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Filename : Messages.pm
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#! /bin/false

# vim: set autoindent shiftwidth=4 tabstop=4:

# Copyright (C) 2002-2016 Guido Flohr <guido.flohr@cantanea.com>,
# all rights reserved.

# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.

# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.

# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.

package Locale::Messages;

use strict;

use vars qw ($package @EXPORT_OK %EXPORT_TAGS @ISA $VERSION);

$VERSION = '1.26';

# Try to load the C version first.
$package = 'gettext_xs';
local @INC = @INC;
pop @INC if $INC[-1] eq '.';
eval <<'EOF';
require Locale::gettext_xs; 
my $version = Locale::gettext_xs::__gettext_xs_version();
die "Version: version mismatch ($VERSION vs. $version)" unless $version eq $VERSION;
EOF
my $no_xs = $@;

# There are systems where setlocale() and the LC_ constants are not
# defined at all, see https://rt.cpan.org/Ticket/Display.html?id=98109
#
# On such systems, we always fall back to gettext_dumb.
if ($no_xs) {
    local @INC = @INC;
    pop @INC if $INC[-1] eq '.';
    eval {
        require POSIX;
        # void
        POSIX::setlocale(POSIX::LC_ALL());
    };
    if ($@) {
        $package = 'gettext_dumb';
        require Locale::gettext_dumb;
    } else {
        $package = 'gettext_pp';
        require Locale::gettext_pp;
    }
}
		
require Exporter;
@ISA = qw (Exporter);
%EXPORT_TAGS = (locale_h => [ qw (gettext
				  dgettext
				  dcgettext
				  ngettext
				  dngettext
				  dcngettext
				  pgettext
				  dpgettext
				  dcpgettext
				  npgettext
				  dnpgettext
				  dcnpgettext
				  textdomain
				  bindtextdomain
				  bind_textdomain_codeset
				  )
			       ],
		 libintl_h => [ qw (LC_CTYPE
				    LC_NUMERIC
				    LC_TIME
				    LC_COLLATE
				    LC_MONETARY
				    LC_MESSAGES
				    LC_ALL)
				],
		 );

@EXPORT_OK = qw (select_package
				 turn_utf_8_on
				 turn_utf_8_off
				 gettext
				 dgettext
				 dcgettext
				 ngettext
				 dngettext
				 dcngettext
				 pgettext
				 dpgettext
				 dcpgettext
				 npgettext
				 dnpgettext
				 dcnpgettext
				 textdomain
				 bindtextdomain
				 bind_textdomain_codeset
				 bind_textdomain_filter
                 nl_putenv
                 setlocale
				 LC_CTYPE
				 LC_NUMERIC
				 LC_TIME
				 LC_COLLATE
				 LC_MONETARY
				 LC_MESSAGES
				 LC_ALL);

BEGIN {
	my ($has_encode, $has_bytes);
	
	if ($] >= 5.006) {
		unless (defined $has_encode) {
			eval "require Encode";
			$has_encode = !$@;
		}

		unless ($has_encode || defined $has_bytes) {
			eval "use bytes";
			$has_bytes = !$@;
		}
	}

	# Turn the UTF-8 flag on or off unconditionally.  The prototypes
	# allow an optional second parameter, so that you can use the
	# functions as callbacks to bind_textdomain_filter.
	if ($has_encode) {
		eval <<'EOF';
sub turn_utf_8_on($;$)
{
	Encode::_utf8_on ($_[0]);
	return $_[0];
}

sub turn_utf_8_off($;$)
{
	Encode::_utf8_off ($_[0]);
	return $_[0];
}

EOF
	} elsif ($has_bytes) {
		eval <<'EOF';
sub turn_utf_8_on($;$)
{
	$_[0] = pack "U0C*", unpack "C*", $_[0];
}

sub turn_utf_8_off($;$)
{
	use bytes;
	$_[0] = join "", split //, $_[0];
}

EOF
	} else {
		eval <<'EOF';
sub turn_utf_8_on($;$)
{
	return $_[0];
}

sub turn_utf_8_off($;$)
{
	return $_[0];
}

EOF
	}
}

# The textdomain could be undef.  We avoid a warning by specifying
# a filter for the undefined textdomain.
my %filters = (undef => \&turn_utf_8_off);

sub select_package {
    my ($pkg, $compatibility) = @_;

    # Compatibility quirk for a bug pre 1.17:
    if (__PACKAGE__ eq $pkg && defined $compatibility) {
        $pkg = $compatibility;
    }

    if ($no_xs && 'gettext_xs' eq $pkg) {
        $pkg = 'gettext_pp';
    }

    if (defined $pkg && 'gettext_pp' eq $pkg) {
        # This branch is not unnecessary.  The next (elsif) branch does
        # essentially the same but catches compilation errors.
        require Locale::gettext_pp;
        $package = 'gettext_pp';
    } elsif (defined $pkg) {
        my $filename = "Locale::$pkg";
        $filename =~ s{::|\'}{/};
	$filename .= '.pm';
        eval {
            local @INC = @INC;
            pop @INC if $INC[-1] eq '.';
            require $filename
        };
	$package = $pkg unless $@;   
    } else {
        local @INC = @INC;
        pop @INC if $INC[-1] eq '.';
        eval "require Locale::gettext_xs";
        $package = 'gettext_xs' unless $@;
    }

    return $package;
}

sub bind_textdomain_filter ($;$$) {
	my ($textdomain, $coderef, $data) = @_;

	$filters{$textdomain} = [ $coderef, $data ];

	return 1;
}

sub textdomain (;$) {
    my $function = "Locale::${package}::textdomain";
    
    no strict 'refs';
    &$function;
}

sub bindtextdomain ($;$) {
    my $function = "Locale::${package}::bindtextdomain";

    no strict 'refs';
    &$function;
}

sub bind_textdomain_codeset ($;$) {
    my $function = "Locale::${package}::bind_textdomain_codeset";

    no strict 'refs';    
    &$function;
}

sub gettext ($) {
    my $textdomain = textdomain;
    $filters{$textdomain} ||= [ \&turn_utf_8_off ];
    my $cb = $filters{$textdomain};

    my $function = "Locale::${package}::gettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dgettext($$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dcgettext($$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dcgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub ngettext($$$) {
    my $textdomain = textdomain;
    $filters{$textdomain} ||= [ \&turn_utf_8_off ];
    my $cb = $filters{$textdomain};

    my $function = "Locale::${package}::ngettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dngettext($$$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dngettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dcngettext($$$$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dcngettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub pgettext($$) {
    my $textdomain = textdomain;
    $filters{$textdomain} ||= [ \&turn_utf_8_off ];
    my $cb = $filters{$textdomain};

    my $function = "Locale::${package}::pgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dpgettext($$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dpgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dcpgettext($$$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dcpgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub npgettext($$$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::npgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dnpgettext($$$$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dnpgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub dcnpgettext($$$$$$) {
    my $cb = $filters{$_[0]} ||= [ \&turn_utf_8_off ];

    my $function = "Locale::${package}::dcnpgettext";
    
    no strict 'refs';
    $cb->[0] (&$function, $cb->[1]);
}

sub setlocale($;$) {
    my $function = "Locale::${package}::setlocale";
    
    no strict 'refs';
    &$function;
}

sub nl_putenv($) {
    my $function = "Locale::${package}::nl_putenv";
    
    no strict 'refs';
    &$function;
}

sub LC_NUMERIC {
    my $function = "Locale::${package}::LC_NUMERIC";
    
    no strict 'refs';
    &$function;
}

sub LC_CTYPE {
    my $function = "Locale::${package}::LC_CTYPE";
    
    no strict 'refs';
    &$function;
}

sub LC_TIME {
    my $function = "Locale::${package}::LC_TIME";
    
    no strict 'refs';
    &$function;
}

sub LC_COLLATE {
    my $function = "Locale::${package}::LC_COLLATE";
    
    no strict 'refs';
    &$function;
}

sub LC_MONETARY {
    my $function = "Locale::${package}::LC_MONETARY";
    
    no strict 'refs';
    &$function;
}

sub LC_MESSAGES {
    my $function = "Locale::${package}::LC_MESSAGES";
    
    no strict 'refs';
    &$function;
}

sub LC_ALL {
    my $function = "Locale::${package}::LC_ALL";
    
    no strict 'refs';
    &$function;
}

1;

__END__

=head1 NAME

Locale::Messages - Gettext Like Message Retrieval

=head1 SYNOPSIS

 use Locale::Messages (:locale_h :libintl_h);

 gettext $msgid;
 dgettext $textdomain, $msgid;
 dcgettext $textdomain, $msgid, LC_MESSAGES;
 ngettext $msgid, $msgid_plural, $count;
 dngettext $textdomain, $msgid, $msgid_plural, $count;
 dcngettext $textdomain, $msgid, $msgid_plural, $count, LC_MESSAGES;
 pgettext $msgctxt, $msgid;
 dpgettext $textdomain, $msgctxt, $msgid;
 dcpgettext $textdomain, $msgctxt, $msgid, LC_MESSAGES;
 npgettext $msgctxt, $msgid, $msgid_plural, $count;
 dnpgettext $textdomain, $msgctxt, $msgid, $msgid_plural, $count;
 dcnpgettext $textdomain, $msgctxt, $msgid, $msgid_plural, $count, LC_MESSAGES;
 textdomain $textdomain;
 bindtextdomain $textdomain, $directory;
 bind_textdomain_codeset $textdomain, $encoding;
 bind_textdomain_filter $textdomain, \&filter, $data;
 turn_utf_8_on ($variable);
 turn_utf_8_off ($variable);
 nl_putenv ('OUTPUT_CHARSET=koi8-r');
 my $category = LC_CTYPE;
 my $category = LC_NUMERIC;
 my $category = LC_TIME;
 my $category = LC_COLLATE;
 my $category = LC_MONETARY;
 my $category = LC_MESSAGES;
 my $category = LC_ALL;

=head1 DESCRIPTION

The module B<Locale::Messages> is a wrapper around the interface to
message translation according to the Uniforum approach that is
for example used in GNU gettext and Sun's Solaris.  It is intended
to allow Locale::Messages(3) to switch between different implementations
of the lower level libraries but this is not yet implemented.

Normally you should not use this module directly, but the high
level interface Locale::TextDomain(3) that provides a much simpler
interface.  This description is therefore deliberately kept
brief.  Please refer to the GNU gettext documentation available at
L<http://www.gnu.org/manual/gettext/> for in-depth and background 
information on the topic.

The lower level module Locale::gettext_pp(3) provides the Perl
implementation of gettext() and related functions.

=head1 FUNCTIONS

The module exports by default nothing.  Every function has to be
imported explicitly or via an export tag (L</"EXPORT TAGS">).

=over 4

=item B<gettext MSGID>

Returns the translation for B<MSGID>.  Example:

    print gettext "Hello World!\n";

If no translation can be found, the unmodified B<MSGID> is returned,
i. e. the function can I<never> fail, and will I<never> mess up your
original message.

Note for Perl 5.6 and later: The returned string will I<always> have
the UTF-8 flag off by default.  See the documentation for function
bind_textdomain_filter() for a way to change this behavior.

One common mistake is this:

    print gettext "Hello $name!";

Perl will interpolate the variable C<$name> I<before> the function
will see the string.  Unless the corresponding message catalog 
contains a message "Hello Tom!", "Hello Dick!" or "Hello Harry!",
no translation will be found.

Using printf() and friends has its own problems:

    print sprintf (gettext ("This is the %s %s."), $color, $thing);

(The example is stupid because neither color nor thing will get
translated here ...).

In English the adjective (the color) will precede the noun, many
other languages (for example French or Italian) differ here.  The 
translator of the message may therefore have a hard time to find
a translation that will still work and not sound stupid in the 
target language.  Many C implementations of printf() allow one to 
change the order of the arguments, and a French translator could
then say:

    "C'est le %2$s %1$s."

Perl printf() implements this feature as of version 5.8 or better.
Consequently you can only use it, if you are sure that your software
will run with Perl 5.8 or a later version.

Another disadvantage of using printf() is its cryptic syntax (maybe
not for you but translators of your software may have their own
opinion).

See the description of the function C<__x()> in Locale::TextDomain(3)
for a much better way to get around this problem.

Non-ASCII message ids ...

You should note that the function (and all other similar functions
in this module) does a bytewise comparison of the B<MSGID> for the
lookup in the translation catalog, no matter whether obscure utf-8
flags are set on it, whether the string looks like utf-8, whether
the utf8(3pm) pragma is used, or whatever other weird method past
or future perl(1) versions invent for guessing character sets of
strings.

Using other than us-ascii characters in Perl source code is a call
for trouble, a compatibility nightmare.  Furthermore, GNU gettext
only lately introduced support for non-ascii character sets in sources,
and support for this feature may not be available everywhere.  If
you absolutely want to use B<MSGID>s in non-ascii character sets,
it is wise to choose utf-8.  This will minimize the risk that perl(1)
itself will mess with the strings, and it will also be a guaranty
that you can later translate your project into arbitrary target
languages.

Other character sets can theoretically work.  Yet, using another
character set in the Perl source code than the one used in your
message catalogs will B<never> work, since the lookup is done bytewise,
and all strings with non-ascii characters will not be found.

Even if you have solved all these problems, there is still one show
stopper left: The gettext runtime API lacks a possibility to specify 
the character set of the source code (including the original strings).
Consequently - in absence of a hint for the input encoding - strings 
without a translation are not subject to output character set conversion.
In other words: If the (non-determinable) output character set differs
from the character set used in the source code, output can be a
mixture of two character sets.  There is no point in trying to address
this problem in the pure Perl version of the gettext functions.  because
breaking compatibility between the Perl and the C version is a price too
high to pay.

This all boils down to: Only use ASCII characters in your translatable
strings!

=item B<dgettext TEXTDOMAIN, MSGID>

Like gettext(), but retrieves the message for the specified 
B<TEXTDOMAIN> instead of the default domain.  In case you wonder what
a textdomain is, you should really read on with Locale::TextDomain(3).

=item B<dcgettext TEXTDOMAIN, MSGID, CATEGORY>

Like dgettext() but retrieves the message from the specified B<CATEGORY>
instead of the default category C<LC_MESSAGES>.

=item B<ngettext MSGID, MSGID_PLURAL, COUNT>

Retrieves the correct translation for B<COUNT> items.  In legacy software
you will often find something like:

    print "$count file(s) deleted.\n";

or

    printf "$count file%s deleted.\n", $count == 1 ? '' : 's';

The first example looks awkward, the second will only work in English
and languages with similar plural rules.  Before ngettext() was introduced,
the best practice for internationalized programs was:

    if ($count == 1) {
        print gettext "One file deleted.\n";
    } else {
        printf gettext "%d files deleted.\n";
    }

This is a nuisance for the programmer and often still not sufficient
for an adequate translation.  Many languages have completely different
ideas on numerals.  Some (French, Italian, ...) treat 0 and 1 alike,
others make no distinction at all (Japanese, Korean, Chinese, ...),
others have two or more plural forms (Russian, Latvian, Czech,
Polish, ...).  The solution is:

    printf (ngettext ("One file deleted.\n",
                     "%d files deleted.\n",
                     $count), # argument to ngettext!
            $count);          # argument to printf!

In English, or if no translation can be found, the first argument
(B<MSGID>) is picked if C<$count> is one, the second one otherwise.
For other languages, the correct plural form (of 1, 2, 3, 4, ...)
is automatically picked, too.  You don't have to know anything about
the plural rules in the target language, ngettext() will take care
of that.

This is most of the time sufficient but you will have to prove your
creativity in cases like

    printf "%d file(s) deleted, and %d file(s) created.\n";

=item B<dngettext TEXTDOMAIN, MSGID, MSGID_PLURAL, COUNT>

Like ngettext() but retrieves the translation from the specified
textdomain instead of the default domain.

=item B<dcngettext TEXTDOMAIN, MSGID, MSGID_PLURAL, COUNT, CATEGORY>

Like dngettext() but retrieves the translation from the specified
category, instead of the default category C<LC_MESSAGES>.

=item B<pgettext MSGCTXT, MSGID>

Returns the translation of MSGID, given the context of MSGCTXT.

Both items are used as a unique key into the message catalog.

This allows the translator to have two entries for words that may
translate to different foreign words based on their context. For
example, the word "View" may be a noun or a verb, which may be
used in a menu as File->View or View->Source.

    pgettext "Verb: To View", "View\n";
    pgettext "Noun: A View", "View\n";

The above will both lookup different entries in the message catalog.

A typical usage are GUI programs.  Imagine a program with a main
menu and the notorious "Open" entry in the "File" menu.  Now imagine,
there is another menu entry Preferences->Advanced->Policy where you have 
a choice between the alternatives "Open" and "Closed".  In English, "Open"
is the adequate text at both places.  In other languages, it is very
likely that you need two different translations.  Therefore, you would
now write:

    pgettext "File|", "Open";
    pgettext "Preferences|Advanced|Policy", "Open";

In English, or if no translation can be found, the second argument
(MSGID) is returned.

The function was introduced with libintl-perl version 1.17.

=item B<dpgettext TEXTDOMAIN, MSGCTXT, MSGID>

Like pgettext(), but retrieves the message for the specified 
B<TEXTDOMAIN> instead of the default domain.

The function was introduced with libintl-perl version 1.17.

=item B<dcpgettext TEXTDOMAIN, MSGCTXT, MSGID, CATEGORY>

Like dpgettext() but retrieves the message from the specified B<CATEGORY>
instead of the default category C<LC_MESSAGES>.

The function was introduced with libintl-perl version 1.17.

=item B<npgettext MSGCTXT, MSGID, MSGID_PLURAL, COUNT>

Like ngettext() with the addition of context as in pgettext().

In English, or if no translation can be found, the second argument
(MSGID) is picked if $count is one, the third one otherwise.

The function was introduced with libintl-perl version 1.17.

=item B<dnpgettext TEXTDOMAIN, MSGCTXT, MSGID, MSGID_PLURAL, COUNT>

Like npgettext() but retrieves the translation from the specified
textdomain instead of the default domain.

The function was introduced with libintl-perl version 1.17.

=item B<dcnpgettext TEXTDOMAIN, MSGCTXT, MSGID, MSGID_PLURAL, COUNT, CATEGORY>

Like dnpgettext() but retrieves the translation from the specified
category, instead of the default category C<LC_MESSAGES>.

The function was introduced with libintl-perl version 1.17.

=item B<textdomain TEXTDOMAIN>

Sets the default textdomain (initially 'messages').

=item B<bindtextdomain TEXTDOMAIN, DIRECTORY>

Binds B<TEXTDOMAIN> to B<DIRECTORY>.  Huh? An example:

    bindtextdomain "my-package", "./mylocale";

Say, the selected locale (actually the selected locale for category
C<LC_MESSAGES>) of the program is 'fr_CH', then the message catalog
will be expected in F<./mylocale/fr_CH/LC_MESSAGES/my-package.mo>.

=item B<bind_textdomain_codeset TEXTDOMAIN, ENCODING>

Sets the output encoding for B<TEXTDOMAIN> to B<ENCODING>.  

=item B<bind_textdomain_filter TEXTDOMAN, CODEREF, DATA>

=item B<bind_textdomain_filter TEXTDOMAN, CODEREF>

By default, Locale::Messages will turn the utf-8 flag of all returned
messages off.  If you want to change this behavior, you can pass
a reference to a subroutine that does different things - for example
turn the utf-8 flag on, or leave it untouched.  The callback function 
will be called with B<DATA> as the first, and the possibly 
translated string as the second argument.  It should return the
possibly modified string.

If you want an object method to be called, pass the object itself
in the data parameter and write a wrapper function.  Example:

    sub wrapper { 
        my ($string, $obj) = @_;
 
        $obj->filterMethod ($string);
    }
    my $obj = MyPackage->new;

    bind_textdomain_filter ('mydomain', \&wrapper, $obj);

The function cannot fail and always returns a true value.

B<Attention:> If you use the function for setting the utf-8 flag,
it is B<your> responsibility to ensure that the output is really
utf-8.  You should only use it, if you have set the environment
variable B<OUTPUT_CHARSET> to "utf-8".  Additionally you should
call bind_textdomain_codeset() with "utf-8" as the second
argument.

Steven Haryanto has written a module Locale::TextDomain::UTF8(3pm)
that addresses the same problem.

This function has been introduced in libintl-perl 1.16 and it is
B<not> part of the standard gettext API.

=item B<turn_utf_8_on VARIABLE>

Returns VARIABLE but with the UTF-8 flag (only known in Perl >=5.6)
guaranteed to be turned on.  This function does not really fit into
the module, but it is often handy nevertheless.

The flag does B<not> mean that the string is in fact valid utf-8!

The function was introduced with libintl-perl version 1.16.

=item B<turn_utf_8_off VARIABLE>

Returns VARIABLE but with the UTF-8 flag (only known in Perl >=5.6)
guaranteed to be turned off.  This function does not really fit into
the module, but it is often handy nevertheless.

The function was introduced with libintl-perl version 1.07.

=item B<select_package PACKAGE>

By default, B<Locale::Messages> will try to load the XS version of
the gettext implementation, i. e. Locale::gettext_xs(3) and will fall
back to the pure Perl implementation Locale::gettext_pp(3).  You can
override this behavior by passing the string "gettext_pp" or
"gettext_xs" to the function select_package().  Passing "gettext_pp"
here, will prefer the pure Perl implementation.

You will normally want to use that in a BEGIN block of your main
script.

The function was introduced with libintl-perl version 1.03 and is not
part of the standard gettext API.

Beginning with version 1.22 you can pass other package names than "gettext_pp"
or "gettext_xs" and use a completely different backend.  It is the caller's
responsibility to make sure that the selected package offers the same
interface as the two standard packages.

One package that offers that functionality is Locale::gettext_dumb(3pm).

=item B<nl_putenv ENVSPEC>

Resembles the ANSI C putenv(3) function.  The sole purpose of this 
function is to work around some ideosyncrasies in the environment
processing of Windows systems.  If you want to portably set or
unset environment variables, use this function instead of directly
manipulating C<%ENV>.

The argument B<ENVSPEC> may have three different forms.

=over 8

=item B<LANGUAGE=fr_CH>

This would set the environment variable C<LANGUAGE> to "fr_CH".

=item B<LANGUAGE=>

Normally, this will set the environment variable C<LANGUAGE> to an
empty string.  Under Windows, however, the environment variable will
be deleted instead (and is no longer present in C<%ENV>).  Since
within libintl-perl empty environment variables are useless, consider
this usage as deprecated.

=item B<LANGUAGE>

This will delete the environment variable B<LANGUAGE>.  If you are
familiar with the brain-damaged implementation of putenv(3) (resp.
_putenv()) in the so-called standard C library of MS-Windows, you
may suspect that this is an invalid argument.  This is not the case!
Passing a variable name not followed by an equal sign will always
delete the variable, no matter which operating system you use.

=back

The function returns true for success, and false for failure.  Possible
reasons for failure are an invalid syntax or - only under Windows -
failure to allocate space for the new environment entry ($! will be
set accordingly in this case).

Why all this hassle?  The 32-bit versions of MS-DOS (currently
Windows 95/98/ME/NT/2000/XP/CE/.NET) maintain two distinct blocks
of environment variables per process.  Which block is considered
the "correct" environment is a compile-time option of the Perl
interpreter.  Unfortunately, if you have build the XS version 
Locale::gettext_xs(3) under Windows, the underlying library may use 
a different environment block, and changes you make to C<%ENV> may
not be visible to the library.

The function nl_putenv() is mostly a funny way of saying

    LANGUAGE=some_value
    
but it does its best, to pass this information to the gettext 
library.  Under other operating systems than Windows, it only
operates on C<%ENV>, under Windows it will call the C library
function _putenv() (after doing some cleanup to its arguments),
before manipulating C<%ENV>.

Please note, that your C<%ENV> is updated by nl_putenv() automatically.

The function has been introduced in libintl-perl version 1.10.

=item setlocale

Modifies and queries program's locale, see the documentation for setlocale()
in POSIX(3pm) instead.

On some systems, when using GNU gettext, a call from C to setlocale() is
- with the help of the C preprocessor - really a call to libintl_setlocale(),
which is in turn a wrapper around the system setlocale(3).  Failure to call
libintl_setlocale() may lead to certain malfunctions.  On such systems,
B<Locale::Messages::setlocale()> will call the wrapper libintl_setlocale().
If you want to avoid problems, you should therefore always call
the setlocale() implementation in Locale::Messages(3pm).

See L<https://rt.cpan.org/Public/Bug/Display.html?id=83980> or
L<https://savannah.gnu.org/bugs/?38162>, and 
L<https://savannah.gnu.org/bugs/?func=detailitem&item_id=44645> for a discussion
of the problem.

The function has been introduced in libintl-perl version 1.24.

=back

=head1 CONSTANTS

You can (maybe) get the same constants from POSIX(3); see there for
a detailed description

=over 4

=item B<LC_CTYPE>

=item B<LC_NUMERIC>

=item B<LC_TIME>

=item B<LC_COLLATE>

=item B<LC_MONETARY>

=item B<LC_MESSAGES>

This locale category was the reason that these constants from POSIX(3)
were included here.  Even if it was present in your systems C include
file F<locale.h>, it was not provided by POSIX(3).  Perl 5.8 and later
seems to export the constant if available, although it is not documented
in POSIX(3).

Locale::Messages(3) makes an attempt to guess the value of this category for
all systems, and assumes the arbitrary value 1729 otherwise.

=item B<LC_ALL>

If you specify the category B<LC_ALL> as the first argument to
POSIX::setlocale(), I<all> locale categories will be affected at once.

=back

=head1 EXPORT TAGS

The module does not export anything unless explicitly requested.
You can import groups of functions via two tags:

=over 4

=item B<use Locale::Messages (':locale_h')>

Imports the functions that are normally defined in the C include
file F<locale.h>:

=over 8

=item B<gettext()>

=item B<dgettext()>

=item B<dcgettext()>

=item B<ngettext()>

=item B<dngettext()>

=item B<dcngettext()>

=item B<pgettext()>

=item B<dpgettext()>

=item B<dcpgettext()>

=item B<npgettext()>

=item B<dnpgettext()>

=item B<dcnpgettext()>

=item B<textdomain()>

=item B<bindtextdomain()>

=item B<bind_textdomain_codeset()>

=back

=item B<use Locale::Messages (':libintl_h')>

Imports the locale category constants:

=over 8

=item B<LC_CTYPE>

=item B<LC_NUMERIC>

=item B<LC_TIME>

=item B<LC_COLLATE>

=item B<LC_MONETARY>

=item B<LC_MESSAGES>

=item B<LC_ALL>

=back

=back

=head1 OTHER EXPORTS

=over 4

=item B<select_package PACKAGE>

=back

=head1 USAGE

A complete example:

    1: use Locale::Messages qw (:locale_h :libintl_h);
    2: use POSIX qw (setlocale);
    3: setlocale (LC_MESSAGES, '');
    4: textdomain ('my-package');
    5: bindtextdomain ('my-package' => '/usr/local/share/locale');
    6:
    7: print gettext ("Hello world!\n");

Step by step: Line 1 imports the necessary functions and constants.
In line 3 we set the locale for category LC_MESSAGES to the default
user settings.  For C programs you will often read that LC_ALL
is the best category here but this will also change the locale for
LC_NUMERIC and many programs will not work reliably after changing
that category in Perl; choose your own poison!

In line 4 we say that all messages (translations) without an explicit
domain specification should be retrieved from the message catalog
for the domain 'my-package'.  Line 5 has the effect that the message
catalog will be searched under the directory F</usr/local/share/locale>.

If the user has selected the locale 'fr_CH', and if the file 
F</usr/local/share/locale/fr_CH/LC_MESSAGES/my-package.mo>
exists, and if it contains a GNU message object file with a translation
for the string "Hello world!\n", then line 7 will print the French
translation (for Switzerland CH) to STDOUT.

The documentation for GNU gettext explains how to extract translatable
strings from your Perl files and how to create message catalogs.

Another less portable example: If your system uses the GNU libc you
should be able to find various files with the name F<libc.mo>, the
message catalog for the library itself.  If you have found these
files under F</usr/share/locale>, then you can try the following:

    use Locale::Messages qw (:locale_h :libintl_h);
    use POSIX qw (setlocale);

    setlocale LC_MESSAGES, "";
    textdomain "libc";

    # The following is actually not needed, since this is
    # one of the default search directories.
    bindtextdomain libc => '/usr/share/locale';
    bind_textdomain_codeset libc => 'iso-8859-1';

    print gettext ("No such file or directory");

See Locale::TextDomain(3) for much simpler ways.

=head1 AUTHOR

Copyright (C) 2002-2016 L<Guido Flohr|http://www.guido-flohr.net/>
(L<mailto:guido.flohr@cantanea.com>), all rights reserved.  See the source
code for details!code for details!

=head1 SEE ALSO

Locale::TextDomain(3pm), Locale::gettext_pp(3pm), Encode(3pm),
Locale::TextDomain::UTF8(3pm), perllocale(3pm), POSIX(3pm), perl(1), 
gettext(1), gettext(3)

=cut

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