Anonymous Monk,
Your insistence on using a hash strengthens my feeling that this is a homework problem. While I do not mind homework problems nearly as much as other monks, if this is homework you should state:

• That it is homework
• What the specific requirements are
• What you have tried so far
• What you "think" may work but do not know how to code

Now to answer your questions, there is no need to use a hash. you could change:

# push @offsets, $_ - $first + 1;
# to
push @offesets, [ $line , $_ - $first + 1 ];
# and
# print "$_\n" for @offsets;
# to
print "$_->[0] : $_->[1]\n" for @offsets;
[download]

Cheers - L~R