my @temp=qw(a_1 b_1 a_2 a_3 a_4 e_2 a_5 b_3 a_6 b_4);

my %router;
@router{'a'..'e'} = \(my (@a, @b, @c, @d, @e));
my $keys = join '', keys %router;

foreach my $value (@temp) {
    push @{$router{$1}}, $2 if $value =~ /([$keys])_(.*)/;
}
print "@a <==> @b, @e\n";