# NAME

perl18n - Perl i18n (internalization)

# DESCRIPTION

Perl supports the language-specific notions of data like ``is this a letter'' and ``which letter comes first''. These are very important issues especially for languages other than English -- but also for English: it would be very na&239;ve indeed to think that `A-Za-z` defines all the letters.

Perl understands the language-specific data via the standardized (ISO C, XPG4, POSIX 1.c) method called ``the locale system''. The locale system is controlled per application using one function call and several environment variables.

# USING LOCALES

If your operating system supports the locale system and you have installed the locale system and you have set your locale environment variables correctly (please see below) before running Perl, Perl will understand your data correctly according to your locale settings.

In runtime you can switch locales using the POSIX::setlocale().

            # setlocale is the function call
            # LC_CTYPE will be explained later
            use POSIX qw(setlocale LC_CTYPE);
            # query and save the old locale.
            $old_locale = setlocale(LC_CTYPE);
            setlocale(LC_CTYPE, "fr_CA.ISO8859-1");
            # for LC_CTYPE now in locale "French, Canada, codeset ISO 8859-1"
            setlocale(LC_CTYPE, "");
            # for LC_CTYPE now in locale what the LC_ALL / LC_CTYPE / LANG define.
            # see below for documentation about the LC_ALL / LC_CTYPE / LANG.
            # restore the old locale
            setlocale(LC_CTYPE, $old_locale);

The first argument of `setlocale()` is called the category and the second argument the locale. The category tells in what aspect of data processing we want to apply language-specific rules, the locale tells in what language-country/territory-codeset - but read on for the naming of the locales: not all systems name locales as in the example.

For further information about the categories, please consult your setlocale(3) manual. For the locales available in your system, also consult the setlocale(3) manual and see whether it leads you to the list of the available locales (search for the `SEE ALSO` section). If that fails, try out in command line the following commands:

locale -a

nlsinfo

ls /usr/lib/nls/loc

ls /usr/lib/locale

ls /usr/lib/nls

and see whether they list something resembling these en_US.ISO8859-1 de_DE.ISO8859-1 ru_RU.ISO8859-5 en_US de_DE ru_RU en de ru english german russian english.iso88591 german.iso88591 russian.iso88595

Sadly enough even if the calling interface has been standardized the names of the locales are not. The naming usually is language-country/territory-codeset but the latter parts may not be present. Two special locales are worth special mention:

            "C"

and ``POSIX''

Currently and effectively these are the same locale: the difference is mainly that the first one is defined by the C standard and the second one is defined by the POSIX standard. What they mean and define is the default locale in which every program does start in. The language is (American) English and the character codeset `ASCII`. NOTE: not all systems have the ```POSIX''` locale (not all systems are POSIX): use the ```C''` locale when you need the default locale.

## Category LC_CTYPE: CHARACTER TYPES

Starting from Perl version 5.002 perl has obeyed the LC_CTYPE environment variable which controls application's notions on which characters are alphabetic characters. This affects in Perl the regular expression metanotation

            \w

which stands for alphanumeric characters, that is, alphabetic and numeric characters (please consult the perlre manpage for more information about regular expressions). Thanks to the LC_CTYPE , depending on your locale settings, characters like `&198;`, `&201;`, `&223;`, `&248;`, can be understood as `\w` characters.

## Category LC_COLLATE: COLLATION

Starting from Perl version 5.003_06 perl has obeyed the LC_COLLATE environment variable which controls application's notions on the collation (ordering) of the characters. `B` does in most Latin alphabets follow the `A` but where do the `&193;` and `&196;` belong?

Here is a code snippet that will tell you what are the alphanumeric characters in the current locale, in the locale order:

            perl -le 'print sort grep /\w/, map { chr() } 0..255'

As noted above, this will work only for Perl versions 5.003_06 and up.

NOTE: in the pre-5.003_06 Perl releases the per-locale collation was possible using the `I18N::Collate` library module. This is now mildly obsolete and to be avoided. The LC_COLLATE functionality is integrated into the Perl core language and one can use scalar data completely normally -- there is no need to juggle with the scalar references of `I18N::Collate`.

# ENVIRONMENT

PERL_BADLANG
  A string that controls whether Perl warns in its startup about failed locale settings. This can happen if the locale support in the operating system is lacking (broken) is some way. If this string has an integer value differing from zero, Perl will not complain. NOTE: this is just hiding the warning message: the message tells about some problem in your system's locale support and you should investigate what the problem is.

The following environment variables are not specific to Perl: they arepart of the standardized (ISO C, XPG4, POSIX 1.c) setlocale method to control an application's opinion on data.

LC_ALL
  LC_ALL is the ``override-all'' locale environment variable. If it is set, it overrides all the rest of the locale environment variables.

LC_CTYPE
  LC_ALL controls the classification of characters, see above.

  If this is unset and the LC_ALL is set, the LC_ALL is used as the LC_CTYPE . If both this and the LC_ALL are unset but the LANG is set, the LANG is used as the LC_CTYPE . If none of these three is set, the default locale ```C''` is used as the LC_CTYPE .

LC_COLLATE
  LC_ALL controls the collation of characters, see above.

  If this is unset and the LC_ALL is set, the LC_ALL is used as the LC_CTYPE . If both this and the LC_ALL are unset but the LANG is set, the LANG is used as the LC_COLLATE . If none of these three is set, the default locale ```C''` is used as the LC_COLLATE .

LANG
  LC_ALL is the ``catch-all'' locale environment variable. If it is set, it is used as the last resort if neither of the LC_ALL and the category-specific `LC_...` are set.

There are further locale-controlling environment variables(`LC_MESSAGES, LC_MONETARY, LC_NUMERIC, LC_TIME`) but Perl does not currently obey them.