use strict;
use warnings;

use Data::Dumper;
my %hash = (a => 1, b => 2);
mysub(\%hash);
print Dumper(\%hash);

my %hash2 = (a => 1, b => 2);
mysub1(%hash2);
print Dumper(\%hash2);

sub mysub{
my $h = shift;
delete $h->{'b'};
}

sub mysub1{
my %h = @_;
delete $h{'b'};
}