## I'd personally use qw( ) here, but this is probalby just sample data
my @temp = ("a_1","b_1","a_2","a_3","a_4","b_2","a_5","b_3","a_6","b_4");

my( @a, @b );
my %arrays;
eval qq{\$arrays{ "$_" } = \\\@$_} for qw( a b );
for( @temp ) {
  die "Invalid prefix on element '$_'\n" unless /^([ab])_(.*)/;
  push @{ $arrays{ $1 } }, $2;
}