{
  open my $fh, "<", "some_file" or last;
}

##</code><code>##

if (/VALID/)
{{ # First bracket is for the if, second is for a loop-like block
  open my $fh, "<", "some_file" or last;
}}

##</code><code>##

while (<>)
{
  if (/INVALID/)
  {
    last;
  }
}