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open FILE, '<', $file or die "...";
while (<FILE>) {
...
  handle(FILE, 'that') if m/that/;
}
close FILE;

open my {I/O}FILE, '<', $file or die "...";
while (<{I/O}FILE>) {
...
  handle({I/O}FILE, 'that') if m/that/;
}
close {I/O}FILE;

open my {I/O}FILE, '<', $file or die "...";
while (defined($_ = {I/O}FILE->readline)) {
...
  handle({I/O}FILE, 'that') if $_ =~ m/that/;
}
{I/O}FILE->close;

sub handle {
  my $fh = shift;
...

  ...
}