perluniintro - Perl Unicode introduction
This document gives a general idea of Unicode and how to
use Unicode in Perl.
Unicode [Toc] [Back]
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. 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
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 (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 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 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
perlunicode.
Perl's Unicode Support
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'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. 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 "F}0, "F}0'
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.
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 [Toc] [Back]
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 [Toc] [Back]
To create Unicode characters in literals for code points
above 0xFF, use the ".}" notation in double-quoted
strings:
my $smiley = "}";
Similarly, it can be used in regular expression literals
$smiley =~ /}/;
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 "." (no "{}" and only two hexadecimal digits),
".}", 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 ".", ".}", or "chr()".
You can also use the "charnames" pragma to invoke characters
by name in double-quoted strings:
use charnames ':full';
my $arabic_alef = "RABIC LETTER ALEF}";
And, as mentioned above, you can also "pack()" numbers
into Unicode characters:
my $georgian_an = pack("U", 0x10a0);
Note that both ".}" and ".}" 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 [Toc] [Back]
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 separate characters, so for example
use charnames ':full';
print length("ATIN CAPITAL LETTER A}OMBINING ACUTE ACCENT}"), "0;
will print 2, not 1. The only exception is that regular
expressions have "
sequence.
Life is not quite so transparent, however, when working
with legacy encodings, I/O, and certain special cases:
Legacy Encodings [Toc] [Back]
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
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, "0;
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)");
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), "0;
close X;
open Y, "<file";
printf "%#x0, 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 "%#x0, ord(<I>), "0; # 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 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 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;
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 [Toc] [Back]
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
".}", control characters (like "0) are displayed as
".", and the rest of the characters as themselves:
sub nice_string {
join("",
map { $_ > 255 ? # if wide character...
sprintf("\x{%04X}", $_) : # .}
chr($_) =~ /[[:cntrl:]]/ ? # else if control character ...
sprintf("\x%02X", $_) : # .
quotemeta(chr($_)) # else quoted
or as themselves
} unpack("U*", $_[0])); # unpack Unicode characters
}
For example,
nice_string("foobar0)
returns the string
'foobarA'
which is ready to be printed.
Special Cases [Toc] [Back]
o 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.
o 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))),
"0;
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 [Toc] [Back]
o 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.uni-
code.org/unicode/reports/tr15/ and http://www.uni-
code.org/unicode/reports/tr21/
As of Perl 5.8.0, the "Full" case-folding of Case Map-
pings/SpecialCasing is implemented.
o 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.uni-
code.org/unicode/reports/tr10/
Miscellaneous
o 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--"L",
or perhaps "{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.
o 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).
Questions With Answers [Toc] [Back]
o 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.
o 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.
o 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, "0;
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-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 = "ab0c";
$b = "";
print "$a = $b0;
the output string will be UTF-8-encoded "ab0c =
0, 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), "0; # will print 1
require Encode;
print length(Encode::encode_utf8($unicode)), "0; #
will print 2
use bytes;
print length($unicode), "0; # will also print 2
# (the 0xC4 0x80 of
the UTF-8)
o 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 '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*",
$string_of_bytes_that_I_think_is_utf8);
If invalid, a "Malformed UTF-8 character (byte 0x##)
in unpack" warning is produced. The "U0" means "expect
strictly UTF-8 encoded Unicode". Without that the
"unpack("U*", ...)" would accept also data like
"chr(0xFF"), similarly to the "pack" as we saw earlier.
o How Do I Convert Binary Data Into a Particular Encoding,
Or Vice Versa?
This probably isn't as useful as you might think.
Normally, you shouldn't need to.
In one sense, what you are asking doesn't make much
sense: encodings are for characters, and binary data
are not "characters", so converting "data" into some
encoding isn't meaningful unless you know in what
character set and encoding the binary data is in, in
which case it's not just binary data, now is it?
If you have a raw sequence of bytes that you know
should be interpreted via a particular encoding, you
can use "Encode":
use Encode 'from_to';
from_to($data, "iso-8859-1", "utf-8"); # from
latin-1 to utf-8
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"
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 believer, 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,
...)".
o 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
o 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 [Toc] [Back]
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..., "0" will show a hexadecimal number in decimal,
and "printf "%x0, $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, "0; # 9
print 0x000a, "0; # 10
print 0x000f, "0; # 15
print 0x0010, "0; # 16
print 0x0011, "0; # 17
print 0x0100, "0; # 256
print 0x0041, "0; # 65
printf "%x0, 65; # 41
printf "%#x0, 65; # 0x41
print hex("41"), "0; # 65
Further Resources [Toc] [Back]
o Unicode Consortium
http://www.unicode.org/
o Unicode FAQ
http://www.unicode.org/unicode/faq/
o Unicode Glossary
http://www.unicode.org/glossary/
o Unicode Useful Resources
http://www.unicode.org/unicode/onlinedat/re-
sources.html
o Unicode and Multilingual Support in HTML, Fonts, Web
Browsers and Other Applications
http://www.alanwood.net/unicode/
o UTF-8 and Unicode FAQ for Unix/Linux
http://www.cl.cam.ac.uk/~mgk25/unicode.html
o Legacy Character Sets
http://www.czyborra.com/
http://www.eki.ee/letter/
o The Unicode support files live within the Perl
installation 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 [Toc] [Back] 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 and back, the code works
even with older Perl 5 versions.
# ISO 8859-1 to UTF-8
s/([0-])/chr(0xC0|ord($1)>>6).chr(0x80|ord($1)&0x3F)/eg;
# UTF-8 to ISO 8859-1
s/([)([0-])/chr(ord($1)<<6&0xC0|ord($2)&0x3F)/eg;
perlunicode, Encode, encoding, open, utf8, bytes, perlretut,
perlrun, Unicode::Collate, Unicode::Normalize, Unicode::UCD
Thanks to the kind readers of the [email protected],
[email protected], [email protected], and uni[email protected] mailing lists for their valuable feedback.
AUTHOR, COPYRIGHT, AND LICENSE
Copyright 2001-2002 Jarkko Hietaniemi <[email protected]>
This document may be distributed under the same terms as
Perl itself.
perl v5.8.5 2002-11-06 17 [ Back ] |
