Encode::Locale - Determine the locale encoding
use Encode::Locale; use Encode; $string = decode(locale => $bytes); $bytes = encode(locale => $string); if (-t) { binmode(STDIN, ":encoding(console_in)"); binmode(STDOUT, ":encoding(console_out)"); binmode(STDERR, ":encoding(console_out)"); } # Processing file names passed in as arguments my $uni_filename = decode(locale => $ARGV[0]); open(my $fh, "<", encode(locale_fs => $uni_filename)) || die "Cant open $uni_filename: $!"; binmode($fh, ":encoding(locale)"); ...
In many applications it's wise to let Perl use Unicode for the strings it processes. Most of the interfaces Perl has to the outside world are still byte based. Programs therefore need to decode byte strings that enter the program from the outside and encode them again on the way out.
The POSIX locale system is used to specify both the language
conventions requested by the user and the preferred character set to
consume and output. The Encode::Locale module looks up the
charset and encoding (called a CODESET in the locale jargon) and
arranges for the Encode module to know this encoding under the name
locale. It means bytes obtained from the environment can be converted to
Unicode strings by calling
Encode::encode(locale => $bytes) and converted back
again with Encode::decode(locale => $string).
Where file systems interfaces pass file names in and out of the program we also need care. The trend is for operating systems to use a fixed file encoding that don't actually depend on the locale; and this module determines the most appropriate encoding for file names. The Encode module will know this encoding under the name locale_fs. For traditional Unix systems this will be an alias to the same encoding as locale.
For programs running in a terminal window (called a Console on some
systems) the locale encoding is usually a good choice for what to expect
as input and output. Some systems allows us to query the encoding set
for the terminal and Encode::Locale will do that if
available and make these encodings known under the Encode
aliases console_in and console_out. For systems where we can't determine
the terminal encoding these will be aliased as the same encoding as
locale. The advice is to use console_in for input known to come from the
terminal and console_out for output to the terminal.
In addition to arranging for various Encode aliases the following functions and variables are provided:
This will decode the command line arguments to perl (the
@ARGV array) in-place. The function will by default replace
characters that can't be decoded by \x{FFFD}, the Unicode replacement
character. Any argument provided is passed as CHECK to underlying
Encode::decode() call. Pass the value
Encode::FB_CROAK to have the decoding croak if not all the
command line arguments can be decoded. See Handling Malformed Data in
Encode for details on other options for CHECK.
Interface to get/set environment variables. Returns the current value
as a Unicode string. The $uni_key and
$uni_value arguments are expected to be Unicode strings as
well. Passing undef as $uni_value deletes the
environment variable named $uni_key. The returned value
will have the characters that can't be decoded replaced by \x{FFFD}, the
Unicode replacement character. There is no interface to request
alternative CHECK behavior as for decode_argv(). If you
need that you need to call encode/decode yourself. For example: my $key
= Encode::encode(locale => $uni_key, Encode::FB_CROAK); my $uni_value
= Encode::decode(locale => $ENV{$key}, Encode::FB_CROAK);
Reinitialize the encodings from the locale. You want to call this
function if you changed anything in the environment that might influence
the locale. This function will croak if the determined encoding isn't
recognized by the Encode module. With argument force
$ENCODING_... variables to set to the given value.
The encoding name determined to be suitable for the current locale. Encode know this encoding as locale.
The encoding name determined to be suitable for file system interfaces involving file names. Encode know this encoding as locale_fs.
The encodings to be used for reading and writing output to the a console. Encode know these encodings as console_in and console_out.
This table summarizes the mapping of the encodings set up by the
Encode::Locale module:
Encode | | | Alias | Windows | Mac OS X | POSIX ------------+---------+--------------+------------ locale | ANSI | nl_langinfo | nl_langinfo locale_fs | ANSI | UTF-8 | nl_langinfo console_in | OEM | nl_langinfo | nl_langinfo console_out | OEM | nl_langinfo | nl_langinfo
Windows has basically 2 sets of APIs. A wide API (based on passing UTF-16 strings) and a byte based API based a character set called ANSI. The regular Perl interfaces to the OS currently only uses the ANSI APIs. Unfortunately ANSI is not a single character set.
The encoding that corresponds to ANSI varies between different
editions of Windows. For many western editions of Windows ANSI
corresponds to CP-1252 which is a character set similar to ISO-8859-1.
Conceptually the ANSI character set is a similar concept to the POSIX
locale CODESET so this module figures out what the ANSI code page is and
make this available as $ENCODING_LOCALE and the locale
Encoding alias.
Windows systems also operate with another byte based character set. It's called the OEM code page. This is the encoding that the Console takes as input and output. It's common for the OEM code page to differ from the ANSI code page.
On Mac OS X the file system encoding is always UTF-8 while the locale can otherwise be set up as normal for POSIX systems.
File names on Mac OS X will at the OS-level be converted to NFD-form. A file created by passing a NFC-filename will come in NFD-form from readdir(). See Unicode::Normalize for details of NFD/NFC.
Actually, Apple does not follow the Unicode NFD standard since not all character ranges are decomposed. The claim is that this avoids problems with round trip conversions from old Mac text encodings. See Encode::UTF8Mac for details.
File systems might vary in what encoding is to be used for filenames. Since this module has no way to actually figure out what the is correct it goes with the best guess which is to assume filenames are encoding according to the current locale. Users are advised to always specify UTF-8 as the locale charset.
I18N::Langinfo, Encode, Term::Encoding
Copyright 2010 Gisle Aas <gisle@aas.no>.
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.