15.5.21.3 How to Extract Hash Keys

Translating messages at runtime is normally performed by looking up the original string in the translation database and returning the translated version. The “natural” Perl implementation is a hash lookup, and, of course, xgettext supports such practice.

print __"Hello world!";
print $__{"Hello world!"};
print $__->{"Hello world!"};
print $$__{"Hello world!"};

The above four lines all do the same thing. The Perl module Locale::TextDomain exports by default a hash %__ that is tied to the function __(). It also exports a reference $__ to %__.

If an argument to the xgettext option --keyword, resp. -k starts with a percent sign, the rest of the keyword is interpreted as the name of a hash. If it starts with a dollar sign, the rest of the keyword is interpreted as a reference to a hash.

Note that you can omit the quotation marks (single or double) around the hash key (almost) whenever Perl itself allows it:

print $gettext{Error};

The exact rule is: You can omit the surrounding quotes, when the hash key is a valid C (!) identifier, i.e. when it starts with an underscore or an ASCII letter and is followed by an arbitrary number of underscores, ASCII letters or digits. Other Unicode characters are not allowed, regardless of the use utf8 pragma.