Depends on what you mean by "STDOUT". 
$ perl -E'
   my $fh = \*STDOUT;
   say $fh "test";
   say $fh == STDOUT || 0;
   say $fh eq STDOUT || 0;
   say $fh == *STDOUT || 0;
   say $fh eq *STDOUT || 0;
   say fileno($fh) == 1 || 0;
   say fileno($fh) == fileno(STDOUT) || 0;
'
test
0
0
0
0
1
1

[download]
perl -E'
   open my $fh, ">&", *STDOUT or die;
   say $fh "test";
   say $fh == STDOUT || 0;
   say $fh eq STDOUT || 0;
   say $fh == *STDOUT || 0;
   say $fh eq *STDOUT || 0;
   say fileno($fh) == 1 || 0;
   say fileno($fh) == fileno(STDOUT) || 0;
'
test
0
0
0
0
0
0

[download]
$ perl -E'
   local *STDOUT;
   open STDOUT, ">&", 1 or die;
   open my $fh, ">&=", *STDOUT or die;
   say $fh "test";
   say $fh == STDOUT || 0;
   say $fh eq STDOUT || 0;
   say $fh == *STDOUT || 0;
   say $fh eq *STDOUT || 0;
   say fileno($fh) == 1 || 0;
   say fileno($fh) == fileno(STDOUT) || 0;
'
test
0
0
0
0
0
1

[download]
$ perl -E'
   local *STDOUT;
   open STDOUT, ">&", 1 or die;
   open my $fh, ">&=", 1 or die;
   say $fh "test";
   say $fh == STDOUT || 0;
   say $fh eq STDOUT || 0;
   say $fh == *STDOUT || 0;
   say $fh eq *STDOUT || 0;
   say fileno($fh) == 1 || 0;
   say fileno($fh) == fileno(STDOUT) || 0;
'
test
0
0
0
0
1
0

[download]

In reply to Re: Testing whether a file handle is attached to STDOUT by ikegami
in thread Testing whether a file handle is attached to STDOUT by rovf

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