How to read file into hash array in perl?-Perl interview

How to read file into hash array in perl?-Perl interview
open (IN, ""(filename in quotes))
or die "Couldn't open file for processing: $!";
while () {
chomp;
$hash_table{$_} = 0;
}
close IN;

print "$_ = $hash_table{$_}\n" foreach keys %hash_table;