my @words = qw(data set); 
 
open FILE1, "file.txt"; 
my @file = <FILE1> 
close FILE1; 
 
open FILE2, ">>file2.txt"; 
foreach (@file){ 
 foreach my $word (@words){ 
     if($word eq $_){ 
         print FILE2 uc($_); 
     }else { 
         print FILE2 $_; 
    } 
 } 
} 
close FILE2