Hi,
because you explicitely ask for the first element $Mdevices[$k][0]. You can get proper access to all elements by dereferencing properly:

#!/usr/bin/perl

use strict;
use warnings;

my (@Cdevices,@Mdevices);

push (@Cdevices, 'UnitID', 'fileno');
push (@Mdevices, \@Cdevices);

# this will show us the actual layout of the array
use Data::Dumper;
print Dumper(\@Mdevices);

# $k=0; $k<=$#Mdevices; $k++ is C-style. Possible, but unnecessary ove
+rhead
for my $ref (@Mdevices) {
    print join(' - ', @{$ref}),"\n";

}
[download]

prints

$VAR1 = [
          [
            'UnitID',
            'fileno'
          ]
        ];
UnitID - fileno
[download]

update: after reading the OP again, it now becomes a bit more clear to me what he actually wants to do and I also found out what the problem is. Look at the following code:

my (@Cdevices,@Mdevices);

push (@Cdevices, 'UnitID1', 'fileno1');
push (@Cdevices, 'UnitID2', 'fileno2'); # <- @Cdevices is now qw(UnitI
+D1 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";
}
[download]

You want the first element of each sub-array, but there is only one sub-array!!! you would need something like this: push (@Cdevices, ['UnitID3', 'fileno3']); # that will store a reference to an anonymous array
Regards,
svenXY

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