The characters \* are not part of the STDOUT name, and they are not there just for fun. They turn a bareword (no sigil) filehandle into a filehandle reference.

$ctx->cat(\*FILE, 'http://127.0.0.1/file.txt', 'HEAD');
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You have to open the filehandle first, though:

open FILE, '>', 'file.txt.HEAD' or die $!;
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Or, use lexical filehandles:

open my $FH, '>', 'file.txt.HEAD' or die $!;
$ctx->cat($FH, 'http://127.0.0.1/file.txt', 'HEAD');
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