Personally I like your last option. Keep all your config/constants/options where you can see 'em!

You may need others, they may grow 'til you need to put them in a separate file. If they're all together in one place this will be easier.

I would also check the variable.

"'$some_variable' can have the values 'x' and 'y' only."

Are you sure! Check it anyway. :-)

#!/usr/bin/perl

use strict;
use warnings;

my $config = {
  count => {
    x => 9,
    y => 14,
  },
  other => {
    a => 1,
    b => 2,
  }
};

my $some_variable = 'x';

die "bad count" unless exists $config->{count}{$some_variable};

for my $i (0 .. $config->{count}{$some_variable}) {
   #do some stuff;
}
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