I wrote a simple test writer and reader and did not have any problems.

Here is the writer.

#!/usr/bin/perl

use GDBM_File;

my %ports;

tie(%ports,'GDBM_File','gdbmtest',&GDBM_NEWDB,0644) or die "$!\n";

for my $switch (0 .. 5) {
    for my $ifnum (0 .. 5) {
        $ports{"$switch:$ifnum"} = "test $switch $ifnum";
    }
}

untie(%ports) or warn "$!\n";
[download]

And a reader

#!/usr/bin/perl

use GDBM_File;

my %ports;

tie(%ports,'GDBM_File','gdbmtest',&GDBM_READER,0644) or die "$!\n";

for my $switch (0 .. 5) {
    for my $ifnum (0 .. 5) {
        print $ports{"$switch:$ifnum"}, "\n";
    }
}

untie(%ports) or warn "$!\n";
[download]