You should always use low precedence or (in preference to ||) with the "or die" idiom. Also, you should normally avoid parens when calling print, so this is the recommended way to write it:

print OUT $line or die "writing 'splat' $!";
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For a working example, see my reply below.

Update: further notice that lexical file handles (e.g. $fh in my reply below) are preferred to the old global file handles (e.g. OUT in your example code).