Programming Perl, 4th Edition

feature

use feature ":5.10";  # this is a "feature bundle"
use feature qw(say state switch unicode_strings);

{
    no feature qw(say);
    ...;
}

Perl future-proofs itself by introducing new keywords and features through the feature pragma. This pragma enables or disables features in the lexical scope. Specify the ones you want to turn on or off either by a version tag or the feature name.

say

Enables the say keyword, which is like print but with a free newline.

state

Enables state, which allows persistent subroutine variables.

switch

Enables Perl’s super-charged switch structure, called given–when.

unicode_strings

This feature isn’t a keyword. Instead, it causes all string operations within the lexical scope to use Unicode semantics. This also applies to regexes compiled within the scope, even if they should eventually be executed outside of it. See “The Unicode Bug” in perlunicode. This feature is the only one not in the :v5.10 bundle, although it is in the :v5.12 and later bundles.