#! perl use strict; use warnings; use Data::Dump; sub foo { dd \@_; my $val = $_[0]; } my %bar; my $baz; foo( $bar{$baz} ); #### 18:39 >perl 814_SoPW.pl Use of uninitialized value $baz in hash element at 814_SoPW.pl line 28. [undef] 18:39 >