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-rw-r--r--Master/tlpkg/tlperl/lib/pods/perluniintro.pod205
1 files changed, 120 insertions, 85 deletions
diff --git a/Master/tlpkg/tlperl/lib/pods/perluniintro.pod b/Master/tlpkg/tlperl/lib/pods/perluniintro.pod
index bee286f5eaa..3fbff0024fd 100644
--- a/Master/tlpkg/tlperl/lib/pods/perluniintro.pod
+++ b/Master/tlpkg/tlperl/lib/pods/perluniintro.pod
@@ -5,21 +5,22 @@ perluniintro - Perl Unicode introduction
=head1 DESCRIPTION
This document gives a general idea of Unicode and how to use Unicode
-in Perl.
+in Perl. See L</Further Resources> for references to more in-depth
+treatments of Unicode.
=head2 Unicode
Unicode is a character set standard which plans to codify all of the
writing systems of the world, plus many other symbols.
-Unicode and ISO/IEC 10646 are coordinated standards that provide code
-points for characters in almost all modern character set standards,
-covering more than 30 writing systems and hundreds of languages,
+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 4.0 in April 2003.
+Unicode 1.0 was released in October 1991, and 6.0 in October 2010.
A Unicode I<character> is an abstract entity. It is not bound to any
particular integer width, especially not to the C language C<char>.
@@ -31,7 +32,9 @@ those characters.
Unicode defines characters like C<LATIN CAPITAL LETTER A> or C<GREEK
SMALL LETTER ALPHA> and unique numbers for the characters, in this
case 0x0041 and 0x03B1, respectively. These unique numbers are called
-I<code points>.
+I<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 I<ordinal> is often used interchangeably with it.
The Unicode standard prefers using hexadecimal notation for the code
points. If numbers like C<0x0041> are unfamiliar to you, take a peek
@@ -51,39 +54,41 @@ modelled by a I<base character> (like C<LATIN CAPITAL LETTER A>) followed
by one or more I<modifiers> (like C<COMBINING ACUTE ACCENT>). This sequence of
base character and modifiers is called a I<combining character
sequence>. Some non-western languages require more complicated
-models, so Unicode created the I<grapheme cluster> concept, and then the
-I<extended grapheme cluster>. For example, a Korean Hangul syllable is
-considered a single logical character, but most often consists of three actual
+models, so Unicode created the I<grapheme cluster> concept, which was
+later further refined into the I<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". 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.
-
-For some combinations, there are I<precomposed> characters.
-C<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 I<normalization
-forms> to standardize representations are also defined.
+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
+I<precomposed> characters. There is a single character equivalent, for
+example, to the sequence C<LATIN CAPITAL LETTER A> followed by
+C<COMBINING ACUTE ACCENT>. It is called C<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 I<normalization
+forms> are also defined. Thus, C<LATIN CAPITAL LETTER A WITH ACUTE> is
+in I<Normalization Form Composed>, (abbreviated NFC), and the sequence
+C<LATIN CAPITAL LETTER A> followed by C<COMBINING ACUTE ACCENT>
+represents the same character in I<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 also not true: some code points do not have an assigned
+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.
@@ -128,24 +133,36 @@ 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.
-
-B<Starting from Perl 5.8.0, the use of C<use utf8> is needed only in much more restricted circumstances.> In earlier releases the C<utf8> pragma was used to declare
+Perl 5.14.0 is the first release where Unicode support is
+(almost) seamlessly integrable without some gotchas (the exception being
+some differences in L<quotemeta|perlfunc/quotemeta>). To enable this
+seamless support, you should C<use feature 'unicode_strings'> (which is
+automatically selected if you C<use 5.012> or higher). See L<feature>.
+(5.14 also fixes a number of bugs and departures from the Unicode
+standard.)
+
+Before Perl 5.8.0, the use of C<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. Only one case remains where an explicit C<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
+operations.
+Starting with Perl 5.8.0, only one case remains where an explicit C<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 C<use utf8>. This is not the default because
scripts with legacy 8-bit data in them would break. See L<utf8>.
=head2 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 (mostly) transparently upgraded
-to Unicode. There are some problems--see L<perlunicode/The "Unicode Bug">.
+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 5.14, the upgrade was not completely
+transparent (see L<perlunicode/The "Unicode Bug">), and for backwards
+compatibility, full transparency is not gained unless C<use feature
+'unicode_strings'> (see L<feature>) or C<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
@@ -182,10 +199,11 @@ handles, default C<open()> layer, and C<@ARGV> by using either
the C<-C> command line switch or the C<PERL_UNICODE> environment
variable, see L<perlrun> for the documentation of the C<-C> switch.
-Note that this means that Perl expects other software to work, too:
+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 complain
-about the malformed UTF-8.
+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:
@@ -248,7 +266,7 @@ characters:
Note that both C<\x{...}> and C<\N{...}> are compile-time string
constants: you cannot use variables in them. if you want similar
-run-time functionality, use C<chr()> and C<charnames::vianame()>.
+run-time functionality, use C<chr()> and C<charnames::string_vianame()>.
If you want to force the result to Unicode characters, use the special
C<"U0"> prefix. It consumes no arguments but causes the following bytes
@@ -273,16 +291,18 @@ 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 C<\X> for matching an extended grapheme cluster.
+have C<\X> for matching an extended grapheme cluster. (Thus C<\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:
=head2 Legacy Encodings
-When you combine legacy data and Unicode the legacy data needs
-to be upgraded to Unicode. Normally ISO 8859-1 (or EBCDIC, if
-applicable) is assumed.
+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 C<Encode> module knows about many encodings and has interfaces
for doing conversions between those encodings:
@@ -321,9 +341,10 @@ and on already open streams, use C<binmode()>:
The matching of encoding names is loose: case does not matter, and
many encodings have several aliases. Note that the C<:utf8> layer
must always be specified exactly like that; it is I<not> subject to
-the loose matching of encoding names. Also note that C<:utf8> is unsafe for
+the loose matching of encoding names. Also note that currently C<:utf8> is unsafe for
input, because it accepts the data without validating that it is indeed valid
-UTF8.
+UTF-8; you should instead use C<:encoding(utf-8)> (with or without a
+hyphen).
See L<PerlIO> for the C<:utf8> layer, L<PerlIO::encoding> and
L<Encode::PerlIO> for the C<:encoding()> layer, and
@@ -344,7 +365,8 @@ layer when opening files
The I/O layers can also be specified more flexibly with
the C<open> pragma. See L<open>, or look at the following example.
- use open ':encoding(utf8)'; # input/output default encoding will be UTF-8
+ use open ':encoding(utf8)'; # input/output default encoding will be
+ # UTF-8
open X, ">file";
print X chr(0x100), "\n";
close X;
@@ -355,7 +377,8 @@ the C<open> pragma. See L<open>, or look at the following example.
With the C<open> pragma you can use the C<:locale> layer
BEGIN { $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R' }
- # the :locale will probe the locale environment variables like LC_ALL
+ # 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
@@ -432,13 +455,13 @@ its argument so that Unicode characters with code points greater than
255 are displayed as C<\x{...}>, control characters (like C<\n>) are
displayed as C<\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
+ 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
}
@@ -513,7 +536,7 @@ C<LATIN CAPITAL LETTER A>?)
The short answer is that by default Perl compares equivalence (C<eq>,
C<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.
+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 L<Unicode::Normalize>, Unicode Technical Report #15,
@@ -521,7 +544,8 @@ L<Unicode Normalization Forms|http://www.unicode.org/unicode/reports/tr15> and
sections on case mapping in the L<Unicode Standard|http://www.unicode.org>.
As of Perl 5.8.0, the "Full" case-folding of I<Case
-Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them.
+Mappings/SpecialCasing> is implemented, but bugs remain in C<qr//i> with them,
+mostly fixed by 5.14.
=item *
@@ -575,6 +599,8 @@ 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
+L<Unicode::UCD/num()>.
=back
@@ -601,13 +627,18 @@ 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
+C<use feature 'unicode_strings'> (or C<use 5.012> or higher) to your
+script.
=item *
How Do I Know Whether My String Is In Unicode?
-You shouldn't have to care. But you may, because currently the semantics of the
-characters whose ordinals are in the range 128 to 255 are different depending on
+You shouldn't have to care. But you may if your Perl is before 5.14.0
+or you haven't specified C<use feature 'unicode_strings'> or C<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 L<perlunicode/When Unicode Does Not Happen>.)
@@ -625,7 +656,7 @@ 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, and
+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,
@@ -638,8 +669,8 @@ C<$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
-C<Encode::encode_utf8()> function or the C<bytes> pragma and
-the C<length()> function:
+C<Encode::encode_utf8()> function or the C<bytes> pragma
+and the C<length()> function:
my $unicode = chr(0x100);
print length($unicode), "\n"; # will print 1
@@ -652,6 +683,12 @@ the C<length()> function:
=item *
+How Do I Find Out What Encoding a File Has?
+
+You might try L<Encode::Guess>, but it has a number of limitations.
+
+=item *
+
How Do I Detect Data That's Not Valid In a Particular Encoding?
Use the C<Encode> package to try converting it.
@@ -731,11 +768,11 @@ or:
You can find the bytes that make up a UTF-8 sequence with
- @bytes = unpack("C*", $Unicode_string)
+ @bytes = unpack("C*", $Unicode_string)
and you can create well-formed Unicode with
- $Unicode_string = pack("U*", 0xff, ...)
+ $Unicode_string = pack("U*", 0xff, ...)
=item *
@@ -748,8 +785,14 @@ L<http://www.cl.cam.ac.uk/~mgk25/unicode.html>
How Does Unicode Work With Traditional Locales?
-In Perl, not very well. Avoid using locales through the C<locale>
-pragma. Use only one or the other. But see L<perlrun> for the
+Perl tries to keep the two separated. Code points that are above 255
+are treated as Unicode; those below 256, generally as locale. This
+works reasonably well except in some case-insensitive regular expression
+pattern matches that in Unicode would cross the 255/256 boundary. These
+are disallowed.
+Also, the C<\p{}> and C<\N{}> constructs silently assume Unicode values
+even for code points below 256.
+See also L<perlrun> for the
description of the C<-C> switch and its environment counterpart,
C<$ENV{PERL_UNICODE}> to see how to enable various Unicode features,
for example by using locale settings.
@@ -810,6 +853,14 @@ L<http://www.unicode.org/glossary/>
=item *
+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:
+L<http://unicode.org/resources/readinglist.html>
+
+=item *
+
Unicode Useful Resources
L<http://www.unicode.org/unicode/onlinedat/resources.html>
@@ -835,22 +886,6 @@ L<http://www.eki.ee/letter/>
=item *
-The Unicode support files live within the Perl installation in the
-directory
-
- $Config{installprivlib}/unicore
-
-in Perl 5.8.0 or newer, and
-
- $Config{installprivlib}/unicode
-
-in the Perl 5.6 series. (The renaming to F<lib/unicore> was done to
-avoid naming conflicts with lib/Unicode in case-insensitive filesystems.)
-The main Unicode data file is F<UnicodeData.txt> (or F<Unicode.301> in
-Perl 5.6.1.) You can find the C<$Config{installprivlib}> by
-
- perl "-V:installprivlib"
-
You can explore various information from the Unicode data files using
the C<Unicode::UCD> module.
@@ -887,6 +922,6 @@ mailing lists for their valuable feedback.
=head1 AUTHOR, COPYRIGHT, AND LICENSE
-Copyright 2001-2002 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
+Copyright 2001-2011 Jarkko Hietaniemi E<lt>jhi@iki.fiE<gt>
This document may be distributed under the same terms as Perl itself.