The following psuedo-code illustrates something I have just recently run into when relying on $_.

while(<FILE>)
{
  if(/matches/)   # use of $_, everything is ok
  {
     $object->doSomething($part_of_line);
  }

  print "$_\n";   # here $_ has a value of undef and causes problems
}
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and from the object module

sub doSomething
{
  ...
   open(FILE2, $file2);
   while(<FILE2>)
   {
      # do more stuff
   }
   # At this point in the code, $_ is undef and since $_ is
   # global...
}
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This is fixed by adding a local($_); to the doSomething subroutine, is it (adding a local($_);) something that I should be doing on a regular basis in the subroutines of my modules or did I just happen upon an out of the ordinary situation?