How to undefined value for hash key in Perl?

Question

I would like to know how to determine the value for a hash key in Perl. Can someone fix my code?

#!/usr/bin/perl use strict; use warnings; my %hash; undef($hash{"a"}); undef($hash{"b"}); print scalar values %hash; # i need here 0 print scalar keys %hash; # and here 2 

Answer 1

The other answer point about certainty and existence is very good, but if you really want to know the number of certain values, you can always do

 print scalar grep { defined $_ } values %hash 

Answer 2

 undef($hash{"a"}); 

equivalently

 $hash{"a"}=undef; 

So you add the key 'a' with the value undef. To delete a value from a hash, use "delete".

 delete $hash{"a"}; 

It is not possible to have different sizes of "keys" and "values" for the same hash. You can use grep to filter out unwanted elements.

Answer 3

 undef $hash{$key}; 

this will override the value for this key:

 print "E" if exists $hash{$key}; # will print E print "D" if defined $hash{$key}; # will not print D