TIMTOWTDI:

use strict;
use warnings;

my @not_sorted = qw(Ape Arg Beep Circus);
my @sorted     = sort {$a cmp $b} @not_sorted;

my @A     = grep {  /^A/ } @sorted;
my @trash = grep { !/^A/ } @sorted;

print join(', ', @A)     , "\n";
print join(', ', @trash) , "\n";
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You can even include the printf(...) in the grep block, i.e. at the beginning since the result of the block should be determined by the filter expression.
Have a look at split to split an array by position. From the title of your OP, I first thought you meant that...