$ntry->DRs->elem does not look like any kind of array. Do you mean that $entry is a Hash of Hashes of Hashes of Arrays? The innermost array reference would then be obtained by:$entry->{'DRs'}->{'elem'}, and dereferenced to an array by @{$entry->{'DRs'}->{'elem'}}. It would be helpful for you to describe you data and your intentions.

Within grep's block, it looks like you are expecting an array reference in $_, but again the syntax is incorrect (well, odd to me ;-). I think you want { $_->[0] eq 'EMBL' } there.

As it is, grep is not working because you are giving it an incorrect code block, and a single element list which has incorrect syntax. I think if you clarify what data you have built, the solution will pop right out at you.

Update: Corrected myself, as shown. ++fever.

After Compline,
Zaxo