$ perl -e'
   my %h = ( a => 4, c => 6 );
   printf( "exists %s return false for elements found in a hash.\n",
      ( grep { !exists( $h{$_} ) } keys %h ) ? "can" : "didn\x27t" );

   my @a; $a[0] = 4; $a[2] = 6;
   printf( "exists %s return false for elements found in an array.\n",
      ( grep { !exists( $a[$_] ) } keys @a ) ? "can" : "didn\x27t" );
'
exists didn't return false for elements found in a hash.
exists can return false for elements found in an array.

##</code><code>##

$ perl -Mv5.14 -e'my @a; \$a[0]; say exists( $a[0] ) || 0;'
1