If you want it to be initialized once at run time and universally accessible for the remainder of the script's life, you could also accomplish this using a closure:

#!/usr/bin/perl
use strict;
use warnings;

sub definer {
    my $value = shift;
    sub outputter {
        no warnings "closure";
        print "$value\n";
    }
}

definer(5);
outputter();
definer(6);
outputter();
[download]

If you are optimizing, do some profiling first to make sure that you are actually optimizing where it is needed - check out Devel::NYTProf. If you are worried about overhead introduced by function calls, it's possible Perl is not the best tool for this job or that you should delve into perlxs. But profile first and often.