You may also be interested in the # line directive (see this section of perlsyn):

# line 42 "This is where it all goes horribly wrong..."
print "<",undef,">\n";
[download]

gives

Use of uninitialized value in print at This is where it all goes horri
+bly wrong... line 42.
[download]

This is even more useful in eval to pin down which eval caused the problem.

Also check out Smart::Comments for even more functionality.