Here is the longer version of the same code:

for ( $ipaddress, $prefix, $interface, $device, $location, $comment )
{
  defined and s/^\s+|\s+$//g;
  # or defined ? s/^\s+|\s+$//g : 1; It does the same thing
  # or even if (defined) { s/^\s+|\s+$//g } 
  
  ## Edit : and there is
  # s/^\s+|\s+$//g if defined; 
  ## That one is quite nice.
  ## Let's just say there's more than one way to do it.
}
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If you have to ask though, I'd advise you to go for the long version because it will run just as fast, it's just another way of writing the same thing. Here is another way to do it, which I find easy to read thanks to the next keyword.

STRING: for( $ipaddress, $prefix, $interface, $device, $location, $com
+ment )
{
  next STRING unless defined; # We skip any element that is not define
+d
  s/^\s+|\s+$//g;
}
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