use strict;
use warnings;

my @big = qw(a b c d e f g h i);
my @small = qw(f c d g);
my %small; $small{$_}=1 for @small;

my @keys_wanted = @small;
foreach ( @big ) {
	push @keys_wanted, $_ unless $small{$_};
}

print "@keys_wanted";