my %unitMap;
my $cmd  = "hpacucli ctrl slot=0 pd all show";;
open my $fd, "$cmd|" or return \%unitMap;
while (my $row = <$fd>) {
        $row =~ /^$/ and next;
        $row =~  s/[,|)|(]//g;
        chomp $row;
        next if  $row =~ /^Smart/g;
        $row =~ s/^\s+//;
        next if $row =~ /^unassigned\n\nOK$/;
# I am trying to delete the line that starts with unassigned and 2 lin
+es after that
        print "$row\n";
[download]

I am pretty sure you are trying to delete 3 lines, in which you are only reading one line at a time.

I could handle this by putting in a counter:

my $counter = 0;

if ( $_ =~ /unassigned/ ) {
    $_ =~ s/.*\n//gi; #delete unassigned line
    $counter++;    #count will be 1 and will be caught by next if stat
+ement
}
if ( $counter = 1 ) {
    $_ =~ s/.*\n//gi;  #delete next line
    $counter++;    #count will be 2 and will be caught by next if stat
+ement
}
if ( $counter = 2 ) {
    s/.*\n//gi;    #delete the 2nd line after unassigned
    $counter = 0;    #make count to 0 until $_ is something you are lo
+oking for
}
[download]

I dont know how good this will work for your particular problem, but it could give you another way to think about it :)

EDIT: I did not read the rest of the comments, seems there was a better answer already given.

Ok, thats code and pattern, but where is the data?

 <code> data
data
data
</code>
[download]

Here is the Data

 data
array A
physicaldrive 2C:1:1 port 2C:box 1:bay 1 SAS 1 TB OK
physicaldrive 2C:1:2 port 2C:box 1:bay 2 SAS 1 TB OK
array B
physicaldrive 2C:1:3 port 2C:box 1:bay 3 SAS 1 TB OK
physicaldrive 2C:1:4 port 2C:box 1:bay 4 SAS 1 TB OK
array C
physicaldrive 3C:1:5 port 3C:box 1:bay 5 SAS 1 TB OK
physicaldrive 3C:1:6 port 3C:box 1:bay 6 SAS 1 TB OK
array D
physicaldrive 3C:1:7 port 3C:box 1:bay 7 SAS 1 TB OK
physicaldrive 3C:1:8 port 3C:box 1:bay 8 SAS 1 TB OK
array E
physicaldrive 4C:2:1 port 4C:box 2:bay 1 SAS 1 TB OK
physicaldrive 4C:2:2 port 4C:box 2:bay 2 SAS 1 TB OK
array F
physicaldrive 4C:2:3 port 4C:box 2:bay 3 SAS 1 TB OK
physicaldrive 4C:2:4 port 4C:box 2:bay 4 SAS 1 TB OK
array G
physicaldrive 5C:2:5 port 5C:box 2:bay 5 SAS 1 TB OK
physicaldrive 5C:2:6 port 5C:box 2:bay 6 SAS 1 TB OK
array H
physicaldrive 5C:2:7 port 5C:box 2:bay 7 SAS 1 TB OK
physicaldrive 5C:2:8 port 5C:box 2:bay 8 SAS 1 TB OK
array I
physicaldrive 6C:3:1 port 6C:box 3:bay 1 SAS 1 TB OK
physicaldrive 6C:3:2 port 6C:box 3:bay 2 SAS 1 TB OK
array J
physicaldrive 6C:3:3 port 6C:box 3:bay 3 SAS 1 TB OK
physicaldrive 6C:3:4 port 6C:box 3:bay 4 SAS 1 TB OK
array K
physicaldrive 7C:3:5 port 7C:box 3:bay 5 SAS 1 TB OK
physicaldrive 7C:3:6 port 7C:box 3:bay 6 SAS 1 TB OK
unassigned
physicaldrive 7C:3:7 port 7C:box 3:bay 7 SAS 1 TB OK
physicaldrive 7C:3:8 port 7C:box 3:bay 8 SAS 1 TB OK
[download]