How do I detect whether a variable has been defined in an enclosing context? I tried 

my $myscale = 1;
if ( defined $scale ) { $myscale = $scale; }

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When $scale does not exist in the outer context, this fails. So then I tried 
my $myscale = $scale // 1;

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with the same result. But "defined" seems to want an existing object (function, array, etc.), So finally, I tried it this way .. 
my $myscale = extscale // 1;
sub extscale { return $scale; }

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I have reread the Camel sections on "defined" and "exists". Neither of these does what I am looking for. Is there some way to do this?

In reply to detecting an undefined variable by LloydRice

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