sub random_string {
  my $length = shift || 2;
  my @chars = ('a'..'z','A'..'Z',0..9);
  @chars = UNIVERSAL::isa($_[0],'ARRAY') ? @{$_[0]} :  @_ if @_;
  join ('',map{ $chars[ rand @chars  ] } (1..$length));    
}

# Example
print random_string(5,[qw(foo bar base )]),"\n";
print random_string(5,'a'..'f',0..9 ),"\n";