Like this ...

for ( ; my $in = <$fh> ; )
{
  ...
}

#  or ...

for ( ;; )
{
  last if eof $fh;
  my $in = <$fh>;
  ...
}
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... ? The first case is very much like while with the additions of empty initialization & increment statements both of which happened to be covered by the loop end condition. So all you gain is obfuscation with for loop in this case.