my $public_key = get_pubkey($fields[2]); # Verified to work
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I don't know what "Verified to work" means, but I won't believe that it doesn't set $public_key to be undef unless you change it to something like:

my $public_key = get_pubkey($fields[2])
    or  die "Can't get public key...";
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        - tye (but my friends call me "Tye")