use strict;
use warnings;
use Data::Dumper;

my @a = qw/a b c d/;
my @b = qw/a b c d/;
my %a;
print '--- my   @a before ---',"\n", Dumper \@a;
undef @a[1,2];
print '--- my   @a after ---',"\n", Dumper \@a;

print '--- my   %a before ---',"\n", Dumper \%a;
undef @a{@b};
print '--- my   %a after ---',"\n", Dumper \%a;