my (@Cdevices,@Mdevices);

push (@Cdevices, 'UnitID1', 'fileno1');
push (@Cdevices, 'UnitID2', 'fileno2'); # <- @Cdevices is now qw(UnitID1 fileno1 UnitID2 fileno2)
push (@Cdevices, 'UnitID3', 'fileno3'); # <- and so on
push (@Mdevices, \@Cdevices);

# this makes it clear:
use Data::Dumper;
print Dumper(\@Cdevices);
print Dumper(\@Mdevices);

for my $ref (@Mdevices) {
    print $ref->[0],"\n";
}