I think that you are asking how to test for definedness

#!/usr/bin/perl -w
use strict;

my @a = qw(1 2 3);

for (@a){
   if ( not defined ($a[$_])){

     print "\$a[$_] can't match 
           because it's not initialized\n" 
           unless $a[$_] =~ m/3/;

     print "\$a[$_] can't be tested for equivalence
            because it's not initialized\n" 
            unless $a[$_] == 3;
   } 
    
}
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