ext/Encode/encoding.pm

# $Id: encoding.pm,v 2.1 2004/10/19 04:55:01 dankogai Exp $
package encoding;
our $VERSION = do { my @r = (q$Revision: 2.1 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };

use Encode;
use strict;

sub DEBUG () { 0 }

BEGIN {
    if (ord("A") == 193) {
        require Carp;
        Carp::croak("encoding: pragma does not support EBCDIC platforms");
    }
}

our $HAS_PERLIO = 0;
eval { require PerlIO::encoding };
unless ($@){
    $HAS_PERLIO = (PerlIO::encoding->VERSION >= 0.02);
}

sub _exception{
    my $name = shift;
    $] > 5.008 and return 0;               # 5.8.1 or higher then no
    my %utfs = map {$_=>1}
        qw(utf8 UCS-2BE UCS-2LE UTF-16 UTF-16BE UTF-16LE
           UTF-32 UTF-32BE UTF-32LE);
    $utfs{$name} or return 0;               # UTFs or no
    require Config; Config->import(); our %Config;
    return $Config{perl_patchlevel} ? 0 : 1 # maintperl then no
}

sub in_locale { $^H & ($locale::hint_bits || 0)}

sub _get_locale_encoding {
    my $locale_encoding;

    # I18N::Langinfo isn't available everywhere
    eval {
        require I18N::Langinfo;
        I18N::Langinfo->import(qw(langinfo CODESET));
        $locale_encoding = langinfo(CODESET());
    };
    
    my $country_language;

    no warnings 'uninitialized';

    if (not $locale_encoding && in_locale()) {
        if ($ENV{LC_ALL} =~ /^([^.]+)\.([^.]+)$/) {
            ($country_language, $locale_encoding) = ($1, $2);
        } elsif ($ENV{LANG} =~ /^([^.]+)\.([^.]+)$/) {
            ($country_language, $locale_encoding) = ($1, $2);
        }
        # LANGUAGE affects only LC_MESSAGES only on glibc
    } elsif (not $locale_encoding) {
        if ($ENV{LC_ALL} =~ /\butf-?8\b/i ||
            $ENV{LANG}   =~ /\butf-?8\b/i) {
            $locale_encoding = 'utf8';
        }
        # Could do more heuristics based on the country and language
        # parts of LC_ALL and LANG (the parts before the dot (if any)),
        # since we have Locale::Country and Locale::Language available.
        # TODO: get a database of Language -> Encoding mappings
        # (the Estonian database at http://www.eki.ee/letter/
        # would be excellent!) --jhi
    }
    if (defined $locale_encoding &&
        lc($locale_encoding) eq 'euc' &&
        defined $country_language) {
        if ($country_language =~ /^ja_JP|japan(?:ese)?$/i) {
            $locale_encoding = 'euc-jp';
        } elsif ($country_language =~ /^ko_KR|korean?$/i) {
            $locale_encoding = 'euc-kr';
        } elsif ($country_language =~ /^zh_CN|chin(?:a|ese)?$/i) {
            $locale_encoding = 'euc-cn';
        } elsif ($country_language =~ /^zh_TW|taiwan(?:ese)?$/i) {
            $locale_encoding = 'euc-tw';
        } else {
            require Carp;
            Carp::croak("encoding: Locale encoding '$locale_encoding' too ambiguous");
        }
    }

    return $locale_encoding;
}

sub import {
    my $class = shift;
    my $name  = shift;
    if ($name eq ':_get_locale_encoding') { # used by lib/open.pm
        my $caller = caller();
        {
            no strict 'refs';
            *{"${caller}::_get_locale_encoding"} = \&_get_locale_encoding;
        }
        return;
    }
    $name = _get_locale_encoding() if $name eq ':locale';
    my %arg = @_;
    $name = $ENV{PERL_ENCODING} unless defined $name;
    my $enc = find_encoding($name);
    unless (defined $enc) {
        require Carp;
        Carp::croak("encoding: Unknown encoding '$name'");
    }
    $name = $enc->name; # canonize
    unless ($arg{Filter}) {
        DEBUG and warn "_exception($name) = ", _exception($name);
        _exception($name) or ${^ENCODING} = $enc;
        $HAS_PERLIO or return 1;
    }else{
        defined(${^ENCODING}) and undef ${^ENCODING};
        # implicitly 'use utf8'
        require utf8; # to fetch $utf8::hint_bits;
        $^H |= $utf8::hint_bits;
        eval {
            require Filter::Util::Call ;
            Filter::Util::Call->import ;
            filter_add(sub{
                           my $status = filter_read();
                           if ($status > 0){
                               $_ = $enc->decode($_, 1);
                               DEBUG and warn $_;
                           }
                           $status ;
                       });
        };
        $@ eq '' and DEBUG and warn "Filter installed";
    }
    defined ${^UNICODE} and ${^UNICODE} != 0 and return 1;
    for my $h (qw(STDIN STDOUT)){
        if ($arg{$h}){
            unless (defined find_encoding($arg{$h})) {
                require Carp;
                Carp::croak("encoding: Unknown encoding for $h, '$arg{$h}'");
            }
            eval { binmode($h, ":raw :encoding($arg{$h})") };
        }else{
            unless (exists $arg{$h}){
                eval { 
                    no warnings 'uninitialized';
                    binmode($h, ":raw :encoding($name)");
                };
            }
        }
        if ($@){
            require Carp;
            Carp::croak($@);
        }
    }
    return 1; # I doubt if we need it, though
}

sub unimport{
    no warnings;
    undef ${^ENCODING};
    if ($HAS_PERLIO){
        binmode(STDIN,  ":raw");
        binmode(STDOUT, ":raw");
    }else{
        binmode(STDIN);
        binmode(STDOUT);
    }
    if ($INC{"Filter/Util/Call.pm"}){
        eval { filter_del() };
    }
}

1;
__END__

=pod

=head1 NAME

encoding - allows you to write your script in non-ascii or non-utf8

=head1 SYNOPSIS

  use encoding "greek";  # Perl like Greek to you?
  use encoding "euc-jp"; # Jperl!

  # or you can even do this if your shell supports your native encoding

  perl -Mencoding=latin2 -e '...' # Feeling centrally European?
  perl -Mencoding=euc-kr -e '...' # Or Korean?

  # more control

  # A simple euc-cn => utf-8 converter
  use encoding "euc-cn", STDOUT => "utf8";  while(<>){print};

  # "no encoding;" supported (but not scoped!)
  no encoding;

  # an alternate way, Filter
  use encoding "euc-jp", Filter=>1;
  # now you can use kanji identifiers -- in euc-jp!

  # switch on locale -
  # note that this probably means that unless you have a complete control
  # over the environments the application is ever going to be run, you should
  # NOT use the feature of encoding pragma allowing you to write your script
  # in any recognized encoding because changing locale settings will wreck
  # the script; you can of course still use the other features of the pragma.
  use encoding ':locale';

=head1 ABSTRACT

Let's start with a bit of history: Perl 5.6.0 introduced Unicode
support.  You could apply C<substr()> and regexes even to complex CJK
characters -- so long as the script was written in UTF-8.  But back
then, text editors that supported UTF-8 were still rare and many users
instead chose to write scripts in legacy encodings, giving up a whole
new feature of Perl 5.6.

Rewind to the future: starting from perl 5.8.0 with the B<encoding>
pragma, you can write your script in any encoding you like (so long
as the C<Encode> module supports it) and still enjoy Unicode support.
This pragma achieves that by doing the following:

=over

=item *

Internally converts all literals (C<q//,qq//,qr//,qw///, qx//>) from
the encoding specified to utf8.  In Perl 5.8.1 and later, literals in
C<tr///> and C<DATA> pseudo-filehandle are also converted.

=item *

Changing PerlIO layers of C<STDIN> and C<STDOUT> to the encoding
 specified.

=back

=head2 Literal Conversions

You can write code in EUC-JP as follows:

  my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
               #<-char-><-char->   # 4 octets
  s/\bCamel\b/$Rakuda/;

And with C<use encoding "euc-jp"> in effect, it is the same thing as
the code in UTF-8:

  my $Rakuda = "\x{99F1}\x{99DD}"; # two Unicode Characters
  s/\bCamel\b/$Rakuda/;

=head2 PerlIO layers for C<STD(IN|OUT)>

The B<encoding> pragma also modifies the filehandle layers of
STDIN and STDOUT to the specified encoding.  Therefore,

  use encoding "euc-jp";
  my $message = "Camel is the symbol of perl.\n";
  my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
  $message =~ s/\bCamel\b/$Rakuda/;
  print $message;

Will print "\xF1\xD1\xF1\xCC is the symbol of perl.\n",
not "\x{99F1}\x{99DD} is the symbol of perl.\n".

You can override this by giving extra arguments; see below.

=head2 Implicit upgrading for byte strings

By default, if strings operating under byte semantics and strings
with Unicode character data are concatenated, the new string will
be created by decoding the byte strings as I<ISO 8859-1 (Latin-1)>.

The B<encoding> pragma changes this to use the specified encoding
instead.  For example:

    use encoding 'utf8';
    my $string = chr(20000); # a Unicode string
    utf8::encode($string);   # now it's a UTF-8 encoded byte string
    # concatenate with another Unicode string
    print length($string . chr(20000));

Will print C<2>, because C<$string> is upgraded as UTF-8.  Without
C<use encoding 'utf8';>, it will print C<4> instead, since C<$string>
is three octets when interpreted as Latin-1.

=head1 FEATURES THAT REQUIRE 5.8.1

Some of the features offered by this pragma requires perl 5.8.1.  Most
of these are done by Inaba Hiroto.  Any other features and changes
are good for 5.8.0.

=over

=item "NON-EUC" doublebyte encodings

Because perl needs to parse script before applying this pragma, such
encodings as Shift_JIS and Big-5 that may contain '\' (BACKSLASH;
\x5c) in the second byte fails because the second byte may
accidentally escape the quoting character that follows.  Perl 5.8.1
or later fixes this problem.

=item tr// 

C<tr//> was overlooked by Perl 5 porters when they released perl 5.8.0
See the section below for details.

=item DATA pseudo-filehandle

Another feature that was overlooked was C<DATA>. 

=back

=head1 USAGE

=over 4

=item use encoding [I<ENCNAME>] ;

Sets the script encoding to I<ENCNAME>.  And unless ${^UNICODE} 
exists and non-zero, PerlIO layers of STDIN and STDOUT are set to
":encoding(I<ENCNAME>)".

Note that STDERR WILL NOT be changed.

Also note that non-STD file handles remain unaffected.  Use C<use
open> or C<binmode> to change layers of those.

If no encoding is specified, the environment variable L<PERL_ENCODING>
is consulted.  If no encoding can be found, the error C<Unknown encoding
'I<ENCNAME>'> will be thrown.

=item use encoding I<ENCNAME> [ STDIN =E<gt> I<ENCNAME_IN> ...] ;

You can also individually set encodings of STDIN and STDOUT via the
C<< STDIN => I<ENCNAME> >> form.  In this case, you cannot omit the
first I<ENCNAME>.  C<< STDIN => undef >> turns the IO transcoding
completely off.

When ${^UNICODE} exists and non-zero, these options will completely
ignored.  ${^UNICODE} is a variable introduced in perl 5.8.1.  See
L<perlrun> see L<perlvar/"${^UNICODE}"> and L<perlrun/"-C"> for
details (perl 5.8.1 and later).

=item use encoding I<ENCNAME> Filter=E<gt>1;

This turns the encoding pragma into a source filter.  While the
default approach just decodes interpolated literals (in qq() and
qr()), this will apply a source filter to the entire source code.  See
L</"The Filter Option"> below for details.

=item no encoding;

Unsets the script encoding. The layers of STDIN, STDOUT are
reset to ":raw" (the default unprocessed raw stream of bytes).

=back

=head1 The Filter Option

The magic of C<use encoding> is not applied to the names of
identifiers.  In order to make C<${"\x{4eba}"}++> ($human++, where human
is a single Han ideograph) work, you still need to write your script
in UTF-8 -- or use a source filter.  That's what 'Filter=>1' does.

What does this mean?  Your source code behaves as if it is written in
UTF-8 with 'use utf8' in effect.  So even if your editor only supports
Shift_JIS, for example, you can still try examples in Chapter 15 of
C<Programming Perl, 3rd Ed.>.  For instance, you can use UTF-8
identifiers.

This option is significantly slower and (as of this writing) non-ASCII
identifiers are not very stable WITHOUT this option and with the
source code written in UTF-8.

=head2 Filter-related changes at Encode version 1.87

=over

=item *

The Filter option now sets STDIN and STDOUT like non-filter options.
And C<< STDIN=>I<ENCODING> >> and C<< STDOUT=>I<ENCODING> >> work like
non-filter version.

=item *

C<use utf8> is implicitly declared so you no longer have to C<use
utf8> to C<${"\x{4eba}"}++>.

=back

=head1 CAVEATS

=head2 NOT SCOPED

The pragma is a per script, not a per block lexical.  Only the last
C<use encoding> or C<no encoding> matters, and it affects 
B<the whole script>.  However, the <no encoding> pragma is supported and 
B<use encoding> can appear as many times as you want in a given script. 
The multiple use of this pragma is discouraged.

By the same reason, the use this pragma inside modules is also
discouraged (though not as strongly discouranged as the case above.  
See below).

If you still have to write a module with this pragma, be very careful
of the load order.  See the codes below;

  # called module
  package Module_IN_BAR;
  use encoding "bar";
  # stuff in "bar" encoding here
  1;

  # caller script
  use encoding "foo"
  use Module_IN_BAR;
  # surprise! use encoding "bar" is in effect.

The best way to avoid this oddity is to use this pragma RIGHT AFTER
other modules are loaded.  i.e.

  use Module_IN_BAR;
  use encoding "foo";

=head2 DO NOT MIX MULTIPLE ENCODINGS

Notice that only literals (string or regular expression) having only
legacy code points are affected: if you mix data like this

        \xDF\x{100}

the data is assumed to be in (Latin 1 and) Unicode, not in your native
encoding.  In other words, this will match in "greek":

        "\xDF" =~ /\x{3af}/

but this will not

        "\xDF\x{100}" =~ /\x{3af}\x{100}/

since the C<\xDF> (ISO 8859-7 GREEK SMALL LETTER IOTA WITH TONOS) on
the left will B<not> be upgraded to C<\x{3af}> (Unicode GREEK SMALL
LETTER IOTA WITH TONOS) because of the C<\x{100}> on the left.  You
should not be mixing your legacy data and Unicode in the same string.

This pragma also affects encoding of the 0x80..0xFF code point range:
normally characters in that range are left as eight-bit bytes (unless
they are combined with characters with code points 0x100 or larger,
in which case all characters need to become UTF-8 encoded), but if
the C<encoding> pragma is present, even the 0x80..0xFF range always
gets UTF-8 encoded.

After all, the best thing about this pragma is that you don't have to
resort to \x{....} just to spell your name in a native encoding.
So feel free to put your strings in your encoding in quotes and
regexes.

=head2 tr/// with ranges

The B<encoding> pragma works by decoding string literals in
C<q//,qq//,qr//,qw///, qx//> and so forth.  In perl 5.8.0, this
does not apply to C<tr///>.  Therefore,

  use encoding 'euc-jp';
  #....
  $kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/;
  #           -------- -------- -------- --------

Does not work as

  $kana =~ tr/\x{3041}-\x{3093}/\x{30a1}-\x{30f3}/;

=over

=item Legend of characters above

  utf8     euc-jp   charnames::viacode()
  -----------------------------------------
  \x{3041} \xA4\xA1 HIRAGANA LETTER SMALL A
  \x{3093} \xA4\xF3 HIRAGANA LETTER N
  \x{30a1} \xA5\xA1 KATAKANA LETTER SMALL A
  \x{30f3} \xA5\xF3 KATAKANA LETTER N

=back

This counterintuitive behavior has been fixed in perl 5.8.1.

=head3 workaround to tr///;

In perl 5.8.0, you can work around as follows;

  use encoding 'euc-jp';
  #  ....
  eval qq{ \$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/ };

Note the C<tr//> expression is surrounded by C<qq{}>.  The idea behind
is the same as classic idiom that makes C<tr///> 'interpolate'.

   tr/$from/$to/;            # wrong!
   eval qq{ tr/$from/$to/ }; # workaround.

Nevertheless, in case of B<encoding> pragma even C<q//> is affected so
C<tr///> not being decoded was obviously against the will of Perl5
Porters so it has been fixed in Perl 5.8.1 or later.

=head1 EXAMPLE - Greekperl

    use encoding "iso 8859-7";

    # \xDF in ISO 8859-7 (Greek) is \x{3af} in Unicode.

    $a = "\xDF";
    $b = "\x{100}";

    printf "%#x\n", ord($a); # will print 0x3af, not 0xdf

    $c = $a . $b;

    # $c will be "\x{3af}\x{100}", not "\x{df}\x{100}".

    # chr() is affected, and ...

    print "mega\n"  if ord(chr(0xdf)) == 0x3af;

    # ... ord() is affected by the encoding pragma ...

    print "tera\n" if ord(pack("C", 0xdf)) == 0x3af;

    # ... as are eq and cmp ...

    print "peta\n" if "\x{3af}" eq  pack("C", 0xdf);
    print "exa\n"  if "\x{3af}" cmp pack("C", 0xdf) == 0;

    # ... but pack/unpack C are not affected, in case you still
    # want to go back to your native encoding

    print "zetta\n" if unpack("C", (pack("C", 0xdf))) == 0xdf;

=head1 KNOWN PROBLEMS

=over

=item literals in regex that are longer than 127 bytes

For native multibyte encodings (either fixed or variable length),
the current implementation of the regular expressions may introduce
recoding errors for regular expression literals longer than 127 bytes.

=item EBCDIC

The encoding pragma is not supported on EBCDIC platforms.
(Porters who are willing and able to remove this limitation are
welcome.)

=item format

This pragma doesn't work well with format because PerlIO does not
get along very well with it.  When format contains non-ascii
characters it prints funny or gets "wide character warnings".
To understand it, try the code below.

  # Save this one in utf8
  # replace *non-ascii* with a non-ascii string
  my $camel;
  format STDOUT =
  *non-ascii*@>>>>>>>
  $camel
  .
  $camel = "*non-ascii*";
  binmode(STDOUT=>':encoding(utf8)'); # bang!
  write;              # funny 
  print $camel, "\n"; # fine

Without binmode this happens to work but without binmode, print()
fails instead of write().

At any rate, the very use of format is questionable when it comes to
unicode characters since you have to consider such things as character
width (i.e. double-width for ideographs) and directions (i.e. BIDI for
Arabic and Hebrew).

=back

=head2 The Logic of :locale

The logic of C<:locale> is as follows:

=over 4

=item 1.

If the platform supports the langinfo(CODESET) interface, the codeset
returned is used as the default encoding for the open pragma.

=item 2.

If 1. didn't work but we are under the locale pragma, the environment
variables LC_ALL and LANG (in that order) are matched for encodings
(the part after C<.>, if any), and if any found, that is used 
as the default encoding for the open pragma.

=item 3.

If 1. and 2. didn't work, the environment variables LC_ALL and LANG
(in that order) are matched for anything looking like UTF-8, and if
any found, C<:utf8> is used as the default encoding for the open
pragma.

=back

If your locale environment variables (LC_ALL, LC_CTYPE, LANG)
contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
the default encoding of your STDIN, STDOUT, and STDERR, and of
B<any subsequent file open>, is UTF-8.

=head1 HISTORY

This pragma first appeared in Perl 5.8.0.  For features that require 
5.8.1 and better, see above.

The C<:locale> subpragma was implemented in 2.01, or Perl 5.8.6.

=head1 SEE ALSO

L<perlunicode>, L<Encode>, L<open>, L<Filter::Util::Call>,

Ch. 15 of C<Programming Perl (3rd Edition)>
by Larry Wall, Tom Christiansen, Jon Orwant;
O'Reilly & Associates; ISBN 0-596-00027-8

=cut
Revision:	1.1.2.1
Committed:	Thu Jun 30 14:58:51 2005 UTC (21 years, 3 months ago) by root
Branch:	PERL
CVS Tags:	PERL-5-8-7
Changes since 1.1:	+0 -0 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	# $Id: encoding.pm,v 2.1 2004/10/19 04:55:01 dankogai Exp $
2			package encoding;
3			our $VERSION = do { my @r = (q$Revision: 2.1 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };
4
5			use Encode;
6			use strict;
7
8			sub DEBUG () { 0 }
9
10			BEGIN {
11			if (ord("A") == 193) {
12			require Carp;
13			Carp::croak("encoding: pragma does not support EBCDIC platforms");
14			}
15			}
16
17			our $HAS_PERLIO = 0;
18			eval { require PerlIO::encoding };
19			unless ($@){
20			$HAS_PERLIO = (PerlIO::encoding->VERSION >= 0.02);
21			}
22
23			sub _exception{
24			my $name = shift;
25			$] > 5.008 and return 0; # 5.8.1 or higher then no
26			my %utfs = map {$_=>1}
27			qw(utf8 UCS-2BE UCS-2LE UTF-16 UTF-16BE UTF-16LE
28			UTF-32 UTF-32BE UTF-32LE);
29			$utfs{$name} or return 0; # UTFs or no
30			require Config; Config->import(); our %Config;
31			return $Config{perl_patchlevel} ? 0 : 1 # maintperl then no
32			}
33
34			sub in_locale { $^H & ($locale::hint_bits \|\| 0)}
35
36			sub _get_locale_encoding {
37			my $locale_encoding;
38
39			# I18N::Langinfo isn't available everywhere
40			eval {
41			require I18N::Langinfo;
42			I18N::Langinfo->import(qw(langinfo CODESET));
43			$locale_encoding = langinfo(CODESET());
44			};
45
46			my $country_language;
47
48			no warnings 'uninitialized';
49
50			if (not $locale_encoding && in_locale()) {
51			if ($ENV{LC_ALL} =~ /^([^.]+)\.([^.]+)$/) {
52			($country_language, $locale_encoding) = ($1, $2);
53			} elsif ($ENV{LANG} =~ /^([^.]+)\.([^.]+)$/) {
54			($country_language, $locale_encoding) = ($1, $2);
55			}
56			# LANGUAGE affects only LC_MESSAGES only on glibc
57			} elsif (not $locale_encoding) {
58			if ($ENV{LC_ALL} =~ /\butf-?8\b/i \|\|
59			$ENV{LANG} =~ /\butf-?8\b/i) {
60			$locale_encoding = 'utf8';
61			}
62			# Could do more heuristics based on the country and language
63			# parts of LC_ALL and LANG (the parts before the dot (if any)),
64			# since we have Locale::Country and Locale::Language available.
65			# TODO: get a database of Language -> Encoding mappings
66			# (the Estonian database at http://www.eki.ee/letter/
67			# would be excellent!) --jhi
68			}
69			if (defined $locale_encoding &&
70			lc($locale_encoding) eq 'euc' &&
71			defined $country_language) {
72			if ($country_language =~ /^ja_JP\|japan(?:ese)?$/i) {
73			$locale_encoding = 'euc-jp';
74			} elsif ($country_language =~ /^ko_KR\|korean?$/i) {
75			$locale_encoding = 'euc-kr';
76			} elsif ($country_language =~ /^zh_CN\|chin(?:a\|ese)?$/i) {
77			$locale_encoding = 'euc-cn';
78			} elsif ($country_language =~ /^zh_TW\|taiwan(?:ese)?$/i) {
79			$locale_encoding = 'euc-tw';
80			} else {
81			require Carp;
82			Carp::croak("encoding: Locale encoding '$locale_encoding' too ambiguous");
83			}
84			}
85
86			return $locale_encoding;
87			}
88
89			sub import {
90			my $class = shift;
91			my $name = shift;
92			if ($name eq ':_get_locale_encoding') { # used by lib/open.pm
93			my $caller = caller();
94			{
95			no strict 'refs';
96			*{"${caller}::_get_locale_encoding"} = \&_get_locale_encoding;
97			}
98			return;
99			}
100			$name = _get_locale_encoding() if $name eq ':locale';
101			my %arg = @_;
102			$name = $ENV{PERL_ENCODING} unless defined $name;
103			my $enc = find_encoding($name);
104			unless (defined $enc) {
105			require Carp;
106			Carp::croak("encoding: Unknown encoding '$name'");
107			}
108			$name = $enc->name; # canonize
109			unless ($arg{Filter}) {
110			DEBUG and warn "_exception($name) = ", _exception($name);
111			_exception($name) or ${^ENCODING} = $enc;
112			$HAS_PERLIO or return 1;
113			}else{
114			defined(${^ENCODING}) and undef ${^ENCODING};
115			# implicitly 'use utf8'
116			require utf8; # to fetch $utf8::hint_bits;
117			$^H \|= $utf8::hint_bits;
118			eval {
119			require Filter::Util::Call ;
120			Filter::Util::Call->import ;
121			filter_add(sub{
122			my $status = filter_read();
123			if ($status > 0){
124			$_ = $enc->decode($_, 1);
125			DEBUG and warn $_;
126			}
127			$status ;
128			});
129			};
130			$@ eq '' and DEBUG and warn "Filter installed";
131			}
132			defined ${^UNICODE} and ${^UNICODE} != 0 and return 1;
133			for my $h (qw(STDIN STDOUT)){
134			if ($arg{$h}){
135			unless (defined find_encoding($arg{$h})) {
136			require Carp;
137			Carp::croak("encoding: Unknown encoding for $h, '$arg{$h}'");
138			}
139			eval { binmode($h, ":raw :encoding($arg{$h})") };
140			}else{
141			unless (exists $arg{$h}){
142			eval {
143			no warnings 'uninitialized';
144			binmode($h, ":raw :encoding($name)");
145			};
146			}
147			}
148			if ($@){
149			require Carp;
150			Carp::croak($@);
151			}
152			}
153			return 1; # I doubt if we need it, though
154			}
155
156			sub unimport{
157			no warnings;
158			undef ${^ENCODING};
159			if ($HAS_PERLIO){
160			binmode(STDIN, ":raw");
161			binmode(STDOUT, ":raw");
162			}else{
163			binmode(STDIN);
164			binmode(STDOUT);
165			}
166			if ($INC{"Filter/Util/Call.pm"}){
167			eval { filter_del() };
168			}
169			}
170
171			1;
172			__END__
173
174			=pod
175
176			=head1 NAME
177
178			encoding - allows you to write your script in non-ascii or non-utf8
179
180			=head1 SYNOPSIS
181
182			use encoding "greek"; # Perl like Greek to you?
183			use encoding "euc-jp"; # Jperl!
184
185			# or you can even do this if your shell supports your native encoding
186
187			perl -Mencoding=latin2 -e '...' # Feeling centrally European?
188			perl -Mencoding=euc-kr -e '...' # Or Korean?
189
190			# more control
191
192			# A simple euc-cn => utf-8 converter
193			use encoding "euc-cn", STDOUT => "utf8"; while(<>){print};
194
195			# "no encoding;" supported (but not scoped!)
196			no encoding;
197
198			# an alternate way, Filter
199			use encoding "euc-jp", Filter=>1;
200			# now you can use kanji identifiers -- in euc-jp!
201
202			# switch on locale -
203			# note that this probably means that unless you have a complete control
204			# over the environments the application is ever going to be run, you should
205			# NOT use the feature of encoding pragma allowing you to write your script
206			# in any recognized encoding because changing locale settings will wreck
207			# the script; you can of course still use the other features of the pragma.
208			use encoding ':locale';
209
210			=head1 ABSTRACT
211
212			Let's start with a bit of history: Perl 5.6.0 introduced Unicode
213			support. You could apply C<substr()> and regexes even to complex CJK
214			characters -- so long as the script was written in UTF-8. But back
215			then, text editors that supported UTF-8 were still rare and many users
216			instead chose to write scripts in legacy encodings, giving up a whole
217			new feature of Perl 5.6.
218
219			Rewind to the future: starting from perl 5.8.0 with the B<encoding>
220			pragma, you can write your script in any encoding you like (so long
221			as the C<Encode> module supports it) and still enjoy Unicode support.
222			This pragma achieves that by doing the following:
223
224			=over
225
226			=item *
227
228			Internally converts all literals (C<q//,qq//,qr//,qw///, qx//>) from
229			the encoding specified to utf8. In Perl 5.8.1 and later, literals in
230			C<tr///> and C<DATA> pseudo-filehandle are also converted.
231
232			=item *
233
234			Changing PerlIO layers of C<STDIN> and C<STDOUT> to the encoding
235			specified.
236
237			=back
238
239			=head2 Literal Conversions
240
241			You can write code in EUC-JP as follows:
242
243			my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
244			#<-char-><-char-> # 4 octets
245			s/\bCamel\b/$Rakuda/;
246
247			And with C<use encoding "euc-jp"> in effect, it is the same thing as
248			the code in UTF-8:
249
250			my $Rakuda = "\x{99F1}\x{99DD}"; # two Unicode Characters
251			s/\bCamel\b/$Rakuda/;
252
253			=head2 PerlIO layers for C<STD(IN\|OUT)>
254
255			The B<encoding> pragma also modifies the filehandle layers of
256			STDIN and STDOUT to the specified encoding. Therefore,
257
258			use encoding "euc-jp";
259			my $message = "Camel is the symbol of perl.\n";
260			my $Rakuda = "\xF1\xD1\xF1\xCC"; # Camel in Kanji
261			$message =~ s/\bCamel\b/$Rakuda/;
262			print $message;
263
264			Will print "\xF1\xD1\xF1\xCC is the symbol of perl.\n",
265			not "\x{99F1}\x{99DD} is the symbol of perl.\n".
266
267			You can override this by giving extra arguments; see below.
268
269			=head2 Implicit upgrading for byte strings
270
271			By default, if strings operating under byte semantics and strings
272			with Unicode character data are concatenated, the new string will
273			be created by decoding the byte strings as I<ISO 8859-1 (Latin-1)>.
274
275			The B<encoding> pragma changes this to use the specified encoding
276			instead. For example:
277
278			use encoding 'utf8';
279			my $string = chr(20000); # a Unicode string
280			utf8::encode($string); # now it's a UTF-8 encoded byte string
281			# concatenate with another Unicode string
282			print length($string . chr(20000));
283
284			Will print C<2>, because C<$string> is upgraded as UTF-8. Without
285			C<use encoding 'utf8';>, it will print C<4> instead, since C<$string>
286			is three octets when interpreted as Latin-1.
287
288			=head1 FEATURES THAT REQUIRE 5.8.1
289
290			Some of the features offered by this pragma requires perl 5.8.1. Most
291			of these are done by Inaba Hiroto. Any other features and changes
292			are good for 5.8.0.
293
294			=over
295
296			=item "NON-EUC" doublebyte encodings
297
298			Because perl needs to parse script before applying this pragma, such
299			encodings as Shift_JIS and Big-5 that may contain '\' (BACKSLASH;
300			\x5c) in the second byte fails because the second byte may
301			accidentally escape the quoting character that follows. Perl 5.8.1
302			or later fixes this problem.
303
304			=item tr//
305
306			C<tr//> was overlooked by Perl 5 porters when they released perl 5.8.0
307			See the section below for details.
308
309			=item DATA pseudo-filehandle
310
311			Another feature that was overlooked was C<DATA>.
312
313			=back
314
315			=head1 USAGE
316
317			=over 4
318
319			=item use encoding [I<ENCNAME>] ;
320
321			Sets the script encoding to I<ENCNAME>. And unless ${^UNICODE}
322			exists and non-zero, PerlIO layers of STDIN and STDOUT are set to
323			":encoding(I<ENCNAME>)".
324
325			Note that STDERR WILL NOT be changed.
326
327			Also note that non-STD file handles remain unaffected. Use C<use
328			open> or C<binmode> to change layers of those.
329
330			If no encoding is specified, the environment variable L<PERL_ENCODING>
331			is consulted. If no encoding can be found, the error C<Unknown encoding
332			'I<ENCNAME>'> will be thrown.
333
334			=item use encoding I<ENCNAME> [ STDIN =E<gt> I<ENCNAME_IN> ...] ;
335
336			You can also individually set encodings of STDIN and STDOUT via the
337			C<< STDIN => I<ENCNAME> >> form. In this case, you cannot omit the
338			first I<ENCNAME>. C<< STDIN => undef >> turns the IO transcoding
339			completely off.
340
341			When ${^UNICODE} exists and non-zero, these options will completely
342			ignored. ${^UNICODE} is a variable introduced in perl 5.8.1. See
343			L<perlrun> see L<perlvar/"${^UNICODE}"> and L<perlrun/"-C"> for
344			details (perl 5.8.1 and later).
345
346			=item use encoding I<ENCNAME> Filter=E<gt>1;
347
348			This turns the encoding pragma into a source filter. While the
349			default approach just decodes interpolated literals (in qq() and
350			qr()), this will apply a source filter to the entire source code. See
351			L</"The Filter Option"> below for details.
352
353			=item no encoding;
354
355			Unsets the script encoding. The layers of STDIN, STDOUT are
356			reset to ":raw" (the default unprocessed raw stream of bytes).
357
358			=back
359
360			=head1 The Filter Option
361
362			The magic of C<use encoding> is not applied to the names of
363			identifiers. In order to make C<${"\x{4eba}"}++> ($human++, where human
364			is a single Han ideograph) work, you still need to write your script
365			in UTF-8 -- or use a source filter. That's what 'Filter=>1' does.
366
367			What does this mean? Your source code behaves as if it is written in
368			UTF-8 with 'use utf8' in effect. So even if your editor only supports
369			Shift_JIS, for example, you can still try examples in Chapter 15 of
370			C<Programming Perl, 3rd Ed.>. For instance, you can use UTF-8
371			identifiers.
372
373			This option is significantly slower and (as of this writing) non-ASCII
374			identifiers are not very stable WITHOUT this option and with the
375			source code written in UTF-8.
376
377			=head2 Filter-related changes at Encode version 1.87
378
379			=over
380
381			=item *
382
383			The Filter option now sets STDIN and STDOUT like non-filter options.
384			And C<< STDIN=>I<ENCODING> >> and C<< STDOUT=>I<ENCODING> >> work like
385			non-filter version.
386
387			=item *
388
389			C<use utf8> is implicitly declared so you no longer have to C<use
390			utf8> to C<${"\x{4eba}"}++>.
391
392			=back
393
394			=head1 CAVEATS
395
396			=head2 NOT SCOPED
397
398			The pragma is a per script, not a per block lexical. Only the last
399			C<use encoding> or C<no encoding> matters, and it affects
400			B<the whole script>. However, the <no encoding> pragma is supported and
401			B<use encoding> can appear as many times as you want in a given script.
402			The multiple use of this pragma is discouraged.
403
404			By the same reason, the use this pragma inside modules is also
405			discouraged (though not as strongly discouranged as the case above.
406			See below).
407
408			If you still have to write a module with this pragma, be very careful
409			of the load order. See the codes below;
410
411			# called module
412			package Module_IN_BAR;
413			use encoding "bar";
414			# stuff in "bar" encoding here
415			1;
416
417			# caller script
418			use encoding "foo"
419			use Module_IN_BAR;
420			# surprise! use encoding "bar" is in effect.
421
422			The best way to avoid this oddity is to use this pragma RIGHT AFTER
423			other modules are loaded. i.e.
424
425			use Module_IN_BAR;
426			use encoding "foo";
427
428			=head2 DO NOT MIX MULTIPLE ENCODINGS
429
430			Notice that only literals (string or regular expression) having only
431			legacy code points are affected: if you mix data like this
432
433			\xDF\x{100}
434
435			the data is assumed to be in (Latin 1 and) Unicode, not in your native
436			encoding. In other words, this will match in "greek":
437
438			"\xDF" =~ /\x{3af}/
439
440			but this will not
441
442			"\xDF\x{100}" =~ /\x{3af}\x{100}/
443
444			since the C<\xDF> (ISO 8859-7 GREEK SMALL LETTER IOTA WITH TONOS) on
445			the left will B<not> be upgraded to C<\x{3af}> (Unicode GREEK SMALL
446			LETTER IOTA WITH TONOS) because of the C<\x{100}> on the left. You
447			should not be mixing your legacy data and Unicode in the same string.
448
449			This pragma also affects encoding of the 0x80..0xFF code point range:
450			normally characters in that range are left as eight-bit bytes (unless
451			they are combined with characters with code points 0x100 or larger,
452			in which case all characters need to become UTF-8 encoded), but if
453			the C<encoding> pragma is present, even the 0x80..0xFF range always
454			gets UTF-8 encoded.
455
456			After all, the best thing about this pragma is that you don't have to
457			resort to \x{....} just to spell your name in a native encoding.
458			So feel free to put your strings in your encoding in quotes and
459			regexes.
460
461			=head2 tr/// with ranges
462
463			The B<encoding> pragma works by decoding string literals in
464			C<q//,qq//,qr//,qw///, qx//> and so forth. In perl 5.8.0, this
465			does not apply to C<tr///>. Therefore,
466
467			use encoding 'euc-jp';
468			#....
469			$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/;
470			# -------- -------- -------- --------
471
472			Does not work as
473
474			$kana =~ tr/\x{3041}-\x{3093}/\x{30a1}-\x{30f3}/;
475
476			=over
477
478			=item Legend of characters above
479
480			utf8 euc-jp charnames::viacode()
481			-----------------------------------------
482			\x{3041} \xA4\xA1 HIRAGANA LETTER SMALL A
483			\x{3093} \xA4\xF3 HIRAGANA LETTER N
484			\x{30a1} \xA5\xA1 KATAKANA LETTER SMALL A
485			\x{30f3} \xA5\xF3 KATAKANA LETTER N
486
487			=back
488
489			This counterintuitive behavior has been fixed in perl 5.8.1.
490
491			=head3 workaround to tr///;
492
493			In perl 5.8.0, you can work around as follows;
494
495			use encoding 'euc-jp';
496			# ....
497			eval qq{ \$kana =~ tr/\xA4\xA1-\xA4\xF3/\xA5\xA1-\xA5\xF3/ };
498
499			Note the C<tr//> expression is surrounded by C<qq{}>. The idea behind
500			is the same as classic idiom that makes C<tr///> 'interpolate'.
501
502			tr/$from/$to/; # wrong!
503			eval qq{ tr/$from/$to/ }; # workaround.
504
505			Nevertheless, in case of B<encoding> pragma even C<q//> is affected so
506			C<tr///> not being decoded was obviously against the will of Perl5
507			Porters so it has been fixed in Perl 5.8.1 or later.
508
509			=head1 EXAMPLE - Greekperl
510
511			use encoding "iso 8859-7";
512
513			# \xDF in ISO 8859-7 (Greek) is \x{3af} in Unicode.
514
515			$a = "\xDF";
516			$b = "\x{100}";
517
518			printf "%#x\n", ord($a); # will print 0x3af, not 0xdf
519
520			$c = $a . $b;
521
522			# $c will be "\x{3af}\x{100}", not "\x{df}\x{100}".
523
524			# chr() is affected, and ...
525
526			print "mega\n" if ord(chr(0xdf)) == 0x3af;
527
528			# ... ord() is affected by the encoding pragma ...
529
530			print "tera\n" if ord(pack("C", 0xdf)) == 0x3af;
531
532			# ... as are eq and cmp ...
533
534			print "peta\n" if "\x{3af}" eq pack("C", 0xdf);
535			print "exa\n" if "\x{3af}" cmp pack("C", 0xdf) == 0;
536
537			# ... but pack/unpack C are not affected, in case you still
538			# want to go back to your native encoding
539
540			print "zetta\n" if unpack("C", (pack("C", 0xdf))) == 0xdf;
541
542			=head1 KNOWN PROBLEMS
543
544			=over
545
546			=item literals in regex that are longer than 127 bytes
547
548			For native multibyte encodings (either fixed or variable length),
549			the current implementation of the regular expressions may introduce
550			recoding errors for regular expression literals longer than 127 bytes.
551
552			=item EBCDIC
553
554			The encoding pragma is not supported on EBCDIC platforms.
555			(Porters who are willing and able to remove this limitation are
556			welcome.)
557
558			=item format
559
560			This pragma doesn't work well with format because PerlIO does not
561			get along very well with it. When format contains non-ascii
562			characters it prints funny or gets "wide character warnings".
563			To understand it, try the code below.
564
565			# Save this one in utf8
566			# replace non-ascii with a non-ascii string
567			my $camel;
568			format STDOUT =
569			non-ascii@>>>>>>>
570			$camel
571			.
572			$camel = "non-ascii";
573			binmode(STDOUT=>':encoding(utf8)'); # bang!
574			write; # funny
575			print $camel, "\n"; # fine
576
577			Without binmode this happens to work but without binmode, print()
578			fails instead of write().
579
580			At any rate, the very use of format is questionable when it comes to
581			unicode characters since you have to consider such things as character
582			width (i.e. double-width for ideographs) and directions (i.e. BIDI for
583			Arabic and Hebrew).
584
585			=back
586
587			=head2 The Logic of :locale
588
589			The logic of C<:locale> is as follows:
590
591			=over 4
592
593			=item 1.
594
595			If the platform supports the langinfo(CODESET) interface, the codeset
596			returned is used as the default encoding for the open pragma.
597
598			=item 2.
599
600			If 1. didn't work but we are under the locale pragma, the environment
601			variables LC_ALL and LANG (in that order) are matched for encodings
602			(the part after C<.>, if any), and if any found, that is used
603			as the default encoding for the open pragma.
604
605			=item 3.
606
607			If 1. and 2. didn't work, the environment variables LC_ALL and LANG
608			(in that order) are matched for anything looking like UTF-8, and if
609			any found, C<:utf8> is used as the default encoding for the open
610			pragma.
611
612			=back
613
614			If your locale environment variables (LC_ALL, LC_CTYPE, LANG)
615			contain the strings 'UTF-8' or 'UTF8' (case-insensitive matching),
616			the default encoding of your STDIN, STDOUT, and STDERR, and of
617			B<any subsequent file open>, is UTF-8.
618
619			=head1 HISTORY
620
621			This pragma first appeared in Perl 5.8.0. For features that require
622			5.8.1 and better, see above.
623
624			The C<:locale> subpragma was implemented in 2.01, or Perl 5.8.6.
625
626			=head1 SEE ALSO
627
628			L<perlunicode>, L<Encode>, L<open>, L<Filter::Util::Call>,
629
630			Ch. 15 of C<Programming Perl (3rd Edition)>
631			by Larry Wall, Tom Christiansen, Jon Orwant;
632			O'Reilly & Associates; ISBN 0-596-00027-8
633
634			=cut