Are you sure you need to change the STDOUT? Any chance you actually need to change the select()ed filehandle?

open my $FH, '>', $POST_FILE or die "Can't redirect STDOUT";
my $oldFH = select($FH);
...
select($oldFH);
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Of course this depends on whether you need to change the STDOUT for a subprocess or want to change where print "foo\n"; goes. In the later case you'd rather use the select(). Keep in mind that the select()ed filehandle may already be changed and then your STDOUT change will not have any effect.