$s = undef;
say 'Nothing to see here' if ! defined $s;  
say $s = '';                                
say 'Empty string' if $s eq '';             
say $s = 'be';                              
say $t = $s;                                
say 'Same' if $t eq $s;                     
say $t = $t .'e'                            
say $t .= 'keeper';                         
$t =~ s/ee/ook/; say $t;                    
say $u = substr $t, 2, 2;                   
say 'Oklahoma' . ' is ' . uc $u;