NAME¶
perluniintro - Perl Unicode introduction
DESCRIPTION¶
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¶
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
also 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
65536) characters from 0x0000 to 0xFFFF would be needed. This soon proved to
be false, 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 perhaps the most popular. UTF-8 is a variable length
encoding that encodes Unicode characters as 1 to 6 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.
Perl's Unicode Support¶
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, which 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's Unicode Model¶
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".
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.
Later Perl releases have added code that will not work on EBCDIC platforms, and
no one has complained, so the divergence has continued. If you want to run
Perl on an EBCDIC platform, send email to perlbug@perl.org
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()".
You can invoke characters by name in double-quoted strings:
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::string_vianame()".
If you want to force the result to Unicode characters, use the special
"U0" prefix. It consumes no arguments but causes the following bytes
to be interpreted as the UTF-8 encoding of Unicode characters:
my $chars = pack("U0W*", 0x80, 0x42);
Likewise, you can stop such UTF-8 interpretation 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 perlunicode and perlretut).
Note that Perl considers grapheme clusters to be separate characters, so for
example
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 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:
Legacy Encodings¶
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
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)");
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
open(my $fh,'<:encoding(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 ':encoding(utf8)'; # input/output default encoding 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;
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 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 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, ">:encoding(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 ':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.
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("W*", $_[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
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:
# this prints c4 80 for the UTF-8 bytes 0xc4 0x80
print join(" ", unpack("U0(H2)*", 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 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
<http://www.unicode.org/unicode/reports/tr15> and sections on case
mapping in the Unicode Standard <http://www.unicode.org>.
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/>
Miscellaneous¶
- •
- 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.
You can use Unicode code points as the end points of character ranges, and
the range will include all Unicode code points that lie between those end
points.
- •
- 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.
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 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 semantics of 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:
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)
no bytes;
- •
- 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,
use Encode 'decode_utf8';
if (eval { decode_utf8($string, Encode::FB_CROAK); 1 }) {
# $string is valid utf8
} else {
# $string is not valid utf8
}
Or use "unpack" to try decoding it:
use warnings;
@chars = unpack("C0U*", $string_of_bytes_that_I_think_is_utf8);
If invalid, a "Malformed UTF-8 character" warning is produced. The
"C0" means "process the string character per
character". Without that, the "unpack("U*", ...)"
would work in "U0" mode (the default if the format string starts
with "U") and it would return the bytes making up the UTF-8
encoding of the target string, something that will always work.
- •
- How Do I Convert Binary Data Into a Particular Encoding, Or Vice Versa?
This probably isn't as useful as you might think. Normally, you shouldn't
need to.
In one sense, what you are asking doesn't make much sense: encodings are for
characters, and binary data are not "characters", so converting
"data" into some encoding isn't meaningful unless you know in
what character set and encoding the binary data is in, in which case it's
not just binary data, now is it?
If you have a raw sequence of bytes that you know should be interpreted via
a particular encoding, you can use "Encode":
use Encode 'from_to';
from_to($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:
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("W*", unpack("U*", $Unicode_string));
$Unicode_string = pack("U*", unpack("W*", $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);
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
use open ':locale';
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".
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 learning to use hexadecimal just makes life easier with the Unicode
standard. The "U+HHHH" notation uses hexadecimal, for example.
The "0x" prefix means a hexadecimal number, the digits are 0-9
and a-f (or A-F, case doesn't matter). Each hexadecimal digit
represents four bits, or half a byte. "print 0x..., "\n""
will show a hexadecimal number in decimal, and "printf "%x\n",
$decimal" will show a decimal number in hexadecimal. If you have just the
"hex digits" of a hexadecimal number, you can use the
"hex()" function.
print 0x0009, "\n"; # 9
print 0x000a, "\n"; # 10
print 0x000f, "\n"; # 15
print 0x0010, "\n"; # 16
print 0x0011, "\n"; # 17
print 0x0100, "\n"; # 256
print 0x0041, "\n"; # 65
printf "%x\n", 65; # 41
printf "%#x\n", 65; # 0x41
print hex("41"), "\n"; # 65
Further Resources¶
- •
- Unicode Consortium
<http://www.unicode.org/>
- •
- Unicode FAQ
<http://www.unicode.org/unicode/faq/>
- •
- Unicode Glossary
<http://www.unicode.org/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
<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/>
- •
- 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.
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¶
perlunitut, perlunicode, Encode, 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 feedback.
AUTHOR, COPYRIGHT, AND LICENSE¶
Copyright 2001-2011 Jarkko Hietaniemi <jhi@iki.fi>
This document may be distributed under the same terms as Perl itself.