as a whole" view of characters, the number of characters is
-open-ended. But in the programmer's "one unit is one character" point of
-view, the concept of "characters" is more deterministic, and so we take
-that point of view in this document: one "character" is one Unicode
-code point, be it a base character or a combining character.
+open-ended. But in the programmer's "one unit is one character" point
+of view, the concept of "characters" is more deterministic, and so we
+take that point of view in this document: one "character" is one
+Unicode code point, be it a base character or a combining character.
For some of the combinations there are I<precomposed> characters,
for example C<LATIN CAPITAL LETTER A WITH ACUTE> is defined as
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
-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.)
+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.)
=head2 Perl's Unicode Model
Internally, Perl currently uses either whatever the native eight-bit
character set of the platform (for example Latin-1) or UTF-8 to encode
Unicode strings. Specifically, if all code points in the string are
-0xFF or less, Perl uses Latin-1. Otherwise, it uses UTF-8.
+0xFF or less, Perl uses the native eight-bit character set.
+Otherwise, it uses UTF-8.
A user of Perl does not normally need to know nor care how Perl happens
to encodes its internal strings, but it becomes relevant when outputting
binmode(STDOUT, ":utf8");
to this sample program ensures the output is completely UTF-8, and
-of course, removes the warning. Another way to achieve this is the
-L<encoding> pragma, discussed later in L</Legacy Encodings>.
+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,
-which didn't work much at all for EBCDIC platform). On EBCDIC
-platforms the internal encoding form used 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").
+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 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
-C<\x{...}> notation in doublequoted strings:
+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
-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()>.
+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 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
-used on strings containing Unicode characters. The results are
-consistent with the internal UTF-8 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.
+The bit complement operator C<~> may produce surprising results if used on
+strings containing characters with ordinal values above 255. In such a
+case, the results are 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 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.
(Is C<LATIN CAPITAL LETTER A WITH ACUTE> equal to
C<LATIN CAPITAL LETTER A>?)
-The short answer is that by default Perl compares equivalence
-(C<eq>, C<ne>) based only on code points of the characters.
-In the above case, the answer is no (because 0x00C1 != 0x0041). But sometimes any
+The short answer is that by default Perl compares equivalence (C<eq>,
+C<ne>) based only on code points of the characters. In the above
+case, the answer is no (because 0x00C1 != 0x0041). But sometimes any
CAPITAL LETTER As being considered equal, or even any As of any case,
would be desirable.
to mean "all alphabetic letters" (not that it does mean that even for
8-bit characters, you should be using C</[[:alpha]]/> for that).
-For specifying things like that in regular expressions, you can use the
-various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>, in this particular case. You can
-use Unicode code points as the end points of character ranges, but
-that means that particular code point range, nothing more. For
-further information, see L<perlunicode>.
+For specifying things like that in regular expressions, you can use
+the various Unicode properties, C<\pL> or perhaps C<\p{Alphabetic}>,
+in this particular case. You can use Unicode code points as the end
+points of character ranges, but that means that particular code point
+range, nothing more. For further information, see L<perlunicode>.
=item *
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:
-If you have Latin-1 (or want Latin-1), you can just use pack/unpack:
+ use Translate;
+ my $phrase = "Yes";
+ Translate::from_to($phrase, 'english', 'deutsch');
+ ## phrase now contains "Ja"
- $latin1 = pack("C*", unpack("U*", $utf8));
- $utf8 = pack("U*", unpack("C*", $latin1));
+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.
-(The same works for EBCDIC.)
+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.
+
+ $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?
four bits, or half a byte. C<print 0x..., "\n"> will show a
hexadecimal number in decimal, and C<printf "%x\n", $decimal> will
show a decimal number in hexadecimal. If you have just the
-"hexdigits" of a hexadecimal number, you can use the C<hex()>
-function.
+"hexdigits" of a hexadecimal number, you can use the C<hex()> function.
print 0x0009, "\n"; # 9
print 0x000a, "\n"; # 10
If you have the GNU recode installed, you can also use the
Perl frontend C<Convert::Recode> for character conversions.
+The following are fast conversions from ISO 8859-1 (Latin-1) bytes
+to UTF-8 bytes, the code works even with older Perl 5 versions.
+
+ # ISO 8859-1 to UTF-8
+ s/([\x80-\xFF])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
+
+ # UTF-8 to ISO 8859-1
+ s/([\xC2\xC3])([\x80-\xBF])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
+
=head1 SEE ALSO
L<perlunicode>, L<Encode>, L<encoding>, L<open>, L<utf8>, L<bytes>,
projects / p5sagit/p5-mst-13.2.git / blobdiff