foreach (in $root): Perl doesn't have a built-in function called in, so I'm assuming you've defined one somewhere, and this makes sense.

You call Roundup($thong), but the Roundup function seems to expect two arguments, not one.

This bit:

my $string;
$string .= $thing->{employeeID}; 
$string .=  "\t" ;
$string .=  $thing->{sAMAccountName} ;
$string .=  "\t" ;
$string .=  $thing->{department} ;
$string .=  "\t" ;
$string .=  $thing->{o} ;
$string .=  "\t" ;
$string .=  $thing->{physicalDeliveryOfficeName} ;
$string .=  "\n";
[download]

Might be clearer expressed as:

my $string = join("\t",
    $thing->{employeeID},
    $thing->{sAMAccountName},
    $thing->{department},
    $thing->{o},
    $thing->{physicalDeliveryOfficeName},
)."\n";
[download]

Or even:

my $string = join("\t", @$thing{ qw(
    employeeID
    sAMAccountName
    department
    o
    physicalDeliveryOfficeName
) })."\n";
[download]