I guess i might need to in case of typo?

Yes, exactly. But since you already have an array of valid PIDs, it might be a better idea to change the logic of the subroutine and present each PID to the user instead. Like this:

my @pids = ...;

...

kill_processes(\@pids);

...

sub kill_processes
{
    my $pids = shift;

    for my $pid (@$pids)
    {
        print "Kill process $pid? ([y]es, [n]o, [q]uit)?\n";
        my $ans = <>;

        last if     $ans =~ /^Q/i;
        next unless $ans =~ /^Y/i;

       `kill $pid`;
        print "Process $pid killed\n";
    }
}
[download]

Using this approach there is no possibility of a user-input typo. And as a bonus, the loop logic is simpler.

Hope that helps,