Programming Perl, 4th Edition

sort

sort USERSUB LIST
sort BLOCK LIST
sort LIST

This function sorts the LIST and returns the sorted list value. Undefined values sort before defined null strings, which sort before everything else. By default, it sorts in simple numeric codepoint order (or whatever the cmp operator returns in case of overloading). For a true lexicographic sort, you must use the Unicode::Collate module; see Comparing and Sorting Unicode Text in Chapter 6. The short story is that the easiest way to get a good alphabetic sort is like this:

use Unicode::Collate;
@alphabetized_list = Unicode::Collate–>new–>sort(@list);

When the locale pragma is in effect, sort LIST sorts LIST according to the current collation locale. Even if such a locale exists, Perl does not support multibyte locales, so this is unlikely to do what you want. See instead the Unicode::Collate::Locale module if you want reliable locale sorting.

USERSUB, if given, is the name of a subroutine that returns an integer less than, equal to, or greater than 0, depending on how the elements of the list are to be ordered. (The handy <=> and cmp operators can be used to do three-way numeric and string comparisons.) If a USERSUB is given but that function is undefined, sort raises an exception.

In the interests of efficiency, the normal calling code for subroutines is bypassed, with the following effects: the subroutine may not be a recursive subroutine ...