slow update & index question

I have a script that is updating the DB by reading in a file with 467 lines.  Each file is named by the shelf the
informationwas gotten from.  Each line is tab seperated and consists of a column name and the value that it should be
updateto.  The update line in the perl script looks like this: update table set "column name" = 'value' where
"Shelf_Name"= '$shelf'  

Now this works.. but it takes almost 1 minute to do the updates.  With nothing else at all touching the DB..  is this
normal? The DB is index'd on the Shelf_Name column.. but how do I know if it is using the index.. or does that not even
matterin this case? 

Travis