DB<189> p "@a"                                                                                                             
Monday Tuesday Wednesday Thursday Friday Saturday Sunday

  DB<190> $a = join "", map { "(?=.*($_))*" } @a

  DB<191> x grep {defined} "Sunday Friday Monday" =~ /^$a/i
0  'Monday'                                                                                                                  
1  'Friday'                                                                                                                  
2  'Sunday'                                                                                                                    
  DB<192>