For your second try, what you want is:

open(OUTPUT,">&STDOUT") or die "couldn't dup stdout: $!";
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This is documented in perldoc -f open.

You can also accomplish what you want with the one-argument form of select. See perldoc -f select.

But I'm not sure why your first attempt won't work. This works fine for me:

#!/usr/bin/perl

open(STDOUT,">/tmp/tempfile.html") or die "open: $!";

foreach my $i (1..10)
{
  print $i,"\n";
}
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Can you reduce your program to a smaller testcase and see if you can still reproduce the problem? Or can you reproduce the problem from the command-line and see what's going on?