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perluniintro - Perl Unicode introduction
This document gives a general idea of Unicode and how to use Unicode in Perl.
Unicode is a character set standard which plans to codify all of the writing systems of the
world, plus many other symbols.
Unicode and ISO/IEC 10646 are coordinated standards that provide code points for characters
in almost all modern character set standards, covering more than 30 writing systems and
hundreds of languages, including all commercially-important modern languages. All characters
in the largest Chinese, Japanese, and Korean dictionaries are also encoded. The standards will
eventually cover almost all characters in more than 250 writing systems and thousands of
languages.
A Unicode character is an abstract entity. It is not bound to any particular integer
width, especially not to the C language char. Unicode is language-neutral and
display-neutral: it does not encode the language of the text and it does not define fonts or
other graphical layout details. Unicode operates on characters and on text built from those
characters.
Unicode defines characters like LATIN CAPITAL LETTER A or GREEK SMALL
LETTER ALPHA and unique numbers for the characters, in this case 0x0041 and 0x03B1,
respectively. These unique numbers are called code points.
The Unicode standard prefers using hexadecimal notation for the code points. If numbers
like 0x0041 are unfamiliar to you, take a peek at a later section, /"Hexadecimal Notation". The Unicode standard uses
the notation U+0041 LATIN CAPITAL LETTER A, to give the hexadecimal code point
and the normative name of the character.
Unicode also defines various properties for the characters, like
"uppercase" or "lowercase", "decimal digit", or
"punctuation"; these properties are independent of the names of the characters.
Furthermore, various operations on the characters like uppercasing, lowercasing, and collating
(sorting) are defined.
A Unicode character consists either of a single code point, or a base character
(like LATIN CAPITAL LETTER A), followed by one or more modifiers (like COMBINING
ACUTE ACCENT). This sequence of base character and modifiers is called a combining
character sequence.
Whether to call these combining character sequences "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, or "character". The whole sequence could be seen as one
"character", however, from the user's point of view, since that's probably what it
looks like in the context of the user's language.
With this "whole sequence" view of characters, the total 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. In this document, we take that second
point of view: one "character" is one Unicode code point, be it a base character or
a combining character.
For some combinations, there are precomposed characters. LATIN CAPITAL LETTER
A WITH ACUTE, for example, is defined as a single code point. These precomposed
characters are, however, only available for some combinations, and are mainly meant to support
round-trip conversions between Unicode and legacy standards (like the ISO 8859). In the
general case, the composing method is more extensible. To support conversion between different
compositions of the characters, various normalization forms to standardize
representations are also defined.
Because of backward compatibility with legacy encodings, the "a unique number for
every character" idea breaks down a bit: instead, there is "at least one number for
every character". The same character could be represented differently in several legacy
encodings. The converse is also not true: some code points do not have an assigned character.
Firstly, there are unallocated code points within otherwise used blocks. Secondly, there are
special Unicode control characters that do not represent true characters.
A common myth about Unicode is that it would be "16-bit", that is, Unicode is
only represented as 0x10000 (or 65536) characters from 0x0000 to 0xFFFF.
This is untrue. Since Unicode 2.0, Unicode has been defined all the way up to 21 bits (0x10FFFF),
and since Unicode 3.1, characters have been defined beyond 0xFFFF. The first 0x10000
characters are called the Plane 0, or the Basic Multilingual Plane (BMP). With
Unicode 3.1, 17 planes in all are defined--but nowhere near full of defined characters, yet.
Another myth is that the 256-character blocks have something to do with languages--that
each block would define the characters used by a language or a set of languages. This is
also untrue. The division into blocks exists, but it is almost completely accidental--an
artifact of how the characters have been and still are allocated. Instead, there is a concept
called scripts, which is more useful: there is Latin script, Greek
script, and so on. Scripts usually span varied parts of several blocks. For further
information see Unicode::UCD.
The Unicode code points are just abstract numbers. To input and output these abstract
numbers, the numbers must be encoded somehow. Unicode defines several character
encoding forms, of which 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 include UTF-16 and UTF-32 and their big- and little-endian
variants (UTF-8 is byte-order independent) The ISO/IEC 10646 defines the UCS-2 and UCS-4
encoding forms.
For more information about encodings--for instance, to learn what surrogates and byte
order marks (BOMs) are--see perlunicode.
Starting from Perl 5.6.0, Perl has had the capacity to handle Unicode natively. Perl 5.8.0,
however, is the first recommended release for serious Unicode work. The maintenance release
5.6.1 fixed many of the problems of the initial Unicode implementation, but for example
regular expressions still do not work with Unicode in 5.6.1.
Starting from Perl 5.8.0, the use of use utf8 is no longer necessary.
In earlier releases the utf8 pragma was used to declare 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, instead of being attached to
the operations. Only one case remains where an explicit use utf8 is needed: if
your Perl script itself is encoded in UTF-8, you can use UTF-8 in your identifier names, and
in string and regular expression literals, by saying use utf8. This is not the
default because scripts with legacy 8-bit data in them would break. See utf8.
Perl supports both pre-5.6 strings of eight-bit native bytes, and strings of Unicode
characters. The principle is that Perl tries to keep its data as eight-bit bytes for as long
as possible, but as soon as Unicodeness cannot be avoided, the data is transparently upgraded
to Unicode.
Internally, Perl currently uses either whatever the native eight-bit character set of the
platform (for example Latin-1) is, defaulting to UTF-8, to encode Unicode strings.
Specifically, if all code points in the string are 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 encode its
internal strings, but it becomes relevant when outputting Unicode strings to a stream without
a PerlIO layer -- one with the "default" encoding. In such a case, the raw bytes
used internally (the native character set or UTF-8, as appropriate for each string) will be
used, and a "Wide character" warning will be issued if those strings contain a
character beyond 0x00FF.
For example,
perl -e 'print "\x{DF}\n", "\x{0100}\x{DF}\n"'
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produces a fairly useless mixture of native bytes and UTF-8, as well as a warning:
Wide character in print at ...
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To output UTF-8, use the :utf8 output layer. Prepending
binmode(STDOUT, ":utf8");
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to this sample program ensures that the output is completely UTF-8, and removes the
program's warning.
If your locale environment variables (LANGUAGE, LC_ALL, LC_CTYPE,
LANG) contain the strings 'UTF-8' or 'UTF8', regardless of case, then the default
encoding of your STDIN, STDOUT, and STDERR and of any subsequent file open, is UTF-8.
Note that this means that Perl expects other software to work, too: if Perl has been led to
believe that STDIN should be UTF-8, but then STDIN coming in from another command is not
UTF-8, Perl will complain about the malformed UTF-8.
All features that combine Unicode and I/O also require using the new PerlIO feature. Almost
all Perl 5.8 platforms do use PerlIO, though: you can see whether yours is by running "perl
-V" and looking for useperlio=define.
Perl 5.8.0 also supports Unicode on EBCDIC platforms. There, Unicode support is somewhat
more complex to implement since additional conversions are needed at every step. Some problems
remain, see perlebcdic for
details.
In any case, the Unicode support on EBCDIC platforms 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, while UTF-EBCDIC is
"EBCDIC-safe".
To create Unicode characters in literals for code points above 0xFF, use the \x{...}
notation in double-quoted strings:
Similarly, it can be used in regular expression literals
At run-time you can use chr():
my $hebrew_alef = chr(0x05d0);
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See /"Further Resources" for how to find all
these numeric codes.
Naturally, ord() will do the reverse: it turns a character into a code point.
Note that \x.. (no {} and only two hexadecimal digits), \x{...},
and 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 pack("U", ...)
instead of \x.., \x{...}, or chr().
You can also use the charnames pragma to invoke characters by name in
double-quoted strings:
use charnames ':full';
my $arabic_alef = "\N{ARABIC LETTER ALEF}";
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And, as mentioned above, you can also pack() numbers into Unicode characters:
my $georgian_an = pack("U", 0x10a0);
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Note that both \x{...} and \N{...} are compile-time string
constants: you cannot use variables in them. if you want similar run-time functionality, use chr()
and charnames::vianame().
Also note that if all the code points for pack "U" are below 0x100, bytes will be
generated, just like if you were using chr().
my $bytes = pack("U*", 0x80, 0xFF);
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If you want to force the result to Unicode characters, use the special "U0"
prefix. It consumes no arguments but forces the result to be in Unicode characters, instead of
bytes.
my $chars = pack("U0U*", 0x80, 0xFF);
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Handling Unicode is for the most part transparent: just use the strings as usual. Functions
like index(), length(), and substr() will work on the
Unicode characters; regular expressions will work on the Unicode characters (see perlunicode and perlretut).
Note that Perl considers combining character sequences to be characters, so for example
use charnames ':full';
print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
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will print 2, not 1. The only exception is that regular expressions have \X
for matching a combining character sequence.
Life is not quite so transparent, however, when working with legacy encodings, I/O, and
certain special cases:
When you combine legacy data and Unicode the legacy data needs to be upgraded to Unicode.
Normally ISO 8859-1 (or EBCDIC, if applicable) is assumed. You can override this assumption by
using the encoding pragma, for example
use encoding 'latin2'; # ISO 8859-2
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in which case literals (string or regular expressions), chr(), and ord()
in your whole script are assumed to produce Unicode characters from ISO 8859-2 code points.
Note that the matching for encoding names is forgiving: instead of latin2 you
could have said Latin 2, or iso8859-2, or other variations. With
just
the environment variable PERL_ENCODING will be consulted. If that variable
isn't set, the encoding pragma will fail.
The Encode module knows about many encodings and has interfaces for doing
conversions between those encodings:
use Encode 'from_to';
from_to($data, "iso-8859-3", "utf-8"); # from legacy to utf-8
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Normally, writing out Unicode data
print FH $some_string_with_unicode, "\n";
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produces raw bytes that Perl happens to use to internally encode the Unicode string. Perl's
internal encoding 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. 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, ">:encoding(ucs2)", "file";
open FH, ">:encoding(UTF-8)", "file";
open FH, ">:encoding(shift_jis)", "file";
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and on already open streams, use binmode():
binmode(STDOUT, ":utf8");
binmode(STDOUT, ":encoding(ucs2)");
binmode(STDOUT, ":encoding(UTF-8)");
binmode(STDOUT, ":encoding(shift_jis)");
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The matching of encoding names is loose: case does not matter, and many encodings have
several aliases. Note that the :utf8 layer must always be specified exactly like
that; it is not subject to the loose matching of encoding names.
See PerlIO for the :utf8
layer, PerlIO::encoding
and Encode::PerlIO for
the :encoding() layer, and Encode::Supported for
many encodings supported by the Encode module.
Reading in a file that you know happens to be encoded in one of the Unicode or legacy
encodings does not magically turn the data into Unicode in Perl's eyes. To do that, specify
the appropriate layer when opening files
open(my $fh,'<:utf8', 'anything');
my $line_of_unicode = <$fh>;
open(my $fh,'<:encoding(Big5)', 'anything');
my $line_of_unicode = <$fh>;
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The I/O layers can also be specified more flexibly with the open pragma. See open, or look at the following
example.
use open ':utf8'; # input and output default layer will be UTF-8
open X, ">file";
print X chr(0x100), "\n";
close X;
open Y, "<file";
printf "%#x\n", ord(<Y>); # this should print 0x100
close Y;
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With the open pragma you can use the :locale layer
$ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';
# the :locale will probe the locale environment variables like LC_ALL
use open OUT => ':locale'; # russki parusski
open(O, ">koi8");
print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
close O;
open(I, "<koi8");
printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
close I;
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or you can also use the ':encoding(...)' layer
open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
my $line_of_unicode = <$epic>;
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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 open pragma affects all
the open() calls after the pragma by setting default layers. If you want to
affect only certain streams, use explicit layers directly in the open() call.
You can switch encodings on an already opened stream by using binmode(); see perlfunc/binmode.
The :locale does not currently (as of Perl 5.8.0) work with open()
and binmode(), only with the open pragma. The :utf8 and
:encoding(...) methods do work with all of open(), binmode(),
and the open pragma.
Similarly, you may use these I/O layers 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 $nihongo, '<:encoding(iso2022-jp)', 'text.jis');
open(my $unicode, '>:utf8', 'text.utf8');
while (<$nihongo>) { print $unicode }
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The naming of encodings, both by the open() and by the open
pragma, is similar to the encoding pragma in that it allows for flexible names: koi8-r
and KOI8R will both be understood.
Common encodings recognized by ISO, MIME, IANA, and various other standardisation
organisations are recognised; for a more detailed list see Encode::Supported.
read() reads characters and returns the number of characters. seek()
and tell() operate on byte counts, as do sysread() and sysseek().
Notice that because of the default behaviour of not doing any conversion upon input if
there is no default layer, it is easy to mistakenly write code that keeps on expanding a file
by repeatedly encoding the data:
# BAD CODE WARNING
open F, "file";
local $/; ## read in the whole file of 8-bit characters
$t = <F>;
close F;
open F, ">:utf8", "file";
print F $t; ## convert to UTF-8 on output
close F;
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If you run this code twice, the contents of the file will be twice UTF-8 encoded. A use
open ':utf8' would have avoided the bug, or explicitly opening also the file for
input as UTF-8.
NOTE: the :utf8 and :encoding features work only if your
Perl has been built with the new PerlIO feature.
Sometimes you might want to display Perl scalars containing Unicode as 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:
sub nice_string {
join("",
map { $_ > 255 ? # if wide character...
sprintf("\\x{%04X}", $_) : # \x{...}
chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
sprintf("\\x%02X", $_) : # \x..
chr($_) # else as themselves
} unpack("U*", $_[0])); # unpack Unicode characters
}
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For example,
nice_string("foo\x{100}bar\n")
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returns:
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Bit Complement Operator ~ And vec()
The bit complement operator ~ 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.
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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 layers). 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 unpack("C*",
... to get the bytes or unpack("H*", ...) to display the
bytes:
# this prints c4 80 for the UTF-8 bytes 0xc4 0x80
print join(" ", unpack("H*", pack("U", 0x100))), "\n";
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Yet another way would be to use the Devel::Peek module:
perl -MDevel::Peek -e 'Dump(chr(0x100))'
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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 is_utf8 function of
the Encode module.
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String Equivalence
The question of string equivalence turns somewhat complicated in Unicode: what do you
mean by "equal"?
(Is LATIN CAPITAL LETTER A WITH ACUTE equal to LATIN CAPITAL LETTER
A?)
The short answer is that by default Perl compares equivalence (eq, 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 should be considered equal, or
even As of any case.
The long answer is that you need to consider character normalization and casing issues:
see Unicode::Normalize,
Unicode Technical Reports #15 and #21, Unicode Normalization Forms and Case
Mappings, http://www.unicode.org/unicode/reports/tr15/ and http://www.unicode.org/unicode/reports/tr21/
As of Perl 5.8.0, the "Full" case-folding of Case Mappings/SpecialCasing
is implemented.
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String Collation
People like to see their strings nicely sorted--or as Unicode parlance goes, collated.
But again, what do you mean by collate?
(Does LATIN CAPITAL LETTER A WITH ACUTE come before or after LATIN
CAPITAL LETTER A WITH GRAVE?)
The short answer is that by default, Perl compares strings (lt, le,
cmp, ge, gt) based only on the code points of the
characters. In the above case, the answer is "after", since 0x00C1
> 0x00C0.
The long answer is that "it depends", and a good answer cannot be given
without knowing (at the very least) the language context. See Unicode::Collate, and
Unicode Collation Algorithm http://www.unicode.org/unicode/reports/tr10/
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Character Ranges and Classes
Character ranges in regular expression character classes (/[a-z]/) and in
the tr/// (also known as y///) operator are not magically
Unicode-aware. What this means that [A-Za-z] will not magically start to mean
"all alphabetic letters"; not that it does mean that even for 8-bit characters,
you should be using /[[:alpha:]]/ in that case.
For specifying character classes like that in regular expressions, you can use the
various Unicode properties--\pL, or perhaps \p{Alphabetic}, in
this particular case. You can use Unicode code points as the end points of character
ranges, but there is no magic associated with specifying a certain range. For further
information--there are dozens of Unicode character classes--see perlunicode.
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String-To-Number Conversions
Unicode does define several other decimal--and numeric--characters besides the familiar
0 to 9, such as the Arabic and Indic digits. Perl does not support string-to-number
conversion for digits other than ASCII 0 to 9 (and ASCII a to f for hexadecimal).
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Will My Old Scripts Break?
Very probably not. Unless you are generating Unicode characters somehow, old behaviour
should be preserved. About the only behaviour that has changed and which could start
generating Unicode is the old behaviour of chr() where supplying an argument
more than 255 produced a character modulo 255. chr(300), for example, was
equal to chr(45) or "-" (in ASCII), now it is LATIN CAPITAL LETTER
I WITH BREVE.
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How Do I Make My Scripts Work With Unicode?
Very little work should be needed since nothing changes until you generate Unicode
data. The most important thing is getting input as Unicode; for that, see the earlier I/O
discussion.
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How Do I Know Whether My String Is In Unicode?
You shouldn't care. No, you really shouldn't. No, really. If you have to care--beyond
the cases described above--it means that we didn't get the transparency of Unicode quite
right.
Okay, if you insist:
use Encode 'is_utf8';
print is_utf8($string) ? 1 : 0, "\n";
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But note that this doesn't mean that any of the characters in the string are necessary
UTF-8 encoded, or that any of the characters have code points greater than 0xFF (255) or
even 0x80 (128), or that the string has any characters at all. All the is_utf8()
does is to return the value of the internal "utf8ness" flag attached to the $string.
If the flag is off, the bytes in the scalar are interpreted as a single byte encoding. If
the flag is on, the bytes in the scalar are interpreted as the (multi-byte,
variable-length) UTF-8 encoded code points of the characters. Bytes added to an UTF-8
encoded string are automatically upgraded to UTF-8. If mixed non-UTF8 and UTF-8 scalars
are merged (double-quoted interpolation, explicit concatenation, and printf/sprintf
parameter substitution), the result will be UTF-8 encoded as if copies of the byte strings
were upgraded to UTF-8: for example,
$a = "ab\x80c";
$b = "\x{100}";
print "$a = $b\n";
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the output string will be UTF-8-encoded ab\x80c\x{100}\n, but note that $a
will stay byte-encoded.
Sometimes you might really need to know the byte length of a string instead of the
character length. For that use either the Encode::encode_utf8() function or
the bytes pragma and its only defined function length():
my $unicode = chr(0x100);
print length($unicode), "\n"; # will print 1
require Encode;
print length(Encode::encode_utf8($unicode)), "\n"; # will print 2
use bytes;
print length($unicode), "\n"; # will also print 2
# (the 0xC4 0x80 of the UTF-8)
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How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the Encode package to try converting it. For example,
use Encode 'encode_utf8';
if (encode_utf8($string_of_bytes_that_I_think_is_utf8)) {
# valid
} else {
# invalid
}
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For UTF-8 only, you can use:
use warnings;
@chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
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If invalid, a Malformed UTF-8 character (byte 0x##) in unpack warning is
produced. The "U0" means "expect strictly UTF-8 encoded Unicode".
Without that the unpack("U*", ...) would accept also data like chr(0xFF),
similarly to the pack as we saw earlier.
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How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
This probably isn't as useful as you might think. Normally, you shouldn't need to.
In one sense, what you are asking doesn't make much sense: encodings are for
characters, and binary data are not "characters", so converting "data"
into some encoding isn't meaningful unless you know in what character set and encoding the
binary data is in, in which case it's not just binary data, now is it?
If you have a raw sequence of bytes that you know should be interpreted via a
particular encoding, you can use Encode:
use Encode 'from_to';
from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
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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 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"
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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.
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));
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If you have a sequence of bytes you know is valid UTF-8, but Perl doesn't know
it yet, you can make Perl a believer, too:
use Encode 'decode_utf8';
$Unicode = decode_utf8($bytes);
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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 unpack("C*", $string) for the
former, and you can create well-formed Unicode data by pack("U*", 0xff,
...).
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How Do I Display Unicode? How Do I Input Unicode?
See http://www.alanwood.net/unicode/ and http://www.cl.cam.ac.uk/~mgk25/unicode.html
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How Does Unicode Work With Traditional Locales?
In Perl, not very well. Avoid using locales through the locale pragma. Use
only one or the other.
The Unicode standard prefers using hexadecimal notation because that more clearly shows the
division of Unicode into blocks of 256 characters. Hexadecimal is also simply shorter than
decimal. You can use decimal notation, too, but learning to use hexadecimal just makes life
easier with the Unicode standard. The U+HHHH notation uses hexadecimal, for
example.
The 0x prefix means a hexadecimal number, the digits are 0-9 and a-f
(or A-F, case doesn't matter). Each hexadecimal digit represents four bits, or half a byte. print
0x..., "\n" will show a hexadecimal number in decimal, and printf
"%x\n", $decimal will show a decimal number in hexadecimal. If you have just
the "hex digits" of a hexadecimal number, you can use the hex()
function.
print 0x0009, "\n"; # 9
print 0x000a, "\n"; # 10
print 0x000f, "\n"; # 15
print 0x0010, "\n"; # 16
print 0x0011, "\n"; # 17
print 0x0100, "\n"; # 256
print 0x0041, "\n"; # 65
printf "%x\n", 65; # 41
printf "%#x\n", 65; # 0x41
print hex("41"), "\n"; # 65
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Unicode Consortium
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Unicode FAQ
http://www.unicode.org/unicode/faq/
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Unicode Glossary
http://www.unicode.org/glossary/
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Unicode Useful Resources
http://www.unicode.org/unicode/onlinedat/resources.html
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Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
http://www.alanwood.net/unicode/
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UTF-8 and Unicode FAQ for Unix/Linux
http://www.cl.cam.ac.uk/~mgk25/unicode.html
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Legacy Character Sets
http://www.czyborra.com/
http://www.eki.ee/letter/
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The Unicode support files live within the Perl installation in the directory
$Config{installprivlib}/unicore
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in Perl 5.8.0 or newer, and
$Config{installprivlib}/unicode
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in the Perl 5.6 series. (The renaming to lib/unicore was done to avoid naming
conflicts with lib/Unicode in case-insensitive filesystems.) The main Unicode data file is
UnicodeData.txt (or Unicode.301 in Perl 5.6.1.) You can find the $Config{installprivlib}
by
You can explore various information from the Unicode data files using the Unicode::UCD
module.
If you cannot upgrade your Perl to 5.8.0 or later, you can still do some Unicode processing
by using the modules Unicode::String, Unicode::Map8, and Unicode::Map,
available from CPAN. If you have the GNU recode installed, you can also use the Perl front-end
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;
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perlunicode, Encode, encoding, open, utf8, bytes, perlretut, Unicode::Collate, Unicode::Normalize, Unicode::UCD
Thanks to the kind readers of the perl5-porters@perl.org, perl-unicode@perl.org,
linux-utf8@nl.linux.org, and unicore@unicode.org mailing lists for their valuable feedback.
Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
This document may be distributed under the same terms as Perl itself.
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