PERLUNIINTRO(1) Perl Programmers Reference Guide PERLUNIINTRO(1)NAMEperluniintro - Perl Unicode introduction
DESCRIPTION
This document gives a general idea of Unicode and how to use
Unicode in Perl.
Unicode
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 sys-
tems 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.
Unicode 1.0 was released in October 1991, and 4.0 in April
2003.
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 char-
acters, 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 norma-
tive name of the character.
Unicode also defines various properties for the characters,
like "uppercase" or "lowercase", "decimal digit", or "punc-
tuation"; these properties are independent of the names of
the characters. Furthermore, various operations on the char-
acters like uppercasing, lowercasing, and collating (sort-
ing) are defined.
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A Unicode character consists either of a single code point,
or a base character (like "LATIN CAPITAL LETTER A"), fol-
lowed 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 "charac-
ters" depends on your point of view. If you are a program-
mer, 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 char-
acter". 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 (July 1996), Unicode has been defined all the
way up to 21 bits (0x10FFFF), and since Unicode 3.1 (March
2001), 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 (yes,
seventeen) planes in all were defined--but they are nowhere
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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 char-
acters 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 charac-
ters 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 or serialised 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 perlun-
icode.
Perl's Unicode Support
Starting from Perl 5.6.0, Perl has had the capacity to han-
dle Unicode natively. Perl 5.8.0, however, is the first
recommended release for serious Unicode work. The mainte-
nance release 5.6.1 fixed many of the problems of the ini-
tial Unicode implementation, but for example regular expres-
sions 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.
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Perl's Unicode Model
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. Other-
wise, 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"'
produces a fairly useless mixture of native bytes and UTF-8,
as well as a warning:
Wide character in print at ...
To output UTF-8, use the ":utf8" output layer. Prepending
binmode(STDOUT, ":utf8");
to this sample program ensures that the output is completely
UTF-8, and removes the program's warning.
You can enable automatic UTF-8-ification of your standard
file handles, default "open()" layer, and @ARGV by using
either the "-C" command line switch or the "PERL_UNICODE"
environment variable, see perlrun for the documentation of
the "-C" switch.
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.
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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".
Unicode and EBCDIC
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".
Creating Unicode
To create Unicode characters in literals for code points
above 0xFF, use the "\x{...}" notation in double-quoted
strings:
my $smiley = "\x{263a}";
Similarly, it can be used in regular expression literals
$smiley =~ /\x{263a}/;
At run-time you can use "chr()":
my $hebrew_alef = chr(0x05d0);
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()".
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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}";
And, as mentioned above, you can also "pack()" numbers into
Unicode characters:
my $georgian_an = pack("U", 0x10a0);
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()".
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("U0C*", 0x80, 0x42);
Likewise, you can force the result to be bytes by using the
special "C0" prefix.
Handling Unicode
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 perlun-
icode and perlretut).
Note that Perl considers combining character sequences to be
separate characters, so for example
use charnames ':full';
print length("\N{LATIN CAPITAL LETTER A}\N{COMBINING ACUTE ACCENT}"), "\n";
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:
Legacy Encodings
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
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assumption by using the "encoding" pragma, for example
use encoding 'latin2'; # ISO 8859-2
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
use encoding;
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 'decode';
$data = decode("iso-8859-3", $data); # convert from legacy to utf-8
Unicode I/O
Normally, writing out Unicode data
print FH $some_string_with_unicode, "\n";
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";
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>;
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;
With the "open" pragma you can use the ":locale" layer
BEGIN { $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;
or you can also use the ':encoding(...)' layer
open(my $epic,'<:encoding(iso-8859-7)','iliad.greek');
my $line_of_unicode = <$epic>;
These methods install a transparent filter on the I/O stream
that converts data from the specified encoding when it is
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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 "binmode" in perlfunc.
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(iso-2022-jp)', 'text.jis');
open(my $unicode, '>:utf8', 'text.utf8');
while (<$nihongo>) { print $unicode $_ }
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 charac-
ters. "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 (which is
the default on most systems).
Displaying Unicode As Text
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", $_) : # \x..
quotemeta(chr($_)) # else quoted or as themselves
} unpack("U*", $_[0])); # unpack Unicode characters
}
For example,
nice_string("foo\x{100}bar\n")
returns the string
'foo\x{0100}bar\x0A'
which is ready to be printed.
Special Cases
+ 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 charac-
ters, but not with much else. So don't do that. Simi-
larly for "vec()": you will be operating on the
internally-encoded bit patterns of the Unicode charac-
ters, not on the code point values, which is very prob-
ably 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";
Yet another way would be to use the Devel::Peek module:
perl -MDevel::Peek -e 'Dump(chr(0x100))'
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 "utf8::is_utf8()"
function.
Advanced Topics
+ String Equivalence
The question of string equivalence turns somewhat com-
plicated 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 Normali-
zation 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 Col-
lation Algorithm
http://www.unicode.org/unicode/reports/tr10/
Miscellaneous
+ 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.
+ 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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Questions With Answers
+ 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 pro-
duced 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.
+ 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.
+ 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:
print utf8::is_utf8($string) ? 1 : 0, "\n";
But note that this doesn't mean that any of the charac-
ters 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 inter-
preted 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-UTF-8 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 $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)
+ How Do I Detect Data That's Not Valid In a Particular
Encoding?
Use the "Encode" package to try converting it. For exam-
ple,
use Encode 'decode_utf8';
if (decode_utf8($string_of_bytes_that_I_think_is_utf8)) {
# valid
} else {
# invalid
}
For UTF-8 only, you can use:
use warnings;
@chars = unpack("U0U*", $string_of_bytes_that_I_think_is_utf8);
If invalid, a "Malformed UTF-8 character (byte 0x##) in
unpack" warning is produced. The "U0" means "expect
strictly UTF-8 encoded Unicode". Without that the
"unpack("U*", ...)" would accept also data like
"chr(0xFF"), similarly to the "pack" as we saw earlier.
+ How Do I Convert Binary Data Into a Particular Encoding,
Or Vice Versa?
This probably isn't as useful as you might think. Nor-
mally, you shouldn't need to.
In one sense, what you are asking doesn't make much
sense: encodings are for characters, and binary data are
not "characters", so converting "data" into some encod-
ing isn't meaningful unless you know in what character
set and encoding the binary data is in, in which case
it's not just binary data, now is it?
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If you have a raw sequence of bytes that you know should
be interpreted via a particular encoding, you can use
"Encode":
use Encode 'from_to';
from_to($data, "iso-8859-1", "utf-8"); # from latin-1 to utf-8
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 encod-
ing 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"
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));
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 beli-
ever, too:
use Encode 'decode_utf8';
$Unicode = decode_utf8($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
"unpack("C*", $string)" for the former, and you can
create well-formed Unicode data by "pack("U*", 0xff,
...)".
+ How Do I Display Unicode? How Do I Input Unicode?
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See http://www.alanwood.net/unicode/ and
http://www.cl.cam.ac.uk/~mgk25/unicode.html
+ 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. But see
perlrun for the description of the "-C" switch and its
environment counterpart, $ENV{PERL_UNICODE} to see how
to enable various Unicode features, for example by using
locale settings.
Hexadecimal Notation
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 learn-
ing 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
Further Resources
+ Unicode Consortium
http://www.unicode.org/
+ Unicode FAQ
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http://www.unicode.org/unicode/faq/
+ Unicode Glossary
http://www.unicode.org/glossary/
+ Unicode Useful Resources
http://www.unicode.org/unicode/onlinedat/resources.html
+ Unicode and Multilingual Support in HTML, Fonts, Web
Browsers and Other Applications
http://www.alanwood.net/unicode/
+ UTF-8 and Unicode FAQ for Unix/Linux
http://www.cl.cam.ac.uk/~mgk25/unicode.html
+ Legacy Character Sets
http://www.czyborra.com/
http://www.eki.ee/letter/
+ The Unicode support files live within the Perl installa-
tion in the directory
$Config{installprivlib}/unicore
in Perl 5.8.0 or newer, and
$Config{installprivlib}/unicode
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
perl "-V:installprivlib"
You can explore various information from the Unicode
data files using the "Unicode::UCD" module.
UNICODE IN OLDER PERLS
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.
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The following are fast conversions from ISO 8859-1 (Latin-1)
bytes to UTF-8 bytes and back, 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;
SEE ALSO
perlunicode, Encode, encoding, open, utf8, bytes, perlretut,
perlrun, Unicode::Collate, Unicode::Normalize, Unicode::UCD
ACKNOWLEDGMENTS
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 feed-
back.
AUTHOR, COPYRIGHT, AND LICENSE
Copyright 2001-2002 Jarkko Hietaniemi <jhi@iki.fi>
This document may be distributed under the same terms as
Perl itself.
perl v5.8.8 2006-06-30 18
