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2.3.2 Locale Environment Variables

A locale is composed of several locale categories, see Aspects in Native Language Support. When a program looks up locale dependent values, it does this according to the following environment variables, in priority order:

1. LANGUAGE
2. LC_ALL
3. LC_xxx, according to selected locale category: LC_CTYPE, LC_NUMERIC, LC_TIME, LC_COLLATE, LC_MONETARY, LC_MESSAGES, ...
4. LANG

Variables whose value is set but is empty are ignored in this lookup.

LANG is the normal environment variable for specifying a locale. As a user, you normally set this variable (unless some of the other variables have already been set by the system, in /etc/profile or similar initialization files).

LC_CTYPE, LC_NUMERIC, LC_TIME, LC_COLLATE, LC_MONETARY, LC_MESSAGES, and so on, are the environment variables meant to override LANG and affecting a single locale category only. For example, assume you are a Swedish user in Spain, and you want your programs to handle numbers and dates according to Spanish conventions, and only the messages should be in Swedish. Then you could create a locale named ‘sv_ES’ or ‘sv_ES.UTF-8’ by use of the localedef program. But it is simpler, and achieves the same effect, to set the LANG variable to es_ES.UTF-8 and the LC_MESSAGES variable to sv_SE.UTF-8; these two locales come already preinstalled with the operating system.

LC_ALL is an environment variable that overrides all of these. It is typically used in scripts that run particular programs. For example, configure scripts generated by GNU autoconf use LC_ALL to make sure that the configuration tests don’t operate in locale dependent ways.

Some systems, unfortunately, set LC_ALL in /etc/profile or in similar initialization files. As a user, you therefore have to unset this variable if you want to set LANG and optionally some of the other LC_xxx variables.

The LANGUAGE variable is described in the next subsection.