Programming Perl, 4th Edition

locale

@x = sort @y;       # ASCII sorting order
{
    use locale;
    @x = sort @y;   # Locale–defined sorting order
}
@x = sort @y;       # ASCII sorting order again

This lexically scoped pragma tells the compiler to enable (or disable, under no locale) POSIX locales for built-in operations. Enabling locales tells Perl’s string comparison and case-related functionality to be respectful of your POSIX language environment. If this pragma is in effect and your C library knows about POSIX locales, Perl looks to your LC_CTYPE setting for regular expressions and to your LC_COLLATE setting for string comparisons like those in sort.

Since locales are more a form of nationalization than of internationalization, the use of locales may interact oddly with Unicode. It’s more portable and more reliable to use Perl’s native Unicode facilities for matters of casing and comparison, which are standard across all installations, instead of relying on possibly dodgy vendor locales. See the sections “Comparing and Sorting Unicode Text” and “Locale Sorting” in Chapter 6.