perluniintro - Perl Unicode introduction
This document gives a general idea of Unicode and how to use Unicode in Perl. See Further Resources for references to more in-depth treatments of 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 unify almost all other modern character set standards, covering more than 80 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 6.0 in October 2010.
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 generally 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. A code point is essentially the position of the
character within the set of all possible Unicode characters, and thus in
Perl, the term ordinal is often used interchangeably with it.
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 logical "character" can actually consist of more than one internal
actual "character" or code point. For Western languages, this is adequately
modelled by 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. Some non-western languages require more complicated
models, so Unicode created the grapheme cluster concept, which was
later further refined into the extended grapheme cluster. For
example, a Korean Hangul syllable is considered a single logical
character, but most often consists of three actual
Unicode characters: a leading consonant followed by an interior vowel followed
by a trailing consonant.
Whether to call these extended grapheme clusters "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". However from the user's point of view, the whole sequence could be seen as one "character" since that's probably what it looks like in the context of the user's language. In this document, we take the programmer's point of view: one "character" is one Unicode code point.
For some combinations of base character and modifiers, there are
precomposed characters. There is a single character equivalent, for
example, for the sequence LATIN CAPITAL LETTER A
followed by
COMBINING ACUTE ACCENT
. It is called LATIN CAPITAL LETTER A WITH
ACUTE
. 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 ISO 8859). Using
sequences, as Unicode does, allows for needing fewer basic building blocks
(code points) to express many more potential grapheme clusters. To
support conversion between equivalent forms, various normalization
forms are also defined. Thus, LATIN CAPITAL LETTER A WITH ACUTE
is
in Normalization Form Composed, (abbreviated NFC), and the sequence
LATIN CAPITAL LETTER A
followed by COMBINING ACUTE ACCENT
represents the same character in Normalization Form Decomposed (NFD).
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 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.
When Unicode was first conceived, it was thought that all the world's
characters could be represented using a 16-bit word; that is a maximum of
0x10000
(or 65,536) characters would be needed, from 0x0000
to
0xFFFF
. This soon proved to be wrong, and since Unicode 2.0 (July
1996), Unicode has been defined all the way up to 21 bits (0x10FFFF
),
and Unicode 3.1 (March 2001) defined the first characters above 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.
When a new language is being encoded, Unicode generally will choose a
block
of consecutive unallocated code points for its characters. So
far, the number of code points in these blocks has always been evenly
divisible by 16. Extras in a block, not currently needed, are left
unallocated, for future growth. But there have been occasions when
a later release needed more code points than the available extras, and a
new block had to allocated somewhere else, not contiguous to the initial
one, to handle the overflow. Thus, it became apparent early on that
"block" wasn't an adequate organizing principal, and so the Script
property was created. (Later an improved script property was added as
well, the Script_Extensions
property.) Those code points that are in
overflow blocks can still
have the same script as the original ones. The script concept fits more
closely with natural language: there is Latin
script, Greek
script, and so on; and there are several artificial scripts, like
Common
for characters that are used in multiple scripts, such as
mathematical symbols. Scripts usually span varied parts of several
blocks. For more information about scripts, see Scripts in perlunicode.
The division into blocks exists, but it is almost completely
accidental--an artifact of how the characters have been and still are
allocated. (Note that this paragraph has oversimplified things for the
sake of this being an introduction. Unicode doesn't really encode
languages, but the writing systems for them--their scripts; and one
script can be used by many languages. Unicode also encodes things that
aren't really about languages, such as symbols like BAGGAGE CLAIM
.)
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 the most popular. UTF-8 is a variable length encoding that encodes Unicode characters as 1 to 4 bytes. 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 v5.6.0, Perl has had the capacity to handle Unicode
natively. Perl v5.8.0, 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.
Perl v5.14.0 is the first release where Unicode support is
(almost) seamlessly integrable without some gotchas (the exception being
some differences in quotemeta, and that is fixed
starting in Perl 5.16.0). To enable this
seamless support, you should use feature 'unicode_strings'
(which is
automatically selected if you use 5.012
or higher). See feature.
(5.14 also fixes a number of bugs and departures from the Unicode
standard.)
Before Perl v5.8.0, the use of use utf8
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.
Starting with Perl v5.8.0, 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 general 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. Prior to Perl v5.14.0, the upgrade was not completely
transparent (see The Unicode Bug in perlunicode), and for backwards
compatibility, full transparency is not gained unless use feature
'unicode_strings'
(see feature) or use 5.012
(or higher) is
selected.
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"'
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 :encoding
or :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 the same way: 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 likely 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 added support for Unicode on EBCDIC platforms. This support was allowed to lapse in later releases, but was revived in 5.22. Unicode support is somewhat more complex to implement since additional conversions are needed. See perlebcdic for more information.
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", in that all the basic characters (which includes all
those that have ASCII equivalents (like "A"
, "0"
, "%"
, etc.)
are the same in both EBCDIC and UTF-EBCDIC. Often, documentation
will use the term "UTF-8" to mean UTF-EBCDIC as well. This is the case
in this document.
This section applies fully to Perls starting with v5.22. Various caveats for earlier releases are in the Earlier releases caveats subsection below.
To create Unicode characters in literals,
use the \N{...}
notation in double-quoted strings:
Similarly, they can be used in regular expression literals
- $smiley =~ /\N{WHITE SMILING FACE}/;
- $smiley =~ /\N{U+263a}/;
At run-time you can use:
Naturally, ord() will do the reverse: it turns a character into
a code point.
There are other runtime options as well. You can use pack():
Or you can use chr(), though it is less convenient in the general
case:
- $hebrew_alef_from_code_point = chr(utf8::unicode_to_native(0x05d0));
- utf8::upgrade($hebrew_alef_from_code_point);
The utf8::unicode_to_native()
and utf8::upgrade()
aren't needed if
the argument is above 0xFF, so the above could have been written as
- $hebrew_alef_from_code_point = chr(0x05d0);
since 0x5d0 is above 255.
\x{}
and \o{}
can also be used to specify code points at compile
time in double-quotish strings, but, for backward compatibility with
older Perls, the same rules apply as with chr() for code points less
than 256.
utf8::unicode_to_native()
is used so that the Perl code is portable
to EBCDIC platforms. You can omit it if you're really sure no one
will ever want to use your code on a non-ASCII platform. Starting in
Perl v5.22, calls to it on ASCII platforms are optimized out, so there's
no performance penalty at all in adding it. Or you can simply use the
other constructs that don't require it.
See Further Resources for how to find all these names and numeric codes.
On EBCDIC platforms, prior to v5.22, using \N{U+...}
doesn't work
properly.
Prior to v5.16, using \N{...}
with a character name (as opposed to a
U+...
code point) required a use charnames :full
.
Prior to v5.14, there were some bugs in \N{...}
with a character name
(as opposed to a U+...
code point).
charnames::string_vianame()
was introduced in v5.14. Prior to that,
charnames::vianame()
should work, but only if the argument is of the
form "U+..."
. Your best bet there for runtime Unicode by character
name is probably:
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 grapheme clusters to be separate characters, so for example
will print 2, not 1. The only exception is that regular expressions
have \X
for matching an extended grapheme cluster. (Thus \X
in a
regular expression would match the entire sequence of both the example
characters.)
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 the legacy data is assumed to be ISO 8859-1 (or EBCDIC, if applicable).
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
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:
and on already open streams, use binmode():
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. Also note that currently :utf8
is unsafe for
input, because it accepts the data without validating that it is indeed valid
UTF-8; you should instead use :encoding(utf-8)
(with or without a
hyphen).
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
The I/O layers can also be specified more flexibly with
the open pragma. See open, or look at the following example.
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;
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.
The :locale
does not currently 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:
The naming of encodings, both by the open() and by the open
pragma 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:
If you run this code twice, the contents of the file will be twice
UTF-8 encoded. A use open ':encoding(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 PerlIO, which is the default
on most systems.
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:
For example,
- nice_string("foo\x{100}bar\n")
returns the string
- 'foo\x{0100}bar\x0A'
which is ready to be printed.
(\\x{}
is used here instead of \\N{}
, since it's most likely that
you want to see what the native values are.)
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.
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 of whatever the string
encoding happens to be, or unpack("U0..", ...)
to get the bytes of the
UTF-8 encoding:
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.
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 A's should be considered equal, or even A's of any case.
The long answer is that you need to consider character normalization and casing issues: see Unicode::Normalize, Unicode Technical Report #15, Unicode Normalization Forms and sections on case mapping in the Unicode Standard.
As of Perl 5.8.0, the "Full" case-folding of Case
Mappings/SpecialCasing is implemented, but bugs remain in qr//i with them,
mostly fixed by 5.14, and essentially entirely by 5.18.
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/
Character Ranges and Classes
Character ranges in regular expression bracketed character classes ( e.g.,
/[a-z]/
) and in the tr/// (also known as y///) operator are not
magically Unicode-aware. What this means is that [A-Za-z]
will not
magically start to mean "all alphabetic letters" (not that it does mean that
even for 8-bit characters; for those, if you are using locales (perllocale),
use /[[:alpha:]]/
; and if not, use the 8-bit-aware property \p{alpha}
).
All the properties that begin with \p
(and its inverse \P
) are actually
character classes that are Unicode-aware. There are dozens of them, see
perluniprops.
Starting in v5.22, you can use Unicode code points as the end points of regular expression pattern character ranges, and the range will include all Unicode code points that lie between those end points, inclusive.
- qr/ [\N{U+03]-\N{U+20}] /x
includes the code points
\N{U+03}
, \N{U+04}
, ..., \N{U+20}
.
(It is planned to extend this behavior to ranges in tr/// in Perl
v5.24.)
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).
To get safe conversions from any Unicode string, use
num() in Unicode::UCD.
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.
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.
To get full seamless Unicode support, add
use feature 'unicode_strings'
(or use 5.012
or higher) to your
script.
How Do I Know Whether My String Is In Unicode?
You shouldn't have to care. But you may if your Perl is before 5.14.0
or you haven't specified use feature 'unicode_strings'
or use
5.012
(or higher) because otherwise the rules for the code points
in the range 128 to 255 are different depending on
whether the string they are contained within is in Unicode or not.
(See When Unicode Does Not Happen in perlunicode.)
To determine if a string is in Unicode, use:
- print utf8::is_utf8($string) ? 1 : 0, "\n";
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 (variable-length, potentially multi-byte) UTF-8 encoded
code points of the characters. Bytes added to a 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, or
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";
the output string will be UTF-8-encoded ab\x80c = \x{100}\n
, but
$a
will stay byte-encoded.
Sometimes you might really need to know the byte length of a string
instead of the character length. For that use either the
Encode::encode_utf8()
function or the bytes
pragma
and the length() function:
How Do I Find Out What Encoding a File Has?
You might try Encode::Guess, but it has a number of limitations.
How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the Encode
package to try converting it.
For example,
Or use unpack to try decoding it:
If invalid, a Malformed UTF-8 character warning is produced. The "C0" means
"process the string character per character". Without that, the
unpack("U*", ...)
would work in U0
mode (the default if the format
string starts with U
) and it would return the bytes making up the UTF-8
encoding of the target string, something that will always work.
How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
This probably isn't as useful as you might think. Normally, you shouldn't need to.
In one sense, what you are asking doesn't make much sense: encodings are for characters, and binary data are not "characters", so converting "data" into some encoding isn't meaningful unless you know in what character set and encoding the binary data is in, in which case it's not just binary data, now is it?
If you have a raw sequence of bytes that you know should be
interpreted via a particular encoding, you can use Encode
:
- use Encode 'from_to';
- from_to($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:
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.
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);
or:
- $Unicode = pack("U0a*", $bytes);
You can find the bytes that make up a UTF-8 sequence with
- @bytes = unpack("C*", $Unicode_string)
and you can create well-formed Unicode with
- $Unicode_string = pack("U*", 0xff, ...)
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
How Does Unicode Work With Traditional Locales?
If your locale is a UTF-8 locale, starting in Perl v5.20, Perl works
well for all categories except LC_COLLATE
dealing with sorting and
the cmp
operator.
For other locales, starting in Perl 5.16, you can specify
- use locale ':not_characters';
to get Perl to work well with them. The catch is that you have to translate from the locale character set to/from Unicode yourself. See Unicode I/O above for how to
to accomplish this, but full details are in Unicode and UTF-8 in perllocale, including gotchas that happen if you don't specify
:not_characters
.
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.
Unicode Consortium
Unicode FAQ
Unicode Glossary
Unicode Recommended Reading List
The Unicode Consortium has a list of articles and books, some of which give a much more in depth treatment of Unicode: http://unicode.org/resources/readinglist.html
Unicode Useful Resources
Unicode and Multilingual Support in HTML, Fonts, Web Browsers and Other Applications
UTF-8 and Unicode FAQ for Unix/Linux
Legacy Character Sets
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 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;
perlunitut, perlunicode, Encode, open, utf8, bytes, perlretut, perlrun, 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 2001-2011 Jarkko Hietaniemi <jhi@iki.fi>. Now maintained by Perl 5 Porters.
This document may be distributed under the same terms as Perl itself.