I just noticed that the Scalar::Util module by gbarr recently added a function called openhandle().

From the pod:

    openhandle FH

    Returns FH if FH may be used as a filehandle and is open,
    or FH is a tied handle. Otherwise undef is returned.

    $fh = openhandle(*STDIN);           # \*STDIN
    $fh = openhandle(\*STDIN);          # \*STDIN
    $fh = openhandle(*NOTOPEN);         # undef
    $fh = openhandle("scalar");         # undef
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It uses several methods, including fileno(), to try to determine if the scalar is a valif FH.

--
John.