--- name: "perli18n" section: "1p" platform: "linux" package: "perl" version: "5.003.07-11" release: "Debian 1.3 (Bo)" platforms: ["linux"] url: "https://new.carta.tech/perli18n" --- # perli18n(1p) perl18n - Perl i18n (internalization) 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 naïve 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. 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 the *[setlocale(3)](/setlocale/3.md)* manpage manual. For the locales available in your system, also consult the the *[setlocale(3)](/setlocale/3.md)* manpage 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:\ \ \ \ \ 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 `Æ`, `É`, `ß`, `ø`, 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 `Á` and `Ä` 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`.\ 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 are part of the standardized (ISO C, XPG4, POSIX 1.c) setlocale method to control an application's opinion on data.\ `LC_ALL` is the "override-all" locale environment variable. If it is set, it overrides all the rest of the locale environment variables.\ `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_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`.\ 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.