The Perly solution is to exploit the hash capability of the *@ glob -- it is a well-kept secret. You don't want the function to set a scalar or set an array. You want the function to set the 0 key of a hash -- it is easier to test the return value that way.

(Those who answered with die(), with 'best practices', or even with 'common practices' are avoiding to answer directly the poster's question.)

foo();

$@{0}  ?  print "error: $@{0}"
       :  print 'ok';

sub foo { $@{0} = 'proxy error' }
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